A real-time background correction technique is reported for digital data page holographic storage. Two inverted binary
data pages are recorded at the same location in recording media with two inverted random phase coded reference beams
using a rotating half-wave plate. Adding the two detected inverted data pages from same media location creates
background image with noise at that media location. The background image is used to successfully perform the
background correction to reduce the noise of detected digital data pages.
KEYWORDS: 3D displays, Digital holography, Computer generated holography, Holography, Holograms, Spatial light modulators, Algorithm development, Data storage, 3D image processing, 3D optical data storage
Holographic display is a true three-dimensional (3D) display technology presenting all depth cues without using any special
glasses. In this paper, we first introduce a monochrome digital 3D holographic display system developed at Data Storage
Institute (DSI), which is capable of displaying both static and dynamic 3D objects reconstructed from computer-generated
holograms (CGHs). The system can also display 50-Mpixel holograms at 25 Hz refresh rate via a novel hologram tiling
approach, which enables the increase of displayed image size. A futuristic vision for full high-definition (HD) digital 3D
holographic display is then proposed and analyzed. The dynamic reconstruction of full-HD 3D objects from CGHs has been
preliminarily demonstrated. Finally, we introduce the development trends of its enabling technologies such as highperformance
computing, new algorithms, data storage and transmission, spatial light modulator (SLM) and RGB (red, green
and blue) laser sources.
In heat assisted magnetic recording, near field optical transducer is a key component for its success. Due to the near field
properties, the transducer design has to be done combining with media. FePt is a potential recording material for heat
assisted recording. In this paper, the measured optical constant of FePt thin film was introduced, and the design and
simulation of c-aperture transducer with FePt media for multiple Tb/in2 heat assisted magnetic recording application
were performed. The light spot sizes of around 15nm with high efficiency were obtained. Optical transducer is used to
heat the media locally. Its final target is to generate smaller thermal profile to meet the requirement of recording density.
Therefore, using obtained beam spot as heat source, thermal simulations were carried out with media material's thermal
parameters. The simulation results show that recording density of 3Tb/in2 is possible.
This work presents a thermal analysis that explains experimental observation in all-optical magnetic recording (AOMR).
An integrated model is used to describe thermal processes at different time scales in AOMR. The formation of magnetic
marks is discussed and implemented by developing a simulator based on 3-dimensional finite element method (FEM).
The simulator is able to carry out thermal analysis of the thin film media and is a useful tool for design of AOMR media
structure, especially for the thermal sink layer.
The current limitation in pixel count of a single spatial light modulator (SLM) is one of the technological hurdles that must be overcome to produce a holographic 3-D display with a large image size. A conventional approach is to tile subholograms that are predivided from a reconfigurable computer-generated hologram (CGH) with a high pixel count. We develop a new approach to achieve a 50 Mpixel display by tiling reconstructed subholograms computed from a predivided 3-D object. The tiling is done using a two-axis scanning mirror device with a new tiling sequence. A shutterless system design is also implemented to enable effective tiling of subholograms. A high-speed digital micromirror device (DMD) at 6 kHz with 1920×1080 pixels is utilized to reconstruct the subholograms. Our current system shows the potential to tile up to 120 subholograms, which corresponds to about 240 Mpixels. The approach we demonstrate gives a scalable solution to achieve a gigapixel-level display in the future.
Laser interference lithography is applied to fabricate large-area plasmonic nanostructures. This approach has the
advantages of being non-contact process in air and able to achieve large-area and maskless nanolithography at a high
speed with low system investment. Single layer Au or Ag noble metallic thin film and Ag/Au, Ag/Ni or Au/Ni bimetallic
layer thin films are patterned into nano-dot, nano-rod and nano-nut arrays by laser interference lithography. Plasmonic
effects of the fabricated metallic nanostructures are studied. Tunable and multi-peak surface plasmon resonances of these
nanostructures can be obtained, which have potential applications in solar cells, bio-sensing and photonic circuits.
A 3D-shift multiplexing is reported with converging signal and diverging random phase coded reference beam into the
Cu:Ce:Tb:CLN crystal. Shift-selectivity at first null along x,y and z-axis is measured to be 1.5, 5 and 5mm for random
phase-coded reference beam. Low capacity data page with only 1-4 kbits were successfully recorded/retrieved and the
achievable raw areal density of >350 Gbit/in2 will be reported.
In this paper the focusing effect of flat metallic-slit array in micro-meter scale area is discussed and the role of
surface plasmons waves inside slits is recognized. A proximate relationship between the equivalent focal length
and slit material, slit geometrical parameters is built. The theoretically derived focal length and that from Finite
Difference Time Domain (FDTD) simulation is proved to be in good agreement. Additionally, FWHM of focal
point, focal depth and intensity of focal point for the slit array with invariant slit width and the slit array with
variant slit width are compared as well. The slit array with varied slit width is found to have the better
performance than slit array with invariant slit width.
KEYWORDS: Near field, Optical discs, Super resolution, Aluminum nitride, Near field scanning optical microscopy, Optical recording, Antimony, Tellurium, Dielectrics, Data storage
Super-resolution near-field optical disk is one of the solutions to overcome diffraction limit and achieve high
density optical recording. In this paper, a structure of super-resolution near-field phase-change optical disk with
a thin thermal shield layer behind the recording layer is proposed. The optical disks with the new structure were
studied theoretically and experimentally. Thermal simulation shows that the thermal shield layer can reduce the
phase change layer temperature, thus improve the thermal stability of the disks. The disks with this structure
were fabricated and characterized. The experiment results are in good agreement with the simulation results.
A laminated holographic recording medium based on photorefractive lithium niobate crystal is reported for the first time.
The medium consists of a piece of photorefractive crystal, a data tracking layer, an intermediate dichroic mirror layer and
an anti-reflection layer. Such a holographic medium is able to perform hologram recording and retrieving with
compatibility with collinear and coaxial holographic recording schemes.
An integrated analysis tool of optical system and media which combines system with media analysis of the discs is
developed in this project. This software has been used to study the influence of disc tilt, cover layer thickness and
scratches on high density recording, which show that it provides a powerful tool in practical applications.
The modeling for investigating the thermal effect on slider in heat assisted magnetic recording is built and its verification
is conducted by comparing the simulation results and experiment results. The temperature distribution on the slider
induced by locally heated media in 1Tb/in2 is simulated and the results show that the effect is within a very small zone
on the bottom surface. The temperature changes on other surfaces are less than 0.1°C, which can be negligible.
Different definitions of spot size and depth of focus in optical data storage systems are analyzed and compared numerically. It appears that the differences between the definitions become more significant as the numerical aperture of the optical system increases. The relationship between spherical aberration and axial intensity is studied, and a general definition of the depth of focus based on this analysis is proposed.
Surface plasmon propagation properties for nano-sized metal aperture and nano-wire structures are studied based on the
waveguide theory. It is verified that there are only TM0 and HE1 mode existing in both structures. For nano-wire
structure, however, there is no cut-off radii for both TM0 and HE1 mode. On the contrast, there is a cut-off radius for
nano-sized silver aperture structure, and even more, there are several characteristic radius coefficients a/ λ, -0.32, 0.73.
