强近共振激光脉冲驱动下二能级系统中试探脉冲的瞬态反应

我们用缀饰模型研究强近共振激光脉冲驱动下二能级系统与弱试探脉冲的相互作用。当试探脉冲的频率ω₂调到共振频率ω₂=ω₁±<Ω₂₁^D>时,试探脉冲呈现吸收或放大效应。还得到非线性混频效应的瞬态过程。共振增强存在于此非线性混频过程中。 关键词：     

Generation of tunable picosecond pulses in a simple distributed feedback dye laser under N2-laser pumping

Simple possibility of single tunable picosecond pulse generation in a conventional inexpensive distributed feedback dye laser (DFDL) is demonstrated. It is shown that when a TEA N₂-laser is used for pumping no diffraction grating is necessary in the DFDL optical scheme for operation in the picosecond regime. Hence wide-range spectral tuning from 357 to 665 nm was easily achieved. When pumped with a 0.6 ns 40 kW pulse of the TEA N₂-laser the DFDL generated pulses as short as 7 ps with time-bandwidth product better than 0.6 and peak power ? 10 kW. At a repetition rate of 50 pps the shot-to-shot energy stability of a single picosecond pulse was ±18% at ±7% stability of the TEA N₂-laser.     

LD抽运被动调Q固体激光器的脉冲稳定性

报道了二极管激光抽运Cr,Nd∶YAG被动调Q Nd∶YVO₄ 1064nm激光输出.为了提高被动调Q激光的输出稳定性，谐振腔采用长腔，增益介质位于谐振腔中间位置.实验中获得了稳定的被动调Q激光输出.在最高入射抽运功率为17.5W时，脉冲重复频率达到71.3kHz，脉冲宽度为0.4μs.调Q脉冲幅度不稳定性低于±10%，脉冲时间波动性低于±3.5%.     

1kHz窄脉宽高峰值功率MgO∶LN电光腔倒空Nd∶YAG激光器

报道了一种1kHz窄脉冲宽度、高峰值功率的电光腔倒空1 064nm全固态激光器.该激光器采用808nm脉冲LD侧面泵浦Nd:YAG晶体棒的双凹型折叠谐振腔结构和同步延迟MgO∶LN晶体横向加压式电光腔倒空技术,通过优化设计谐振腔结构,在脉冲重复频率200Hz时,获得了最大单脉冲能量46.7mJ、脉冲宽度4.06ns、峰值功率11.50MW的1 064nm脉冲激光稳定输出,脉冲宽度和能量的峰峰值不稳定度分别为±1.52%和±2.02%;在1kHz时,最大单脉冲能量达到18.3mJ,脉冲宽度5.02ns,峰值功率3.69MW,脉冲宽度和能量的峰峰值不稳定度分别为±2.75%和±3.52%,激光束因子为3.849和3.868,远场发散角为3.46mrad和3.55mrad,束腰直径为1 508.84μm和1 477.30μm.     

Threshold behavior of multiple photon dissociation of SF6

Multiple photon dissociation of SF₆ by a short pulse of a CO₂ laser has been investigated by simultaneous measurements of the average number of photons absorbed per molecule 〈n〉 and chemiluminescence intensities which result from the dissociated F atoms. A criterion for the dissociation threshold which is independent of laser wavelength is found to be 〈n〉 = 16 ± 3 photons per molecule. A thermal distribution of the excited molecules is shown to be inconsistent with the behavior just above threshold.     

超短激光脉冲驱动的Thomson散射空间分布特性

研究了超短激光脉冲驱动的Thomson散射的辐射空间分布. 发现辐射的空间分布对称性显著地依赖于超短脉冲的载波相位η₀，在η₀＝0，π时，辐射的空间分布呈现出二重或一重对称性；而在其他载波相位时，这些空间分布对称性遭到破坏. 辐射光的准直性也依赖于驱动脉冲的载波相位，在η₀＝±π/2时辐射光的准直性最好. 这些结果表明可以通过改变驱动激光脉冲的载波相位来控制辐射光的空间分布，也可以利用辐射空间分布对相位的依赖特性来测量超短激光脉冲的载波相位. 关键词： Thomson散射 空间分布 载波相位     

High-repetition-rate megawatt millijoule pulses from a Nd:YVO<Subscript>4</Subscript> laser passively Q-switched by a semiconductor saturable absorber

We exploit an AlGaInAs periodic quantum-well absorber with a large modulation strength to realize a multi-mJ passively Q-switched Nd:YVO₄ laser with a repetition rate up to 200 Hz. At a pump energy of 34 mJ, the output pulse energy and the peak power are found to be 3.5 mJ and 1.1 MW, respectively. The fluctuation of the output pulse energy is generally less than ±2%.     

