NASA is striving to develop a scientific understanding of the universe, the Earth-Sun System and the Earth's response to natural or human-induced changes. Space lasers are vital tools for NASA's missions to advance our understanding of space research and improving our prediction capability for climate, and natural hazards. Unfortunately, several past spaceflight missions that utilized lasers proved to be short-lived and unreliable. In this paper, we are shedding more light on the contamination issue in the absence of gravity. We performed a set of relevant experiments on liquids and subsequently correlated the results to the spaceflight laser environment. We found that in the absence of gravity the contamination plays a major role in spaceflight laser failures. We also proposed a methodology using the adsorption mechanism to be adopted in future spaceflight lasers to minimize the presence of contaminants in the laser compartment.
We have measured the rc (effective electrooptical coefficient) of pure and doped Ferroelectric Lithium Niobate (LN) using a single beam, null detection polarimeter. The polarimeter is adjustable between two adaptive optics configurations--an iris hard stop beam pattern on the one hand and a diffractive optics generated top-hat beam on the other. We clearly show the need to control thermal heating of LN due to the transmitted laser beam. The required heating control has been implemented using a fabricated metallic heat sink called a "Cold Finger." In addition to its electrooptical properties, LN possesses a combination of unique piezoelectric, pyroelectric, and photorefractive properties. These properties make it suitable for applications in optical devices as frequency doublers, modulators, switches, and filters in communication systems and holographic recording medium. We present the classical microscopic anharmonic oscillator description for generating Pockels coefficients, and briefly describe the polarimetry measurement system. Here, the growth of pure and iron doped lithium Niobate is also described using an Automatic Diameter Control Czochralski Design growth technique. The results of growth, electrooptic measurements, adaptive optics implementation and some physical properties are compared and presented.
Space Lasers are vital tools for NASA's space missions and military applications. Although, lasers are highly reliable on the ground, several past space laser missions proved to be short-lived and unreliable. In this communication, we are shedding more light on the contamination and radiation issues, which are the most common causes for optical damages and laser failures in space. At first, we will present results based on the study of liquids and subsequently correlate these results to the particulates of the laser system environment. We present a model explaining how the laser beam traps contaminants against the optical surfaces and cause optical damages and the role of gravity in the process. We also report the results of the second harmonic generation efficiency for nonlinear optical crystals irradiated with high-energy beams of protons. In addition, we are proposing to employ the technique of adsorption to minimize the presence of adsorbing molecules present in the laser compartment.
Photo-thermo-plastic film (PTPF) is a multi-layer structure with the resolving power up to 1000 line pairs per millimeter in the binary and/or half-tone optical data recording modes. These structures are high-sensitive in the spectral range from 400 to 800 nm which is determined by chalcogenide glassy semiconductors (CGS) layer in the PTPF. We technologically challenged the CGS by tin-doping; this allows satisfying to main requirements which high-efficient observation systems are demanding.
PTPF-based devices imply some critical elements for providing PTPF sensitization by means of the corona discharge as well as thermal development of the latent image to the form of superficial relief on the PTPF. Such PTPF-based slit camera was used for airborne monitoring of the Black Sea surface from the 9000-m-altitude. Camera resolving power is high enough for determining of waves heights and spacing as well for discovering of small sea objects and determining of their speed and drift direction. PTPF-based remote sensing seems to be even more advantageous due to the possibility to record different images multiple (up to 100) times on a single PTPF frame within the "recording - read-out - thermal erasing - re-recording" cycle.
An algorithm for automatic measurements of the sea surface conditions is proposed. The measured parameters are height and spacing of waves as well as their motion direction. Mathematical processing includes 2-D smoothing of sample data, forming 1-D profile of the waves, and calculating its Fourier transform. By introducing of the scale factors, it makes possible to obtain certain data on the waves' characteristics. This system allows compressing of 2-D information to numerical data flow which is characterizing the rough seas and transmitting of these data through communication channels.
Photo-thermo-plastic films (PTPF) with high-density recording (up to 1000 lines/mm) can be used repeatedly for structure zoned shooting. However, more work is underway to increase their light sensitivity and make it resistant to action of radioactive and powerful electromagnetic radiation. It was found that chalcogenide glass semidonductors (CGS) combine properties of both glasses and semiconductors that determine possibility of its using in different systems of optical data recording. Most bright prepresentatives of glass semiconductors are being sulfide and selenide of arsenic. Results of complex investigations on photelectric properties of their thin layers are presented.
The paper presents results of technological changing of the field of maximal photosensitivity of CGS layers in the range of optical spectral range from 400 to 800 nm, which satisfies requirements of optical data recording systems for spectrum-zoned-shooting. For increasing of CGS thin layers' photsensitivity the initial materials were doped by tin. Experiments have shown that doping by Sn on the level 1.2-1.4 at % increases photosensitivity of layer by more than one order of magnitude. High photosensitivity of obtained PTPF determines possibility of their wide application in different optical image registration systems, which can be used as board memory devices.
