Nonlinear absorption of non-chain HF laser radiation in germanium

The transmission of high-power HF(DF) laser radiation through Ge single crystals of different quality has been experimentally and numerically investigated. Based on the experimental data for the lasing spectrum, the two-photon absorption coefficient in Ge is estimated to be K₂ =55±10 cmGW?1 at λ=2.8μm. The transmission dynamics of high-power radiation with λ=2.6?3 μm through germanium crystals is numerically simulated.     

Nonlinear absorption of CO2 laser radiation by nonequilibrium carriers in germanium

Nonlinear absorption of CO₂ laser pulses at the multi-MW level has been studied in n-type germanium at room temperature. This nonlinear absorption limits the level of CO₂ laser intensity that can be transmitted through an optical grade germanium crystal. The observed nonlinearity may be interpreted in terms of nonequilibrium electron-hole pairs generated by hot electrons created by the intense laser field. The number of nonequilibrium carriers generated is measured by photoconductivity experiments, and the results are correlated to the absorption measurements.     

Nonlinear frequency conversion of copper vapor laser radiation using convergent and parallel laser beams

Results of experiments are presented on the comparison of the efficiency of radiation generation at the sum frequency (λ=0.271 μm) of copper vapor laser (CVL) in a nonlinear DKDP crystal using either convergent or parallel laser beam. An intensity of UV radiation of 0.34 W and a conversion efficiency of 6% obtained under conditions of strong focusing occur to be substantially lower as compared to those obtained using a parallel laser beam of the same power (0.73 W and 12%, respectively). Experimental data on the structure of a CVL beam generated with an unstable resonator are presented, and physical reasons for the limitation of the efficiency of nonlinear frequency conversion are analyzed.     

Transport of a spherical transparent nanoparticle by radiation forces in the field of a Gaussian laser beam

The motion of a spherical transparent nanoparticle under the influence of radiation forces in the field of a Gaussian laser beam is investigated based on solution of Langevin equation. Expressions governing transverse and longitudinal velocities of the nanoparticle under the action of gradient and scattering forces are derived and analyzed. The possibility of spatial separation of nanoparticles having different sizes and optical properties is discussed.     

Efficiency factors of scattering,absorption, and backscattering of a femtosecond laser pulse train by a transparent spherical particle

Analytical expressions are derived for integral optical characteristics (the scattering, absorption, and backscattering efficiency factors) of aerosol particles irradiated by a femtosecond laser pulse train. The behavior of these integral characteristics attendant to variations of the particle size and pulse period-to-pulse duration ratio is investigated based on the results of numerical calculations. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 33–36, March, 2008.     

Attenuation of powerful ruby laser pulses in the atmosphere by resonant absorption of water vapor

The attenuation of a ruby laser pulse at the wavelength = 6943.8å is calculated under conditions of spectroscopic saturation for a parallel beam and a diverging beam with divergence angle = 10^–5 rad. It is shown that deviation from the Bouguer law may reach 45% at a path length = 2 km for an initial power level of I₀ = 0.5I_s for the parallel beam, and 20% for I₀ = 0.25I_s for the divergent beam (I_s, saturation power).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 7–12, February, 1978.     

Light scattering and absorption by densely packed groups of spherical particles

Light scattering by clusters of spheres is investigated using numerical light scattering simulations. We consider clusters with density of 0.1-30%. Simulations are carried out for various real part of refractive indices (i.e., 1.01, 1.10, 1.31, 1.60, and 2.00) and for two values of the imaginary part of the refractive index (0 and 0.01) of spheres in the cluster. All spheres in the cluster have the same size (kr=4, k=2π/λ, r is the radius of the sphere, λ is the wavelength of the incident light).The obtained results include behaviors of cross sections as functions of densities (up to 30%), investigation of the influence of multiple scattering inside the media on the cross sections, and influence of densities on phase matrix elements (PMEs) and parameters obtained from the PMEs such as the cross polarization ratio, degree of linear depolarization, entropy, etc.In addition, we also investigate the influence of particle size for the same total volume of the cluster on cross sections. The outer radius R of the cluster of spheres was constant and equal to 40/k in all calculations.     

Amplification of radiation in atomic vapor induced by a linearly polarized laser radiation

We present the results of spectroscopic and polarization studies of dilute rubidium vapor exposed to a single-frequency linearly polarized diode laser radiation in a spectral range of atomic D₂ line. We report the origin of a circularly polarized radiation on V-type transitions of ⁸⁷Rb F _g = 2 → F _e = 3 and ⁸⁵Rb F _g = 3 → F _e = 4, and amplification of this radiation in backward direction caused by a partial population inversion among magnetic sublevels of the ground and excited levels. This is confirmed experimentally by high directivity of backward radiation, absence in its spectrum of ⁸⁵Rb F _g = 2 → F _e = 1 (Λ-type) radiation, as well as by different nature of intensity dependences of backward and fluorescence radiations.     

