Compensation method for attenuated planar laser images of optically dense sprays

We present a method for compensating laser attenuation in optically dense sprays, in particular for use in combustion engine research. Images of the fuel sprays are produced by planar laser imaging, where Mie scattered light from a cross section of the spray is imaged onto a CCD camera. The compensation scheme is based on the Beer-Lambert law, which is used here to sum up the loss of light along the path of the laser in the image, and to compensate iteratively, pixel by pixel, for this loss.     

Theory of photothermal spectroscopy in an optically dense fluid

The theory of photothermal spectroscopy in an optically dense fluid is presented. The general case is considered in which the fluid may be flowing or stationary, and the excitation could be cw (modulated or unmodulated) or pulsed (arbitrary pulse length). All three detection schemes, deflection, phase shift, and lensing, are considered. This is the most complete theory of photothermal spectroscopy in fluids to date.     

Failure mechanism of optically transparent solids subjected to a local thermal laser pulse

Experimental data on the failure mechanism of glass plates subjected to a millisecond pulse of focused laser light are presented. It is established as a result of investigation of the failure kinetics of irradiated glass plates that their failure is caused by an increase in gas pressure in the cavity formed at the focal point of the light-collecting lens. This failure mechanism of glass differs from that described earlier for the case of the irradiation of a glass plate by a nanosecond pulse of laser light, according to which the glass fails as a result of the development of a high-amplitude acoustic pressure wave near the front surface of the irradiated plate. The failure mechanism described for the glass plates agrees with a thermodynamic failure model of transparent solids.Translated from Problemy Prochnosti, No. 4, pp. 88–93, April, 1993.     

Interaction of an ultrashort electromagnetic pulse with a molecular hydrogen ion

Analytical expressions that describe the spectrum of reemission during the interaction of an ultrashort electromagnetic pulse with a molecular hydrogen ion are obtained. The role of the orientation of the axis of the molecular ion during this interaction is studied. It is shown that the spectra of reemitted photons strongly depend on the orientation of molecular targets.     

Frequency locking of a 1324 nm DFB laser to an optically pumpedrubidium vapor

Some experimental results and a simple theoretical model on a dither-free frequency-locking technique of a DFB laser operating at 1324 nm are presented. A resonance observed through absorption in an ⁸⁷ Rb vapor optically pumped by a modulated 795-nm laser diode tuned to the D₁ line is used. This approach has the advantage of producing sub-Doppler resonances. Such a technique could be used to generate an unmodulated 1324-nm wavelength reference     

Radiative-conductive transmission of heat through optically dense media

The problem of heat transmission by conduction and radiation through a semiinfinite optically dense medium is analyzed, with incident external radiation and with convective heat transfer taken into account. An expression for the radiant thermal flux is derived from the solution to the equation of radiation flux propagation by the method of associative asymptotic expansions. The effect of the temperature gradient at the surface on the emissivity of the body is established for the medium range of absorptivity values.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 23, No. 3, pp. 459–464, September, 1972.     

Numerical simulation of an optically active medium of an OD-CO2 laser

A quasi-one-dimensional model of an optically active medium of a chemical OD-CO₂ laser with thermal initiation is proposed. Results of calculations are. in good agreement with the experiment. The maximal specific power of generation is 66 J/g.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 61, No. 6, pp. 885–894, December, 1991.     

Dynamic target ionization using an ultrashort pulse of a laser field

Ionization processes under the interaction of an ultrashort pulse of an electromagnetic field with atoms in nonstationary states are considered. As an example, the ionization probability of the hydrogen-like atom upon the decay of quasi-stationary state is calculated. The method developed can be applied to complex systems, including targets in collisional states and various chemical reactions.     

Application of a forward-angle-scattering transmissometer for simultaneous measurements of particle size and number density in an optically dense medium

We consider the multiple-scattering and forward-scattering corrections to the transmission measurements in the case of a detector with a variable field of view. The transmission functions for predicting the angular distribution of forward-scattering transmittance are proposed. We present results of measurements of transmission functions for polystyrene spheres. Numerical estimations of the forward-multiple-scattering corrections are in good agreement with the experimental results.     

Measurements of a nonlinear refractive index with a single laser pulse

We demonstrate a theoretical model and the experimental proof of a new method for n(2) measurements using single pulses. The advantage of the method is fast measurement, a simple setup, and independence from small nonlinear absorptions and thermal effects. We report on first n(2) measurements with the new technique on carbon disulfide, toluene, and a polymer dissolved in toluene to demonstrate the measurement of positive and negative third-order nonlinearities. We achieved a sensitivity of greater than lambda/200 phase-front distortion using picosecond Nd:YLF laser pulses. The given theory shows that attainment of higher sensitivities is possible.     

