脉宽易变的高功率Nd:YAG激光器

本文描述一台由两级Nd:YAG激光器组成的紧凑高功率激光系统的结构及其工作性能。激光系统分成三个部分:对撞脉冲式的主-被动锁模振荡器,单脉冲选择器和四程放大器。振荡器输出锁模脉冲列的包络幅度起伏小于±4％,其脉冲宽度可以在宽范围内(20ps～2.5ns)方便地切换。对于单个0.1mJ、200ps的激光脉冲,四程放大器能提供7×10~2的放大倍数。     

A Compact Diode-Pumped Injection Seeded Nd：YAG Laser with Resonance-Detection Technique

A diode pumped injection seeded single-longit udinal-mode （SLM） Nd： YA G laser is achieved by using the resonancedetection technique in Q-switching operation. The pulsed oscillator laser uses a folded cavity to achieve compact construction. This system operates at 100 Hz and provides over 20 m J/pulse of single-frequency 1064 nm output. The M2 values of horizontal and vertical axes are 1.58 and 1.41, respectively. The probability of putting out single-longitudinal-mode pulses is 100%. The 355 nm laser output produced by frequency tripling has a linewidth less than 200 MHz. The laser can run over eight hours continually without, mode hopping     

Efficient low-voltage operation of a reverse-biased autoprepulse XeCl laser

An improved version of the auto-prepulse excitation scheme for long-pulse operation of the XeCl excimer laser is reported. A pulsed reverse bias on the small peaking capacitance allows efficient (1.7%) operation at 100 mJ output level with a charge voltage limited to 5–7 kV. Analogies and differences with other long-pulse operation schemes are also discussed.     

Two-colour operation of a Free-Electron Laser and applications in the mid-infrared

The two-colour operation of a Free-Electron Laser (FEL) has been demonstrated with the “CLIO” infrared facility. A two section undulator allows the production of picosecond laser pulses at two different wavelengths and simultaneously, in a wavelength range from to , and with a wavelength separation of two colours of up to . The time overlap, between both colours, has been measured on a picosecond time scale and on a microsecond time scale. An initial pump-probe application experiment has been performed with the two colours: stimulated emission has been measured in a 3-level Quantum-Well system. This is the best demonstration of the stability and reliability of the two-colour laser operation. Received: 4 November 1997 / Revised in final form: 31 March 1998 / Accepted: 10 April 1998     

Simulation studies of the prepulse-main-pulse XeCl discharge lasers with magnetic switching

A self-consistent model of a self-sustained discharge XeCl laser (Ne/Xe/HCl mixture) with prepulse-mainpulse excitation and magnetic switching which leads to high efficiency operation is described. The validity of the model is confirmed by comparing the results of the calculations with the measured time dependences of discharge voltage, current and lasing pulse for different operation modes as well as by comparing the results with the dependences of the laser output energy and efficiency on the charging voltage and capacitance of the pulse forming network for two different laser heads. The numerical evaluation has shown that our developed laser system operates under optimum conditions.     

Dye stability under excimer-laser pumping

The stability of laser dyes under the excitation of a XeCl-laser (308 nm) has been investigated. The measurements were performed in an oscillator amplifier device where the amplifier was fully satured. This allows the comparison with the theoretical model showing that the main reason for dye degradation is the absorption of photo-products. Results for the most important dyes are presented. Dye stabilities range from 46 (fluorescein 27) to 3.4×10⁴ (QUI) absorption processes per molecule before the dye solution has degraded to 1/2 of its initial energy output.     

