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1.
V. A. Maisheev 《Journal of Experimental and Theoretical Physics》1997,85(6):1102-1109
The head-on propagation of a beam of γ grays through the field of a laser wave is investigated. The optical properties of the laser wave (as a medium) are described
by the dielectric tensor. The refractive indices are determined, and the polarization characteristics of electromagnetic normal
modes capable of propagating in such a medium are investigated. Relations are derived to describe the variation of the initial
polarization and intensity of a γ-ray beam as it propagates in a laser field. The influence of laser intensity on the investigated process is discussed.
Zh. éksp. Teor. Fiz. 112, 2016–2029 (December 1997) 相似文献
2.
Dispersive solid-state dye laser oscillators 总被引:1,自引:0,他引:1
F. J. Duarte A. Costela I. Garcia-Moreno R. Sastre J. J. Ehrlich T. S. Taylor 《Optical and Quantum Electronics》1997,29(4):461-472
Narrow-linewidth multiple-prism grating solid-state dye laser oscillators are analysed using ray transfer matrices. Attention
is given to beam divergence measurements and the effect on them of thermal lensing, at the solid-state gain medium. It is
found that although thermal lensing leads to an increment of beam divergence, it induces oscillation in the unstable resonator
regime, thus contributing to the attainment of TEM00 beam profiles. In addition, narrow-linewidth emission in dispersive oscillators,
incorporating rhodamine 6 G doped HEMA:MMA gain media, is reported for the first time. Laser efficiency is 4–5% at a laser
linewidth ≤1.8 GHz for double-longitudinal-mode emission. Beam divergence is measured in the 2–2.3 mrad range, in good agreement
with theory.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
3.
The results of investigations of the divergence of an amplified diffracted beam of diameter from 1.5 to 150 mm produced by
a XeCl laser are presented. It has been shown that if the intensity distribution of the amplified radiation is spatially nonuniform,
the wave front in the active medium changes substantially due to the diffraction of the radiation at a small-diameter diaphragm.
The active medium of the amplifier excited by an electron beam makes it possible to amplify without visible distortions a
laser beam with a divergence of ≈10 μrad.
Institute of High-Current Electronics, Siberian Division of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh
Uchebnykh Zavedenii, Fizika, No. 5, pp. 64–68, April, 2000. 相似文献
4.
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We obtained basic analytical expressions for the efficiency of the second harmonic in nonlinear crystals with a regular domain
structure; in these expressions we took into account the angular divergence of the laser beam. The calculation was done in
the geometric-optics approximation of the given field of laser radiation. We show that the expressions obtained are similar
to the corresponding expressions for homogeneous nonlinear crystals.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 134–138, January–February, 2000. 相似文献
7.
Based on the extended Huygens–Fresnel integral, analytical formulas for the cross-spectral density, mean-squared beam width
and angular spread of a partially coherent elegant Hermite–Gaussian (HG) beam in turbulent atmosphere are derived. The evolution
properties of the average intensity, spreading and directionality of a partially coherent elegant HG beam in turbulent atmosphere
are studied numerically. It is found that the partially coherent elegant HG beam with smaller initial coherence width, larger
beam order and longer wavelength is less affected by the atmospheric turbulence. Compared to the partially coherent standard
HG beam, the partially coherent elegant HG beam is less affected by turbulence under the same condition. Furthermore, it is
found that there exist equivalent partially coherent standard and elegant HG beams, equivalent fully coherent standard and
elegant HG beams, and an equivalent Gaussian–Schell-model beam may have the same directionality as a fully coherent Gaussian
beam whether in free space or in turbulent atmosphere. Our results can be utilized in short and long atmospheric optical communication
systems. 相似文献
8.
A mathematical model is proposed for the optical transfer function of a thick two-dimensional volume hologram bounded by a
rectangular periphery. It is shown that the hologram is made up of two parts. The first part is formed by a point reference
beam which reads out the hologram through the longitudinal boundary, while the second part is formed when it is read out through
its transverse boundary. It is established that the principal features of light scattering by a thick hologram involve the
second component of the optical transfer function. It is shown that under conditions of phase detuning the angular dependence
of this component fails to coincide with the corresponding dependence of the first part, and this greatly complicates the
structure of the angular intensity of the reconstructed light beam. This conclusion is confirmed by the experimental results
given which were obtained when investigating holograms of a divergent light beam recorded in a lithium niobate photorefractive
crystal. The results are given of a calculation using the mathematical model discussed as applied to the experimental situation
considered.
State University of Control Systems and Electronics, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika,
No. 7, pp. 114–120, July, 1998. 相似文献
9.
G. V. Kulak 《Journal of Applied Spectroscopy》2000,67(3):510-516
The features of the Bragg diffraction of Gaussian light beams at ultrasound waves in gyrotropic crystals were investigated.
