反射镜双程放大对类氖锗软X射线激光的输出影响研究

纳秒量级激光驱动的类氖锗软X射线激光具有出光稳定和输出强度大等优点,在诸多领域拥有很好的应用价值. 研究了通过在光路中增加一块多层膜反射镜实现双程放大对出光特性的影响. 通过估算和实验,证实了增加反射镜双程放大确实能够提高类氖锗软X射线激光的输出强度,对于24mm的双程放大长度,总输出强度会增加约2.3倍. 但同时这种模式也带来了光束质量的下降,对应用研究并非完全有益. 关键词： 软X射线激光 反射镜双程放大 增益饱和     

类氖锗等离子体中软X激光饱和增益实验研究

进入“冰窗”波段和获得饱和增益输出是当前实验室研究X激光的目标。考察X激光输出的强度随靶长的变化规律,是判断是否达到饱和增益的重要依据,但必须排除折射等因素造成的假像。为了校正折射等的影响,我们曾经提出并实施了“双靶对接”方案,在功率为10~(12)W的LF-12~#钕玻璃激光装置上,获得了高增益的类氖锗等离子体中软X激光输出。最近,在饱和增益研究实验中,我们发展了双靶对接的概念。设计了“多靶串接”方案,获得了趋于饱和的类氖锗等离子体中软X激光输出。     

类氖锗X光激光增益实验

本文介绍了在LF-12激光器上进行的类氖锗X光激光增益实验。当泵浦激光波长为1.053μm,脉宽为1.1～1.4ns、能量为550～650J、线聚焦焦斑为185μm×20mm时,使用片状锗靶测量波长为19.61、23.22、23.63、24.73及28.65nm的五条激光跃迁线的增益分别为3.06、3.99、3.72、2.36及4.59cm^(-1)。实验给出了关于柱形等离子体激光介质发射区厚度及软X射线激光发射角的实验数据。实验也给出了软X射线激光强度随泵浦激光功率密度变化的讯息。最后分析了由薄膜锗X光激光靶进行的增益实验中未看到激光增益线的原因。     

“多靶串接”饱和增益软X光激光实验研究

采用“多靶串接”设计,利用强度为0.8×10~(13)～1.0×10~(13)W/cm~2,波长为1.05μm,脉宽约1ns的两路钕玻璃激光线聚焦辐照四块串接的平面厚锗靶,观察到波长为23.2和23.6nm的接近饱和的类Ne锗软X光激光输出。当总靶长为5.6cm时,这两种波长的软X光激光输出的GL值都达到16左右,沿靶法线和靶平面方向的发散角都只有3～4mrad。     

类氖锗软X射线激光输出达到深度饱和

在国家“863”计划激光技术领域专家委员会的支持下,1992年9月,中国工程物理研究院上海激光等离子体研究所、北京应用物理与计算数学研究所成功地进行了新的一轮四靶串接加反射镜X射线激光实验.波长为23.2和23.6nm两条激光线的有效增益长度积GL达17.5,创世界最高纪录,表明我国 X射线激光技术研究走在世界前列. 实验用我国的“神光”装置作驱动源,在上一轮四靶串接X射线激光实验成功的基础上,把X射线多层膜反射镜放置在四靶的西侧,距靶端3cm处,使由南路激光辐照的一、二靶产生的X射线激光实现了双程放大、经双程放大的X射线.激光输出强度…     

高增益复合泵浦O^＋7X射线激光的理论研究

用一维流体力学程序MEDUSA耦合原子物理程序NIMP,对超短脉冲激光辐照Mylar纤维靶和平面靶产生复合泵浦O~(17)X射线激光的物理过程进行了理论研究,探讨了利用VULCAN激光装置的CPA皮秒脉冲光束进行饱和增益实验的可行性.结果表明,超短脉冲辐照激光靶可能是产生饱和增益的复合泵浦X射线激光的一条有效途径.     

