Picosecond pulse generation in the infrared by stimulated Raman scattering in atomic vapours

We report the generation of high-power picosecond infrared pulses by stimulated electronic Raman scattering in an atomic vapour. Single 30 ps pulses at 532 nm were Raman-shifted in caesium vapour to produce 0.4 mJ pulses at 2.38 μm, with 20% quantum efficiency. This technique can be extended to cover a wide range of infrared wavelenghts by using various Raman transitions.     

Femtosecond pulse generation using stimulated Raman scattering in integrated silicon optical waveguide device

To generate ultrafast femtosecond optical pulses, we propose a model of an integrated device consisting of a Mach-Zehnder interferometer (MZI) with two symmetric 3 dB directional couplers and a straight waveguide based on the single-mode silicon-on-insulator (SOI) optical waveguide. The principle of pulse generation in the presented device is based on the strong stimulated Raman scattering (SRS) in silicon; the center wavelength of the pulse generated is tunable by changing the center wavelength of the co-propagating pump pulse. Numerical results show that, when a continuous wave (CW) with a weak power at 1670 nm wavelength and a pump pulse with a high peak power at 1550 nm wavelength are co-propagating, a narrow femtosecond pulse with a pulse width (full width at half maximum, FWHM) of ∼60 fs (FWHM of the pump pulse is 166.5 fs) can be achieved in the device proposed. In addition, when the waveguide length, pump peak power, and pump-pulse width are fixed, the properties of generated femtosecond pulse depend strongly on the incident chirp of the pump pulse and the CW power.     

利用受激布里渊散射获得皮秒激光脉冲

 采用两级布里渊结构压缩8ns的Nd：YAG激光，研究了基频光和倍频光的受激布里渊散射（SBS）压缩过程。实验中采用四氯化碳作为SBS介质，经第一级双池SBS压缩后，获得了1.5ns左右的Stokes 脉冲；第二级采用单池SBS压缩，分别使用基频光和倍频光作为泵浦光，获得了最短为60ps 的Stokes脉冲。实验证明，在一定条件下，利用SBS压缩脉宽可以获得比介质的声子寿命更短的脉冲。     

Powerful tunable infrared generation by stimulated Raman scattering

We report the generation of powerful infrared radiation continuously tunable between 14 000 and 2 300 cm^-1. The beam is either the output of a dye laser (with a linewidth of 0.07 cm^-1 and a full angle divergence of 0.2 mrd) or its Raman shifted components. We have obtained 20 to 60 MW peak power between 14 000 and 9 700 cm^-1, 5 to 20 MW between 9 700 and 5 500 cm^-1 and 0.5 to 2 MW between 5 500 and 2 300 cm^-1. As an application we measured the hyperpolarizability of some organic molecules.     

Subfemtosecond pulse generation by rotational molecular modulation

We extend a recent suggestion for the generation of subfemtosecond pulses by molecular modulation [Phys. Rev. Lett. 81, 2894 (1998)] to the rotational spectrum of molecular hydrogen (H(2)) . When a rotational transition |a? ? |b? is strongly driven (|rho(ab) |=0.5) the generation and phase-slip lengths are of the same order and the Raman spectrum has approximately Bessel function sideband amplitudes. Numerical simulation predicts that this spectrum (generated in a 14-cm-long cell at 1-atm pressure of H(2)) will compress into a train of pulses with 94-fs pulse separation and a pulse length of 0.5 fs.     

ICF驱动器长脉冲下三倍频晶体中的横向受激拉曼散射

ICF驱动器在脉宽为3ns的长脉冲条件下运行时,三倍频晶体中的横向受激拉曼散射效应将比短脉冲条件下的效应更为显著。针对长脉冲运行时,KDP晶体和KD*P晶体产生的横向受激拉曼散射光对晶体的危害性作了对比分析,并研究了横向受激拉曼散射效应与增益系数之间的关系,为选择何种晶体作为三倍频晶体提供了理论依据。     

Time-domain pulse property of stimulated Raman scattering in a multimode optical fiber

The time-domain pulse property of quasi-steady stimulated Raman scattering (SRS) in a multimode optical fiber, pumped by an A-O Q-switched Nd: YAG laser, is studied both experimentally and theoretically. Good agreement has been achieved between theory and experiment. Discussion shows that the variation of the Stokes pulse width (FWHM)t _s depends on the shape of input pump pulse.     

