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Investigation of the factors determining the modulation characteristics of gas-discharge IR sources
The effect of design parameters and voltage of pulsed cesium sources with sapphire envelopes on their modulation characteristics are considered for the following combinations of operating parameters: the average repetition rate of current pulses up to f{sub i} = 1.0 kHz and the consumed electric power up to P{sub l} = 3 kW for the spectral range 3-5 {mu}m; f{sub i} = 1.0-8.0 kHz and P{sub l} up to 1.0 kW for the spectral range 0.8-2.7 {mu}m. Recommendations on further improvement of the modulation characteristics of lamps are given.
Interaction of near-IR laser radiation with plasma of a continuous optical discharge
The interaction of 1.07-μm laser radiation with plasma of a continuous optical discharge (COD) in xenon and argon at a pressure of p = 3–25 bar and temperature of T = 15 kK has been studied. The threshold power required to sustain COD is found to decrease with increasing gas pressure to P{sub t} < 30 W in xenon at p > 20 bar and to P{sub t} < 350 W in argon at p > 15 bar. This effect is explained by an increase in the coefficient of laser radiation absorption to 20−25 cm{sup –1} in Xe and 1−2 cm{sup –1} in Ar due to electronic transitions between the broadened excited atomic levels. The COD characteristics also depend on the laser beam refraction in plasma. This effect can be partially compensated by a tighter focusing of the laser beam. COD is applied as a broadband light source with a high spectral brightness.
Molecular beam epitaxy of thermodynamically metastable GaInAsSb alloys for medium IR-range photodetectors
The features of growth of GaInAsSb alloy with In content as high as 25 mol % lattice-matched to GaSb by molecular beam epitaxy are studied. These alloys are promising for use as the active region of photodetector structures of the mid-infrared range. The results of the study of these alloys by double-crystal X-ray diffractometry, scanning electron microscopy, and photoluminescence are presented. It is shown that the Ga{sub x}In{sub 1-x}As{sub y}Sb{sub 1-y} alloys with x < 0.8 grown at 500 deg. C show the degradation of structural and optical properties as the layer thickness is increased. In layers with thicknesses above the critical one, spinodal decomposition is observed in complete agreement with thermodynamic calculations of the location of the boundaries of immiscibility regions. The possibilities to optimize the molecular beam growth of the Ga{sub x}In{sub 1-x}As{sub y}Sb{sub 1-y} alloys (x < 0.75) with high optical and structural quality, as well as the characteristics of photodetectors based on the GaInAsSb/AlGaAsSb heterostructures, are discussed.
Study of the processes of carbonization and oxidation of porous silicon by Raman and IR spectroscopy
Porous silicon layers were produced by electrochemical etching of single-crystal silicon wafers with the resistivity 10 {Omega} cm in the aqueous-alcohol solution of hydrofluoric acid. Raman spectroscopy and infrared absorption spectroscopy are used to study the processes of interaction of porous silicon with undiluted acetylene at low temperatures and the processes of oxidation of carbonized porous silicon by water vapors. It is established that, even at the temperature 550 Degree-Sign C, the silicon-carbon bonds are formed at the pore surface and the graphite-like carbon condensate emerges. It is shown that the carbon condensate inhibits oxidation of porous silicon by water vapors and contributes to quenching of white photoluminescence in the oxidized carbonized porous silicon nanocomposite layer.
On a silicon-based photonic-crystal cavity for the near-IR region: Numerical simulation and formation technology
The production technology of a photonic-crystal cavity formed as a group of holes in a silicon strip waveguide by ion-beam etching is described. The parasitic effect associated with hole conicity which develops upon hole formation by the given technology is studied. Numerical simulation shows that the hole-conicity induced decrease in the cavity quality factor can be compensated with consideration for the hole volume. The influence of the waveguide thickness on the resonance wavelength and quality factor of the photonic-crystal cavity is analyzed.
