1.5410.6-μm eyesafe laser rangefinders performance under adverse weather conditions

In this investigation, the performance of a CO₂ laser rangefinder at 10.6 μm and an erbium:glass rangefinder at 1.54 μm are evaluated and compared under various atmospheric conditions. Both systems and the trial site are described. The effect of atmospheric extinction and scattering is discussed. Also, the maximum range capability of the two laser rangefinders under these degraded weather conditions is assessed. The results show that the tested CO₂ laser rangefinder performed better than the Er:glass LRF used for the trials under all weather conditions. However, comparing two state-of-the-art systems does not lead necessarily to the same conclusion.     

Macroinhomogeneity of the properties of semiconductor crystals due to the specifics of the melt’s behavior under microgravity conditions

The effect of convective flows caused by the changing direction of the residual gravitational vector relative to the solidification front on the radial inhomogeneity (macrosegregation) of the dopant distribution in semiconductor crystals is studied within the context of mathematical and physical simulation for terrestrial and space conditions. Theoretical calculations and experimental research are carried out by the example of the growth of Ge crystals and their heavy doping with Ga (10¹⁹ сm^–3). The velocities of convective flows near the solidification front which lead to radial macroinhomogeneity in the grown crystals are theoretically calculated. The requirements to obtain homogeneous semiconductor crystals under real microgravity conditions are formulated.     

Design of segmented cladding fiber for femtosecond laser pulse delivery at 1550 and 1064 nm wavelengths

Segmented cladding fiber (SCF) is capable of single mode operation over an extended range of wavelengths while maintaining large mode area. In this paper we report the design of an SCF with mode area as large as 1,825  $\upmu \hbox {m}^{2}$ , suitable for delivery of high peak power femtosecond laser pulses at 1550 and 1064 nm wavelengths. An SCF with such a large-mode area is a few-moded fiber and its design requires careful choice of design parameters to have robustness against mode-coupling effects and bend loss. In this paper we address these issues and report a design of an SCF showing near distortion-free propagation of 100-fs, 53-kW peak power pulses at 1550-nm wavelength with 1,825- $\upmu \hbox {m}^{2}$ mode area through fundamental mode. The same fiber can also deliver 250-fs, 15-kW peak power pulses at 1064-nm wavelength with 1,793- $\upmu \hbox {m}^{2}$ mode area. The fiber has been analyzed by using the radial effective-index method in conjunction with transfer matrix method and the pulse propagation has been studied by solving the nonlinear Schroedinger equation by split-step Fourier method. Such a fiber would find applications in multiphoton microscopy and in biomedical engineering.     

Design and performance characteristics of a krypton chloride (λ = 222 nm) excimer laser

Development of a discharge-pumped krypton chloride (KrCl) laser operating at 222 nm wavelength is demonstrated. In this paper the design, successful realization and operating characteristics of KrCl excimer laser are reported. The laser is driven by a simple and efficient excitation technique using automatic UV pre-ionization with discharge-pumped self-sustained capacitor–capacitor (C–C) energy transfer circuit. The experimental investigations including output laser energy, temporal pulse parameters, emission spectra and beam profile of the KrCl laser were recorded. For high repetition rate operation, in-built, compact gas circulation system using tangential blower was incorporated. The laser was operated at 25 kV discharge voltage, gas mixture of 5 mbar HCl, 160 mbar kypton and neon as balance with a total gas pressure of ～2.5 bar. These experiments produced an efficient and reliable output energy of 25 mJ from an active volume of 60 cm³.     