For each section, the EM wave may takes on different features, e.g., totally-bounded features along the aperture interface
for a/ λ >0.73, or oscillation inside core or strong attenuation along z direction for 0.32<a/ λ<0.73). HE1 mode of metal
aperture doesn't show cut-off radius as well, but the wave-number along z direction monotonically increase with the
radius coefficient a/ λ in contrast with existence of a characteristic radius coefficient a/ λ of 0.41 for nano-wire.
Two structures super-resolution near-field phase-change optical disks with masks Sb2 Te3 layer and a
thermal shield layer in front of the mask layer on Blu-ray substrates were studied theoretically and
experimentally. Optical simulation was conducted and the modulation transfer function (MTF) was calculated.
MTF calculation results has revealed that the super-RENS optical disk exhibited the maximum response when
nearly half of the laser spot was covered by the mask. The thermal simulation was used to find the optimum
condition meaning that half of the laser beam is covered by the aperture on the mask layer. The recording signal
and thermal stability on different structures were measured and analyzed. The simulation results are in good
agreement with the experiment results.
KEYWORDS: Magnetism, Near field optics, Signal to noise ratio, Head, Temperature metrology, Optical alignment, Interfaces, Data storage, Near field, Laser irradiation
Before reaching the true heat assisted magnetic recording, which is in optical near-field case for high recording density, the component level researches are needed. This requires a platform to support these kinds of researches. In this talk, the platform structure is introduced and its functions of researching on media material and structures, interface, overcoat and lubricant are discussed. Finally, some experimental results are presented.
The advantages of ultrafast laser processing of materials include a minimal thermal penetration region and low processing temperature, precision removal of material, and good-quality feature definition. In this paper, fs laser (800 nm, 100 fs) processing of transparent materials at different focus positions and different laser intensities is investigated. Different morphologies are presented and compared. It is found that at controlled laser fluences, both bowl-shape and hump-like microstructures can be produced at the material surfaces. The lengths of the cracks produced inside the bulk material were measured as a function of the focus positions. The physical mechanisms for the formation of different microstructures are discussed. To reduce the patterning size, we employ transparent particles as microlens on the surfaces by self-assembly. Parallel structures in nanometer scale were produced by single fs laser pulse irradiation. These nanostructures change their shapes at different laser energies. The optical near-field distribution around the particle was also calculated according to exact solution of light scattering problem.
Silver nanoparticles have been fabricated by laser ablation of a silver metal foil in solution. The presence of sodium bis(2-ethylhexyl) sulfosuccinate increases the yield of the nanoparticles and enhances their stability. The optical limiting performance of the silver nanoparticles embedded in a PMMA film is compared to that in an aqueous solution.
A novel direct-write glass metallization based on laser induced plasma assisted ablation (LIPAA) was investigated. Laser is passed through a glass substrate and irradiated onto a metal target placed beneath the substrate. By tuning laser fluence above target ablation threshold, target ablation and plasma generation occur. The plasma flies towards the glass at a high speed and deposits metal materials onto glass backside surface. Metal films were fabricated and their sheet resistances were measured by a four-point probe. It was found that sheet resistances of the metal films vary with processing parameters. Experimental results reveal that low resistivity metal film (< 0.3 Ω/∠) can be obtained at an optimal laser scanning speed and pulse repetition rate. When target-to-substrate distance increases, film resistance also increases. Optimal design of overlap schemes among metal tracks provides a lower film resistance. Meanwhile, thin film and bulk metal targets were used to study their difference on film resistance. It was discovered that deposition using thin film target is more efficient. Laser annealing technique was also applied to activate the deposited metal materials to get higher quality glass surface metallization.
Gallium oxide nanofibers were synthesized by reactive pulsed laser ablation of 99.99% pure GaN target in vacuum condition. The nanofibers have been identified to be β-Ga2O3 by X-ray diffraction and selected area diffraction. The structure and composition of the as-deposited product were determined by high-resolution transmission electron microscopy and scanning electron microscopy. The β-Ga2O3 nanofibers have diameters in the range of 10 - 20 nm and lengths up to tens of microns. Photoluminescence measurements at temperature between 10 K and room temperature show that the nanofibers emit stable and high brightness UV and blue light at 390 nm and 440 nm respectively under the excitation of 325 nm laser source which my find potential applications in one-dimensional optoelectronics nanodevices.
We report the optical limiting response of carbon nanoparticle colloids in different organic solvents. The carbon nanoparticles were prepared by Nd:YAG laser ablation of carbon target immersed in ethanol. Optical limiting properties towards 532 and 1064 nm wavelengths were measured with a 7-ns pulsed Nd:YAG laser. Strong optical limiting effect was detected for the carbon nanoparticle colloids within a solvent having low thermal conductivity. The limiting effect at 532 nm is stronger than that at 1064 nm. Possible mechanisms of optical limiting were discussed.
KEYWORDS: Near field scanning optical microscopy, Photoresist materials, Lithography, Scanning electron microscopy, Atomic force microscopy, Ultraviolet radiation, Data storage, Femtosecond phenomena, Nanolithography, Laser energy
The increasing demand for smaller devices as well as research into novel structures for high density data storage has necessitated the use of advanced nanolithography techniques for fabrication in the sub-100 nm regime. In this paper, nanoscale lines with a minimum full width at half maximum of 20 nm have been achieved, demonstrating resolution of λ/20. Lithography was made by near field scanning microscope (NSOM) in UV photoresist with 120 nm thickness. Second harmonic generation of femtosecond laser was used as light source of NSOM. The lithography results were measured and analyzed by the same tip of NSOM and scanning electron microscopy (SEM). The size of tip aperture used was about 50 nm. The effects of laser energy and writing speed on the size and depth of lines drawn were studied. By controlling these parameters properly, high quality nano-patterning in photoresist would be achieved. The nano-patterning technique will have potential applications in nanodevice fabrication and data storage.
A spherical particle can be used as a lens for focusing laser radiation. It has potential applications in high-density data storage and high-resolution optical lithography for nano-device fabrication.
Phase transformations of 100nm Ge1Sb4Te7 films induced by single 130fs pulse at 800nm have been investigated with time-resolved microscope. With an average fluence of 30mJ/cm2, a reflective intensity increase was observed within 1ps in 100nm as-deposited Ge1Sb4Te7 films after excitation by intense femtosecond pulse, which was consistent to an electronically induced non-thermal phase transformation. XRD measurement confirmed that single femtosecond pulse could induce crystalline marks in 100nm as-deposited Ge1Sb4Te7 films. Our results indicated that single femtosecond pulse could trigger both crystalline and amorphous phase in 100nm Ge1Sb4Te7 films. The fluence for crystallization was higher than that for amorphization.
