【作者】 栾伯晗；

【导师】 王骐；

【作者基本信息】 哈尔滨工业大学 ， 物理电子学， 2007， 博士

【摘要】 X光激光由于具有其他相干光源不可替代的优越特性,因而在许多领域都有着重要的应用。但是,因为X光激光需要很高的泵浦能量,使得泵浦源庞大,带来造价昂贵、能量转换效率低等问题限制了应用的推广。毛细管放电泵浦方案是实现低造价的小型化X光激光最成功的机制之一。自1994年国际上首次实现毛细管放电类氖氩46.9nm激光以来,许多国家都开展了这项研究,因为其激光产生条件的复杂性,到2000-2002年才又有三个研究小组获得了成功。本课题组在独立研制的毛细管放电装置上于2004年6月实现了激光输出,成为国际上第五家在这个领域获得成功的研究小组。本文介绍了在获得激光以后,我们在理论研究、装置改进和提高激光输出能量等方面取得的进展。毛细管放电X光激光的增益介质是放电等离子体,通过Z箍缩过程将泵浦能量转化为激光,因此研究等离子体的演变过程和产生激光时刻的状态对于深入理解激光产生的物理过程及光束质量的决定因素非常重要。本文在这两方面进行了研究,对于等离子体演变过程,基于对Z箍缩物理过程的合理分析,提出了对雪耙模型的改进,使其能够计算更完整的演变过程,并编制了数值模拟程序,特别是通过计算得到了等离子体的多次箍缩过程,这一理论结果是毛细管放电X光激光理论研究上的一个新的观点,并且与本装置上进行的实验观察有很好的吻合。对于产生激光时刻的等离子体状态,根据X光在等离子体中传播的理论模型编制了数值计算程序,突破了解析计算的局限性,使得可以对任意等离子体密度梯度和增益分布计算出激光的空间特性,再结合实验测量结果,就可以判断出产生激光时刻的等离子体状态。本文给出了几种典型密度梯度分布的计算结果,为进行等离子体状态的判断提供了依据。毛细管放电装置是一个很复杂的系统,包括放电脉冲产生系统、脉冲整形系统、预脉冲产生系统和毛细管放电与探测系统。为了克服装置本身对激光输出不利的因素,提高运行的稳定性,进行了大量的维修和改造工作。利用DQ128型汽车点火线圈重新设计制造了预脉冲触发装置,比原来的触发系统更简单可靠。自制了罗可夫斯基线圈,并对其进行了标定,代替原先使用的回流器测量放电电流,解决了无法准确测量流过毛细管电流的问题,为实验分析提供了更准确的依据。改造了Blumlein传输线的前置脉冲隔离开关,消除了长期困扰实验的前置脉冲对激光输出条件的破坏,使激光达到了稳定输出。最后对主开关和放电室进行了改进,提高了放电电流的幅值,抑制了放电室中的旁路放电,提高了装置的性能。首先在15厘米长毛细管上完成了大量的基础实验,包括通过一系列判别实验找到了X射线二极管(XRD)干扰信号的来源,并消除了干扰信号,保证了实验的顺利进行。深入研究了装置中各气体开关的性质,找到了系统联调的方法,保证了装置的稳定运行。完成了放电电流上升沿波形和预主脉冲延时对激光输出影响的实验,确定了最佳的电流波形和预主延时范围,获得了激光的稳定输出。其次,在20厘米毛细管上实现了激光输出,使激光输出能量进一步提高。通过改变放电电极形状和预脉冲电流幅值研究了放电参数对产生激光的影响,确定了最佳预脉冲电流幅值范围。实验验证了XRD探测的多个尖峰信号的来源,提出了XRD设计的改进方案。测量了激光的增益特性、方向性,测量增益系数为0.45cm-1,增益长度积为8.28。设计实验测量了激光的束轮廓,束散角为5.3mrad,并结合理论计算结果对等离子体状态进行了判别。最后,结合实验结果计算了激光输出能量,结果表明实验中获得的低气压(25Pa)下类氖氩46.9nm激光单脉冲能量达到了3.5μJ。本文的内容是理论研究与实验研究紧密结合的结果。这些结果加深了对毛细管放电泵浦产生激光机理的理解,提高了激光输出的能量,完成了激光增益特性和空间特性的测量,为进一步达到激光输出增益饱和指明了方向。更多还原