Time evolution of few-cycle pulse in a dense V-type three-level medium

Propagation of a few-cycle laser pulse in a dense V-type three-level atomic medium is investigated by the numerical solution of the full Maxwell–Bloch equations without the rotating wave and slowly varying envelope approximations, and the numerical solution is obtained by using the predictor–corrector method and the finite-difference time-domain method. It is shown that, due to the strength of the electric field induced by the macroscopic polarization in a dense medium being stronger than that in a dilute medium and the influence of the near dipole–dipole (NDD) interaction, the time evolution of a few-cycle pulse in the dense medium is remarkably different from that in the corresponding dilute medium. In the dilute medium, oscillation arises at the trailing edge of the pulse; while in the dense medium, it appears at both the leading and trailing edges of the pulse; moreover, the oscillation at the leading edge is more obvious with the pulse area decreasing. The carrier-envelope phase has an obvious difference in the two cases with and without NDD interaction. The ratio, γ, of the transition dipole moments has strong influence on the time evolution and split of the pulse. In the dense medium, when?γ?= 1, NDD interaction delays propagation and split of the pulse; while when?γ?> 1, NDD interaction accelerates propagation and split of the pulse, moreover, the phenomenon is more obvious with the input pulse area decreasing. In the dilute medium, the larger area pulse doesn't split when?γ?= 1 while it splits when?γ?> 1.     

Algorithm for calculating the refraction patterns of a planar laser beam in an optically inhomogeneous medium

An algorithm for simulation of the distribution of a planar laser beam in a three-dimensional, optically inhomogeneous medium is proposed. A technique for numerical calculation of the trajectories of the beam in a geometrically optical approximation is described. A calculation of refraction patterns in probing of a thermal boundary layer near a cylindrically shaped heated body that takes into account edge effects is performed. Translated from Izmeritel’naya Tekhnika, No. 5, pp. 36–39, May, 2008.     

Formation of an electret structure by exposure of a dielectric to a laser pulse in an electric field

The appearance of mechanical stresses on the surface of a dielectric exposed to a laser pulse is considered.N. E. Bauman Moscow State Technical University, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 6, pp. 926–929, November–December, 1996.     

Mode matching for a passive resonant ring laser gyroscope

An analytical method of matching the mode of an input laser to the lowest-order mode of a passive resonant ring laser gyro is described, as are the steps in determining the location and focal length of cylindrical mode matching lenses. Results were obtained with no mode matching, with a compromise spherical lens, with horizontal mode matching only, and with the proper cylindrical mode matching lenses. Compared with no mode matching, the latter case shows that the amplitude of the lowest-order mode is increased approximately 2.5 times. In addition, the number and intensity of higher-order modes are reduced to near zero, and the relative intensity of the lowest-order mode to the higher-order mode increased from approximately 5 to approximately 60 times greater.     

Low-power resonant laser ablation of copper

We emphasize two points: (l) the properties and mechanisms of very low-fluence ablation of copper surfaces and (2) the sensitivity and selectivity of resonant laser ablation (RLA). We present results for ablation of bulk copper and copper thin films; spot-size effects; the effects of surface-sample preparation and beam polarization; and an accurate measurement of material removal rates, typically ≤ 10(-3) ? at 35 mJ/cm(2). Velocity distributions were Maxwellian, with peak velocities ≈ 1-2 × 10(5) cm/s. In addition, we discuss the production of diffractionlike surface features, and the probable participation of nonthermal desorption mechanisms. RLA is shown to be a sensitive and useful diagnostic for studies of low-fluence laser-material interactions.     

The density distribution of a weakly interacting bose gas in an external potential

The Gross-Pitaevskii equations are generalized to finite temperatures by means of the self-consistent Hartree-Fock and Bogolyubov approximations that are derived through a variational principle for the optimal set of one-particle eigenstates. A number of sample density profiles are provided for spin-polarized atomic hydrogen when the external potential depends on thez coordinate onlySupported by the National Science Foundation under grant # DMR-80-20429 and by the Sloan Foundation.     

脉冲激光光谱测试仪的设计

设计了一种基于ISP技术的线阵CCD的驱动电路和高速脉冲光谱数据采集卡,建立了一套智能化脉冲激光光谱测试系统。该系统主要由分光系统、CCD传感器、光脉冲同步信号发生器、数据采集卡及计算机等部分组成。CCD将光强信号转换为电信号输出,经A/D转换器转换后的数字信号存入数据采集卡的帧存储器中,由计算机控制进行光谱数据的分析、处理。提出了用重心法对脉冲激光器的重复频率进行评估的方法,使测量精度达到了亚像素级。对系统所用脉冲激光器谱线峰值波长的复现性进行了测量,其标准差为0.0327nm。