Initial testing of a high-repetition-rate electron-beam-pumped KrF laser amplifier

The initial test results of the high-repetition-rate (rep-rate) electron-beam (e-beam) pumped KrF laser amplifier under development in our laboratory are reported. This amplifier is aimed at producing a laser energy of 20 J per pulse at a rep rate of 1 Hz. Thus far, 700 consecutive e-beampulses (250 kV, 270 J/pulse) were generated at a rep rate of 1 Hz. The laser gas was repetitively pumped by the e-beams injected through the water-cooled diaphragm foils. Received: 5 February 2001 / Published online: 21 March 2001     

Small signal gain measurement of KrF and XeF laser amplifiers

Effective amplification has been found in the double discharge TEA amplifier of KrF. The small signal gains measured in KrF and XeF are 2.3%/cm and 1.0%/cm respectively.     

Optimization of multiple-pass off-axis KrF amplifiers

Multiple-pass short-pulse off-axis amplification using spherical and cylindrical expansion schemes has been analyzed for different conventional discharge-pumped KrF gain modules. It is shown that using a single-gain module in a three-pass optimized off-axis arrangement, output energies up to several 1OO mJ can be reached with excellent contrast, starting from 10–20 µJ input energies.     

Dynamic absorption effects in KrF* amplifiers

The results of transient loss measurements performed in a self-sustained discharge KrF^* amplifier are reported. Analysis of these results gives a minimum value of 20 for the effective gain to loss ratiog ₀/_eff, indicating that efficient extraction of energy in subpicosecond KrF^* amplifiers in the 1 J range should be achievable.     

A single-mode KrF laser

Single-mode operation of a KrF laser oscillator has been achieved for the first time. The laser medium is pumped by an electron beam which allows excitation for a much longer duration than with discharge pumping. The long excitation time, together with the use of a short oscillator cavity with a low single-pass gain, allows many roundtrips before saturation is reached. This makes line-narrowing easier and single-mode operation has been achieved using only two intracavity etalons.Technical Research Centre of Finland, Helsinki, Finland     

Tuning ranges of KrF and ArF excimer laser amplifiers and of associated vacuum ultraviolet anti-Stokes Raman lines

Measurements of tuning ranges for narrow-bandwidth ( ) radiation amplified in KrF and ArF laser amplifiers are reported. Generation of high-order anti-Stokes Raman lines in H₂ down to 116 nm is described as well as measurements of the corresponding tuning ranges. Generation of rotational side-bands opens the possibility to tune most of the vacuum-ultraviolet (vuv) lines over intervals in excess of 1400 cm^–1. Absolute values of the power measured for the various vuv lines are communicated.     

KrF pulsed laser ablation of polyimide

In the present paper, polyimide surfaces were processed with pulsed KrF laser radiation at fluences near the ablation threshold. The morphology of the processed surfaces was studied by scanning electron microscopy and chemical analyses performed by electron dispersive spectroscopy. The formation of conical structures was observed for radiation fluences lower than 0.5 J/cm². The areal density of cones increases with the number of pulses and decreases with the radiation fluence. At low fluences (<150 J/cm²), cones are formed due to shadowing by calcium phosphate impurities while for higher fluences the main mechanism of cones formation is believed to be radiation hardening.     

50mJ超短脉冲KrF激光系统的参数优化

介绍了原子能院建立的钛宝石 /KrF混合型激光装置 ,主要输出参数的测量和性能优化。放电泵浦准分子激光器采用离轴放大结构 ,结合棱镜对进行GVD补偿 ,获得 5 0mJ,2 2 0fs的紫外超短脉冲。用4 0cm透镜聚焦 ,靶上功率密度达到 10 17W/cm2 。     

Ionization via an ultrashort high-power KrF laser

Received: 10 January 1997     

KrF激光脉冲整形研究

 实验研究了脉冲堆积法对KrF激光的整形能力。利用受激布里渊散射(SBS)压缩脉冲获得了脉宽为3~5 ns的短脉冲，用4束激光堆积获得了脉宽为10~15 ns、平顶宽度为5~10 ns的整形脉冲。利用实测SBS脉冲数据，对脉冲堆积法进行了数值模拟，模拟的脉冲宽度为12.7 ns，平顶宽度为7.7 ns，该结果与实验相符。对脉冲堆积法的任意整形能力进行了模拟，讨论了脉冲宽度变化对整形的影响，发现脉宽变化在5%以内时，对整形脉冲的影响较小。对整形脉冲的放大进行了定性研究，结果表明：平顶脉冲通过放大器后，前沿部分放大较多，由于饱和作用，后沿放大较少；如果前端整形脉冲前沿为斜坡状，放大后可以得到近平顶的脉冲。     

The effect of prepulse on X-ray laser development using a powerful subpicosecond KrF laser

