Analysis of ion-channel laser using the Madey's theorem

Ion-Channel Laser (ICL) is a new form of laser, which can produce tunable coherent radiation with frequencies ranging from microwaves to soft X-rays. In this paper, the ICL with slab geometry in the low gain is studied. Using the Madey's theorem, the gain formula of the ICL is derived. The result shows that the Madey's theorem is a valuable guide in research with new types of FEL's.This work was supported by the National Science Foundation of China.     

On the reactions from cov-channel to ion-channel in LCNO theory

The alpha transfer mechanism for heavy-ion reactions from a cov-channel to an ion-channel is studied using the nuclear molecular orbital theory. Both a direct potential and an exchange potential are included in the calculations. The oscillatory structure appeared in the differential cross section of certain heavy-ion reactions, such as the ¹⁶O(¹⁶O, ¹²C)²⁰Ne reaction, may be explained in terms of this method.     

On the excitation mechanism of the He-Ar hollow cathode laser

Investigations were carried out on the Ar-II 476.5 nm laser to obtain information on possible excitation mechanisms. The He-Ar hollow cathode discharge was excited by square wave current pulses. From the results of measurements it could be concluded that collisions of the second kind between He 2³ S metastable atoms and ground state Ar ions are dominant in the excitation of the upper laser level. This is also supported by results obtained in the case of the He-Kr hollow cathode laser, where the upper level of the Kr-II 469.4 nm laser is excited by a similar collision process.     

Gain calculation of a free-electron laser operating with a non-uniform ion-channel guide

Amplification of an electromagnetic wave by a free electron laser (FEL) with a helical wiggler and an ion channel with a periodically varying ion density is examined. The relativistic equation of motion for a single electron in the combined wiggler and the periodic ion-channel fields is solved and the classes of possible trajectories in this configuration are discussed. The gain equation for the FEL in the low-gain-per-pass limit is obtained by adding the effect of the periodic ion channel. Numerical calculation is employed to analyse the gain induced by the effects of the non-uniform ion density. The variation of gain with ion-channel density is demonstrated. It is shown that there is a gain enhancement for group I orbits in the presence of a non-uniform ion-channel but not in a uniform one. It is also shown that periodic ion-channel guiding is used to reach the maximum peak gain in a low ion-channel frequency (low ion density).     

On the mechanism of quartz surface crimping under laser irradiation

The influence of an artificial inhomogeneity on the surface of a solid on the formation of periodic structures under laser irradiation has been studied experimentally. Inhomogeneities of this kind are found to catalyse the arising of periodic structures which appear in the vicinity of inhomogeneities and are of a regular nature. A theory is suggested to explain the principal experimental patterns such as the size of a periodic structure, its only weak dependence on laser radiation intensity, angular dependences, etc.     

On the mechanism of frequency-selective biological effects of EHF radiation and methods of their amplification

A proof is offered that there is an acoustic maser effect and acoustoelectric oscillations with a frequency 5·10¹⁰ Hz are generated in parts of biological membranes in which the energy release exceeds 10^–9 W/m². It is concluded that interaction with these oscillations is the initial physical cause of EHF bioeffects. Methods are proposed for increasing the effectiveness of EHF therapy. The role of acoustoelectric membrane waters in vital processes is examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 1, pp. 103–110, January, 1994.     

双脉冲序列激光放大实验研究

掺Yb3+类高饱和通量增益介质的储能提取,会给激光器带来严重的安全风险,因此提出一种激光脉冲的时分复用放大技术。利用激光的偏振特性以及自由空间传输延迟,获得脉冲参数可变的脉冲序列,并进行验证实验。结果表明,时分复用放大与单脉冲放大的增益没有明显差别,且在约1.4 J/cm2的工作通量下,子脉冲时间间隔（14~22 ns）对激光增益的影响可以忽略不计。时分复用放大在保持总激光通量不变的前提下,降低了子脉冲的激光通量,降低了光学元件的损伤风险,保证了储能的有效提取。     

双脉冲序列激光放大实验研究

掺Yb~(3+)类高饱和通量增益介质的储能提取,会给激光器带来严重的安全风险,因此提出一种激光脉冲的时分复用放大技术。利用激光的偏振特性以及自由空间传输延迟,获得脉冲参数可变的脉冲序列,并进行验证实验。结果表明,时分复用放大与单脉冲放大的增益没有明显差别,且在约1.4 J/cm~2的工作通量下,子脉冲时间间隔(14~22 ns)对激光增益的影响可以忽略不计。时分复用放大在保持总激光通量不变的前提下,降低了子脉冲的激光通量,降低了光学元件的损伤风险,保证了储能的有效提取。     

