He／K系统两步激励产生极紫外相干辐射机制中的斯托克斯及反斯托克…

讨论了Ｈｅ／Ｋ混合蒸汽中两步激励产生极紫外（ＸＵＶ）相干辐射机制中存在的斯托克斯及反斯托克斯跃迁过程，计算了有关跃迁的振子强度、极紫外辐射过程及其竞争过程的受激拉曼散射增益系数和阈值，结果表明，其中６４．３ｎｍ极紫外相干辐射的产生过程与其竞争过程相比，具有最大的增益及最小的阈值；但到能级Ｋ［３ｐ＾５４ｓ＾２ ＾２Ｐ１／２，３／２］的反斯托克斯跃迁及到能级Ｋ［３ｐ＾５３ｄ（＾３Ｐ）４ｓ＾２ ＾２Ｐ１     

负碳离子(2s~2p~3)和(2s~12p~4)的光离解

电子关联效应在负离子中的作用相当重要，本文讨论了负碳离子（２ｓ２ｐ３）和（２ｓ１２ｐ４）的能级结构、光谱跃迁、寿命和光离解通道等。碳负离子（１ｓ２２ｓ１２ｐ４）的双重态比四重态稳定，（２ｓ２ｐ３）和（２ｓ１２ｐ４）之间各辐射谱线波长位于超紫外区域的上限附近，其光谱强度很大的波长有６条，为研制Ｘ射线激光提供了有利的工作物质。     

NⅢ—ArⅩⅣ离子的双电子激发六重态跃迁的理论计算

根据相对论多组态理论，采用ＧＲＡＳＰ２（１９９２）程序计算了ＮⅢ—ＡｒⅩⅣ的１ｓ２ｓ２ｐ３６Ｓ０－１ｓ２ｓ２ｐ２３ｄ６Ｐ跃迁精细结构，计算的波长值与Ｊ．Ｈ．Ｂｌａｎｋｅ［１］等人的计算值和实验值进行了比较，并为六重态离子谱线辨识提供了有益的参考。     

Hg原子6~3P_1→6~1S_0态的系际交叉跃迁及其6~1P_1态与6~3P

Ｈｇ原子６￣３Ｐ＿１→６￣１Ｓ＿０态２５３．６５２ｎｍ紫外辐射是系际交叉跃迁最著名的一例，可归因于其单重态６￣１Ｐ＿１与三重态６￣３Ｐ＿１的组态混合．计算结果表明，对于Ｈｇ原子的６ｓ６ｐ组态，ＬＳ耦合方式仍是其较好描述．     

“天光”一号MOPA系统光学元件加工与镀膜的进展

本文阐述了在中国原子能科学研究院“天光一号”ＫｒＦ激光核聚变实验装置上，ＭＯＰＡ系统光学元件加工与镀膜研究工作的进展。实验测量结果表明，加工后的基片表面均方根粗糙度对于Ｋ９光学玻璃与熔融石英玻璃来说分别为σｒｍｓ＝１．８±０．５ｎｍ，σｒｍｓ＝２．０±０．４ｎｍ。镀ＨｆＯ２／ＳｉＯ２高反射膜的光学元件的反射率与破坏阈值分别为Ｒ＞９９．５％，Ｅｔｈ＝１．３０～１．３３Ｊ／ｃｍ２。镀Ａｌ２Ｏ３／ＭｇＦ２增透膜的光学元件的透射率与破坏阈值分别为Ｔ＞９９．５％，Ｅｔｈ＝１．３～１．９７Ｊ／ｃｍ２。     

负碳离子（2s^22p^3）和（2s^12p^4）的光离解

电子关联效应在负离子中的作用相当重要，本文讨论了负碳离子（２ｓ＾２２ｐ＾２）和（２ｓ＾１２ｐ＾４）的能级结构、光谱跃迁、寿命和光离解通道等。碳负离子（１ｓ＾２２ｓ＾１ｐ＾４）的双重态比四重态稳定，（２ｓ＾２２ｐ＾４）和（２ｓ＾１２ｐ＾４）之间各辐射谱线波长位于超紫外区域的上限附近，其光谱强度很大的波长有６条，为研制Ｘ射线激光提供了有利的工作物质。     

Zn Ⅰ-BrⅥ离子n=4(Δn=0)跃迁谱线波长和振子强度的理论计算

对类锌ＺｎⅠ－ＢｒⅥ离子４ｓ２、４ｓ４ｐ、４ｓ４ｄ、４ｓ５ｓ组态能级进行了系统的理论拟合计算。发现了文献［１－３］中有个别辨认的错误。给出了４ｓ２—４ｓ４ｐ，４ｓ４ｐ—４ｓ４ｄ跃迁谱线波长值和相应的ＨＸＲ方法计算的振子强度。     