Investigation of electro-optic modulation in nonlinear materials placed within a Fabry-Perot modulator cavity is presented. Enhanced modulation at lower driving voltages is demonstrated in several materials including, LiNbO3 as well as thin films of organic compounds like COANP and NPP. Associated mechanical factors contributing to modulation are also described.
We have observed regenerative optical and electrical pulsations in Fe-doped photogalvanic/photorefractive crystals LiNbO3 (LN). Rise time of the emitted electromagnetic pulses was 2 ns and amplitude of up to 10V for Continuous Wave (CW) laser power 50-200 mW. Optical pulsators, predicted by our theoretical approach were realized in LiNbO3:Fe crystals using Ar-ion laser, of wavelength 514 and 457 nm, and power P= 50-200 mW, with frequencies of pulsation ranging from sec to msec. The arrays of the Optical Photogalvanic Pulsators (OPP) may be constructed as a testing field for a novel parallel processing logic based on the pulsed-couple neural networks (PCNN). We have also tested the synchronous nature of the optical, electrical and piezoelectric signals.
We have observed the conversion of CW laser Ar-ion beam power into pulsating multi-channel outputs: optical, electric and piezoelectric with simultaneous dynamic pattern formation. Frequencies of multi-channel pulsations have characteristic sigmoidal dependence (with threshold) on laser intensity. We have also demonstrated the possibility of synchronization of two optical pulsators, through regulated optical coupling in a photorefractive LiNbO3 crystal. Spatial distribution of scattered light is selforganized in different patterns (hexagonal and cross-type)
The volume holographic gratings in polymer materials are promising candidates for spectrally selective optical elements, dense data storage, optical communication, and spectral selective imaging. Recently new application of volume reflection-type grating for fast all-optical temporal/spatial light modulators was suggested. Spatial modulation of diffracted red beam by green laser was demonstrated. We also suggest and analyze theoretical model for material with diffusional amplification for different modes of recording: (1) Fast recording with following annealing; (2) Slow recording (real-time grating).
Polydiacetylene derivative of 2-methyl-4-nitroaniline (PDAMNA) shows a picosecond switching property, which illustrated a partial all-optical picosecond NAND logic gate. The switching phenomenon was demonstrated by waveguiding two collinear beams at 633 nm and 532 nm through a hollow fiber of 50 micrometers diameter, coated from inside with a thin film of PDAMNA. A Z-scan investigation of a PDAMNA thin film on quartz substrate revealed that the switching effect was attributed to an excited state absorption in the systems. The studies also showed that the polymer suffers a photo-oxidation beyond an intensity level of 2.9x106 w/cm2. The photo-oxidized film has different physical properties that are different from the original film before oxidation. The lifetime of both excited states before and after oxidation as well as their absorption coefficients were estimated by fitting a three level system model to the experimental results.
We suggest to use modulation of distributed feedback in the volume reflection type diffractive periodic structures for the fast all-optical spatial-temporal light modulators. Different types of periodic structures are discussed: cholesteric liquid crystals, static and dynamic reflection gratings in the photorefractive crystals and photopolymers.
Recently, we have demonstrated a picosecond all-optical switch, which also functions as a partial all-optical NAND logic gate using a novel polydiacetylene that is synthesized in our laboratory. The nonlinear optical properties of the polydiacetylene material are measured using the Z-scan technique. A theoretical model based on a three level system is investigated and the rate equations of the system are solved. The theoretical calculations are proven to match nicely with the experimental results. The absorption cross-sections for both the first and higher excited states are estimated. The analyses also show that the material suffers a photochemical change beyond a certain level of the laser power and its physical properties suffer radical changes. These changes are the cause for the partial NAND gate function and the switching mechanism.
A numerical simulation model of two-beam interaction in photorefractive polymers is presented. Higher diffraction orders and beam fanning are included in the model. The simulation results were found to agree precisely with theoretical predictions and experiments. Edge enhancement of images in a two-beam coupling geometry is predicted.
Phthalocyanine films have been synthesized by vapor deposition on quartz substrates. Some substrates were coated with a very thin gold film for introducing electrical fie.d These films have been characterized by x-ray diffraction and scanning electron microscopy. The films have excellent chemical and optical stability. However, the surface of these films grown without electrical field shows whisk-like morphology. When films are deposited under an electrical field, a dense film with flat surface is obtained. A change of film in growth orientations and solid state phase is also observed for the film synthesized under electrical fields.
