Tunable subnanosecond laser pulse generation using an active mirror concept

We report (theory, experimental check) an improved approach for generation of a tunable, subnanosecond pulse (0.1–0.4 ns), based on a single pulsation (“spike”) separation from the transient oscillations in a dye laser with active mirror (AMIR). A pumping by 20–50 ns pulses from Q-switched Nd:YAG laser is considered. The separation is in original, two-spectral selective channels cavity, where the forced by AMIR quenched generation at one of the wavelength stops initially started spiking generation at the other wavelength after the first spike development. The AMIR quickly starts the quenching generation at a precisely controlled moment and with necessary intensity thus assuring the desired separation. An advantage is a high reproducibility of the separation for high (~250%) pump power fluctuations combined with tuning in large range (~20 nm). To obtain such an operation we form ~1 ns leading front pump pulse by electrooptical temporal cutting of the input pump pulse and use an optical delay line. This increases also a few times the power in the separated spike (to be ~100 kW). Our approach widens the combinations of lasers for effective applications of spike separation technique (dye lasers excited by Q-switched solid-state or Cu-vapor lasers).     

Transformation of the spectrum of the longitudinal modes of a semiconductor laser on introduction of its radiation into fiber light guides

We investigated the influence exerted by the radius of the bend of fiber light guides with light-transmitting cores of different diameters on the transformation of the spectrum of longitudinal modes of the semiconductor laser radiation introduced into them. It is shown that the bended segment of the light guide acts as a spectrum selector, and the spectral composition of the radiation at the output of a light guide is different in different spots of the speckle structure. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 260–263, March–April, 2000.     

New laser media based on bifluorophore coumarin molecules

The effect of heterocycles of different types on the fluorescence and generation properties of ten new bifluorophores is investigated experimentally. It is shown that a number of 7-diethylaminocoumarins with a triazole cycle or an oxydiazole cycle are characterized by the highest generation efficiency in the region of 500–515 nm. The maximum generation energy was 2.5 J in lamp pumping, which exceeds widely known coumarin 334 in efficiency by a factor of 1.7. Stabilization of the coumarin fragment by the nucleus of julolidine—7-N(CH₂)₆—has a favorable effect on the photostability of these molecules. The effect and the role of the isomer form of the thiazole fragment on the spectral and generation properties of the molecule are established. A favorable effect on the generation efficiency of the imino group in the coumarin fragment of the molecule is shown. Reported at the Second International Scientific and Technical Conference on Quantum Electronics, Minsk, November 23–25, 1998. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 675–681, September–October, 1999.     

Optimization of pulse lamps for dye lasers

We carry out investigations of the generation efficiency of a dye laser in which, as a source of pumping, tubular lamps are used that are enclosed in shells to withstand the pressure of the xenon filling them. It is found that the optimum pressure is 60–80 torr, which ensures the greatest luminous efficiency of the lamps in the short-wave region of the spectrum at standard electrical parameters of the power supply system. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 134–137, January–February, 1998.     

Luminescence and lasing properties of neodymium- and uranium-activated inorganic laser liquids

An attempt was made to describe and show the possibilities of new inorganic neodynium- and uranium-activated laser liquids: SO₂-GaCl₃-NdCl₄; SO₂Cl₂-GaCl₃-NdCl₃-UO₂Cl₂; POCl₂-MCl_n-NdCl₃-UO₂Cl₂ for development and synthesis of direct nuclear reaction-excited lasers. Luminescence data presented in the work were used to calculate the luminescence parameters of the laser liquids such as oscillator strengths f, probability of spontaneous radiation A, intermultiplet luminescence branching coefficient β, cross-section for induced radiation σ, luminescence decay time τ, quantum yield η, and others. It is shown that the oscillator strengths of the normal absorption bands of Na³⁺, which play the main part in the pumping processes, exceed the oscillator strengths of Na³⁺ for aqueous and many other nonaqueous systems. In the luminescence excitation spectra of the Na³⁺ ion, bands are isolated in the range 400–1000 nm atλ _rec =1.06 μm. With excitation, luminescence occurs through the⁴F_3/2→⁴I_{9/2,11/2.13/2} channels. Luminescence spectral data are related to the lasing parameters. The threshold lasing energy is∼18 J/cm³. For a resonator with mirros h₁=100% and h₂=20, 40, 56, and 80%, the lasing energy is∼20–120 MJ/cm³ in the pumping energy range 18–180 J/cm³. The differential efficiency is ∼0.2% The substantial angular radiation divergence (θ∼4·10⁻² rad) and strong thermostatic distortions that occur in the active element (dn/dT≈−1.9·10⁻⁴K⁻¹) are a disadvantage of laser liquids. It is shown that operation of neodymium- and uranium-activated inorganic liquid lasers is stable under the present conditions. A. I. Gertsen Russian State Pedagogical University, Moika Embankment, 48, St. Petersburg, 191186, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 607–619, September–October, 1997.     