KEYWORDS: Near field, Surface plasmons, Near field optics, Magnetism, Dielectrics, Surface plasmon polaritons, Data storage, Metals, Silver, Analytical research
The influence of the grating structures which include triangle, trapezoidal and rectangle geometries on the transmission efficiency in nano-aperture system is studied by use of 2D FDTD method.
This paper reviews the past analytical and non-analytical approaches for the Surface Plasmons (SPs) effect, present a simple description to the widely adopted curvilinear coordinate method. Based on the concept of Fourier decomposition of any complicated grating profiles, a comprehensive analysis is given to the contribution of every order components to the overall behavior of the practical zero-order metal gratings. It successfully predicts the energy gap, resonant SPs modes, the red-shift behavior and the broadening effect of energy gap by higher order components. At the same time, it's found that within certain wavelength range of interest, only first several orders of components are needed to be taken into account to predict the behavior of the non-sinusoidal gratings. As an application, this analysis approach is extended to behavior of the triangular gratings. The limitation and possible generalization of this method are also discussed.
In this paper we introduce the Hankel transform based channel model of Two-Dimensional Optical Storage (TwoDOS) system. Based on this model, the two-dimensional (2D) minimum mean-square error (MMSE) equalizer has been derived and applied to some simple but common cases. The performance of the 2D Viterbi detector (VD) for different partial response (PR) targets in TwoDOS system is investigated. And an easy way of jointly designing the target and equalizer with suitable constraints on the target for 2D data storage systems is proposed by reducing the 2D target into its one-dimensional (1D) form. Finally, systems with different target constraints are compared and the results show that "2D monic constraint" is a reasonable target constraint for TwoDOS system.
Laser-induced plasma-assisted ablation (LIPAA), in which a single conventional pulsed laser of small size is employed (typically 2nd harmonic of Nd:YAG laser), enables to process transparent materials like glass with micron order spatial resolution, high speed and low cost. In this process, a laser beam is first directed to a glass substrate placed in vacuum or air. The laser beam passes through the substrate since the wavelength of laser beam must have no absorption by the substrate for the LIPAA process. The transmitted laser beam is absorbed by a solid target (typically metal) located behind the substrate. The target is then ablated, resulting in plasma generation. Due to the interaction of the laser beam and the laser-induced plasma, significant ablation takes place at the rear surface of substrate. This process demonstrates surface microstructuring, crack-free marking, color marking, painting and selective metallization of glass. Based on these achievements, we have developed a prototype of workstation of LIPAA microfabrication system which is now commercially available. The discussion includes mechanism and practical applications in industry of LIPAA process.
The three-dimensional model of the packaging device is established based on ANSYS simulation platform. The thermal properties such as time response, axial and radial temperature distributions at different applied voltages are exhibited. With aids of Real Time Optical Spectrum Analyzing System and IR Camera System, time response of the device and axial temperature distribution along the coated fiber with intracore FBG are both demonstrated. Temperature responses to different applied voltages are achieved after measuring voltage induced wavelength shift and temperature dependent wavelength shift. Simulation shows results in agreement with those of experiment. Finally, regulations on length of the metal coating, size of the package, power consumption and tuning properties of the packaging device are discussed.
Lithium Niobate is an important material in optical communication due to its special characteristics (high electrooptic coefficients and high optical transparency in the near infrared wavelengths). In this paper, we investigated the effects of 775-nm, femtosecond laser radiation on the Lithium Niobate crystal. By focusing the laser beam through a microscope objective, a certain refractive index change may be induced in Lithium Niobate substrate. Based on this effect, channel waveguides and other waveguide structures were fabricated. The output optical fields through them were measured, and the refractive index change of ~6×10-4 was calculated with the Near-field Method. The properties of these waveguide structures were discussed. We also investigated the waveguides effect induced with different fabrication conditions. The experimental results revealed that different fabrication conditions affect the waveguide effect greatly.
KEYWORDS: Near field scanning optical microscopy, Near field optics, Femtosecond phenomena, Nanofabrication, Ultrafast lasers, Fiber lasers, Atomic force microscopy, Nanostructures, Data storage, Nanoprocess
We have developed the laser nanoprocessing technique by the integration of the ultrafast laser and near-field scanning microscopy (NSOM). The second harmonic femtosecond laser working in the optical near-field with the assistance of NSOM equipment was applied to expose the photosensitive polymer material. The nanopatterns with feature size smaller than the laser wavelength can be fabricated. The optical diffraction limitation is therefore broken through by the near-field nanoprocessing. It was found in our experiment that the nanofabrication feature size depends strongly on the gap between the fiber probe tip and the substrate surface, as well as the laser coupling efficiency. The approach offers the advantages of high precision, speed and selectivity in nanopatterning, and is promising to be used in data storage device manufacture for higher density recording.
A method for surface metallization on transparent substrate with laser induced plasma deposition was described. A laser beam goes through the transparent substrate first and then irradiates on a metal target behind. For laser fluence above ablation threshold for the target, the generated plasma flies forward at a high speed to the substrate and induces metal materials deposition on its rear side surface and even doping into the substrate. The diffusion distribution of metallic particles was measured with Time of Flight Secondary Ion Mass Spectrometer (TOF-SIMS). Electrically conducting films are formed on the substrate with laser beam scanning. The near 1Ω/Square lower resistivity can be formed with precise control of the processing parameters. Laser fluence, pulse repetition rate and scanning speed, distance between the substrate and metal target and overlapping of the metal lines. This technology can be used to form electrodes, resistors, LCD or electronic circuits on the transparent substrates.
Our previous paper reported on pulsed CO2 laser induced periodic microstructures on the silicon substrates, which are coated with a thin material layer at the bottom surface to promote optical absorption. Our further study shows that two sets of parallel fringes generated at right angles can overlap and produce crossed-grid patterns when the laser pulse energy just crosses the thershold required for fringe formation. The fringe period is of sub-wavelength scale and the crossed-grid pattern is of grid size 2 μm by 2 μm. The fringes are considered to be due to the laser induced periodic surface structure (LIPSS) effect. The crossed-grid patterns are only possible when thermal bumps due to the thermal capillary wave effect are minimized, and they become re-writable at higher pulse energies.
It has been proved that NiTi shape memory alloy thin film is the best one for micro actuators as compared with the others, e.g., electrostatic, electromagnetic and piezoelectric thin films. If the deposition of NiTi thin films on silicon wafers is carried out at room temperature, the resultant thin films are normally amorphous without shape memory. Subsequent annealing in a high vacuum chamber is required for re-crystallization. In this paper, we present an alternative annealing approach, namely by CO2 laser. After laser annealing, optical microscope, X-ray diffraction (XRD) and atomic force microscope (AFM) were applied to characterize the NiTi thin films. Strong austenite/martensite lattice structures were observed by XRD. The relationship between the surface roughness of the annealed NiTi thin film and temperature was obtained using AFM. The results indicate that the CO2 laser annealed NiTi thin films are with shape memory.