A high power UV laser has been developed as a pump source for short wavelength (down to 1 nm) X-ray lasers. Various schemes are considered and theoretical analysis is discussed. Spectroscopic studies of laser-target interaction have been performed and, in particular, the effect of a prepulse on plasma generation has been investigated. Analysis of the observed spectra indicates that reduction of the prepulse energy results in a higher temperature plasma. Investigation of the interaction using thin layered targets is also presented. These data provide evidence for initially hot plasma conditions generated from target layers 150 Å. Discussions of proposed laser schemes at 1–5 nm are presented.Also at the Mechanical and Aerospace Engineering Department, Princeton University, Princeton, NJ     

Rapid discharge-pumped wide aperture X-ray preionized KrF laser

A wide aperture X-ray preionized discharge-pumped KrF excimer laser has been constructed. A flat plate pulse-forming line (36 nF, 340 kV) charges a peaking capacitor (6 nF) through a rail-gap to facilitate a rapid discharge in the laser head. Collimated X-ray preionization is employed to obtain a wide and uniform discharge. The laser is intended to be used as a short pulse amplifier and results are presented when characterized as an oscillator. The active cross-section of the laser beam is 10×8 cm² with 50 cm effective electrode length. The laser pulse energy exceeds 4.7 J in a 28 ns pulse (FWHM).     

Nonlinearities in semiconductor laser amplifiers

This review discusses the physical mechanisms of absorptive and dispersive nonlinearity in amplifiers resulting from interband and intraband electron transitions, with an assessment of the relative strengths and response times of these nonlinearities. Where appropriate, the potential applications of these nonlinearities in optical networks are also indicated.     

Theory of two-section laser amplifiers

A new theory of two-section amplifiers has been developed in order to account explicitly for dispersive effects arising from the carrier dependence of the refractive index. It has been found that non-linear and bistable effects in two-section devices, which are conventionally attributed to saturable absorption, contain a stong component of dispersive non-linearity. The implication is that the advantages claimed for two-section amplifiers over single-section devices may not be as great as had hitherto been thought.     

Spectral line competition in a coaxial electron-beam-pumped high pressure Ar/Xe laser

In order to study the kinetic mechanism of the e-beam pumped Ar/Xe laser, the temporal profiles of individual laser lines during multiline oscillation have been measured as a function of power deposition (1–12MW/cm³) and gas laser pressure (2–14 bar) using a short pulse (30 ns) coaxial electron beam as excitation source. It was found that the optimum output energy at each pressure was obtained at the same specific power deposition.Strong line competition has been observed between the 2.65 and 1.73 m transitions. In order to explain our results we suggest that besides electron collision mixing (ECM) between the 5d and 6p levels of Xe, there is also a redistribution between all 6p levels which strongly favours the lower levels at higher pumping densities.     

用于ps脉冲放大的大口径放电泵浦KrF激光器

 以简单的火花间隙作为放电开关，建立了一种用于ps脉冲激光放大的大口径放电泵浦KrF准分子激光器。该激光器的有效增益口径截面为4cm×3cm，在自由运转情况下最大激光输出能量为1.3J，脉宽20ns。用作ps放大器时，利用光学偏振放大方式获得了激光能量140mJ，脉冲宽度10ps的激光输出。利用XeCl激光泵浦的染料激光作为探针测量了不同放电条件下和不同气分比条件下激光的增益和吸收系数。     

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.     

Investigation of stimulated Brillouin scattering for broadband KrF laser

Stimulated Brillouin scattering (SBS) numerical mode for broadband multimode KrF laser pump with optical breakdown has been built up in this paper. The basic premises of the model are that KrF spectrum is composed of an umber of lines and SBS arises from these lines with coupling to some extent. The broadband SBS threshold strongly depends on pump bandwidth. SBS and optical breakdown occur nearly simultaneously when broadband SBS and breakdown have the same threshold. The decrease of saturation reflectivity for broadband pump radiation is explained with this model. Experimental results agree well with the model.     

Subpicosecond UV pulse generation for a multiterawatt KrF laser

A 180-fs UV pulse has been generated based on a hybrid synchronously pumped mode-locked dye laser for a multiterawatt KrF laser system. The pulse width was measured by the single shot autocorrelation technique with the three-photon fluorescence of the XeF C-A transition. The pulse width broadening due to dispersive media was investigated. The results show that the observed pulse width broadening from 210 fs to 390 fs through the entire system is explained mostly by the linear dispersion of the optical elements for near-transform-limited input pulses.     

宽带KrF激光抽运的受激布里渊散射反射率研究

实验上研究了宽带KrF激光抽运的受激布里渊散射(SBS)随抽运功率密度、介质气压和透镜焦距这三个实验参数的变化规律.在较低的抽运功率密度情况下，SBS反射率随抽运功率密度呈非线性增长；当抽运功率密度提高到一定程度，SBS反射率接近饱和；当功率密度继续增大，SBS 反射率随之下降.介质气压提高能够促进SBS的转换.透镜焦距长度的变化使SBS饱和反射率存在一峰值.理论上建立了宽带多模SBS模型，数值模拟结果与实验结果符合得很好，解释了宽带SBS反射率对实验参数的变化规律. 关键词： 宽带 KrF激光 受激布里渊散射(SBS) 反射率