Quantum Nonlinear Oscillator with Two Degrees of Freedom in a Laser Field

The semiclassical dynamics of a quantum nonlinear oscillator with two degrees of freedom and anharmonicity of the fourth order in a periodic laser field is studied both analytically and numerically. In the absence of external excitation and dissipation, the equations of motion for the mean values of the coordinate and momentum operators of both degrees of freedom reduce to the equation of a onedimensional nonlinear pendulum. The general solution of this equation is written in terms of the Jacobian elliptic functions. As can be expected, the energy of the free oscillator is redistributed periodically between degrees of freedom. The periodic excitation of the nonlinear oscillator may substantially change its motion pattern. Using as an example an oscillator with two coupled vibrational degrees of freedom, it is numerically shown that the amount of laser photons absorbed depending on the parameter values and initial conditions may vary with time in a rather complex manner, including chaotic oscillations. A nonlinear oscillator is capable of manifesting bistable behavior with allowance for dissipation. The analytical condition for the origination of bistability is found. Examples of the bistable dependence of the number of quanta in the oscillator vibrational mode on the level of laser excitation are presented.     

Yield optimisation aspects in two-photon excitation

The question of choosing optimum laser intensities, detunings and relaxation rates in two-photon excitation is considered. It is shown that under steady state conditions the best excitation efficiency is achieved when rather modest laser powers are used and the atoms excited are not extracted too rapidly. The latter conclusion relates to coherence effects playing a non-negligible role in the excitation, which fact can be exploited to enhance the yield. On leave of absece from the Physics Department, University of Helsinki, Siltavuorenpenger 20, SF-00170, Helsinki, Finland.     

基于10 m光子晶体光纤的放大自相似锁模振荡器研究

基于单根10 m大模场面积保偏光子晶体光纤, 搭建了带有色散图的放大自相似振荡器; 通过仔细调节腔内色散量的大小以及位于色散补偿端的端镜前的狭缝位置和大小, 实现了稳定的锁模运转, 获得了抛物线形脉冲输出. 输出脉冲的重复频率为8.6 MHz, 脉冲宽度为6.2 ps, 光谱宽度为3.84 nm, 平均功率820 mW, 对应单脉冲能量95 nJ. 这是第一次在自相似振荡器中直接获得重复频率在10 MHz 以下的脉冲输出, 95 nJ也是目前自相似振荡器直接输出的最高脉冲能量. 通过数值模拟证实了在第一个光栅的零级反射处和狭缝滤波后可以分别实现抛物线型脉冲和高斯脉冲的两种锁模脉冲输出.     

Self-starting Nd:YAG holographic laser oscillator with a thermal grating

Self-starting operation of a self-conjugating loop oscillator is achieved, for the first time to our knowledge, by use of an optically induced thermal hologram in a nonsaturable absorbing medium. Self-Q-switched single-longitudinal-mode pulses of 12-ns duration are obtained in a near-diffraction-limited spatial mode and with an output energy of >250 mJ . Good correction of intracavity phase distortions is obtained, as well as good extraction efficiency in the laser mode volume. It is shown that one has to set an additional nonreciprocal phase-shift element in the loop to ensure resonant operation of the system.     

Efficient generation of 200 mJ nanosecond pulses at 100 Hz repetition rate from a cryogenic cooled Yb:YAG MOPA system

A diode-pumped Master Oscillator Power Amplifier (MOPA) laser system based on cryogenic cooled Yb:YAG has been designed, developed and its output performance characterised. The laser system consists of a fibre oscillator, an active mirror regenerative amplifier and a four pass main amplifier. 2.4 mJ, 10 ns, 100 Hz seed pulses from the fibre oscillator/regenerative amplifier arrangement were amplified up to pulse energies of over 200 mJ by using the four pass main amplifier arrangement. As a further study we have obtained an increased slope efficiency of 40% and an optical-to-optical efficiency of 30% using a pinhole vacuum spatial filter/image relay for laser mode control. With 1.8 mJ input seed pulses, output pulse energies of around 150 mJ were achieved.     

Flash-lamp pumped dye laser excited by a transverse discharge

A flash-lamp pumped dye laser has been described in which the discharge responsible for the working medium excitation was transverse to the capillary filled with the dye. It was shown that such arrangement allows for the lamp operation at the atmospheric pressure and makes possible generation of short pulses of light.     