Precise laser microfabrication of glass is a high challenge task due to the stress-induced microcracks generated during laser ablation. In this paper, the results of high quality glass microfabrication by low energy Nd:YAG laser (355 nm, 30 ns) ablation and pocket scanning technique are presented. The pocket scanning is to scan the laser beam along parallel overlapped paths with the last path along the structure edge, while the conventional direct scanning is to scan the beam just along the structure edge. It is found that the cracks formed around the edges by pocket scanning are reduced significantly compared to that by direct scanning. Minimum crack sizes of less than 10 μm have been obtained at optimized parameters. The ablation depth is also enhanced greatly by pocket scanning to increase almost linearly with the laser fluence and scanning loop. There are no limitations of saturation as that observed in the cases of direct scanning.
Laser assisted nanofabrication for surface nanopatterning is investigated. To overcome the limitation of light wavelength, pulsed lasers were applied to combine with atomic force microscope (AFM) and nanoparticle self-assembled mask to achieve sub-30 nm patterning on the metallic surfaces. The mechanisms of the formation of nanostructure patterns are discussed. Progress on numerical simulation and physical modeling of laser assisted nanofabrication has been demonstrated. The method of AFM tip or particle enhanced laser irradiation allows the study of field enhancement effects as well as its potential applications for nanolithography.
Regular and tidy periodic structures hae been directly induced on glasses using a CW CO2 laser beam with linear polarization. It is experimentally shown that precise periodic structures with the period of several microns can be formed by means of well-set laser parameters. The orientation of the periodic structures formed is the same as that of the laser polarization no matter what the scanning direction is. The occurrence of periodic structures is very sensitive to laser power level and scanning velocity. To obtain appropriate periodic patterns, a combined condition of laser energy and scanning velocity must be satisfied. The period, width and height of the structures are dependent on processing parameters. An interesting phenomenon is that the period decreases with increasing scanning velocity. Permanent relieves with periods, widths and heights varied with the laser parameters are also studied.
A method of high-density optical disk structure design using computational electromagnetic FDTD analysis is proposed. A staircase method is used to simulate the realistic sidewall geometrical structure of the land-groove of phase-change optical disk. The phase-change materials appear as different optical characteristics under irradiation of different frequency laser beam. Materials models in the FDTD scheme have been studied to solve the computational instability. Using this FDTD method, the structures of the phase-change optical disk with blue laser and high-NA system are investigated.
KEYWORDS: Optical storage, Gold, Rhodamine B, Polymethylmethacrylate, Quartz, Glasses, 3D optical data storage, Scanning electron microscopy, Absorption, Data storage
The feasibility of multilayered optical data storage is examined in glass, quartz, polycarbonate and a rhodamine B and Au (III) doped PMMA medium by using a focused 800 nm, 100-fs pulsed laser. Refractive-index or fluorescent data patterns are recorded by use of an objective to focus laser pulses inside these transparent medium. The laser pulse produces a submicrometer-diameter structurally altered region in the material. For glass, quartz and polycarbonate materials, we record binary information by writing such bits in multiple planes and read it out with a microscope. We demonstrate data storage and retrieval with 0.6-μm in-plane bit spacing and 10-μm interplane spacing (100 Gbits/cm3). Scanning electron microscopy (SEM) are used to characterize structural changes in these materials. For the rhodamine B and Au (III) doped PMMA medium, fluorescent spectra are measured before and after laser treatment. Writing three-dimensional data bit inside the transparent medium based on a multi-photon absorption process is expected to become a useful method used to fabricate optical memory with both an ultra-high storage density and an ultra-high storage density and an ultra-high recording speed.
Ultrafast phase transitions triggered by single femtosecond laser pulse in Ge1Sb2Te4 films were investigated. By proper control of the film thickness, ultrafast crystalline and amorphous phase transformations have been achieved in Ge1Sb2Te4 films. These utlrafast phase transitions were confirmed by reflectivity change and x-ray diffraction measurement.
KEYWORDS: Near field optics, Near field scanning optical microscopy, Femtosecond phenomena, Optical storage, Data storage, Ultrafast lasers, Magnetism, Fiber lasers, Pulsed laser operation, Atomic force microscopy
We have explored the optical near-field technology for the fabrication of subwavelength-size binary bit by the combination of the femtosecond laser of the second harmonic output with the near-field scanning optical microscopy (NSOM). The photosensitive polymer material was exposed, and the nanopatterns with feature size smaller than the laser wavelenght can be generated. It was found that the feature size depends strongly on the gap between the fiber probe tip and substrate surface. The approach offers the advantages of high precision, speed and selectivity in nanopatterning, and is promising to be used in data storage device manufacture for high density data storage.
Teflon, polytetrafluorethylene (PTFE), is an important material in bioscience and medical application due to its special characteristics (non-flammable, anti-adhesive, heat-resistant and bio-compatible). The advantages of ultrashort laser processing of Teflon include a minimal thermal penetration region and low processing temperatures, precision removal of material, and good-quality feature definition. In this paper, laser processing of Teflon by Ti:Sapphire femtosecond laser (780 nm, 110 fs), Nd:YAG laser (532 nm, 7 ns) and CO2 laser (10.6 μm, 10 μs) has been investigated. For femtosecond laser processing, clear ablation takes place and provides high-quality groove on Teflon surface. Both the groove depth and the width increase as the laser fluence increase, and decrease almost linearly as the scanning speed increase for laser fluence below 5.0 J/cm2. For Nd:YAG processing, Teflon surface roughness is improved but no clean ablation is accessible, which makes it difficult to micromachine Teflon by Nd:YAG laser. For CO2 laser processing, laser-induced bumps were formed on Teflon surface with controlled laser parameters. The physics mechanisms for different pulse duration laser processing of Teflon are also discussed.
Cobalt nanoparticles have been fabricated by laser ablation of metal target at laser wavelengths of 1064 nm and 532 nm. The target was immersed in water during the ablation. Size of the resulted nanoparticles was determined by optical microscope and field emission scanning electron microscope (FESEM). It was observed that the minimum particle was 6 nm in diameter. Ultraviolet to visible (UV-vis) spectra and photoluminescence (PL) spectra were applied to characterize the optical properties of these products. In order to investigate the magnetic properties, the particles were spread on clean substrates for vibrating sample magnetometer (VSM) measurement. It was fond that magnetic properties of generated cobalt nanoparticles were obviously influenced by their sizes. Effects for the different laser wavelengths on particle formation were compared.
Laser ablation of GaN thin film and GaN/Sapphire structure for the application o flight emitting diodes (LEDs) has been performed. Edge quality and surface roughness of the specimens are compared using scanning electron microscopy (SEM) and atomic force microscopy (AFM) after laser processing by the 3rd harmonic Nd:YAG laser, KrF excimer laser and Ti-sapphire femtosecond laser. Dependence of laser ablation rate on the processing parameters, such as laser fluence, scanning speed and pulse repetition rate with the laser irradiation is also investigated. Device characteristics of the specimens after the laser microprocessing are also analyzed.