The dependence of the diffraction efficiency on the intensity of an ultrasound beam, the cross-section radius of a light beam,
and their divergence ratio was found. An asymptotic expression for the transverse distribution of a diffracted beam was derived.
The crystal gyrotropy has been found to affect significantly the change in the amplitude profile of the diffracted light at
ultrasound frequencies of f ∼ 102–103 MHz. The maximum diffraction efficiency in the gyrotropic medium is shown to be reached at a certain ratio between the divergences,
ultrasound intensity, and specific gyration of the crystal.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 370–374, May–June, 2000. 相似文献
10.
D. F. Zaretskii É. A. Nersesov 《Journal of Experimental and Theoretical Physics》1997,85(6):1081-1084
For phase-locked emitters, provided a certain relation exists between the pump wave and atomic beam parameters, a saturation
effect is shown to be possible for which the intensity of the high-order harmonics ceases to depend on the atomic density.
By means of a simple model that includes variations in the intensity of the pump wave in the plane transverse to the focal
axis, an expression is obtained for the optimum atomic density of the medium corresponding to intensity saturation. The dependence
of the optimum atomic density on the laser power and harmonic number obtained is found to be in qualitative agreement with
recently published experimental data.
Zh. éksp. Teor. Fiz. 112, 1978–1984 (December 1997) 相似文献
11.
The aim of the current study is to simulate the laser photon through biological tissue during PDT therapy using Monte Carlo
simulation technique. The model is coded using MATLAB. Interaction of laser light with turbid medium e.g. human tissue depends
on the optical properties of the medium i.e. refractive index n, absorption coefficient μ
a
, scattering coefficient μ
s
and anisotropy factor g. Laser light transport through tissue is governed by the radiative transport equations based on absorption and scattering.
Direct sampling is used for step-size generation before interaction via absorption or scattering with the transmitting medium,
for deflection and azimuthal angle (θ and ϕ) when the scattering even occurs. The tissue medium considered is divided into
radial, axial and angular grid elements and an infinite narrow beam with normal incidence on the tissue is considered. The
laser light absorbance inside the tissue, reflectance at the top boundary of the tissue and transmittance at the bottom are
estimated and these quantities are shown varying radially and angularly. Results of reflectance, transmittance and fluence
are compared with the already published results to confirm the authenticity of our coding and these results are found to lie
at only 3–4% error. 相似文献
12.
S. E. Skipetrov S. S. Chesnokov S. D. Zakharov M. A. Kazaryan V. A. Shcheglov 《JETP Letters》1998,67(9):635-639
The time correlation function of light reflected diffusely from a semi-infinite randomly inhomogeneous medium is calculated
with allowance for the acceleration of the scatterers in the field of the laser beam incident on the medium. An analytical
expression is found for the characteristic coherence time due to the ponderomotive action of light. It is shown that even
with laser radiation power densities of the order of 1–10 W laser-acceleration effects substantially alter the character of
the time autocorrelation function of the scattered light and must be taken into account in theoretical calculations.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 611–615 (10 May 1998) 相似文献
13.
This paper deals with three-dimensional redistribution of intensity over the cross section of a powerful light beam of a ruby laser saturating the absorption in the atmospheric vapor line 694.380 nm. Calculation of the beam contraction near the axis with the initial angular divergence taken into account, was carried out within the framework of the transfer equation for conditions corresponding to nonturbid atmosphere. The change of the effective light beam radius was also considered as a function of path length and initial radiation intensity.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 58–62, March, 1980. 相似文献
14.
The beam propagation factor, M2 of the master-oscillator power-amplifier (MOPA) CuBr laser emission compliant with ISO 11146 is studied methodically. Statistical
parameters of 2D intensity profile of the near and far fields of MOPA laser radiation are measured by a beam analyzing technique
as functions of timing delay between MO and PA. For first time the influence of the gas buffer (causing the radiation profile
to change from annular to top-hat and Gaussian-like) and light polarization on CuBr laser beam focusability (M2) was under investigation. The MOPA gain curve is found and the influence of gain on the input signal (from MO into PA) due
to the absorption/amplification in PA on the field profiles is shown. For annular radiation M2 range is from 13–14 (small delays) to 5–6 (large delays) and for filled-center radiation M2 is 6–7 (small delays) and at the end of gain curve is as much as 4. With polarized light, M2 drops to 3 at the end of gain curve. The brightness of laser emission with hydrogen goes up 3–5 times and the linearly-polarized
beam is at least 40% brighter than that of partial or non-polarized beams. 相似文献
15.