Calculation of spatial intensity distribution of InAsSb/InAsSbP laser diode emission

The spatial distribution of emission intensity in the active layer of a laser diode (LD) based on an InAsSb/InAsSbP heterostructure (generation wavelength λ_gen ∼ 3.3 μm) is obtained for various stripe widths w by means of numerical solution of the wave equation in the 2D approximation taking into account the refractive index nonlinearity. It has been shown that the special distribution of emission intensity becomes strongly inhomogeneous at w values exceeding 9–10 μm, which results in the appearance of additional maxima in the far-field pattern. Calculated far-field patterns in the active layer plane of the LD agree with corresponding experimental data. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 804–808, November–December, 2008.     

Laser-induced photodynamic effects of chlorinse 6 andp 6 on an isolated neuron

Photodynamic effects of chlorins e₆ and p₆ on an isolated mechanoreceptor neuron of a fluvial crayfish are investigated. A He−Ne laser (632.8 nm, 0.3 W/cm²) was used as an excitation source. The impulsive activity of neurons was found to be extremely sensitive to the photodynamic effect of low concentrations of chlorins e₆ and p₆ (0.005–6.000 and 0.05–0.50 μM, respectively). Cell reactions consisted of several phases of acceleration and inhibition of pulsations followed by an irreversible cancellation of nervous pulse generation. The type of reaction depended on the photosensitizer form and concentration. It is supposed that the phases of acceleration of impulsive activity are connected with the photodynamic damage of the cell membrane, and the inhibition phases are connected with the photodynamic effect on intracell organells. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 250–255, March–April, 1999.     

Double-exposure recording of a lensless fourier spectrogram for forming a shear interferogram

Results of theoretical estimation of the sensitivity of a shear speckle interferometer intended for testing of wavefront aberrations are presented. It is shown that in the case of the spherical aberration the sensitivity of the interferometer is doubled to an accuracy of 12.5% for a fixed shear magnitude. Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 35–39, May, 1999.     

Generation of coherent tunable deep UV radiation for detection and absorption studies of explosives RDX and TNT

We report a technique for the efficient generation of tunable coherent deep UV radiation and its application in studies of RDX and TNT at the ppm level on the basis of their absorption characteristics. The obtained experimental absorption data are compared with conventional spectrophotometric data. The UV radiation in the range 200–260 nm has been generated by the type-I noncollinear third harmonic of the dye laser radiation (600–700 nm) and also by sum frequency mixing (SFM) of Nd:YAG output (1064 nm) with the second harmonic of the dye laser in β-barium borate (BBO) crystal. The maximum conversion efficiency of the generated signal is estimated to be 57.5% at λ = 218.9 nm wavelength. Apart from measurements of the absorbance of RDX and TNT at different concentrations in their respective solutions, the minimum detection concentrations have also been ascertained. The estimated minimum detectable concentration of RDX is 8.47·10⁻⁹ M, whereas that for TNT is 35.7·10⁻⁹ M. The data were obtained using only ∼100 μJ/pulse of laser energy. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 516–521, July–August, 2007.     

Low-Noise single-frequency He-Ne laser with stable output power at a wavelength of 1.52 µm

The results of investigation of the energy and spectral characteristics of a He-Ne laser (λ_rad=1.52 μm) with transverse microwave discharge are presented. A single-frequency generation mode at a pressure above 6.0 mm Hg was obtained with radiation power 7.0 mW and low level of amplitude noise (10⁻⁵ Hz^−1/2). Active stabilization of the laser power was carried out, which allows reduction in radiation intensity fluctuations from 1–5 to 0.1 %. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 127–128, January–February, 2000.     

Recording of selective intracavity absorption at doubled frequencies of multimode laser radiation

We carried out measurements of the spectral distribution of wideband dye laser generation intensity within the limits and in the vicinity of an absorption line with its simultaneous recording at the frequencies of the fundamental and second harmonics of laser radiation. In the laser cavity we placed optical cuvettes with active and absorbing media, as well as selecting and nonlinear-optical elements. We show that at double frequencies the contrast of the narrow-band hole in the multimode laser generation spectrum increases. The gain in the concentration sensitivity of measurements depends in this case on the value of the absorption coefficient being determined. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., 220072, Minsk, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 516–521, July–August, 1998.     

Background noise suppression in wide-band lasers with a nonlinear mirror in the cavity

An effective method for suppressing free background generation is proposed. It is based on polarization separation of the narrow-band output radiation of a controlled laser with a nonlinear mirror in the cavity. An increase in the integral ratio between the energy of the narrow generation line and the integral value of the energy of the background over the entire gain band of a wide-band laser from 0.17 to 55.00 has been attained. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 169–171, March–April, 2000.     