类氧Pr^5^1^＋离子辐射跃迁几率和辐射寿命的GRASP计算

根据扩展的相对论多组态Ｄｉｒａｃ—Ｆｏｃｋ方法，使用我们新近开发的“多功能相对论原子结构程序（ＧＲＡＳＰ）”计算了类氧Ｐｒ５１＋离子的精细结构能级、跃迁波长、自发辐射跃迁几率、受激辐射跃迁几率、振子强度和辐射寿命。从计算结果中发现：在３ｐ－３ｓ跃迁中有１６个跃迁的上、下能级间很有可能实现粒子数反转而辐射激光。这个结果与Ｅｌｔｏｎ［１］的预言进行了比较。     

ZnI—BrⅥ离子n=4（Δn=0）跃迁谱线波长和振子强度的理论计算

对类锌ＺｎＩ－ＢｒⅥ离子４ｓ＾２、４ｓ４ｐ、４ｓ４ｄ、４ｓ５ｓ组态能级进行了系统的理论拟合计算。发现了文献［１－３］中有个别辨认的错误。给出了４ｓ＾２－４ｓ４ｐ，４ｓ４ｐ－４ｓ４ｄ跃迁谱线波长值和相应的ＨＸＲ方法计算的振子强度。     

存在缓冲气体的Na—Cs混合蒸汽中的三体碰撞

Ｎａ－Ｃｓ混合蒸汽中的碰撞能量合并已在［２］中研究过。当在池中充入缓冲气体后，碰撞过程出现新的特点，缓冲气体增大了Ｎａ（３Ｐ）和Ｃｓ（６Ｓ）间的能量转移，这可从测量由Ｎａ（３Ｐ）／Ｃｓ（６Ｐ）和Ｃｓ（６Ｐ）／Ｃｓ（５Ｄ）碰撞而被布居的高能级所发射的荧光得到证实。得到三体碰撞速率系数ｋ３＝５．９×１０－２７ｃｍ６ｓ－１。     

Tunable XUV radiation generated by nonresonant frequency tripling in argon

Nonresonant frequency tripling of the ultraviolet (UV) radiation of a frequency doubled pulsed dye laser generates in argon coherent radiation in the extreme ultraviolet (XUV). The radiation is tunable in spectral regions of negative dispersion λ_XUV = 97.4–104.75 nm, λ_XUV = 86.8–86.98 nm and λ_XUV = 85.7–86.68 nm located at the high energy side of the transitions 3p-4s′ [$\text{1}\text{2}$,1], 3p-5s′ [$\text{1}\text{2}$,1] and 3p-3d′ [$\text{3}\text{2}$,1], respectively. At UV input pulse powers of 1–2 MW the pr oduced. XUV power was typically 1–8 W (0.2–1.6 × 10¹⁰ photons/pulse).     

Tunable XUV radiation generated by nonresonant frequency tripling in neon

Nonresonant frequency tripling of ultraviolet (UV) radiation (λ_uv = 216–223 nm, generated by sum frequency mixing of the outputs of a frequency doubled pulsed dye laser and of the Nd-YAG pump laser) generates in neon coherent light in the extreme ultraviolet (XUV). The XUV radiation is tunable in spectral regions of negative dispersion λ_xuv = 72.05- 73.58 nm and λ_xuv = 74.3–74.36 nm at the high energy side of the transitions $\text{2p-3s′[}\text{built1}\text{2}\text{, 1]}$ and $\text{2p-3s[}\text{built3}\text{2}\text{, 1]}$. At UV input powers of 0.1-0.3 MW the generated XUV power was typically P_xuv = 0.1-0.4 W (1.5–6 x 10⁸ photons/pulse). Since present UV dye laser systems provide at λ_uv pulse powers of almost 1 MW the XUV output could easily be increased by more than one order of magnitude.     

Generation of 10- microJ coherent extreme-ultraviolet light by use of high-order harmonics

We demonstrate the generation of 10-microJ coherent extreme-ultraviolet (XUV) light at wavelengths from 73.6 to 42.6 nm, using high-order harmonics. The peak power of this coherent XUV light is estimated to be 0.13 GW at 62.3 nm, and the peak brightness achieved was 3x10(28) photons/(mm(2)mrad(2)s) . To our knowledge, this XUV energy is the highest value achieved with high-order harmonics.     

Short-pulse high-intensity excimer lasers — A powerful tool for the generation of coherent VUV and XUV radiation

Different approaches for the generation of coherent VUV and XUV radiation with a 400 fs KrF excimer-laser system are studied. In nonlinear optical experiments it is shown that four-wave difference-frequency mixing in Xe, using a near two-photon resonance with the KrF laser radiation, is well suited for the generation of tunable VUV radiation in the range 130–200 nm. Conversion efficiencies of 2% and output energies up to 260 J have been demonstrated. Further prospects to achieve J energies are discussed. Using this VUV source and the KrF laser, powerful XUV radiation can be generated by different low-order frequency mixing processes. In first experiments on this subject, direct frequency tripling of the KrF laser pulse has resulted in 14 J XUV radiation at 83 nm.For the realization of soft-X-ray lasers, specific advantages of short-pulse KrF drivers are discussed. Novel scenarios based on a hybrid KrF/Ti: sapphire laser system and multiphoton resonant excitation are considered.Prof. F. P. Schäfer on the occasion of his 65th birthday.     