A theoretical study about the chirped pulse amplification laser

Starting from the Maxwell‘s equation,and using the resonant-dipole equation together with the multilevel rate equations which take the effects of energy relaxation into consideration,we have derived a more realistic numerical model of the chirped pulse amplification for an ultra-broad band width laser amplifier.Numerical simulations of this model show that both the intensity profile and the energy fluence of the amplified chirped pulse are closely connected with the two relaxation effects:the relaxation of the thermalization among the components of the laser multiplets and the depletion of the lower laser level.The results are valuable for the design of ultra-broad bandwidth chirped pulse amplification lasers.     

Electromagnetic pulse amplification in a Cherenkov laser

An investigation is made of the amplification of a Gaussian electromagnetic pulse in a Cherenkov waveguide laser for the cases of long and short waveguides. It is shown that in the first case, the concept of a characteristic pulse duration τ ₀ can be introduced. It is established that when the pulse duration is short (τ<τ ₀) the gain is determined only by its spectral width, and the amplification process leads to a change in the pulse envelope. It is shown that in a short waveguide pulse amplification can be achieved without any change in shape. Zh. Tekh. Fiz. 69, 79–83 (April 1999)     

X-ray amplification by laser controlled coherent bremsstrahlung

A coherent x-ray generation scheme is proposed which involves characteristics of free electron lasers and atomic high harmonic generation schemes. A thin solid layer or any other periodic atomic structure with limited dimensions is exposed to a short, superintense laser pulse. The electrons are extracted from the layer due to the extreme force and penetrate periodically through the ionic structure. Consequently, thousands of harmonics of the laser radiation field are shown to coherently amplify along the interaction length. The small signal gain of the generated x-ray radiation exceeds that arising from the multiphoton Compton process in plasmas and is competitive with that in the leading x-ray free electron lasers.     

Compact curved-grating stretcher for laser pulse amplification

A compact pulse stretcher using curved diffraction gratings is presented. It introduces positive group-delay dispersion and can operate in conjunction with a standard grating-pair compressor in chirped-pulse amplification systems. It presents several advantages over other systems proposed: It has no degrees of freedom and so is not highly sensitive to alignment errors, it is easy to align, it has a compact and robust design, and it uses standard optics. The frequency-dependent delay, dispersions up to third order, and the design parameters of the stretcher-compressor system that will yield good matching are analyzed. Examples of design specifications for a 40-fs pulse with a central wavelength of lambda=800 nm are given.     

High efficiency Tm fiber laser of seed amplification

We use all-fiber single-mode lasers as seed source, amplifiers and pump laser coupling amplifier has been experimentally investigated, respectively. The maximum output power is 10.4 W, with the slope efficiency of 54.4% when the seed laser power is 1 W, and the slope efficiency is 48.7% when the seed laser power is 2 W. The slope efficiency of this scheme is higher than that of the all-fiber amplifier. This can be explained by the loss of pump power at the splice dots. The wavelength of the fiber amplifier is 1947.6 nm, the same as the seed laser's, with a linewidth of 2 nm. We estimate the beam quality to be M² = 2.39, clearly indicating nearly diffraction-limited beam propagation.     

Reaching the nonlinear regime of Raman amplification of ultrashort laser pulses

The intensity of a subpicosecond laser pulse was amplified by a factor of up to 1000 using the Raman backscatter interaction in a 2 mm long gas jet plasma. The process of Raman amplification reached the nonlinear regime, with the intensity of the amplified pulse exceeding that of the pump pulse by more than an order of magnitude. Features unique to the nonlinear regime such as gain saturation, bandwidth broadening, and pulse shortening were observed. Simulation and theory are in qualitative agreement with the measurements.     