NiTi Shape Memory Alloy (SMA) is with great potential for actuation in microsystems. It is particularly suitable for medical applications due to its excellent biocompatibility. In MEMS, local annealing of SMA is required in the process of fabrication. In this paper, local annealing of Ni52Ti48 SMA with excimer laser is proposed for the first time. The Ni52Ti48 thin film in a thickness of 5 μm was deposited on Si (100) wafer by sputtering at room temperature. After that, the thin film was annealed by excimer laser (248nm KrF laser) for the first time. Field-Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM) were used to characterize the surface profile of the deposited film after laser annealing. The phase transformation was measured by Differential Scanning Calorimeter (DSC) test. It is concluded that NiTi film sputtering on Si(100) substrate at room temperature possesses phase transformation after local laser annealing but with cracks.
In recent years, femtosecond (fs) laser ablation has attracted much interest in both basic and applied physics, mainly because of its potential application in micromachining and pulsed laser deposition. Ultrashort laser ablation have the capability to ablate materials precisely with little or no collateral damage, even with materials that are impervious to laser energy from conventional pulsed lasers. The extreme intensities and short timescale at which ultrashort pulsed lasers operate differentiate them from other lasers such as nanosecond laser. In this work, we investigate the expansion dynamics of Cu (copper) plasma generated by ultrashort laser ablation of pure copper targets by optically examining the plasma plume. Time-integrated optical emission spectroscopy measurements by using intensified charged couple detector array (ICCD) imaging were used to detect the species present in the plasma and to study the laser-generated plasma formation and evolution. Temporal emission profiles are measured. Our interest in the dynamics of laser-generated copper plasma arises from the fact that copper has been considered as a substitute for Aluminum (Al) interconnects/metallization in ULSI devices (for future technology). It is important to know the composition and behavior of copper plasma species for the understanding of the mechanisms involved and optimizing the micro-machining processes and deposition conditions.
Laser-ablation-based microfabrication technology is applied to fabricate micro-electro-mechanical-systems (MEMS) devices on polymer substrates. A micromachining apparatus is designed and developed which includes a 355 nm laser, an uncoated focusing lens, computer-controlled precision x-y-z stages and in-situ process monitoring systems. Concentric rings microstructures are formed by efficiently changing the laser intensity distribution. Tiny via holes and micro-nozzles with different diameters have been obtained by low power laser direct drilling. Optical microscopy and scanning electron microscopy (SEM) are used to evaluate the processing results at different laser processing parameters. This method has the advantages of low-cost and time-saving in circle via holes fabrications. Potential applications of this novel MEMS fabrication technique are also briefed.
It is a high challenge to fabricate glass microstructures in Photonics and LCD industries. Different from direct ablation with ultrafast or short wavelength lasers, laser-induced-plasma-assisted ablation (LIPAA) is one of the potential candidates for transparent substrate microfabrication with conventional visible laser sources. In the processing, laser beam goes through glass substrate first and then irradiates on a solid target behind. For laser fluence above target ablation threshold, plasma generated from target ablation flies forward at a high speed. At a small target-to-substrate distance, there are strong interactions among laser light, target plasma and glass substrate at its rear side surface. With target materials deposition on glass surface or even doping into the substrate, light absorption characteristic at the interaction zone is modified, which causes the glass ablation. LIPAA is used to get color printing of characters, structures and even images on the glass substrate. It is also used to obtain the glass surface metallization for electrodes and circuits fabrication. Potential application of this technique to fabricate functional microstructures, such as micro-Total-Analysis-System (TAS) for DNA analysis and holographic diffuser for IR wireless home networking, is also discussed.
Hybrid laser processing for precision microfabrication of glass materials, in which the interaction of a conventional pulsed laser beam and another medium on the material surface leads to effective ablation and modification, is reviewed. The main role of the medium is to produce strong absorption of the nanosecond laser beam by the materials. Simultaneous irradiation of the vacuum ultraviolet (VUV)laser beam, which possesses extremely small laser fluence, with the ultraviolet (UV) laser greatly improves the ablation quality and modification efficiency for fused (VUV-UV multiwavelength excitation processing). Metal plasma generated by the laser beam effectively for assists high- quality ablation of transparent materials, resulting in microstructuring, cutting, color marking, printing and selective metallization of glass materials (laser-induced plasma-assisted ablation (LIPAA)). The detailed discussion described in this paper includes the ablation mechanism of hybrid laser processing.
Laser microprocessing has been extensively studies with applications in microelectronics, data storage and photonics. In addition to the fundamental aspects of laser materials interactions, we have investigated various applications of laser microprocessing in different areas. Laser cleaning has been studies systematically both theoretically and experimentally for dry surface cleaning and steam surface cleaning. This technology has been applied for cleaning magnetic head, magnetic sliders, suspension, laser mold cleaning and laser deflash for IC packages. Laser texturing and related processes such as laser bumping, laser tagging have been studied for magnetic recording applications. The other laser works include real-time monitoring of laser surface processing, laser-induced controllable periodic structures, laser nanopatterning by scanning probe microscope tip-enhanced laser irradiation. The further prospects of using laser microprocessing for applications in formation of ultrashallow (less than 50 nm) pn junction for next-generation MOS devices, laser generation of Si nanoparticles for quantum-dot flash memory and light emission devices are addressed.
Laser-induced -plasma-assisted ablation for crack-free laser processing of glass substrate is investigated. Different form laser breakdown at high laser fluence, a pulsed green laser is used to achieve the glass processing in air at much lower laser fluence. Laser beam goes though eh substrate first and then irradiates on a solid target behind. For laser fluence above target ablation threshold, plasma generated from target behind. For laser fluence above target ablation threshold, plasma generated from target ablation flies forward at a high speed. At a small target-to- substrate distance, there are strong interactions among laser light, target plasma and glass substrate at its rear side surface. With the target materials deposition on the glass surface or even doping into the glass substrate, light absorption characteristic at the near side surface is modified. The laser processing result is closely related to target-to-substrate distance, laser scanning speed and its repetition rate. Color marking, glass metalization and structuring can be achieved with the fine tune of the laser processing parameters.
Laser processing has large potential in the packaging of integrated circuits (IC). It can be used in many applications such as laser cleaning of IC mold tools, laser deflash to remove mold flash form heat sinks and lead wires of IC packages, laser singulation of BGA and CSP, laser reflow of solder ball on GBA, laser marking on packages and on SI wafers. During the implementation of all these applications, laser parameters, material issues, throughput, yield, reliability and monitoring techniques have to b taken into account. Monitoring of laser-induced plasma and laser induced acoustic wave has been used to understand and to control the processes involved in these applications.