CdHgTe heterostructures for new-generation IR photodetectors operating at elevated temperatures
The parameters of multilayer Cd{sub x}Hg{sub 1–x}Te heterostructures for photodetectors operating at wavelengths of up to 5 μm, grown by molecular-beam epitaxy (MBE) on silicon substrates, are studied. The passivating properties of thin CdTe layers on the surface of these structures are analyzed by measuring the C–V characteristics. The temperature dependences of the minority carrier lifetime in the photoabsorption layer after growth and thermal annealing are investigated. Samples of p{sup +}–n-type photodiodes are fabricated by the implantation of arsenic ions into n-type layers, doped with In to a concentration of (1–5) × 10{sup 15} cm{sup –3}. The temperature dependences of the reverse currents are measured at several bias voltages; these currents turn out to be almost two orders of magnitude lower than those for n{sup +}–p-type diodes.
On the laser lift-off of lightly doped micrometer-thick n-GaN films from substrates via the absorption of IR radiation in sapphire
The intense absorption of CO{sub 2} laser radiation in sapphire is used to separate GaN films from GaN templates on sapphire. Scanning of the sapphire substrate by the laser leads to the thermal dissociation of GaN at the GaN/sapphire interface and to the detachment of GaN films from the sapphire. The threshold density of the laser energy at which n-GaN started to dissociate is 1.6 ± 0.5 J/cm{sup 2}. The mechanical-stress distribution and the surface morphology of GaN films and sapphire substrates before and after laser lift-off are studied by Raman spectroscopy, atomic-force microscopy, and scanning electron microscopy. A vertical Schottky diode with a forward current density of 100 A/cm{sup 2} at a voltage of 2 V and a maximum reverse voltage of 150 V is fabricated on the basis of a 9-μm-thick detached n-GaN film.
The temperature dependence of the conductivity peak values in the single and the double quantum well nanostructures n-InGaAs/GaAs after IR-illumination
The dependences of the longitudinal and Hall resistances on a magnetic field in n-InGaAs/GaAs heterostructures with a single and double quantum wells after infrared illumination are measured in the range of magnetic fields Ð’ = 0–16 T and temperatures T = 0.05–4.2 K. Analysis of the experimental results was carried out on a base of two-parameter scaling hypothesis for the integer quantum Hall effect. The value of the second (irrelevant) critical exponent of the theory of two-parameter scaling was estimated.
Effect of H{sup +} implantation on the optical properties of semi-insulating GaAs crystals in the IR spectral region
The optical properties of semi-insulating GaAs crystals subjected to multienergy hydrogen-ion implantation and treatment in a high-frequency electromagnetic field are studied in the infrared spectral region. It is established that such combined treatment provides a means for substantially increasing the transmittance of GaAs crystals to values characteristic of crystals of high optical quality. On the basis of analysis of the infrared transmittance and reflectance data, Raman spectroscopy data, and atomic-force microscopy data on the surface morphology of the crystals, a physical model is proposed to interpret the effects experimentally observed in the crystals. The model takes into account the interaction of radiation defects with the initial structural defects in the crystals as well as the effect of compensation of defect centers by hydrogen during high-frequency treatment.
On the Formation of IR-Light-Emitting Ge Nanocrystals in Ge:SiO{sub 2} Films
The study is concerned with light-emitting Ge nanocrystals formed during the annealing of Ge{sub x}[SiO{sub 2}]{sub 1–x} films produced by the high-vacuum cosputtering of germanium and quartz targets onto substrates at a temperature of 100°C. In accordance with the conditions of growth, the Ge molar fraction was varied from 10 to 40%. By means of electron microscopy and Raman spectroscopy, amorphous Ge nanoclusters ~4–5 nm in dimensions are detected in as-deposited films with a Ge content higher than 20 mol %. To crystallize amorphous nanoclusters, annealing at temperatures of up to 650°C is used. The kinetics of the crystallization of Ge nanoclusters is studied, and it is established that up to ~1/3 of the amorphous phase is retained in the system, supposedly at the interfaces between nanocrystals and the surrounding amorphous SiO{sub 2} matrix. It is found that, upon annealing in normal atmosphere, germanium nanoclusters are partially or completely oxidized (at a Ge molar fraction of 30% and smaller). An intense infrared photoluminescence signal from quantum-confined Ge nanocrystals and a visible photoluminescence signal defined by defect complexes (oxygen vacancy + excess Ge atoms) are observed.