High-power Nd:YVO4/BaWO4 intracavity Raman laser emitting at 1,103?nm

A compact BaWO₄ Raman laser is realized with a diode-end-pumped acousto-optically Q-switched YVO₄/Nd:YVO₄ laser. Based on the Raman shift at 332?cm^?1 of BaWO₄, first-Stokes generation at 1,103?nm is generated. At a pump power of 11.3?W and a repetition rate of 45?kHz, an average power of 1.59?W is obtained. The pulse width is measured to be 36.8?ns and the beam quality factor (M ²) in the horizontal and vertical directions is determined to be 1.56?±?0.1 and 1.41?±?0.1, respectively. The thermal focal lengths of the laser medium and Raman medium are calculated theoretically.     

A passively mode-locked Nd:YAG laser using a half-symmetric unstable resonator with continuous output coupling

A mode-locked Nd:YAG laser has been operated using a half-symmetric unstable resonator consisting of a totally reflecting convex mirror and a 8% reflecting plane mirror formed by one end of the laser rod. The performance of this laser is reported for two resonator lengths. In the case of the longer resonator the far-field distribution retained the same radial symmetric form even when an intra-cavity aperture was adjusted to produce different near-field patterns. Beam divergence at the 1/e² point was measured to be (4.0±0.4) × 10^-4 radians. Pulse widths were confirmed as 30±3 ps within a pulse train of 52±5 mJ.     

Key methods for intensifying soft X-ray emission from a laser plasma for lithography

A two-pulse two-wave (Nd and CO₂ lasers) scheme is proposed for irradiating a laser target, which ensures the highest factor of laser radiation conversion to the X-ray range (13.5 nm ± 1%). Analytic estimates are obtained for parameters of pulses and of the target made of Xe or Li. Numerical optimization is performed for X-ray emission from a spherical Xe target exposed to a CO₂ laser pulse. The maximal factor of conversion of laser radiation to X rays is ～1%. Angular and spectral characteristics of X-ray radiation are obtained. The flux of fast Xe ions ejected from the target and damaging the Mo/Si coating of X-ray mirrors is estimated.     

Capillary discharge soft X-ray laslng in Ne-like Ar pumped by long current pulses

A capillary discharge soft X-ray laser operating at 46.9 nm on the transition 3p-3s (J = 0-1) of the Ne-like Ar has been realized by exciting the active medium with a long half-cycle duration current pulse of 140 ns. The current is produced by discharging a 10 nF water dielectric capacitor, initially charged to voltages lower than 200 kV by a six stage Marx generator, through a 15-cm long capillary channels. The laser amplification has been obtained by properly adjusting all the other experimental parameters. Utilizing a 3-mm in diameter Al₂O₃ capillary channel initially filled with 0.3 torr of Ar pressure, a laser beam, which has a 4-mrad divergence and a time duration of 1.3 ns, is characterized by a gain of 0.6±0.1 cm^-1. The stability of the plasma compression followed by the laser emission is verified. Received 13 December 2001     

Characteristics of laser and current pulses in a He–SrCl2 vapor laser

An experimental investigation on the characteristics of laser and current pulses in a He–SrCl₂ vapor laser is carried out. The temporal dependences of the discharge current pulse on the laser pulses at the 1.09 μm, ～3 μm and 6.45 μm lines in strontium atoms and ions are measured and analyzed under different laser output powers. It is found that all laser pulses appear at the falling edge of the current pulse and shift forward to the current pulse with increasing laser output power.     

