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.
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.
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.
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.
Fabrication of an object image inside glass material can be realized by laser direct writing with a programmable motion system. In the focus depth direction, namely Z-direction, the really formed dimension will have some difference from the distance moved by the motion system because of light refraction effect, which causes a deformation of the image from the object. Therefore, it is necessary to modify the object dimension in Z-direction in the executive program. The required amount of the dimension modification depends on the refractive index of the glass and the numerical aperture of the focus lens used. A formula for the dependence of the amount of dimension modification on the refractive index and the numerical aperture is presented based on Snell’s law. Experimental results show that the image created inside glass really reflects the dimension feature of the object with a programming dimension modification in Z-direction in terms of the formula presented. A comparison of a sphere and a cub images created inside glass with the dimension modification with that without the modification is produced for making sure the importance of the dimension modification.
In this paper, we will describe a new method to fabricate optical diffractive gratings on glass surface with direct CW CO2 laser irradiation. A laser beam with linear polarization was focused and scanned on a glass substrate. The interaction of the beam with the material irradiated results in a periodic ridge structure formation on the substrate under a well-controlled laser irradiation dose. Using multi-path scanning method, with a suitable overlap, diffractive grating with large area can be achieved. In this experiment, laser irradiation dose was 50 J/cm2, laser scanning speed was 0.2 mm/s, the diameter of focused beam was 30 ?m, and the grating period was about 8 ?m.
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.
The separation of IC packages from a BGA board is realized by means of laser multi-scan method. The laser used in the study is a double frequency Nd-YAG laser with wavelength of 532 nm. The big problem in the laser processing approach mainly arises from the multi-layer materials of BGA board with copper, polyethylene and epoxy glass fiber, because of their different absorption coefficient to the laser beam and their different absorption coefficient to the laser beam and their different heat conductivity. In the experiment approach, the effects of laser parameters, such as wavelength, on the dicing efficiency has been investigated for choosing laser. The influence of sample side for laser incidence on cut profile and, the influence of the focused extent of laser beam on singulation speed are discussed. The experimental results show that laser singulation of IC packages is efficient and reliable.
Laser bumps have been formed on the silicon surface with anisotropic patterns induced by the pulsed CO2 laser under the backside effect conditions. The microstructures are formed with periodic patterns, and vary with the laser parameters. The parallel narrow fringes have period around 2 micrometers , and the fringe orientation is in parallel with the laser polarization direction. The circular fringes with spacing around 1 micrometers appear when the laser energy increase. The fringe patterns were found to be independent on the laser pulses, therefore are re-writable. The bump formation mechanism is considered to be thermal capillary wave effect during the material melting and resolidification processes under laser irradiation. Whereas, the laser absorption may be induced by the hot electrons, or the thermal energy resulting from the laser interaction with the backside coating material.
In this paper, we are reporting a new way to do marking on IC package. In this way, white ink is wrapped in microcapsules that are coated on a transparent tape. Laser is irradiated on the tape surface, the microcapsules are broken and the ink is released onto the IC package surface. After an UV light treatment, the ink will stick on the IC surface, forming a high contrast marking. It is found that the quality of the marking depends on tape configuration, tape-IC distance, laser peak power, scan speed of laser irradiation and other laser parameters.
Laser induced temporary degeneration of transmissivity in optical materials has been observed under strong laser irradiation. In the experiment, a green light laser beam was focused onto a transparent sample, an ultra fast photo-tube was used to detect the laser signals behind the sample, an oscilloscope was used to record the amplitude change of the signals. When the laser power density on the sample increases to some levels, the detected signal starts to decrease relatively, which means the transmissivity of the sample commences to degenerate. In this case, if the laser power density is reduced back a little bit, the transmittance of the sample can restore. This means that the degeneration of the transmittance is temporary. When the laser power density increases further more after the degeneration has commenced, damage to the material will happen. Therefore, there is a transition course in material before it is damaged. The transition course is from the beginning of transmittance degeneration to damage rising. The influence of laser repetition rate on the damage formation has been also investigated.