X光激光在等离子体中的传播

由于等离子体柱中有垂直于轴向的电子密度梯度,致使X光激光在等离子体柱内传播时发生折射。折射效应限制了增益区的长度,采用“双靶对接”的实验方法,能有效地抑制折射的影响。本文从理论上阐述了折射效应对激光增益的影响相当于在小讯号增益系数上加了一个负项;并给出X光激光出靶端的强度角分布及偏离轴向的折射角;为“双靶对接”实验提供靶面的夹角值。理论计算结果与实验结果符合得很好。     

诊断技术领域的新设备——平焦场光栅光谱仪

<正> 平焦场光栅光谱仪是由中国工程物理研究院上海激光实验室自行研制的用于X光激光研究的诊断设备。在1990年5月的锗双靶对接X光激光实验中,该谱仪已与西安光机所生产的软X光扫描相机相接,在国内首次测出了类氖锗高增益X光激光时间分辨谱线。用脉宽1ns的激光打靶时,产生的X     

19.6nm波长类氖锗X光激光光源理论模拟

 波长19.6nm的类氖锗X光激光适合作为诊断激光等离子体界面不稳定性的光源。用经过实验检验的系列程序对预-主短脉冲驱动类氖锗进行了系统的优化设计和理论分析。采用2%~3%的预脉冲强度，6~8ns的预-主脉冲时间间隔，在4×10¹³W/cm²功率密度驱动下, 波长19.6nm增益区的宽度可以超过60μm，增益区的维持时间可以达到90ps。对于16mm长的平板靶，增益系数可达11.8/cm；弯曲靶增益系数可达13.3/cm；单靶小增益长度积可达21.3，单靶就可以获得饱和增益。采用双靶对接，其小讯号增益可达38.4，可以获得深度饱和增益，能满足应用演示所需的X光激光光源。     

“四靶串接”类氖锗软X光激光趋向饱和增益的理论研究

介绍了“四靶串接”设计思想,继对接方式之后,又提出了顺接方式来提高X光激光增益,使四靶总长度达到5.6cm。我们研制了程序系列来模拟这一实验,直接给出测点处的X光激光的强度。先用上轮“双靶对接”实验结果检验我们的程序系列,使得23.2nm激光线的结果与实验数据相符合,再用它模拟“四靶串接”实验。在实验之前,对各靶之间距离和角度,以及这些数据对实验结果的敏感程度作了预估,用以指导实验。实验结果证明理论模拟是正确的。23.2nm和23.6nm两条激光线已明显趋于饱和,其小讯号增益长度积GL分别达到18.3和17.6,有效GL分别达到16.4和15.7。X光激光的发散角已减小到3～4mrad,超过美国利弗莫尔实验室(LLNL)已发表的最好结果。     

Review of collisional excitation neon-like and nickel-like soft X-ray lasers pumped by multiple infrared laser pulses at the Institute of Laser Engineering,Osaka University

We report on the soft X-ray laser developments performed at the Institute of Laser Engineering, Osaka University especially for the collisional excitation X-ray lasers at wavelengths between 25 nm and 4 nm. The performance of neon-like and nickel-like ion X-ray lasing pumped by a train of short laser pulses has been investigated. We have also demonstrated double pass amplification using a soft X-ray multi-layer mirror at wavelengths of 19.6 nm and 7.9 nm. Based on these results and experimental technique, two targets were placed in series to double the gain length. Two opposing laser beams irradiated the double targets with a suitable time difference for quasi-traveling wave pumping. The double target amplification was successfully demonstrated with two beam irradiation for Ag, Nd, Yb, Hf and Ta lasing. The estimated absolute photon flux from the saturated amplification Ag X-ray laser was ∼300 μJ. Based on the experimental results, we also discuss the applications of an X-ray laser as a super-high brightness soft X-ray source.     

输出环状光束的新型激光谐振腔

提出一种输出环状光束的新型激光谐振腔,即在稳定激光谐振腔中采用外环耦合方式得到环状光束的输出。利用For-Li数值迭代算法求解此类激光谐振腔的积分方程,通过计算机编程计算了平面一凹球面稳定谐振腔的输出端平面镜在不同半径的情况下,谐振腔镜面上和衍射耦合输出场基模的振幅和相位分布。计算结果预示了当输出端平面镜半径小于通常的稳定腔的基模半径时,衍射耦合输出场有稳定的环状光束输出。实验中TEA CO2激光器采用印刷电路板预电离结构,增益长度90cm,腔长5m,球面全反射镜曲率半径20m,输出端平面镜半径4．5mm,得到了内环半径为4．5mm、外环半径为5．5mm的基模环形光斑输出。从而在理论上和实验上证实了该方案产生环状光束的可行性。     

用光线矩阵元描述X射线激光输出特性

采用矩阵光学方法，研究了串接多靶，弯曲靶加反射镜“双程放大”Ｘ射线激光输出特性，给出了发散角普遍公式，分析了电子密度梯度分布，反射镜角失调对Ｘ射线激光输出场分布的影响，所得结果与已有实验符合较好，最后，对如何从靶，Ｘ光学元件空间排布来实现衍射极限的输出发散角提出了新的设想，作了半定量的探讨。     