Nonlinear optical characteristics of carbon disulfide

The nonlinear refractive index γ of CS₂ is studied using laser pulses of various durations (from 110 fs to 75 ns). It is found that γ increases with increasing pulse duration within the picosecond region (from (3 ± 0.6) × 10^?15 cm² W^?1 at 110 fs to (3.5 ± 0.7) × 10^?14 cm² W^?1 at 75 ns) due to orientational nonlinearities. Variations in the sign of γ caused by the thermal effect at different pulse durations and repetition rates are analyzed. It is demonstrated that the fast electronic component, the component associated with molecular processes, causing positive nonlinear refraction, and the acoustic component, responsible for negative nonlinear refraction, manifest themselves simultaneously. The results of a study of the nonlinear absorption of carbon disulfide are presented. The two-and three-photon absorption coefficients of CS₂ are determined to be (5 ± 1.5) × 10^?11 cm W^?1 and (2.8 ± 0.8) × 10^?23 cm³ W^?2, respectively.     

Single-frequency, injection-seeded Q-switched operation of a resonantly pumped Ho:YAlO3 laser at 2,118 nm

A 1.91 μm-pumped, injection-seeded 2,118 nm Q-switched Ho:YAlO₃ laser was demonstrated in this paper. Single-frequency and nearly transform-limited operation of Q-switched Ho:YAlO₃ laser was achieved by injection-seeded. The single-frequency Q-switched Ho:YAlO₃ laser output energy of 8 mJ at 100 Hz with a pulse width of 151 ns was obtained. The half-width of pulse spectrum measured by a heterodyne technique was 3.7 MHz.     

Laser-diode-pumped Nd:YVO<Subscript>4</Subscript>/Nd:YAG MOPA burst-mode laser

We report a high-repetition-rate, high-peak-power laser diode (LD) pumped burst-mode 1064 nm laser from a Nd:YVO₄/Nd:YAG master oscillator power amplifier. 10–100 kHz pulse burst in a duration up to 2 ms is achieved in LD end-pumped Nd:YVO₄ acousto-optically Q-switched laser. After amplification with LD side-pumped Nd:YAG rod amplifiers, the single pulse energy reaches 73 mJ in 10 kHz pulse burst laser with a peak power of 7.8 MW.     

Long pulse ultraviolet laser emissions in an aerodynamically cooled electron-beam excited Ne-NF3 mixture

Long pulse laser action has been achieved at 3378.28 and 3481.96 Å in an electron beam excited supersonic flow. These laser emissions, attributed to NeII transitions, have been obtained when a mixture of Ne and NF₃ at a pressure of 0.2 atm. and aerodynamically cooled to 80 K was excited by a medium intensity electron beam. Laser pulse duration, about 350 ns fwhm for both lines, was only limited by the electron beam pulse length. The second of these laser lines had not been previously reported.     

Development of 385-μm D2O laser for plasma diagnostics

An optically-pumped 385-μm D₂O laser has been constructed for Thomson scattering ion temperature measurements in tokamak plasma. Stable single mode and stable tunable (over ±1 GHz) operation of the pump 9R (22) TEA CO₂ laser is performed by using an intracavity ZnSe etalon which is temperature-controlled within ±0.01°C. The saturation broadening with D₂O absorption line is observed for the first time using the tunable 9R (22) CO₂ laser. The pressure broadening coefficient of the N₂O absorption line is measured to be 7.6 MHz/torr using the ±1 GHz tunable 385-μm D₂O Raman laser. At 385 μm, an output quantum efficiency as high as 21% is obtained.     

Preionization kinetics of an X-ray preionized XeCl gas discharge laser

The influence of preionization conditions on the performance of a XeCl gas discharge laser preionized by a short, high intensity x-ray pulse, has been studied. The laser output energy and optical pulse temporal characteristics have been used to determine the roles of initial electron density and of electron attachment to HCl and to impurities. Although the short pulse preionization technique functions well for XeCl when the laser voltage pulse has a short risetime (?20 ns), it is less well suited to XeCl lasers using slowly rising voltage pulses (>50 ns), or to F₂ containing gas mixtures (KrF and XeF lasers).     

Eye-safe Raman laser based on BaTeMo2O9 crystal

An eye-safe Raman laser is realized with BaTeMo₂O₉ (BTM) nonlinear crystal for the first time. By using a diode-end-pumped acousto-optically Q-switched Nd:YVO₄ laser as the pumping source, the BTM crystal converts the fundamental laser at 1,342 nm to first-Stokes laser at 1,531 nm successfully. With an incident power of 10.8 W and a pulse repetition rate of 25 kHz, the average output power at 1,531 nm is obtained to be 0.83 W, corresponding to a diode-to-Stokes conversion efficiency of 7.7 %. The pulse width is 11 ns, and the peak power is 3.0 kW.