The strontium-vapor laser pumping efficiency under running-wave excitation

The effect of the design features of the gas-discharge tube on the processes proceeding in the discharge circuit of a metal-vapor laser has been investigated. The position of electrodes in the gas-discharge tube has been found to significantly affect the processes at work in the discharge circuit and the energy characteristics of the laser. For instance, gas-discharge tubes with electrodes placed in the hot region of the discharge channel are typified by high metastable-population rates at the leading edge of the excitation pulse, whereas with electrodes positioned in cold buffer regions, the leading edge of the voltage pulse across the resistive component of the tube impedance is seen to peak. Conditions for running-wave generation in the active media of lasers on self-terminated transitions of metal atoms and the running-wave use efficiency for laser pumping are discussed, considering a strontium-vapor laser as an illustration. It is shown that the running wave is generated as the result of the breakdown in the anode end of the gas-discharge tube and is maintained by the energy stored in the capacitive component of the impedance of the gas-discharge tube. The lasing pulse duration under running-wave excitation corresponds to the time it takes an ionization wave to propagate from the anode to the cathode of the gas-discharge tube, with pumping efficiency being ~6–8% for a strontium-vapor laser. The average lasing power varies within 10–15% depending on whether the totally reflecting cavity mirror is placed near the anode or the cathode of the tube. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 79–87, December, 2008.     

A continuously-tunable picosecond laser radiation source in the UV spectral region

We present the results of research on continuous tuning of a neodymium laser radiation frequency in the UV and vacuum ranges. We obtained generation of the total frequency of the waves of the second harmonic and of parametric light generator radiation in the UV region (338–366 nm). We investigate the optimum conditions for tuning UV radiation in the 113.5–117.0 nm range in the process of generation of the third harmonic in xenon and its mixtures with other gases. In the vacuum UV range investigated, an efficiency of generation of the third harmonic of ∼5·10⁻⁴ and a tuning range above 2600 cm⁻¹ are realized. Scientific Industrial Association “Akadempribor”, Academy of Sciences of Uzbekistan, Akademgorodok, Tashkent, 700143, Uzbekistan. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 528–535, July–August, 1997.     

Transformation of quantum size levels into virtual levels at the boundary between p-GaAs and an AlAs/GaAs superlattice

It is shown that the intensity fluctuations in the speckle pattern arising when light is reflected from a disordered sample are negatively correlated. The relative amplitude of the correlations is two times larger in the exactly backward direction than far from this direction. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 2, 104–109 (25 January 1999)     

空间散斑场捕获大量吸光性颗粒及其红外显微观测

光镊技术被广泛应用于捕获和操纵微纳米尺寸颗粒,主要包括捕获水中透明性颗粒和空气中吸光性颗粒两种类型.本文用激光束照射毛玻璃散射片,透射光经透镜会聚后在透镜的像平面附近产生了主观散斑场.该散斑场为空间分布,包含大量的亮斑和暗斑.大量由亮斑包围的暗斑如同一个个空间能量陷阱,被用来捕获大量的吸光性墨粉颗粒,被捕获颗粒的尺寸约2—8μm,密度约1—2 g/cm3.采用红外显微镜拍摄到空间散斑场捕获颗粒的红外像,红外图像显示被捕获颗粒吸光后温度升高,证实了空间散斑场捕获吸光性颗粒的机理为光泳力原理.     

Determination of optical density at the center of an absorption line contour from the spacing between the frequencies of the two-component radiation spectrum of a laser having a phase-polarization selector

A method for determining optical density at the center of an atomic absorption line contour from the spacing between the components of the two-frequency generation spectrum of a laser with a phase-polarization selector is suggested. It is shown that the method makes it possible to measure the largest possible optical densities, but it is not suitable for measuring optical densities smaller than unity. Optical densities at the center of the D-lines of sodium are measured experimentally. A good agreement between experimental and predicted data is obtained. Institute of Molecular and Atomic Physics of the Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 738–743, November–December, 1997.     

Formation of lateral-shift speckle interferograms in diffusely scattered fields

The formation of lateral-shift speckle interferograms that characterize the axial wave aberrations of the optical system used in the coherent matte-screen illumination channel is analyzed in the Fresnel approximation based on coincidence of the objective speckle fields of two exposures in the photoplate plane. It shown theoretically and in experiment that speckle-interferometer sensitivity is doubled at a given lateral shift. Tomsk State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 36–42, September, 1996.     

Design and verification of LSR module in laser display

The LSR module of optical engine in laser display has been designed and discussed in this paper. It has also been tested and verified with the scattering sheet of 5°, 10° and 20°. The experiment demonstrates that the method of rotating the scattering sheet with 10° can effectively suppress laser speckle in our system. It can make the speckle contrast of large power projection system drop to 4.2% < 5%, which reaches the acceptable range of the human eyes.     

Recording a speckle interferogram to control the longitudinal displacement of a diffusively scattering flat surface

The formation of a speckle interferogram under a double-exposure recording of a speckle photograph to reduce the interferometer sensitivity threshold to a longitudinal displacement of a scattering flat surface is analyzed. It is shown that the proposed technique of recording, where a photoplate is displaced transversely before the second exposure, allows us to determine the sign of the longitudinal scatterer displacement. The experimental results obtained are in agreement with the theoretical calculations. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 53–59, July, 2008.