Collisional excitation soft X-ray laser at 23.6 nm in a laser-produced cylindrical target

We have tested soft X-ray lasing in neon-like germanium with cylindrical targets where wave guiding and plasma confinement may affect lasing. An intense soft X-ray laser beam of 0.05 MW peak power and a narrow beam divergence (8 mrad) was produced at 23.6 nm with a 4 cm long straight cylindrical target of 0.72 mm inner diameter. Bending the cylindrical target to form a toroidal shape increased the lasing intensity by a factor of 3 accompanied with reduction of the beam divergence from 8 to 6 mrad.     

High beam quality in a HyBrID copper laser operating with an unstable resonator made of a concave mirror and a plano-convex BK7 lens

This paper presents a very simple unstable resonator, made of a concave mirror (total reflector) and a bare plane–convex BK7 lens working as a convex coupling mirror, which is quite efficient for HyBrID copper laser. In addition to a good quality factor (M²=4.9), experimental results showed that it is possible to control the laser output power by introducing a variable aperture iris inside the cavity, close to the coupling lens, without spoiling beam quality. A rough theoretical model helped to explain these results as a combined effect of unstable resonator plus radial gain distribution.     

离子辅助沉积大口径传输反射镜面形控制研究

 针对大型激光系统中光束质量低和波前畸变等特点,采用离子辅助电子束蒸发技术成功实现对多层膜残余应力的精确控制。通过分析氧化铪、氧化硅单层膜残余应力变化规律,研究了离子源束压、束流参量对膜层折射率、残余应力性质及大小的影响。540 mm×340 mm×60 mm规格大口径传输反射镜面形PV值达到0.5λ(λ=632 nm),小光束损伤测试情况下,样品元件的损伤阈值大于30 J/cm2(N-on-1,1 064 nm,5 ns),利用该技术制备的大口径传输反射镜已获得成功应用。     

LD泵浦掺铥(Tm3+)光纤激光器的数值分析

首先从掺铥光纤激光器的速率方程和光传输方程出发,建立数学模型,通过Matlab软件进行数值计算,分析了泵浦光和激光沿光纤的分布以及各能级离子数的变化.在不同掺杂浓度下,研究了小信号增益与入纤泵浦功率的关系以及泵浦光和激光功率与增益介质长度的关系.在不同泵浦功率下,研究了输出功率与输出耦合镜反射率的关系.进一步对不同泵浦吸收系数,研究了斜率效率和泵浦阈值与光纤长度的关系.分析结果表明存在最佳光纤长度和最佳耦合输出透过率,使得激光输出功率达到最佳值.     

1.5 J high-beam-quality Nd:LuAG ceramic active mirror laser amplifier

A 1.5 J Nd:LuAG ceramic active mirror laser amplifier with a high beam quality is demonstrated in which a 0.8%(atomic fraction)Nd-doped Nd:LuAG ceramic disk with a diameter of 64 mm and a thickness of 5.5 mm is used as a laser gain medium.A maximum single-pass small-signal gain of 2.59 is measured when the pump energy is 11.5 J,with an injected seed energy of 0.4 J;a maximum output energy of 1.5 J is obtained at the repetition rate of 10 Hz.A far-field beam spot 1.25 times the diffraction limit(DL)is achieved by using a stimulated Brillouin scattering phase conjugation mirror(SBS-PCM)for wavefront correction.     

Walk-Off Ring Coupling Type CO Laser

As a complementary scheme to a coupling-hole type laser, a walk-off ring coupling type laser is proposed to extract a donut shaped beam by shrinking the diameter of one of the stable resonator mirrors. This was successfully applied to a conventional slow axial-flow CO laser. First, finding the intensity distribution close to the Gaussian profile by using a partially transparent mirror in a hemispherical configuration for coupling, we obtain the relationship between the mirror radius and the effective transmittance. Then, using several mirrors with a diameter smaller than the Gaussian profile above instead of the partially transparent mirror, the output power with the donut shape was optimized to yield the maximum power, together with theoretical treatments. This resulted in an optimum mirror diameter of 4.2 mm, which corresponds to the optimum transmittance of 5-6% for the CO laser having the gain parameter G≅0.34, the inherent loss ā ≅ 0.07, and the measure of partial homogeneity m¯ =; 0.5. This value is exactly the same as that of the coupling-hole mirror. Some application feasibilities are also discussed.