Conventional electronic logic circuits in today's computers impose extreme limitations on computational speed, complexity, compactness. In highly dense electronic logic circuits the connections simply cannot handle electric signals swiftly and reliably. On the other hand, optical interconnections and optical integrated circuits are sought to provide answers to future computing and compactness demands. Optical devices are immune from electromagnetic interference and free from electrical short circuits. They have low-loss transmission and provide large bandwidth (i.e. multiplexing capability), and are manufacturable in compact sizes, are lightweight and inexpensive.
Recently, we demonstrated an all-optical NAND logic gate having nanosecond response time by waveguiding two collinear nanosecond white light caused by focusing a pulsed Nd:YAG laser at 1064 nm along with a cw He-Ne laser at 632.8 nm through a polydiacetylene derivative of 2-methyl-4- nitroaniline (PDAMNA) thin film. The physics involved in the process was explained based on Z-scan studies of the same polymer using He-Ne laser. These studies show an induced absorption by an excited state, resulting in a reverse saturable absorption (RSA) in the system. The RSA figure of merit in PDAMNA was estimated. The size and sign of the real and imaginary parts of the third order nonlinearity were evaluated. These studies also demonstrate for the first time to our knowledge, that reverse saturable absorption in an optical system can be used to build similar logic gates.
We describe a simple yet efficient technique of delineation of various polymer MEMS structures using computer driven liquid jet dispenser. A syringe-type dispenser with a replaceable needle is filled with a polymer solution and mounted on a vertical translation stage. The substrate is mounted on two-coordinate horizontal translation stage. Additional vertical translation arm is connected to the plunger of the syringe. Vertical translation provides positioning of the needle at a certain height over the substrate. Delineation is accomplished when the syringe plunger, being pushed down by the vertical translation arm, dispenses the liquid on the substrate at a programmable flow rate simultaneously with horizontal motion of the substrate with respect to the needle. Horizontal motion is done along a programmable trajectory at a programmable sped. Comparing to conventional methods, the proposed device consumes three order of magnitude less amount of material for the fabrication of similar MEMS structures. In addition, we describe a supplement to the liquid delineation system in the form of a microscope objective head connected to a noncoherent UV source with a multimode optical fiber. The head can serve as a tool for UV curing of the polymer material deposited with the jet dispenser as well as a separate UV writing tool. In conclusion, we describe the calculation technique for the distribution of the electric field in electrically or optically controlled ferroelectric polymer MEMS fabricated by the proposed technique.
Polydiacetylenes (PDAs) are attractive materials for both electronic and photonic applications because of their highly conjugated electronic structures. They have been investigated for applications as both 1D conductors and nonlinear optical (NLO) materials. One of the chief limitations to the use of PDAs has been the inability to readily process them into useful forms such as films and fibers. In our laboratory we have developed a novel process for obtaining amorphous films of a PDA derived from 2- methyl-4-nitroaniline using photodeposition with UV light from monomer solutions onto transparent substrates. Photodeposition from solution provides a simple technique for obtaining PDA films in any desired pattern with good optical quality. This technique has been used to produce PDA films that show potential for optical applications such as holographic memory storage and optical limiting, as well as third-order NLO applications such as all-optical refractive index modulation, phase modulation and switching. Additionally, copolymerization of diacetylenes with other monomers such as methacrylates provides a means to obtain materials with good processibility. Such copolymers can be spin cast to form films, or drawn by either melt or solution extrusion into fibers. These films or fibers can then be irradiated with UV to photopolymerize the diacetylene units to form a highly stable cross-linked PDA-copolymer network. If such films are electrically poled while being irradiated, they can achieve the asymmetry necessary for second-order NLO applications such as electro-optic switching. On Earth, formation of PDAs by the above mentioned techniques suffers from defects and inhomogeneities caused by convective flows that can arise during processing. By studying the formation of these materials in the reduced-convection, diffusion- controlled environment of space we hope to better understand the factors that affect their processing, and thereby, their nature and properties. Ultimately it may even be feasibly to conduct space processing of PDAs for technological applications.
We present the results on fabrication of plastic integrated optical elements using molding, liquid jet delineation, and UV irradiation. Coupling gratings with a period of 620 mm-1 and a diffraction efficiency of 3.3 percent were molded in a preheated poly(methyl methacrylate) planar waveguide using master saw shaped grating. An experimental device is also described which uses computer controlled micro syringe to dispense polymer solution onto a moving substrate. This device consumes thousand times less material to produce integrated optical circuits than equivalent spin- casting equipment.We have made various structures such as Y- branches and Mach-Zehnder interferometers. All the structures demonstrated good performance. The same device was also equipped with a microscope-type UV illuminator for noncontact delineation of optical structures in polyimide films. The operation is based on the refractive index increase due to photo-oxidative decomposition of the material. The index difference 0.02 between exposed and unexposed regions is sufficient to define light guiding channels in polyimide without using liquid developing. UV radiation was also used to make graded-index polyimide waveguides. Their refractive index profile was successfully reconstructed by a specially developed calculation technique. All the techniques combined together give us the cost efficient tool for the fabrication of plastic integrated optics.