【Abstract】 X-ray laser has important application in many fields because of its predominant characteristics that can not be replaced by other coherent light sources. At the same time, the bulky pumping facility of x-ray laser for very high pumping energy brings the problems of high cost and low conversion efficiency, which limit its widespread use.Capillary discharge pumped soft x-ray laser is one of the most successful schemes for low cost small-scale x-ray laser. Since the first demonstration of Ne-like argon laser at 46.9nm in a capillary discharge in 1994, many countries started this investigation, but until 2000-2002 only three other groups succeeded by reason of complexity of the lasing conditions. Our group demonstrated successful experiment on independently developed capillary discharge device in 2004 and became the fifth researching group in the world that succeeded in this field. This dissertation reports the progress of theoretic research, device improvement and increasing output energy after the first observation of lasing.The active medium of capillary discharge pumped laser is the discharge-created plasma and the pumping energy is converted to lasing emission through Z-pinch, so that investigating the evolution of plasma and the plasma estate of lasing time is very important for deep understanding the physics process of lasing and the key determining factor for quality of laser beam. This dissertation investigates the two aspects. For the evolution of plasma an improvement of“snow-plow”model, that allows calculating the whole evolution process of plasma, has been made based on reasonable analysis of Z-pinch process. A simulation program has been worked out and the calculated result show that the plasma is pinched several times. This result is in good agreement with the time of lasing onset and other experimental phenomena. For the plasma estate of lasing time a ray tracing code, that can break through the limit of the analytic calculation and compute the spatial characteristic of laser by any gain and plasma density distributions, has been programmed. And through the comparison between the simulated results and the measurements the plasma state of lasing time can be estimated. In this dissertation the calculation for several typical plasma density distributions is reported and can serve as the base for estimating the plasma estate. The capillary discharge device is a very complex system that includes the sections of discharge pulse generation, current pulse transmission, predischarge pulse generation and detection. A lot of maintaining and improving works has been conducted for overcoming the disadvantage of the device for laser output and increasing the stability. A new predischarge trigger generator, that is more simple and stable than the former one, has been designed and fabricated using the car ignition loop DQ128. A Rogowski coil, that instead of the former device can much more accurately measures the current flowing through capillary, has been made and calibrated. The insulation switch of inherent prepulse of the Blumlein transmission line has been improved, that results in removing the influence of the inherent prepulse and the stability of laser output. The improvement of the main switch and the discharge chamber was also conducted, that leads to increasing the discharge current amplitude and restraining the unwished discharge paths.Firstly, a lot of basic experiments were conducted on 15cm-long capillary. The source of XRD disturbing signal has been found and deleted by a series of experiments. The characteristics of the gas switches in the device have been experimentally studied and the adjusting method of experimental system has been found. Moreover, the influence of the rising slope waveform of discharge current and the delay time between prepulse and main pulse on the laser output also has been experimentally studied, so that the best current waveform and the most suitable range of the delay time has been determined. On basis of preceding works the stability of laser output has been reached. Secondly, the laser output has been realized also on 20cm-long capillary and the laser energy has been increased much more. The relationship between the discharge parameters and the laser output has been investigated through changing the shape of the discharge electrode and the amplitude of prepulse current and the optimal range of the prepulse amplitude were determined. The origin of the multi-spike of XRD signal has been verified experimentally and the improved electrocircuit scheme of the XRD has been proposed. The laser properties including gain coefficient and directivity has been measured, that results in the gain of 0.45cm-1 and the gain-length product of 8.28. The measurements of the laser beam profile have been conducted and the measured divergence is 3.8mrad, furthermore, the plasma state has been estimated by comparing the measured profile with the theoretical simulations. Finally, the laser energy has been calculated according to experimental results and the calculated value proves that the Ne-like 46.9nm laser energy of per pulse obtained at low pressure (25Pa) is above 1μJ.The contents of this dissertation are concluded by closely combining the theoretical study and the experimental study. The effort of this dissertation completed the following achievements: the mechanism of capillary discharge pumped laser was understood more deeply, the laser energy has been increased, and the laser properties of amplification and spatial intensity distribution has been measured. And all these achievements indicate the clear direction for increasing the laser output up to a gain saturated regime.更多还原