Design and performance of a video-based laser beam automatic alignment system

A laser alignment system is applied to a high power laser facility for inertial confinement fusion. A design of the automated, close-loop laser beam alignment system is described. Its function is to sense beam alignment errors in a laser beam transport system and automatically steer mirrors preceding the sensor location as required to maintain beam alignment. The laser beam is sampled by a sensor package, which uses video cameras to sense pointing and centering errors. The camera outputs are fed to a personal computer, which includes video digitizers and uses image storage and software to sense the centroid of the image. Signals are sent through the computer to a stepper motor controller, which drives stepper motors on mirror mounts preceding the beam sampling location to return the beam alignment to the prescribed condition. Its optical principles and key techniques are given. The pointing and centering sensitivities of the beam alignment sensor package are analyzed. The system has been verified on the     

Comparison of the performance of uncooled CdHgTe PC and PEM 10.6 μm detectors

The ultimate performance of uncooled CdHgTe photon detectors for 10.6 μm radiation has been analysed. PC and PEM detectors based on CdHgTe homogeneous epitaxial layers or graded-gap structures are considered. The performance has been calculated numerically using a generalized model of PC and PEM effects in heterogeneous structures. Relatively high ultimate voltage responsivity and normalized detectivity for the detectors mentioned have been predicted. It has been shown that these detectors are better than other types of uncooled detectors as far as high-frequency modulation and the 10.6 μm wavelength range are concerned.     

Some results of the growth of semiconductor crystals in microgravity conditions (to the 50th anniversary of Yuri Gagarin’s flight into space)

The history of the growth of semiconductor crystals aboard space vehicles and their subsequent investigation has been described shortly. It has been shown using Ge(Ga), GaSb(Si), and GaSb(Te) crystals as an example that the formation of segregation growth striations can be avoided during their recrystallization by the vertical Bridgman method in conditions of physical simulation of microgravity on the Earth, mainly due to the essential weakening of the thermal gravitation convection. By their structure and impurity distribution, they approach the crystals grown in space. The investigation of recrystallization of Te has made it possible to determine the role of the detachment effect characteristic of the microgravity conditions and the features of the microstructure of the samples that crystallize with a free surface. The analysis of the results obtained from experiments in space allows us to better understand the processes occurring during the crystallization of the melts and to improve the crystal growth in terrestrial conditions.     

Temperature dependence of pressure broadening and shifts of acetylene at 1550 nm by He, Ne, and Ar

Pressure broadening and shift coefficients for the ν₁+ν₃ band of ¹²C₂H₂ have been measured for He, Ne, and Ar at a temperature of 195 K using high resolution diode laser spectroscopy. The pressure broadening and shifts follow patterns with rotational assignment that are similar to those at room temperature but are generally larger in magnitude. The change in magnitude is qualitatively described by assuming, for each transition, a constant cross section for pressure broadening or shifting. Better agreement may be obtained for pressure broadening coefficients by using empirically determined temperature exponents; better agreement still is obtained from close coupling calculations of the pressure broadening cross sections. PACS 33.70.Jg     

Judd-Oflet analysis of spectrum and laser performance of Ho：YAP crystal end-pumped by 1.91μm Tm：YLF laser

The Ho:YAP crystal is grown by the Czochralski technique.The room temperature polarized absorption spectra of Ho:YAP crystal was measured on a c cut sample with 1 at% holmium.According to the obtained Judd-Ofelt intensity parameters Ω2 = 1.42 × 10-20 cm2,Ω4 = 2.92 × 10-20 cm2,and Ω6 = 1.71 × 10-20 cm2,this paper calculated the fluorescence lifetime to be 6 ms for 5I7 →5 I8 transition,and the integrated emission cross section to be 2.24×10-18 cm2.It investigates the room temperature Ho:YAP laser end pumped by a 1.91 μm Tm:YLF laser.The maximum output power was 4.1 W when the incident 1.91 μm pump power was 14.4 W.The slope efficiency is 40.8%,corresponding to an optical to optical conversion efficiency of 28.4%.The Ho:YAP output wavelength was centred at 2118 nm with full width at half maximum of about 0.8 nm.     

