共查询到20条相似文献,搜索用时 15 毫秒
1.
Theoretical analysis of the spatial, noise, and energy characteristics of an amplifier has been performed in the mode of spectral and time selection using subnanosecond stimulated Raman Scattering gain of weak echo signals in crystalline active media that are known for high (up to 10–1 cm/MW) gain coefficients. The possibility to reach high gain values has been demonstrated for weak signals from objects at acceptable angular sizes of the field of vision of an amplifier. To provide a signal-to-noise ratio that exceeds unity over the entire field of vision, the number of photons at the input to an amplifier that is required has to exceed the number of its resolution elements. Accurate determination of the possibilities of recording of weak echo signals and quality of images of targets that are obtained using amplifiers under stimulated Raman Scattering requires additional special experiments. 相似文献
2.
The effect of the generation of higher Stokes and anti-Stokes components of steady-state and transient stimulated Raman scattering (SRS) on the realization of quasi-phase-matching conditions in the course of generation of the first anti-Stokes SRS component is numerically analyzed by using a system of coupled equations derived with regard to diffraction effects. The calculations show that the application of a periodic layered structure in order to realize quasi-phase-matching conditions virtually does not reduce the anti-Stokes SRS efficiency and allows efficient conversion of pulses with a duration of 3 ns or longer. It is found that focusing of waves inside the medium allows partial compensation for diffraction spreading and provides for an increase in the efficiency of anti-Stokes SRS conversion, and, at a Fresnel number above three, the effect of diffraction on the realization of quasi-phase-matching conditions during SRS can be disregarded. 相似文献
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S. G. Karpenko F. N. Marchevskii V. L. Strizhevskii 《Applied Physics A: Materials Science & Processing》1978,17(4):393-400
Stimulated Raman scattering by polaritons when employing a nonlinear crystal inside the cavity of the laser with Q-switching
and locked to fundamental frequency was theoretically studied. The equations were formulated describing the dynamics of the
fundamental, Stokes and polariton waves under the assumption of instant Q-switching and uniformity of radiation except in
the longitudinal direction. Numerical solutions of the equations were found and analysed. We demonstrate the influence, on
generation characteristics, of the most important parameters, such as the effective nonlinearity, the initial level of population
inversion, the feedback of the Stokes wave and the group mismatch between a Stokes and a pump wave. Optimum generation conditions
are determined. Possibilities of the method are discussed for the generation of a) giant pulses which are controllable with
regard to carrier frequency and duration but are unachievable with other methods, b) Stokes pulses of very small duration
and high energy having sharp trailing edges, and c) analogous polariton pulses in the middle and far infrared range. The generation
using a number of polariton branches in LiNbO3 was considered as an example. Calculations are in qualitative agreement with experimental data. 相似文献
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We report the first experimental observation of a nonlinear laser effect, stimulated Raman scattering (SRS), in manmade diamond grown from the gaseous phase by the chemical vapor deposition (CVD) technique. Multiple Stokes and anti-Stokes generation in the visible and near-IR ranges was excited under nanosecond and picosecond pumping in a 350-μ-thick plate. All the registered Raman-induced lasing wavelengths were identified. We classify the CVD-diamond as a promising χ(3)-active material for Raman laser converters in a record wide spectral range. 相似文献
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Prof.Dr. Koichi Shimoda 《Zeitschrift für Physik A Hadrons and Nuclei》1970,234(4):293-306
A semi-classical calculation of the three-level system consisting of the ground state, the vibrationally excited state and the electronic excited state under the laser and the Stokes perturbation is given. The induced molecular polarization produces gain modulation of the Stokes and loss modulation of the laser at a frequency that is dependent on the optical intensity. With the optical intensity in self-trapped filaments in nonlinear liquids such as CS2, the period of modulation becomes of the order 10?11 s and a large amplitude modulation of the laser and the Stokes waves will result. The amplitude modulation is not much reduced, if the molecular relaxation time of the order 10?11 s is taken into account. Effects of non-uniform field distribution and the width and shape of the incident laser pulse are discussed. The frequency broadening caused by the three-level effect is shown to be larger than, or at least as large as, the broadening caused by the optical Kerr effect. 相似文献
6.
N. I. Shamrov 《Journal of Applied Spectroscopy》2010,77(4):527-533
A semiclassical model for light amplification by stimulated Raman scattering is presented. The phases of the Stokes, anti-Stokes,
and laser waves are assumed to be perfectly matched. Depletion of the laser pump is neglected. The corresponding system of
equations for input pulses of arbitrary shape is solved analytically by the Riemann-Volterra method. Gain is suppressed for
close Raman polarizations. 相似文献
7.