In this report, a new way of wafer dicing is carried out by laser induced thermal shock process. This system consists of the use of a Nd:YAG laser to heat up the wafer surface following by a cooling fluid along the scanned line. The temperature gradient created by the laser heating and the gas cooling will cause a micro-crack on the wafer surface along the scanned line and the resulting crack propagation finally separate the silicon wafer into two pieces. As there is no material loss and removal during the separation process, the wafer dicing line width can be as small as sub-micron. The cross section of the wafer is smooth comparing with other separation methods and a high separation speed of 70 mm/s is achieved.
The YBa2Cu3O7-x (YBCO) superconducting thin films with Tc(R equals 0) of 84 K and Jc of 2 X 103 A/cm2 at 77 K, on polycrystalline Ni-based alloys with buffer layers of Yttria-Stabilized-Zirconia (YSZ), have been prepared in situ by excimer laser. The orientation of laser-deposited YSZ buffer layers on NiCr alloys can be improved by choosing the suitable preparing parameters. The microstructure of YBCO thin films, investigated with a scanning tunneling microscopy, shows that the spiral growth structure may be an important characteristic of the high quality YBCO superconducting thin films.
Pulsed green laser with 532 nm wavelength and 270 ns pulse duration was first used to produce a textured zone on a Ni-P disk substrate. Combining a so-called tip-writing method, typical small bumps of interest with bump diameter around 3 micrometer and with bump height about 10 - 20 nm were successfully created. A dependence of bump height on bump diameter was discussed under the case of tip-writing. And the changes of bump shapes with laser pulse energy were studied and bumps with sunflower-like shape were observed under low laser pulse energy.
A new real-time measuring method, which can simultaneously monitor laser power of 10-1500 W and mode on line has been proposed in detail. The experimental result are in well agreement with the real situations and is very useful in high power laser applications in industry.
In-situ laser deposition was used to fabricate YBa2Cu3O7-x superconducting films on YSZ substrates. The surface topography of YBa2Cu3O7-x thin films has been studied with both atomic force microscopy (AFM) and scanning tunneling microscopy (STM). A stepped surface is clearly observed on the mounds with a single step edge the originates from a screw dislocation at the center of the mound and moves out to the edge in a spiral fashion. The experimental result show that the spiral growth structure is an intrinsic character of superconductor films. The existence or absence of the spiral growth structure and the quality of the spiral structures may have significant implications for properties of the high temperature superconducting thin films. The new visual details may lead to improvements of YBCO films.
Diamondlike thin films were prepared by irradiation of high purity graphite with a high power density( 1.178 x I 09 Watt I cm2 ) laser (XeCI 308 nm) in the vacuum ( I x 10-s Torr) . Raman spectra show the thin film with the properties of diamond, the scatter peak is in round 1330 cm-1 . The IR spectra show the thin film containing C-H bonds, and the ratio ofH to C is about 45%. The resistivity and optical energy gap of the thin film are 1.89 x 106 .0 .cm and 1.55 e. V, respectively. Keywords: Pulsed Laser deposition, Diamondlike thin film, Raman spectra.
Laser induced permanent electrical conductivity was observed in polyimide and in initially non-conducting Ag/polyimide composites using the fourth harmonic of a Q-switched Nd:YAG laser. The critical number of laser pulses required for the metal-insulator phase transition in polyimide was less than 100, compared to the 300-350 pulses required when using a KrF excimer laser. The presence of the Ag in the composite contributed to the conducting volume fraction in the material and therefore further lowered the critical number of laser pulses to less than 50. These experiments represent a unique experimental demonstration of 'two-color' percolation, in which percolation occurs with two different types of conductors.