On the effect of ultraviolet radiation on water vapor absorption of submillimeter waves

The submillimeter absorption spectra of pure water vapor and a water vapor + dry air mixture are experimentally studied under the conditions of illumination of the gas sample by ultraviolet (UV) radiation. The measurements were carried out by a vacuum echelette spectrometer in the wave number range 21.5–56 cm⁻¹ with spectral resolution 0.4–0.9 cm⁻¹, using a DRT-375 mercury-vapor discharge lamp as the source of UV radiation. In contrast to the results of similar experiments performed by other researchers, the data presented here demonstrate the absence of a noticeable effect of the UV radiation on the absorption spectra of the gas samples used. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 5, pp. 581–587, May, 1998.     

Novel optical techniques for measurements of light extinction,scattering and absorption by single aerosol particles

Aerosol particles play important roles in a broad range of scientific disciplines, from atmospheric chemistry and physics, to the delivery of fuels for combustion and drugs to the lungs, and extending to industrial processes such as spray drying. Measurements of the light extinction, scattering and absorption by ensembles of aerosol particles can be used to non‐intrusively characterise aerosol particle samples. However, such measurements often lead to ambiguity in interpreting the properties and processes occurring on individual particles. In this review, recent developments in the use of laser based techniques to isolate and manipulate single particles and to characterise them will be highlighted. In particular, the use of cavity ring down spectroscopy, Bessel beams and optical tweezers for investigating light extinction, scattering and absorption, respectively, will be considered. The prospects for using optical techniques to interrogate the fundamental processes occurring in aerosol at the single particle level are discussed.     

Measurements of the temperature and water vapor concentration in a hot zone by tunable diode laser absorption spectrometry

A tunable diode laser absorption spectroscopy (TDLAS) technique and appropriate instrumentation was developed for the measurement of temperature and water vapor concentrations in heated gases. The technique is based on the detection of the spectra of H₂O absorption lines with different energies of low levels. The following absorption lines of H₂O were used: 7189.344 cm⁻¹ (E″=142 cm⁻¹), 7189.541 cm⁻¹ (E″=1255 cm⁻¹), 7189.715 cm⁻¹ (E″=2005 cm⁻¹). Spectra were recorded using fast frequency scanning of a single distributed feedback (DFB) laser. A unique differential scheme for the recording of the absorption spectra was developed. An optimal technique for fitting the experimental spectra was developed.     

Nonlinear Compton scattering of strong laser radiation on channeled particles in a crystal

A version for intense γ-ray radiation based on the multiphoton scattering of strong laser radiation on relativistic particle beam channeled in a crystal is proposed. The incident laser beam and charged particles beam are counter-propagating and the laser radiation is resonant to the energy levels of transversal motion of channeled particles.     

Nonlinear absorption of monochromatic radiation in gases

The absorption coefficient as a function of the density of monochromatic collimated radiation is discussed for an arbitrary ratio of natural to Doppler width, with allowance for the effects of collisions between molecules.We are indebted to M.A. El'yashevich for a discussion and to Ya. S. Vasilevskaya and UP. Pesotskaya in preparing the paper.     

Study of nanostructure of highly purified water by measuring scattering matrix elements of laser radiation

Experiments on modulation interference microscopy and measurement of light scattering matrix elements showed that double distilled water purified from solid impurities contains macroscopic scatterers of optical radiation. It follows from numerical calculation that these scatterers can be micrometer-scale clusters formed by polydisperse air bubbles with effective radii of 70 to 90 nm. The fractal dimension of such clusters is within 2.4–2.8 and their concentration is ∼ 10⁶ cm⁻³.     

Review of scattering and extinction cross-sections, damping factors, and resonance frequencies of a spherical gas bubble

Perhaps the most familiar concepts when discussing acoustic scattering by bubbles are the resonance frequency for bubble pulsation, the bubbles' damping, and their scattering and extinction cross-sections, all of which are used routinely in oceanography, sonochemistry, and biomedicine. The apparent simplicity of these concepts is illusory: there exist multiple, sometimes contradictory definitions for their components. This paper reviews expressions and definitions in the literature for acoustical cross-sections, resonance frequencies, and damping factors of a spherically pulsating gas bubble in an infinite liquid medium, deriving two expressions for "resonance frequency" that are compared and reconciled with two others from the reviewed literature. In order to prevent errors, care is needed by researchers when combining results from different publications that might have used internally correct but mutually inconsistent definitions. Expressions are presented for acoustical cross-sections associated with forced pulsations damped by liquid shear and (oft-neglected) bulk or dilatational viscosities, gas thermal diffusivity, and acoustic re-radiation. The concept of a dimensionless "damping coefficient" is unsuitable for radiation damping because different cross-sections would require different functional forms for this parameter. Instead, terms based on the ratio of bubble radius to acoustic wavelength are included explicitly in the cross-sections where needed.     

水下弹性球壳被激振动和辐射声的时域特性研究

本文在时域上对水下球壳在球冠形均匀单频填充脉冲力源作用下的振动和辐射声问题进行分析和计算。结果表明:在长脉冲力作用下,根据填充频率不同,会激起不同模态振动和产生长的共振辐射声或拍频辐射声,但有一部分模态对远场声辐射的贡献甚微;在短脉冲力作用下,脉冲波在球壳上传播一般会发生展宽和变形。文中还应用DAA2方法简化水——壳体耦合关系和边界元方法计算辐射声场。与精确解比较可知,DAA2方法的结果是令人满意的。