Spectroscopic properties and diode-pumped 1594 nm laser performance of Er:Yb:Li6Y(BO3)3 crystal

An Er³⁺/Yb³⁺-codoped Li₆Y(BO₃)₃ crystal was grown by the Czochralski method. The polarized absorption spectra and the fluorescence decay curve were recorded. The efficiency of energy transfer from Yb³⁺ to Er³⁺ ions was estimated. Quasi-continuous-wave output power of 325 mW at 1594 nm was realized under the absorbed pump power of 10.4 W in a hemispherical cavity. The absorbed pump threshold and slope efficiency of the laser are 6.0 W and 7.2%, respectively. PACS 42.55.Xi; 42.70.Hj     

Light scattering and 2-μm laser performance of Tm:YAG ceramic

The scattering effect of Tm:YAG ceramic has been investigated and the scattering coefficient at 1064 nm wavelength is measured to be 0.014 cm⁻¹. Furthermore, a high power Tm:YAG ceramic laser with a slope efficiency of 10.7% has been built, which is end-pumped at a central wavelength of 805 nm. The 2-μm maximum output power is 7.1 W with an optical-optical conversion efficiency of 7.2%.     

Techniques of laser spectroscopy in investigations of lanthanides’ free atoms and ions

Various experimental methods, used in Chair of Quantum Engineering and Metrology for determination of the hyperfine structure of electronic levels in lanthanides atoms and ions, are presented. In turn the spectroscopic methods on an atomic beam (laser induced fluorescence and laser-rf double resonance ABMR-LIRF), laser-rf double resonance in a Paul trap and spectroscopic methods in a hollow cathode discharge (optogalvanic detection and laser induced fluorescence) are presented. Each method has been characterized with its potential accuracy and domain of application. The results achieved for the atoms and the ions of lanthanum, praseodymium, neodymium and europium have been published in numerous articles (compiled in the reference list).     

Comparison of frequency stabilities of the Rb standard and of the He−Ne/CH4 laser stabilized to theE line in methane

The paper reports on the production of an optical time standard on the basis of the He?Ne laser stabilized to theE line in methane and on a comparison of its frequency stability with that of the rubidium standard. It is shown that the stability of the optical standard is better than that of the rubidium one. Frequency measurements of theE line gavev _E=88373149031.2±1.2 kHz. We have also made new measurements on the frequency of the He?Ne laser stabilized to theF ₂ ⁽²⁾ methane line: $$v_F = 88376181602.9 \pm 1.2kHz.$$      

Investigation of enhanced HgBr(B 2Σ+−X 2Σ+) laser emission due to collisions of Xe ions and HgBr2

Electronic excitation of Hg and the HgBr radical has been observed during collisions of HgBr₂ with Xe⁺ ions at different laboratory kinetic energies. Emission cross-sections of the most intense band of the HgBr(B ²⁺, v=0–X ²⁺, v=22) transition at 502 nm have been measured at different energies of the projectile ions.     

Nanometric size control and treatment of historic paper manuscript and prints with laser light at 157 nm

Laser cleaning of historic paper infected by foxing is far more effective at 157 nm than in other laser wavelengths because at 157 nm localized photo-dissociation of organic matter is taking place at low laser energy. In addition spatial control over exposed areas with resolution better than 100 nm is possible at this wavelength. In order to optimize the methods of laser cleaning of historic paper, foxing ablation experiments at 157 nm indicate that infected paper areas can be removed with controllable spatial resolution in the nanometer scale. In addition foxing samples were investigated by scanning electron microscopy and X-ray analysis. It was found that biological activity was present on paper areas containing traces of iron. PACS  87.50.Hj; 42.62.-b; 87.15.Mi     

Epitaxial growth and optical characterization of compound semiconductor β-FeSi2 prepared by pulsed laser deposition