All-fiber linearly polarized laser oscillator by fiber coiling loss control

In this paper,we demonstrate an all-fiber linearly polarized fiber laser oscillator.The single polarization of the oscillator is achieved through the careful designing of the active fiber coiling.The relationship between fiber coiling diameter and polarization extinction ratio and optical efficiency is studied,whose results lead to an optimized system.The thermal management of the oscillator is also refined,which allows the oscillator to reach a maximum output power of44.1 W with an optical-to-optical efficiency of 57.9%.A high average polarization extinction ratio of 21.6 d B is achieved during a 2-hour stability test.The oscillator also owns a narrow 3-d B bandwidth of 0.1 nm,as well as near-diffraction-limit beam quality of M~2~ 1.14.     

Injection-locked single-frequency laser with an output power of?220?W

A solid-state laser system for the next generation of gravitational wave detectors with an output power of 220?W at the wavelength of 1064?nm is presented. Single-frequency operation of the laser was achieved by injection-locking of a high-power ring oscillator to an amplified non-planar ring oscillator (NPRO) following the Pound?CDrever?CHall scheme. The high-power stage which features four longitudinally pumped Nd:YAG laser crystals as active media in a ring resonator configuration was designed for reliable long term operation. Using a non-confocal ring cavity to filter the output beam, a pure TEM₀₀ mode with 168 W output power was obtained.     

Reduction of copper bromide molecules in the plasma of a CuBr laser during the interpulse period

The operation of a CuBr laser in an excitation pulse train mode has been investigated. The experimental data obtained allow one to determine the characteristic time for which copper atoms are lost by the active medium of the laser. The analysis performed based on a numerical simulation of the laser operation has shown that the copper atoms are lost in the processes of reduction of CuBr molecules due to reactions of interaction of copper atoms with bromine ions. The predicted time for which copper atoms are lost by the laser active medium (150 μs) is in good agreement with the experimental one.     

Tunable light source for coherent anti-Stokes Raman scattering microspectroscopy based on the soliton self-frequency shift

We present a photonic crystal fiber (PCF)-based light source for generating tunable excitation pulses (pump and Stokes) that are applicable to coherent anti-Stokes Raman scattering (CARS) microspectroscopy. The laser employed is an unamplified Ti:sapphire femtosecond laser oscillator. The CARS pump pulse is generated by spectral compression of a laser pulse in a PCF. The Stokes pulse is generated by redshifting a laser pulse in a PCF through the soliton self-frequency shift. This setup allows for probing up to 4000 cm(-1) with a spectral resolution of approximately 25 cm(-1). We characterize the stability and robustness of CARS microspectroscopy employing this light source.     

北京自由电子激光器外注入实验系统设计研究

北京自由电子激光器(BFEL)是一台工作于中红外区Compton型FEL振荡器。本文结合BFEL装置,设计了一套完整的激光外注入光路,利用声光调QCO_2激光器产生的10.6μm激光做激励源注入到BFEL光腔中,以缩短振荡建立时间,提高BFEL输出能量,改善输出激光的相干性。模拟计算结果是:当BFEL光腔中的外注入光强为自发辐射强度的10~5倍时,可使饱和振荡建立时间缩短35％,输出能量提高2倍。     

Passively mode-locked Yb:KLu(WO4)2 thin-disk oscillator operated in the positive and negative dispersion regime

We demonstrate a passively mode-locked femtosecond Yb:KLu(WO(4))(2) thin-disk laser oscillator. Chirped-pulse operation in the positive dispersion regime as well as solitary operation have been realized, and the laser performance of both configurations are compared. In the solitary mode-locking regime the output power exceeds 25 W in a diffraction-limited beam, and pulse durations as short as 440 fs at a 34.7 MHz repetition rate have been generated. For the first time we present a chirped-pulse operation of a thin-disk oscillator that yields a maximum average output power of 9.5 W with a Fourier limit of 450 fs.