The spin-flip Raman (SFR) laser is shown to be an excellent tool to investigate different processes in the conduction band
of the SFR laser crystal itself. For the case ofn-InSb, intracavity spectroscopy of inter-Landau transitions is demonstrated to be much more sensitive than conventional transmission
spectroscopy. Data on cyclotron harmonic transitions, both free and LO-phonon assisted, are obtained from the output power
characteristics of the SFR laser versus magnetic field. The spin-splitting energy and the effectiveg-factor up to 14 T are derived from the SFR laser frequency. The influence of temperature on SFR laser power, threshold and
frequency is investigated. The relaxation following the SFR laser pulse is observed in the electrical conductivity. This yields
in a direct way the spin-lattice relaxation time at high magnetic fields, which is of the order of 200 ns. 相似文献
8.
Interaction of coherent light pulses with a three-level medium of the “lambda” configuration is studied analytically and numerically. It is shown that in the course of Raman scattering the Stokes wave can be captured in the region of inversion. Conditions are found for complete energy transfer from the pump 2π-pulse to the Stokes wave. 相似文献
9.
We have studied the interaction of stimulated spin-flip Raman scattering and stimulated recombination radiation in n-InSb
using a CW CO pump laser. A change in linewidth and output power of second Stokes spin-flip radiation is observed when the
tuning curve of the first Stokes stimulated spin-flip radiation and the stimulated recombination radiation cross. The observations
are explained using a simple rate equation model. 相似文献
10.
区别于传统的受激布里渊散射(SBS)发生器和放大器,提出了一种新型的SBS模型:自供种子光模型 (self Stokes seeding,SSS)。数值求解了SBS耦合波方程组,得到了SBS诱导应力的时空分布。基于SSS建立了高功率激光辐照下光学材料破坏阈值的计算模型,研究了SBS破坏阈值与激光脉宽以及作用区长度的关系。研究发现,SBS作为一种破坏机制,表现为前表面破坏,且破坏阈值与激光脉宽以及作用区长度均成反比。 相似文献
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A Ghizzo P Bertrand M.M Shoucri T.W Johnston E Fualkow M.R Feix 《Journal of computational physics》1990,90(2)
Numerical simulations of the stimulated Raman scattering are presented using an Eulerian relativistic Vlasov code. Such a code allows a finer resolution in phase space than a particle code and provides a better understanding of the acceleration process for the particles at relativistically high energy. Forward Raman scattering as well as backward Raman scattering are considered to illustrate the possibilities of the Eulerian Vlasov code. 相似文献
13.
F. Munhoz S. Brustlein R. Hostein P. Berto S. Brasselet H. Rigneault 《Journal of Raman spectroscopy : JRS》2012,43(3):419-424
Polarization resolved stimulated Raman scattering (SRS) signal is described in the case of isotropic media and linearly polarized incident fields. The model gives simple expressions for the two perpendicularly polarized SRS signals IX and IY, detected along the X and Y directions, respectively, as a function of the incident pump and Stokes polarization angles. We find that Raman depolarization ratio can be simply obtained from the ratio of the SRS intensities detected along the X and Y axis. These theoretical findings are supported by polarization resolved SRS measurements performed on polarized and depolarized bands of cyclohexane. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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A theory of quantum beats in a Stokes signal observed in pump-probe experiments upon excitation of four-level atoms with two close upper lying levels by femtosecond laser pulses is developed. Quantum beats arise in the intensity of the Stokes field due to the interference of two atomic wave packets generated by ultrashort pump and probe pulses. An analytical solution of the non-steady-state Maxwell-Bloch equations is obtained, and the dependence of the Stokes radiation intensity on the delay time between two laser pulses is investigated. The theoretical results describe qualitatively well the observed features of quantum beats. 相似文献
16.
The present study evaluates the photodynamic damage with 5-aminolevulinic acid (5-ALA) using HeLa as experimental model. HeLa
cell line was irradiated with red light (He-Ne laser, λ = 632.8 CW nm). The influence of different incubation times and concentrations
of 5-ALA, different irradiation doses and various combinations of photosensitizer and light doses on the cellular viability
of HeLa cells were studied. The optimal uptake of photosensitizer ALA in HeLa cells was investigated by means of PpIX fluorescence
intensity by exciting the HeLa cell suspension at 450 nm and a detection wavelength set at 690 nm. Cells viability was determined
by means of trypan blue solution. The spectrometric measurements showed that the maximal cellular uptake of 5-ALA occurred
after 4 h in vitro incubation. We found that the combination with 5-ALA and laser irradiation leads to time/concentration-dependent
increase of cells death and also energy doses-dependent enlarge the cells death. The fluorescence intensity after PDD of carcinoma
cells reduce when compared with the control group. The fluorescence emission spectral profiles after PDD of carcinoma cells
showed a dip around 425–525 nm when compared with the control group. This may be due to the damage of mitochondria component
of cells. The percentage of HeLa cells after PDD shows that the percentage of cells survival rate as function of laser dose
(power). Hence it is clear that at 200 μg/ml ALA and 20 mW laser irradiation, more than 70% of HeLa cells were dead after
15 min. 相似文献
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