β-FeSi₂ thin films were prepared on FZ n-Si (1 1 1) substrates by pulsed laser deposition (PLD). The structural properties and crystallographic orientation of the films were investigated by X-ray diffraction (XRD) analysis. This indicates that β-FeSi₂/Si (2 0 2/2 2 0) and the single-crystalline β-FeSi₂ can be prepared using PLD. In photoluminescence (PL) measurements at 8 K detected by Ge detector, the PL spectra of the samples annealed at 900 °C for 1, 5, 8 and 20 h showed that the PL intensity of the A-band peak increased depending on annealing time in comparison with those of as-deposited samples. The intrinsic PL intensity of the A-band peak at 0.808 eV of the β-FeSi₂ from the 20-h-annealed sample was investigated for the first time by the PLD method detected by an InGaAs detector. This result has been confirmed by temperature dependence and excitation power density of the 20-h-annealed sample with the comparison of other defect-related band peaks of the sample. Cross-sectional scanning electron microscopy (SEM) observation was also performed and the thickness of the thin films was found to be at 75 nm for 20-h-annealed. The thermal diffusion for the epitaxial growth of β−FeSi₂/Si was observed when the compositional ratio of Fe to Si was around Fe:Si=1:2 for 20-h-annealed carried out by energy dispersive X-ray spectroscopy (EDX). We discussed high crystal quality of the epitaxial growth and optical characterization of β-FeSi₂ achieved after annealing at 900 °C for 20 h.     

Effects of Nd:YAG (532 nm) laser radiation on ‘clean’ cotton

The use of pulsed laser radiation in order to remove small particles from a substrate has gained a growing interest in the last decade, finding applications in several fields ranging from the microcircuits industry to cultural heritage restoration and conservation. The application of such a technique requires the knowledge of the correct laser irradiation parameters to be used in order to obtain a desired result avoiding substrate damage. In this paper we have studied the effect of frequency-doubled (532 nm) Nd:YAG laser radiation on clean cotton samples. We have observed that yellowing is present even at low fluences. This suggests that less invasive laser assisted particle removal techniques, some of which have already been proposed by different authors, must be considered. PACS 42.62.-b; 61.80.-x     

Application of reactor neutrons to the investigation of the radiation resistance of semiconductor materials of Group III–V and sensors

The investigation of the radiation resistance of Group III–V semiconductor materials is an important and urgent problem. Magnetic sensors based on radiation resistant semiconductor materials are widely used in magnetomeasuring systems of thermonuclear industrial and experimental reactors. The basic approaches to the study of semiconductor materials under conditions of neutron irradiation and the results of some experiments on testing indium-containing semiconductor materials InSb, InAs, and their alloys InAs _x Sb_{1 ? x} are presented. The presented experience of the development of equipment for on-line testing of materials and magnetic diagnostic sensors under radiation conditions can be used for testing a wide range of materials under conditions close to those of the ITER and other thermonuclear reactors.     

Production of microstructures in wide-band-gap and organic materials using pulsed laser ablation at 157 nm wavelength

New results on three-dimensional microstructuring of fused silica, sapphire, calcium fluoride, magnesium fluoride, and PTFE using pulsed laser ablation at 157 nm wavelength are presented. A largely automated high-precision fluorine laser micromachining station was used for the investigations.     

Using the system function to analyze the performance of transducer’s impedance measurement method

Prom investigation of the advantages and disadvantages of conventional tri-voltage method,a method for the measurement of the transmitting transducer’s impedance was presented to solve the difficult problem of examining the consistency of the transmitting phased array on the single-mode excitation sea spot.In the method based on the system function, the circuit structure of tri-voltage method was used but new parameters were measured.The principle of the method was given first.Then when resistors with different nominal values were used in the circuit,the measured results for the impedance of transducers were reported.The results were compared with the higher precision impedance analyzer.Finally,the error analysis was performed according to the impedance formula and the equivalent circuit parameters were fitted.Under the condition of guaranteeing the sampling precision,by performance analyzing, the resistor value in series was chosen relatively smaller than the impedance of transducer,the measurement of impedance could achieve the same precision as the higher precision impedance analyzer.Finally,the least squares curve-fitting of measured curves indicated that the transducer equivalent electrical parameters could be extracted accurately and used to design the matching network.