Pulsed laser ablation of mold compounds for IC packaging in air and with steam assistance is investigated. It is applied to decap IC packages and expose computer CPU dies for the device failure analyses. Compared with chemical decapping, the laser ablation has advantages of being fast speed, non- contact and dry processing. Laser ablation with the steam assistance results in higher ablation rate and wider ablated crater with much smoother surface morphology. It implies that the steam assisted laser ablation can achieve a faster and better quality laser processing. Audible acoustic wave and plasma optical signal diagnostics are also carried out to have a better understanding of the mechanisms behind. Light wavelength and laser fluence applied in the decapping are two important parameters. The 532 nm Nd:YAG laser decapping at a low laser fluence can achieve a large decapping area with a fine ablation profile. IC packages decapped by the laser ablation show good quality for the device failure analyses.
A solid polythiophene pellet was ablated by a KrF excimer laser beam to deposit thin films on silicon substrates. The laser-ablated plasma was studied by optical emission spectroscopy to identify the photon-breaking of C-S bonds in the ablated heterocycles. The selective photon-induced bond breaking was also supported by Raman and X-ray photoelectron spectroscopy measurements of the deposited thin films. The thin films appeared to be composed of cubic nanocrystals with an uniform size of 240 nm. X-ray diffraction measurement determined the cubic crystal structures with a lattice constant of aequals 3.38angstrom and suggested a quasi-one-dimensional carbon chain structure along the body diagonal of the cube.
Signal generation, diagnostics and real-time monitoring during pulsed laser ablation of solid materials (silicon, metal and IC molding component) are investigated. It is found that there is rich signal emission in the laser ablation. Wide band microphone, ultrafast phototube and tiny metal probe are applied to detect acoustic, optical and electric signals generated during the laser ablation. Optical emission spectrum analyzer and high-speed ICCD photography are used to study laser-ablation-induced plasma dynamics. Signal variation with laser processing conditions during the laser ablation is analyzed. Formation of the signals is also discussed and modeled. Based on the signal diagnostics and analyses, relations between signal characteristic parameters and the laser processing conditions can be established for different applications of laser ablation in industry.
Aluminum nitride (AIN) thin films have been grown on Si(111) and Al2O3(001) substrates by pulsed KrF excimer laser (wavelength 248nm, duration 30ns) ablation of AIN target with assistance of nitrogen ion beam bombardment. The influence of process parameters such as laser fluence and laser repetition rate has been investigated to obtain high quality AIN films. The XRD spectra of AIN films on Si(111) and Al2O3(001) substrates yield full-width-half- maximum (FWHM) values of approximately 2.1-1.7 degree(s). The chemical composition of the films is characterized by X-ray photoelectron spectroscopy (XPS). The surface morphology of the films is measured by atomic force microscope (AFM). Al2O3(0001) substrate shows better matching with the AIN films since highest crystallite size can be achieved among the different type of substrates evaluated. Better quality AIN films (with bigger crystallite size) can be achieved with higher laser fluence of 6J/cm2 and an optimum laser repetition rate 7Hz.
Laser cleaning technology has been demonstrated to be an effective cleaning technique for removing particulate and film-type contaminants from solid surfaces in this paper. Dry and steam laser cleaning mechanisms and applications in semiconductor and disk drive industry will be addressed.
Laser technologies have been applied to material processing for data storage industry in a number of areas: laser cleaning of magnetic heads, laser cleaning of magnetic media, laser microtexturing of magnetic media, laser microbumping and disk tagging, laser-induced periodic structures and laser nano-etching and nanolithography by tip-enhanced laser irradiation.
Multi-level recording on rewritable phase change optical disk was studied using a simulation and experiments. The possibility of using multi-level reflection effects to increase the storage capacity was considered using a computer simulation software called phase change optical disk design. Optical and thermal simulations were carried out on disks with phase change material GeSbTe to study its performance. Using a suitable disk structure, the mark shapes of various sizes that give rise to multi-level reflection effects were written on the disk and examined. In order to solve the problem of the difference in the absorption between the crystalline and amorphous states, a thermal compensation layer of Sb was used. Simulation and experiment results have shown that the effect of the difference can be significantly reduced by the thermal compensation layer.
The Sb film is proposed as new absorption control layer for high-density phase-change optical disk. The computer simulation results show an absorption control layer in a phase-change optical disk can improve the thermal balance and direct overwriting properties of disk, and Sb film as an absorption control layer is better than Si and Ge films. The experiment results show Sb is a good absorption control layer of high-density phase-change optical disk.
Glass is a hard transparent material with many applications in Photonics and advanced display industries. It is a high challenge to achieve crack-free glass microfabrication due to its special material characteristics. Laser-induced-plasma- assisted ablation is applied in this study to get the high quality glass microfabrication. In this processing, the laser beam goes through the glass substrate first and then irradiates on a solid target behind. For laser fluence above ablation threshold for the target, the generated plasma flies forward at a high speed. At a small target-to-substrate distance, there are strong interactions among laser light, target plasma and glass materials at the rear side of the substrate. Light absorption characteristic at the glass substrate is modified since the plasma may soften and dope into the glass in the interaction area. To have a better understanding of this processing, signal diagnostics are carried out to study the dynamic interaction. It is found that glass microfabrication is closely related to laser fluence, target-to-substrate distance, laser spot size and laser beam scanning speed. With proper control of the processing parameters, glass surface marking patterning and cutting can be achieved. With different materials as the targets, color marking of glass substrate can be obtained.
The electronics structures of the Ga1-xINxNyAs1-y/GaAs compressive strained quantum wells(QWs) are investigated using 6x6 kxp Hamiltonian including the heavy hole, light hole and spin-orbit splitting band. By varying the well width and mole fraction of N in the well material, the effects of quantum confinement and compressive strain are examined. The curves of dependence of transition energy on well width and N mole fraction are obtained. The valence subband energy dispersion curves, density of states, TE and TM squared optical transition matrix elements and optical gain spectra of three possible quantum well structures for emitting 1.3micrometers wavelength are given.
The out-radial movements of pickup head in optical data storage systems are studied, and its influences on Push-pull track error signals and Differential Phase Detection (DPD) track error signals are analyzed.
KEYWORDS: Optical recording, Near field optics, Signal to noise ratio, Optical storage, Semiconductor lasers, Near field, Objectives, Data storage, Refractive index, Solids
The limitations of the conventional optical storage technology are first analyzed in this paper. The fundamental issues regarding terabytes optical recording are then discussed. Finally, the storage capacity of various approaches is presented.
A wideband and ultrafast phototube is applied to diagnose laser-induced plasma-assisted ablation of fused quartz. It is found that signal waveform is closely related to laser fluence and target-to-substrate distance. For the distance less than a threshold, below which quartz ablation takes place even by single pulse irradiation, there are three peaks detected. Signal analyses show that the first peak is attributed to laser scattering, the second and third ones to Ag target and quartz substrate ablation. It confirms that there is a direct influence of target plasma on substrate ablation. The third peak moves forward and overlaps with other peaks as the distance decreases and laser fluence increases. Peak amplitude and its arrival time of the quartz plasma are used to characterize the ablation dynamics. Signal variation with pulse number shows that at a higher distance, there are only two optical peaks attributed to laser scattering and target ablation in the first pulse. While by further pulse irradiation, the peak for quartz ablation is recorded. It is due to Ag thin film deposited on quartz rear side surface after the first pulse irradiation. As the distance increases further, the peak for quartz ablation moves to the right and finally disappears because of no thin film deposited.