Prospects for Practical Applications of a Discharge Chemical HF Laser as a Coherent Source for IR Holography
Preliminary experimental results on recording of phase and amplitude holograms using the radiation of electric-discharge HF lasers are presented, and prospects for applications of such lasers in diagnostics of various objects are discussed. It is shown that lasers with homogeneous working medium may generate coherent radiation with a coherence length of greater than 6 m in the absence of mode selection. Methods for control of spatial distribution of electron concentration in excimer and discharge chemical HF (DF) lasers and distributions of the main combustible components are considered. Deposition of holographic identification marks on artworks is studied.
IR challenges and the machine detector interface at FCC-ee
The FCC-ee, with its unprecedented luminosity goal and high energy reach, creates challenges and requires solutions to many issues in order to produce a realistic design for the complex machine detector interface. The interaction region design for the FCC-ee adopts the crab-waist collision scheme and proposes an elegant local chromaticity correction system. An asymmetric layout of nearby dipoles suppresses the critical energy of synchrotron radiation incoming to the detector at the interaction point to a maximum value of 100 keV. The main challenge of the FCC-ee machine detector interface design is to combine the many conflicting accelerator and 2 T detector constraints, aiming for the optimal trade-off choices that simultaneously allow for a best machine performance in terms of integrated luminosity and data taking efficiency. Much of the success of the FCC-ee will be related to the interaction region design, as a result of the ingredients coming from areas of accelerator physics, mechanical engineering and detector optimization.
Temperature-Dependent Kinetics and Reaction Mechanism of Ammonia Oxidation on Pt, Ir, and PtIr Alloy Catalysts
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Short-Lived Intermediate in the N2O Generation by P450 NO Reductase Captured by Time-Resolved IR Spectroscopy and XFEL Crystallography
Diffraction images were collected using an MX300-HS CCD detector. For each cryoloop, 2D raster scan with 50 μm step in each direction was performed twice. In the second pass, the raster-scan grid was shifted 25 μm in each direction. In cheetah directory, - {puck_name}/{pin_id}_hits.h5 correspond to the first scan, and - {puck_name}/{pin_id}-2_hits.h5 correspond to the second scan.
ComPile: A Large IR Dataset from Production Sources
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Near-IR absorption in high-purity photothermorefractive glass and holographic optical elements: measurement and application for high-energy lasers
Volume Bragg gratings (VBGs) in photothermorefractive (PTR) glass are widely used for laser beam control including high-power laser systems. Among them, spectral beam combining based on VBGs is one of the most promising. Achieving 100+ kW of combined laser beams requires the development of PTR glass and VBGs with an extremely low absorption coefficient and therefore methods of its measurement. This paper describes the calorimetric method that was developed for measuring a low absorption coefficient in PTR glass and VBGs. It is based on transmission monitoring of the intrinsic Fabry-Perot interferometer produced by the plane-parallel surfaces of the measured optical elements when heated by high-power laser radiation. An absorption coefficient at 1085 nm as low as 5x10{sup -5} cm{sup -1} is demonstrated in pristine PTR glass while an absorption coefficient as low as 1x10{sup -4} cm{sup -1} is measured in high-efficiency reflecting Bragg gratings with highest purity. The actual level of absorption in PTR glass allows laser beam control at the 10 kW level, while the 100 kW level would require active cooling and/or decreasing the absorption in PTR Bragg gratings to a value similar to that in virgin PTR glass.
IR permittivities for silicides and doped silicon
The complex permittivity for Pt, Pd, Ni, and Ti-silicide films as well as heavily doped p- and n-type silicon were determined by ellipsometry over the energy range 0.031 eV to 4.0 eV. Fits to the Drude model gave bulk plasma and relaxation frequencies. Rutherford backscattering spectroscopy, X-ray diffraction, scanning electron microscopy, secondary ion mass spectrometry, and four-point probe measurements complemented the optical characterization. Calculations from measured permittivities of waveguide loss and mode confinement suggest that the considered materials are better suited for long-wavelength surface-plasmon-polariton waveguide applications than metal films.