Hydrogenated amorphous silicon films have been crystallized by the irradiations of XeCl excimer laser. The crystallized films have been examined by the use of scanning electron microscopy (SEM), x-ray diffraction (XRD) and conductivity measurements to clarify their morphologies, structure and electrical properties. The results show that a high conductive super thin layer is formed by a single pulse laser irradiation with the energy density of 75mJ/cm2. The conductivity increases quickly at laser energy density threshold which decreases when the hydrogen in a-Si:H films is removed by pre-annealing. During crystallization process, oxygen atoms from the air ambient have been introduced into the films and such an introducing process is hindered by the hydrogen eruption. When the oxygen content is high enough, the carrier-transport mechanism includes thermionic emission and thermionic field emission in the vicinity of room temperature, which is similar to semi-insulating polycrystalline silicon.
A high current density YBa2Cu3O7-x (YBCO) superconducting thick film on a flexible NiCr alloy substrate tape with ZrO2 + 10 percent Y2O3 (YSZ) as buffer layer was prepared by pulsed laser deposition. The buffer layer YSZ of thickness 0.3 micrometers was formed on the NiCr alloy substrate tape of length 6.0 cm by ion-assisted pulsed laser deposition. The YBCO superconducting thick film with thickness 1.5 micrometers was deposited on the YSZ/NiCr alloy substrate tape by a KrF laser. The x-ray diffraction pattern indicates that the YBCO superconducting thick film is with strongly C-axis oriented. The critical current densities versus temperature and magnetic field were measured by standard four-point probe method, the values of critical current density and the critical temperature of the YBCO/YSZ/NiCr alloy superconducting tape are 8.75 X 104 A/cm2 and 88.7 K, respectively.
The paper studies the process of photostimulated aggregation of ultradispersoidal silver particles into fractal clusters observed in some colloidal solutions irradiated by different types of pulsed and continuous-wave lasers and by a nonmonochromatic light. A photoaggregaton mechanism has been proposed, based on mutual charging of different-size particles in a conducting medium when the Fermi potentials become equal because of their dimensional dependence.
This paper is aimed at discussing the basic principles of light-induced drift (LID) and estimating the characteristic of the effect, produced by quasi-black-body radiation. Many astrophysical objects as well as laser-produced plasmas may be described by that model in the first approximation. The feasibility is analyzed of converting the radiation of the most efficient cw laser (a technological CO2 laser) via laser-produced plasma into a broad-band radiation to be used as a source of LID of a wide range of substances.
High Tc superconducting films with zero resistance temperature of 91 K and critical current density about 105 A/cm2 at 77 K have been reproductively fabricated using oxygen discharge plasma-assisted excimer laser ablation method. Scanning electron micrographs and x-ray diffraction patterns of the films showed that these kinds of in situ prepared films had excellent epitaxial quality with its C axis oriented perpendicular to the substrate surface.
Superconducting thin films of Y-Ba-Cu-O on zirconia substrate are prepared using excimer laser (308 nm, 28 ns) ablation of a superconducting Y-Ba-Cu oxide disk without plasma assistance in the substrate temperature range from 450 - 550 degree(s)C. The high or low- temperature post-annealing in an oxygen atmosphere is not necessary. The highest zero resistance temperature of the produced film is up to 91.5 K. X-ray diffraction spectra reveal that the thin films are preferential x-axis orientation normal to the surface. The key to the success is increasing the oxygen pressure in the deposition chamber to about 220 mTorr and making the ejected oxygen interact with the laser beam before it comes to the deposition area. The influences of the oxygen pressure ejected into the chamber, of the laser flux density and of the substrate temperature on the superconducting property of the produced thin films are discussed.
The luminescence spectra of the ejected particles from laser ablation of the superconductor was measured with the optical spectrum analyzer. In the experiment, the Y-Ba-Cu-O superconductor was adopted as target. When it was bombarded with excimer laser pulse, the target materials evaporated and luminescence plasma plume was formed above the target surface. By identifying the emission spectrum lines, the types and excited states of the ejected particles was determined. Meanwhile, the characteristics of the velocity distribution and luminescence intensity distribution of the ejected particles were studied by time- and space- resolved spectroscopic techniques.
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