Guided scrambling (GS) is proposed as channel coding for digital holographic data storage. Its property is investigated in the context of Fourier frequency domain. We show that GS provides, with a very small cost in terms of code redundancy, an effective tool for removing detrimental array patterns.
Aluminium nitride thin films were deposited at room temperature on silicon substrates by nitrogen-ion-assisted pulsed laser ablation of a hexagonal AlN target. A KrF excimer laser with pulse duration of 23 ns and wavelength of 248 nm was used as a laser source for the ablation. With this technology, it is possible to independently control the energy of the AlN radicals in the ablated plasma and the nitrogen ions in the ion beam to improve the quality of the deposited thin films. Moreover, the nitrogen ion implantation can also compensate the loss of nitrogen species in the ablation process. X-ray diffraction (XRD), Raman spectrum and x-ray photoelectron spectroscopy (XPS) were used to characterize the deposited thin films. The deposited thin films exhibit good crystal properties with sharp XRD peaks. The influences of the nitrogen ion beam energy on the electronic and structural properties of the deposited thin films were studied. The nitrogen ions can effectively promote the formation of stable Al-N bonds and improve the crystal properties of the deposited thin films. A nitrogen ion energy of 400 eV is proposed.
KEYWORDS: Imaging systems, Tolerancing, Spatial frequencies, Point spread functions, Image acquisition, Digital holography, Holographic data storage systems, Data storage, Optical engineering, Signal detection
Boron-Carbon-Nitride BxCyNz thin films were deposited by excimer laser ablation of boron carbide under nitrogen ion-beam bombardment. Thin films were deposited in the intersection of the ablated B-C plasma and nitrogen ion beam on the silicon substrates. The laser pulse energy was selected in the range of 30-100 mJ with pulse duration of 23 ns. The electronic and compositional properties of the deposited thin films were analyzed by x-ray photoelectron spectroscope, Raman and IR spectroscope, scanning tunneling microscopy and ellipsometry measurements. The influence of the ion beam bombardment on the optical, electrical and electronic properties of the deposited thin films was studied.
KEYWORDS: Finite-difference time-domain method, Optical storage, Optical discs, Multilayers, Fourier transforms, Data storage, Diffraction, Free space, Near field optics, Near field
With the development of high density optical disk storage, the characteristic size of the interaction object is comparable to the wavelength of the light which is used to read/write the disk. In this resonance region, the conventional scalar diffraction theory can not be applied to analyze the system anymore. Vector diffraction theories have been proposed to address this problem: thin film theory for treatment of the multilayer structure of flat surface, rigorous grating theory for treatment of the pre-grooved multilayer coated disk, finite methods for treatment of the pre-grooved multilayer coated disk with the presence of irregular data marks. Among the various finite methods, finite-difference time-domain (FDTD) method can treat the complex disk structure and is relatively easy to implement.5,6* But when treating focusing problem, the incident focusing beam was approximated as Gaussian plane beam previously. This is not the case in high NA optical storage system. In this paper, we propose a three dimensional FDTD method which can be used to analyze the high NA optical disk storage system.
The phase-change media, such as GeSbTe and AglnSbTe, are widely applied in rewritable DVD-RAM, CD-RW, and PD optical disks. Before information can be recorded on these disks, the initialization process that changes phase-change media from as-deposited amorphous state to crystalline state must be completed.
KEYWORDS: Point spread functions, Digital holography, Data storage, Holography, Holographic data storage systems, Charge-coupled devices, Error analysis, Digital filtering, Mathematical modeling, Optical storage
Digital holographic data storage, featuring high capacity and fast data transfer rate, has been investigated extensively in the past few years as one of the potential candidates for next generation high density data storage.
Phase change (PC) optical disk is one important type of rewritable optical disk available currently. In PC optical recording, a bit of information is written by using a laser beam to heat the disk which has been initialized to the crystalline state.
Near-field optical recording is a potential way to get higher recording density. In this technology, the Solid Immersion Lens is used to increase optical system numerical aperture, thus reduce the focused beam spot.
In an optical disk drive, seeking and following servo guarantees correct track jumps and continuous read-out signals mainly through controlling the sled movement. Till now there are much more works and publications contributed to focusing and tracking servo than to seeking and following servo, which involves non-linear effects such as friction of the sled and thus is difficult to characterise. However, to enhance the performance of an optical disk drive, a close study of the sled system is necessary to improve the seeking and following control strategy. In this paper, experiments are conducted on a SONY CD-ROM drive and a physical model of the sled system is drawn from experiment data.
KEYWORDS: Actuators, Head, Finite element methods, Optical tracking, Digital video discs, Optics manufacturing, Objectives, 3D modeling, Optical discs, Servomechanisms
Vibration analysis is an integral part of the design process for precise components, especially for higher density optical disk drives (e.g. DVD ROM/RAM). The designer often encounters challenges arising due to undesirable vibration modes in the components. The demands for precise track accessing and focusing are of importance in higher density optical disk drives. However, structural resonant vibration of mechanical components in the optical pickup head limits the tracking and focusing servo performances. Such tighter design specifications require the designer to have in-depth understanding of how structured resonance of the actuator in the optical pickup head responds to its tracking or focusing mechanism.
KEYWORDS: Digital holography, Holography, Data storage, Neural networks, Charge-coupled devices, Detector arrays, Spatial light modulators, Holographic data storage systems, Signal detection, Digital imaging
In view of the potential advantages of digital holographic data storage, such as the large storage capacity, high data transfer rate and fast access time as compared to other data storage technologies, there is intense interest in making holographic data storage technology a reality.
KEYWORDS: 3D modeling, Thermal modeling, Near field, Optical discs, Near field optics, Optical recording, Near field scanning optical microscopy, Crystals, Data storage, Diffraction
The data density of the optical recording disk is mainly dependent on the light beam spot size. In conventional optical recording system, the beam spot size, which is limited by the optical diffraction limit, can be reduced by using a shorter wavelength light source or objective lens with larger NA. Recently, near-field optical techniques have been developed to overcome the diffraction limit. In particular, Betzig et al have applied the scanning near-field optical microscope (SNOM) optics, which as a tapered fiber prove with sub-micron aperture, for use in the recording of magneto-optical (MO) media. However, the low optical coupling efficiency ofthis fiber prove need further improvement before it is practical for application in data storage. Terris et al have developed another near-field optical recording optics using the solid immersion lens that has been developed as the optics for a microscope by Mansfield and Kino. They have demonstrated the recording of the 350nm diameter mark on MO media by using the truncated spherical shaped Solid Immersion Lens (SIL).