M. Moore 《Optical and Quantum Electronics》1973,5(2):189-200
A time-dependent theoretical treatment of the intensity distribution within a thermally self-defocused laser beam is presented, based on a ray-geometrical approach. Well-modulated interference fringes are predicted extending over most of the beam. This treatment is applicable to beam propagation in media for which the heat transfer by convection can be neglected when compared with that due to conduction. Numerically determined intensity distributions are given and compared with ones obtained experimentally using a laser beam of 488 nm wavelength and an absorbing medium of glycerol doped with iodine. Good agreement is obtained. 相似文献
16.
Jiang ShaoEn Zhang BaoHan Liu ShenYe Yang JiaMin Sun KeXu Huang TianXuan Ding YongKun Zheng ZhiJian 《中国科学G辑(英文版)》2007,50(6):716-730
Gold disk targets were irradiated using focusing and beam smoothing methods on Xingguang (XG-II) laser facilities with 350 nm wavelength, 0.6 ns pulse width and 20-80 Joules energies. Laser absorption, light scattering and X-ray conversion were experimentally investigated. The experimental results showed that laser absorption and scattered light were about 90% and 10%, respectively, under focusing irradiation, but the laser absorption increased 5%-10% and the scattered light about 1% under the condition of beam smoothing. Compared with the case of focusing irradiation, the laser absorption was effectively improved and the scattered light remarkably dropped under uniform irradiation; then due to the decrease in laser intensity, X-ray conversion increased. This is highly advantageous to the inertial confinement fusion. However, X-ray conversion mechanism basically did not change and X-ray conversion efficiency under beam smoothing and focusing irradiation was basically the same. 相似文献
17.
The peak-power-density stability and beam-wander precision of a probe laser are important factors affecting the inspection
results in precise thin-film optical measurements. These factors are also key to evaluating a probe laser for in-line long-time
operation of precise thin-film optical measurements. The peak-power density and beam wander of liner helium–neon (He–Ne) lasers,
random He–Ne lasers, and diode lasers as functions of time are investigated experimentally using a beam profiler. It is found
that the linear polarized He–Ne laser is considered to be a promising candidate for a probe laser employed in precise thin-film
optical measurements due to better peak-power-density stability and beam-wander precision. Both the peak-power-density stability
and beam-wander precision of He–Ne lasers are usually better than that of diode lasers, but an adequate warm-up of He–Ne laser
for 30 min is required before thin-film optical measurements are made. After 12 h operation, the linear polarized He–Ne laser
is suitable for precise thin-film optical measurements because both the peak-power-density stability and the beam-wander precision
reach the minimum level. A cost-effective system composed of two linear polarized He–Ne lasers for long-term operation is
proposed. This system can operate for around 0.5–1.2 years in precise thin-film optical measurements under the normal operating
life of a He–Ne laser by switching the probe laser every 18 h. 相似文献
18.
S. N. Antonov O. A. Byshevskii-Konopko A. V. Vainer V. V. Proklov Yu. G. Rezvov 《Technical Physics》2008,53(5):609-613
Applicability of the acoustooptic method for raising the time-averaged thermal efficiency of laser radiation is substantiated
theoretically and confirmed experimentally. The effect produced by laser radiation on materials being processed (laser cutting,
welding, engraving, etc.) has a threshold in light intensity. Importantly, a beam with the most frequently used normal (Gaussian)
angular distribution of intensity is not optimal from the technological viewpoint. A method proposed for its optimization
is based on acoustooptic refraction, i.e., fast nonlinear scanning of the initial beam around its central position, which
improves (at certain values of the parameters) the time-averaged angular distribution of the beam intensity. In the experiment,
the thermal efficiency of laser radiation is raised by several times. 相似文献
19.
We have experimentally studied the characteristic features of a laser beam, polarized at angles of ± 45° to the horizontal
(vertical), passing through plates of varying thickness cut from a CdP2 crystal and placed between crossed polarizers, as a function of their angle of rotation relative to the vertical axis. We
show that a periodic variation in the intensity is connected with the variation in polarization of the laser beam. We have
established that the laser beam remains linearly polarized not only when it passes through the sample along the optic axis,
but also when it travels at up to a 17.5° angle to the optic axis. In this case, the specific rotation of the plane of polarization
along the optic axis is 68.2 degrees/mm for a thicker plate and 83.3 degrees/mm for a thin plate.
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Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 690–693, September–October, 2006. 相似文献
20.
The accuracy of an interference experiment is known to depend on the interference imaging conditions. The effect of the Gaussian
inhomogeneity of laser beam intensity on the wave-front reconstruction uncertainty is investigated. The effective size of
the illuminating laser beam is shown to influence the measurement uncertainty. The effect is more pronounced in evaluation
of the interferograms with a small number of fringes.
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Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 51–55, May, 2005. 相似文献