Dependence of parabolic pulse amplification on stimulated Raman scattering and gain bandwidth

An analytical model has been developed and verified by numerical simulations to determine limits induced by stimulated Raman scattering (SRS) on parabolic pulse evolution in high-power, high-energy Yb-fiber amplifiers. Our results show that the maximum achievable parabolic pulse energies are limited by SRS at low amplifier gains and by the finite gain bandwidth at high gains. Therefore, an optimum gain value exists that maximizes the achievable output pulse energy.     

ICF驱动器长脉冲下三倍频晶体中的横向受激拉曼散射

 ICF驱动器在脉宽为3ns的长脉冲条件下运行时，三倍频晶体中的横向受激拉曼散射效应将比短脉冲条件下的效应更为显著。针对长脉冲运行时，KDP晶体和KD*P晶体产生的横向受激拉曼散射光对晶体的危害性作了对比分析，并研究了横向受激拉曼散射效应与增益系数之间的关系，为选择何种晶体作为三倍频晶体提供了理论依据。     

Chaos in stimulated Raman scattering

Coherent state technique and maximal Lyapunov exponent method are used for the study of deterministic chaos in a system governing stimulated Raman scattering. The influence of the external pumping on dynamics of the system is investigated. Phase portraits and FFT spectra are presented.The author would like to express his sincere thanks to prof. J. Peina for his comments and stimulating discussions.     

The generation of stimulated resonance Raman scattering using external dye fluorescence

Different dyes in locally separated cells have been investigated in order to obtain information about the mechanisms responsible for the generation of stimulated resonance Raman scattering. The experiments show in agreement with the theoretical results that the appearance of initial signals as well as the effect of dye amplification influences the behaviour of stimulated resonance Raman scattering.     

Stabilization of stokes pulse energies in the nonlinear regime of stimulated Raman scattering

An experimental study of quantum mechanical pulse energy fluctuations in stimulated Raman scattering from hydrogen is presented. The probability density function P(W) for Stokes pulse energy W is measured for highly transient scattering in both the linear and nonlinear gain regimes. While large pulse energy fluctuations (100%) occur in the linear gain regime, the fluctuations are reduced to about 20% in the nonlinear regime where the laser pulse is depleted significantly. The results are in excellent agreement with the theoretical predictions of Lewenstein.     

皮秒激光瞬态受激喇曼散射的实验研究

本文采用对撞脉冲锁模Nd:YAG激光器输出10ps脉冲串,经KTP非线性晶体腔外倍频,泵浦喇曼介质为二甲亚砜(DMSO)液体.实验研究了不同透镜焦长、焦点位置及不同喇曼介质氏度对瞬态受激喇曼散射的影响,获得了能量转换效率分别为45.6%和10.5%的前、后向一阶斯托克斯-喇曼散射光,并对实验结果进行了讨论.     

Femtosecond soliton generation induced by intrapulse stimulated Raman scattering in optical fibers

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Applications of stimulated Raman scattering

The applications of stimulated Raman scattering reviewed in this paper include: determination of spontaneous Raman parameters and nonlinear susceptibilities by gain measurements and coherent anti-Stokes Raman spectroscopy, excitation of molecular vibrations and lattice waves and measurement of their relaxation times, generation of intense tunable light in the infrared region of the spectrum. The main results of the theory of stimulated Raman scattering relevant to the understanding of these applications are discussed.     

Studies of stimulated Raman scattering

The dependence of the excitation threshold and the intensity of the first Stokes component on the properties of the scattering material, the concentration of its molecules, and the exciting light intensity has been studied. It has been found that the intensity of stimulated Raman scattering lines depends exponentially on the intensity of the exciting light and the concentration of the scattering molecules. This dependence is in agreement with the theory developed.The author are gratful to P. A. Bazhuln, N. G. Basov, and A. M. Prokhorov for the present study.     

The buildup of stimulated Raman scattering from spontaneous Raman scattering

We present a quantum electrodynamic theory which shows for the first time how stimulated Raman scattering builds up, both spatially and temporally, from spontaneous Raman scattering. We analytically solve operator Maxwell-Bloch equations to find the Stokes field operator, and thus the Stokes intensity, for both monochromatic and broad-band (phase diffusion) pump lasers.     

Generation of single dispersion precompensated 1-fs pulses by shaped-pulse optimized high-order stimulated Raman scattering

We propose and theoretically analyze a new approach for generating and shaping 1-fs pulses. It combines the ideas of strong-field molecular optics and optimal control to manipulate light generation in a pump-probe Raman regime. Flexible phase control over the generated spectrum of about 3 eV width is achieved by controlling the input pulses and maximizing the coherence of medium excitation by adiabatically aligning molecules in the medium with a specially shaped pump pulse. The generated pulse is optimized for an output window, precompensating for its dispersion to all orders.