The development of phase change recording is spurred by the demand of high capacity, low cost and rewritable optical data storage. In phase change optical disk, recording and erasing are achieved by laser heating that induces the crystallographic structural changes in the media. The difference in reflectivities of crystalline and amorphous states determines the information stored. Hence the dependence of optical and thermal effects arising from the laser irradiation on the disk needs to be thoroughly investigated. In today’s competitive marketplace, companies are looking into ways of producing better product at lower cost and shorter development time. Thus the capability of performing interactive computer modeling and analyses of the optical disk becomes inevitable to achieve these ends.
KEYWORDS: Dielectrics, Near field, Optical discs, Near field optics, Diffraction, Optical storage, Dielectric polarization, Data storage, Solids, Objectives
A variety of CD and DVD recordable and rewritable disc formats have or shortly will transition into mass market products. Apart from the inherent manufacturing complexity, this development has created very demanding requirements on unit manufacturing cost, production yields, and quality. The dynamic storage marketplace has placed additional, constantly evolving demands on product capabilities. All of this is reflected in the current approach to optical disc manufacturing equipment through their emphasis on modularity, flexibility, and upgradeability. The developments in the CD-R arena encapsulate and serve to highlight these issues and will be used as a case study.
KEYWORDS: Near field, Dielectrics, Optical discs, Near field optics, Diffraction, Optical storage, Dielectric polarization, Data storage, Solids, Objectives
Recently, the near field recording using a Solid Immersion Lens (SIL) is getting much attention to be a promising candidate of super high density optical recording. The high density recording is achieved by introducing a highindex SIL between the recording medium and the objective lens, thereby increasing the numerical aperture (NA) of the optical system and reducing the focal spot size. The SIL lens is usually a hemisphere or a super-hemisphere. The preliminary analyses of readout signal in this case have been reported.
A new thermal model to study the laser induced temperature profile of a multilayered phase change optical recording disk is proposed. The new model considers the thermal effect generated by both the transmission and reflection light. The calculation formulae are listed. The model is used to simulate the Ge2Sb2Te5 phase change optical disks with five layers structure. In order to study the differences between the new and existing models, simulations are carried out using both models and the differences are compared. The differences get larger as the phase change layer becomes thinner. It is also revealed that the differences get larger as the wavelength becomes shorter. The idea proposed in this paper is also suitable for the analysis of magneto-optical disks as well as for improved accuracy in the measurement of thermal parameters.
KEYWORDS: Tolerancing, Optical recording, Near field optics, Wavefront aberrations, Solids, Objectives, Near field, Refractive index, Data storage, Computer simulations
The tolerances of Supersphere Solid Immersion Lens (SSIL) system in aberration were analyzed. The maximum deviation between objective lens and SSIL was given in several different optical parameters. The optical coupling efficiency of the SSIL to the air space were also calculated in these cases.
A pulsed Nd:YVO4 mini disc laser pumped by a laser diode array is reported in this paper based on the end-pumping configuration with the linear plane-parallel cavity and the V- folded cavities respectively. The input-output properties and the output beam are characterized, analyzed and compared. The optical-to-optical conversion efficiency is about 51% for the plane-parallel cavity, 48% for the V-folded plane-plane cavity and high up to 68% for the V-folded concave-plane cavity. The V-folded cavities offer good TEM00 mode while the linear plane-parallel cavity operates in a multi-mode statue.
We calculate the optical gain of wurtzite (WZ) GaN/AlGaN QWs grown on the (0001) and (1010) oriented substrates, taking into account the valence subband structure modification due to the crystal orientation effect and the pseudomorphic strain which is anisotropic in the QW plane. We show that, for the (1010) GaN/AlGaN quantum well (QW), the two topmost valence subbands are more widely separated than the HH1 and LH1 subbands in the (0001) GaN/AlGaN QW. The in-plane energy dispersion of the (1010) QW also becomes anisotropic, giving rise to a reduced band-edge density-of-states in comparison with the (0001) QW. Moreover, states constituting the topmost valence subband at the (Gamma) point favor TE mode gain. A combination of the reduced band-edge density-of- states and the existence of the preferred symmetry at the valence band maximum contributes to an improvement of the TE optical gain. A comparison of the QWs of both orientations shows that the (1010) QW is capable of achieving lower transparency current densities. Therefore, the (1010) orientation is promising in improving the threshold performance of WZ GaN-based QW lasers.
A 2-D in-plane displacement sensitive fiber electronic speckle pattern interferometry (ESPI) is developed. With a fiber optics beam splitter of one input and four outputs, two sets of dual-beam interferometrical configuration are constructed in orthogonal directions to determine in-plane displacements completely. A CCD camera with a zoom lens is located at 320 mm to approximately 550 mm away from the specimen to provide adequate space for operation. A testing area ranging from 1.4 mm X 1 mm up to 30 mm X 24 mm can be examined in quasi real-time. In general, the system is capable of determining in-plane displacement and deformation generated by any means. Incorporating with the hole drilling technique, it is currently used to measure residual stress. Two applications are reported in this paper. One is to determine residual stress of a thick cylinder consisting of two concentric circular tubes with interference fit. A simple approach to interpret the value of residual stress from the displacement contour is presented. The other application is to analyze residual stress of recordable optical compact discs (CD-R).
In this presentation, the valence band mixing effect in strained quantum well structures based on the multiband effective mass theory is first presented. By using the envelope function approximation and the direct variation method, the valence band structures of some strained III-V semiconductor quantum well systems which are of interest to photonic applications are discussed. With the knowledge of the electronic wave functions and the energy band structures, optical gain behaviors of the strained quantum well systems are analyzed using the density matrix theory. The polarization dependence of the optical gain in strained layers is discussed in association with the dipole moment between the conduction band and the valence band. It is shown that biaxial compressive strain can reduce the asymmetry between conduction band and heavy-hole band masses, thus resulting in the reduction of laser threshold current as well as losses due to Auger recombination in semiconductor lasers.
Single stripe gain-guided semiconductor lasers are generally fabricated with a stripe width limited to about 3 micrometers to obtain single lateral mode operation. For lasers with larger stripe widths, the carriers under the stripe induce index antiguiding that leads to near field instability. To improve on the stability of the near field, a number of quasi-index structures have been introduced such as the rib waveguide, ridge waveguide and the channeled substrate planar striped that make use of the evanescent field coupling to induce an effective lateral index step over the striped region. Quasi-index structures control only the optical field and for stripe widths larger than 5 micrometers , control of the carrier distribution becomes important as the optical field depletes the carriers leading to an inhomogeneous distribution that aids multi- lateral mode excitation. This paper presents a V-grooved stripe contact structure that preferentially channels the carrier to the center of the stripe as well as maintaining a stable carrier distribution induced by the V-groove contact. Such a laser has been successfully fabricated by liquid phase epitaxy and is able to emit in a single lateral mode with a FWHP of 20 micrometers at up to two times threshold current. The GaAlAs laser typically has an active layer of 0.1 micrometers , cladding layer thicknesses of 3 micrometers and a p-GaAs cap layer, 6 micrometers thick, with a flat-bottom V-groove etched into it. Power output of 20 mW is measured for this prototype.
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