Tunable UV-radiation by stimulated Raman scattering in hydrogen

We observed tunable UV radiation down to 175 nm by SRS of the output of a frequency-doubled dye laser in H₂. The high power output of the 4th anti-Stokes to 5th Stokes line generated by the frequency doubled dye laser and the 8th anti-Stokes to 3rd Stokes line generated by the undoubled dye laser represents a broadly tunable coherent radiation source between 189 nm and 2064 nm.     

Kilohertz extreme-ultraviolet light source based on femtosecond high-order harmonic generation from noble gases

A compact, versatile table-top kilohertz source of coherent extreme-ultraviolet (XUV) radiation in the wavelength region 18–100 nm, based on high-order harmonic generation from noble gases induced by a 40-femtosecond Ti:sapphire laser system, is presented. The XUV beamline delivers at its output 10⁸ photons/s at a wavelength of 23 nm. The monochromatized XUV radiation is directly focused onto a 10^-2-mm² spot by a toroidal grating, allowing one to reach intensities higher than 10⁶ W/cm². Optimization results are presented for a new XUV-generating geometry, utilizing a ‘semi-infinite’ quasi-static gas cell and strong focusing. In those conditions, we observe an anomalous inversion between the cutoffs of argon and krypton, with the krypton spectrum extending to much higher orders than expected in an adiabatic limit. Received: 9 July 2001 / Revised version: 1 August 2001 / Published online: 7 November 2001     

分子在真空紫外区的相干辐射光谱及转动温度的测量

本文报道的是作者利用分子作为介质,通过非线性光学过程（四波和频,三次谐波）在真空紫外波段产生宽带可调谐相干光的理论和实验研究及其结果,实验产生的宽波段可调谐激光输出为建成完备的小型真空紫外激光光源奠定了基础。此文还报道了作者用该光源在XUV波希成功测量分子转动温度的方法和结果。     

A tunable XUV monochromatic light source based on the time preserving grating selection of high-order harmonic generation

We accomplish a laboratory facility for producing a femtosecond XUV coherent monochromatic radiation with a broad tunable spectral range of 20 eV-75 eV. It is based on spectral selected single-order harmonics from intense laser driven high harmonic generation in gas phase. The time preserving for the selected harmonic radiation is achieved by a Czerny-Turner type monochromator designed with a conical diffraction grating mount for minimizing the time broadening caused by grating diffraction and keeping a relatively high diffraction efficiency. Our measurement shows that the photon flux of the 23-order harmonic(H23) centered at 35.7 eV is 1×10~9 photons/s approximately with a resolving power E/?E ≈ 36.This source provides an ultrashort tunable monochromatic XUV beam for ultrafast studies of electronic and structural dynamics in a large variety of matters.     

Limiting the intensity of femtosecond pulses with anti-stokes excitation of organic dye solutions

Results of experimental investigations into the nonlinear absorption of the symmetric polymethine 1-butyl -3,3-dimethyl-2-[5-(1-butyl-3,3-dimethyl-3H-benz[e]indoline-2-uledene)-1,3-pentadienyl]-3H-benz[e]indolium perchlorate dye solution excited by radiation of a femtosecond titanium-sapphire laser (20 fs, 800 nm, 75 MHz, and 300 mW) by the open aperture z-scan method are presented. Record limitation of the femtosecond laser radiation intensity (by 300 times at a 93% linear transmission of the medium) was achieved. The nonlinear absorption mechanisms in organic dyes with anti-Stokes excitation by wideband high-power pulsed radiation to the absorption band edge and the prospects for organic dye application for limitation of the femtosecond laser radiation intensity are discussed.     

激发态Cs2和H2的电子-振转能级的碰撞转移

利用相干反斯托克斯拉曼光谱(CARS)探测技术, 研究了激发态Cs2与H2间的电子-振转能级的碰撞转移。用波长为532 nm和中心波长为716 nm的两束激光同时聚焦到样品池中, 扫描CARS谱确认了H2分子的S支(△v =1, △J=2)仅在v=1, J=4,5及v=2, J=3,4能级上有布居, 用n1、n2、n3、n4分别表示(2,4)、(2,3)、(1,4)及(1,5)上的粒子数密度。从CARS线的峰值得到n2/n1、n3/n1、n4/n1分别为6.34±1.27、3.66±0.73和1.45±0.29。转移能配置到振动、转动和平动的比例分别为0.44、0.06和0.50, 能量主要分配在振动和平动上。在T=523 K和PH2=2.5×103 Pa条件下, 通过求解速率方程组和对时间分辨CARS线轮廓的分析, 得到碰撞转移速率系数k1=(6.0±1.2)×10-14 cm-3s-1和k2=(4.0±0.8)×10-13cm-3 s-1。