Electron acceleration in the inverse free electron laser with a helical wiggler by axial magnetic field and ion-channel guiding

Electron acceleration in the inverse free electron laser (IFEL) with a helical wiggler in the presence of ion-channel guiding and axial magnetic field is investigated in this article. The effects of tapering wiggler amplitude and axial magnetic field are calculated for the electron acceleration. In free electron lasers, electron beams lose energy through radiation while in IFEL electron beams gain energy from the laser. The equation of electron motion and the equation of energy exchange between a single electron and electromagnetic waves are derived and then solved numerically using the fourth order Runge-Kutta method. The tapering effects of a wiggler magnetic field on electron acceleration are investigated and the results show that the electron acceleration increases in the case of a tapered wiggler magnetic field with a proper taper constant.     

Excitonic light-absorption and amplification bands in the presence of laser radiation

We examine the absorption and amplification bands of a weak probe signal in the presence of Bose-Einstein condensation of excitons that emerges in nonequilibrium conditions in the field of coherent laser radiation with a wave vector k ₀. We assume that the detuning from resonance between the energy ħω _ex (k ₀)+L ₀ of the exciton level, which is shifted because of exciton-exciton interaction, and the laser photon energy ħω _L , is generally nonzero. The elementary excitation spectrum consisting of the quasiexcitonic and quasienergy branches determines the optical properties of the system. When there is real induced Bose-Einstein condensation, at the two branches touch, as they do in spontaneous Bose-Einstein condensation. In virtual induced Bose-Einstein condensation, when , instabilities emerge in the spectrum in certain regions of the k-space. These instabilities are caused by a real transformation of two laser photons into two extracondensate particles. Nonequilibrium extracondensate excitons strongly affect the absorption and amplification of the probe light signal. We show that light absorption is due to the quantum transition from the ground state of the crystal to the quasiexcitonic branch of the spectrum. On the other hand, amplification of the signal is caused by the transition from the quasienergy branch to the ground state of the crystal. The same transition can be explained by a real transformation of two laser photons into a vacuum photon of frequency ħcq and a crystal exciton with a wave vector 2k ₀−q. Finally, we show that the excitonic absorption and light-amplification bands are essentially anisotropic at and depend on the orientation of the vectors q and k ₀. Zh. éksp. Teor. Fiz. 112, 167–179 (July 1997)     

介质参数对KrF激光放大器的影响

本文对对KrF激光产生的动力学过程及发光机制进行了研究,利用激发态二能级稳定态理沦,得到了介质的增益、饱和光强以及腔内最佳光强随介质成分和压强的依赖关系,可以作为准分子激光器介质参数选择的依据.并介绍一种用Goblin装置放大短脉冲的方法.     

Ultrafast laser system based on noncollinear optical parametric amplification for laser spectroscopy

We report the experimental demonstration of transform-limited sub-6 fs pulses at an optimal central wavelength by a tunable noncollinear optical parametric amplification(NOPA) source. Meanwhile, a white light continuum in the near-infrared(NIR) range from 900 to 1100 nm is also successfully generated by focusing the unconverted800 nm beam during NOPA generation on a sapphire rod. Both visible-pump/visible-probe and visible-pump/NIR-probe experiments are realized using the same laser system. As examples, ultrafast photo-induced exciton dynamics inside two kinds of materials are investigated by the visible-pump/visible-probe and visible-pump/NIR-probe spectroscopy, respectively.     

Time-division-multiplexing laser seeded amplification in a tapered amplifier

We demonstrate time-division-multiplexing(TDM) laser seeded optical amplification in a diode laser amplifier. With an acousto-optic modulator we combine two seeding beams of different frequencies and inject them alternately in the time domain into the tapered amplifier(TA) chip at a switching speed of 200 ns. The output high-power dual frequency components from the TA are time separated. The TDM seeded TA works safely and efficiently, which is useful for compact precision measurement instruments such as optical clocks and atom interferometers.     

离子通道中相对论电子注的切连科夫辐射

对入射等离子体的相对论电子注(REB)在离子通道中可能产生切连科夫(Cherenkov)辐射的问题进行了论证与研究.利用线性理论分析了离子背景下的注-波互作用关系，导出了系统的色散方程与同步辐射条件.结果表明，系统的电磁不稳定性是由离子通道中TM模与电子注模通过电子注耦合所致，其微观机理是离子对电子注的聚焦.对处于运动等离子体状态下的离子-注系统进行了严格地理论分析，获得了通道内辐射波的频偏与波增长率公式，并通过数值模拟计算讨论了系统有关参数对它们的影响. 关键词： 离子通道 等离子体 切连科夫辐射