We present the results of study of thin film optical waveguides based on photocrosslinkable polyimide with glass transition temperature approaching 400 degrees C. The birefringence of the waveguides can possibly be reduced by eliminating the effect of gravity on the conditions of the film fabrication. We propose fabrication technique that allows us to change the orientation of the substrate and to analyze the gravity effect on the polyimide waveguide. This technique uses UV assisted film deposition from polyimide solution on a transparent substrate mounted as a removable wall of the container with the solution. The technique is also suitable for film fabrication at low gravity conditions. In order to investigate possible effects that can occur during UV assisted liquid deposition at low gravity, we studied UV exposed polyimide films made by spin coating at normal conditions. We describe the appearance of a gradient index waveguide on the top of polyimide coat exposed to UV light. The proposed mechanism of the waveguide formation includes photocrosslinking followed by UV assisted modification of the material which leads to the increase of the optical absorbance in UV region accompanied by the refractive index increase in visible region. Theoretical model based on this approach allowed us to reconstruct the refractive index profile n the waveguide. The profile is in good agreement with that obtained from the waveguide mode spectrum measured with prism coupling technique.
In this paper, we will take a closer look at the state of the art of polydiacetylene, and metal-free phthalocyanine films, in view of the microgravity impact on their optical properties, their nonlinear optical properties and their potential advantages for integrated optics. These materials have many attractive features with regard to their use in integrated optical circuits and optical switching. Thin films of these materials processed in microgravity environment show enhanced optical quality and better molecular alignment than those processed in unit gravity. Our studies of these materials indicate that microgravity can play a major role in integrated optics technology. Polydiacetylene films are produced by UV irradiation of monomer solution through an optical window. This novel technique of forming polydiacetylene thin films has been modified for constructing sophisticated micro-structure integrated optical patterns using a pre-programmed UV-laser beam. Wave guiding through these thin films by the prism coupler technique has been demonstrated. The third order nonlinear parameters of these films have been evaluated. Metal-free phthalocyanine films of good optical quality are processed in our laboratories by vapor deposition technique. Initial studies on these films indicate that they have excellent chemical, laser, and environmental stability. They have large nonlinear optical parameters and show intrinsic optical bistability. This bistability is essential for optical logic gates and optical switching applications. Waveguiding and device making investigations of these materials are underway.
The transient multiple diffraction rings associated with self-phase modulation is observed from PMMA doped with different dyes. The phenomenon is shown to be the result of laser-induced refractive-index change. The experiment is done on three different films fo PMMA doped with sulfrodamine, DCM, and Accriden yellow. The films were fabricated using the spin coating technique. The Ar+ laser at 514 nm was used as the exciting beam to the thin film. The transmitted laser formed interference fringes on a projection screen. It is observed that by increasing the thickness of the film, the number of rings increased. The relation between the thickness of the thin film and the number of rings was found to be different for the three films. This could be explained as the induced thermal refractive index coefficient in each of the samples depending on the strength of absorption of the 541 nm line by each material. It is also found that the third order nonlinear susceptibility enhanced with increasing the thickness of PMMA doped with Accriden yellow. The results also indicate the sensitivity of the transport phenomena in PMMA by changing the guest/host combination and the polymer doped with dye could be optimized for certain applications.
The charactertization of light guiding and nonlinear optical properties of thin films based on poly(methyl methacrylate) doped with organic dyes 4-dicyanomethylene-2-methyl-6-p- dimethylaminostyryl-4H-pyran (DCM), Pyrromethene 567, and sulforhodamin was done using the prism coupling technique and nonlinear optical spectroscopy. Stimulated light emission in DCM doped waveguide with apparent pump threshold and spectrum narrowing was observed at transverse pumping with frequency doubled Q-switched Nd:YAG laser. PM-567 doped waveguide being transversely pumped with CW Ar+ laser at 514 nm demonstrated fluorescence with 0.19% energy conversion slope efficiency at 616 nm spectral peak. Upconverted fluorescence was found in the same waveguide at longitudinal CW infrared pumping. Sulforhodamin doped films demonstrated multiphoton excited fluorescence and surface enhanced second harmonic generation.
It was demonstrated experimentally, that recording of photorefraction gratings BaTiO3 crystals can be realized with nonoverlapping in time 80 ps pulses of Nd:YAG laser ((lambda) equals 532 nm). This phenomenon of dynamic memory is explained by asymmetry of writing-reading mechanisms with simultaneous phase-conjugation.
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