Demonstration of Mo Soft X-Ray Lasers with a Grazing Incidence Pumping Scheme in the XL-II Facility

A Ni-like Mo soft x-ray laser （SXRLs） operating at 18.9nm has been demonstrated by employing a grazing incidence pumping scheme with 120m^3 in the 200ps pre-pulse and 140mJ in the 200fs main pulse. The SXRL gain is estimated to be 1.5-3cm^-1 when a grazing incidence angle of 14° is applied. Numerical simulations are also performed to investigate the dynamics of the ion distribution. It is found that a high intensity at 2.4× 10^14 W/cm^2 of the 200fs main pulse could heat the pre-plasma rapidly to an appropriate temperature for population inversion, and could compensate for the shortage of the total pump energy to a certain extent.     

Theoretical study of Ni-like Ag 13.9nm TCE x-ray laser driven by two picosecond pulses

The Ni-like Ag 13.9nm x-ray laser has been previously demonstrated that the higher gain near critical surface contributes little to the amplification of the x-ray laser because of severe refraction. In this paper, the transient collision excitation (TCE) Ni-like Ag 13.9nm x-ray laser is simulated, driven by two 3ps short pulse preceded by a 330ps long prepulse, optimization of the peak to peak delay time of the two short pulses is made to get the best results. Simulation indicates that by producing lowly ionized preplasma with smoothly varying electron density, it is possible to decrease electron density gradient in higher density region, and thus higher gains near this region could be utilized, and if the main short pulse is delayed by 900ps, local gains where electron density larger than ～ 4×10²⁰cm^-3 could be utilized.     

利用皮秒脉冲激光驱动瞬态X射线激光

报道了利用皮秒激光驱动产生瞬态类镍银X射线激光的实验结果.采用一路脉冲宽度为数百皮秒的激光作为预脉冲，配合另一路皮秒激光作为主脉冲联合驱动平面靶，获得了一定强度的类镍银X射线激光输出，输出能量约为5—10nJ. 关键词： 瞬态X射线激光 长短脉冲联合驱动 皮秒脉冲激光     

High-repetition-rate grazing-incidence pumped x-ray laser operating at 18.9 nm

We have demonstrated a 10 Hz Ni-like Mo x-ray laser operating at 18.9 nm with 150 mJ total pump energy by employing a novel pumping scheme. The grazing-incidence scheme is described, where a picosecond pulse is incident at a grazing angle to a Mo plasma column produced by a slab target irradiated by a 200 ps laser pulse. This scheme uses refraction of the short pulse at a predetermined electron density to increase absorption to pump a specific gain region. The higher coupling efficiency inherent to this scheme allows a reduction in the pump energy where 70 mJ long pulse energy and 80 mJ short pulse energy are sufficient to produce lasing at a 10 Hz repetition rate. Under these conditions and by optimizing the delay between the pulses, we achieve strong amplification and close to saturation for 4 mm long targets.     

Valley density profile for highly efficient x-ray lasers with good beam quality

A plasma with a valley density profile at the required electron density for high-gain operation of an x-ray laser could be obtained using a normally incident 300 ps laser pulse followed by a grazing-incident 300 ps laser pulse. Sudden heating of the valley plasma region by another grazing-incident 300 fs laser pulse would then yield a highly efficient x-ray laser beam with a deflecting angle of 2 mrad and a divergence angle of 4 mrad. Saturation operation of the x-ray laser beam at 32.6 nm could be achieved with a total pump energy of less than 100 mJ.     

Pulse duration measurements of grazing-incidence-pumped high repetition rate Ni-like Ag and Cd transient soft x-ray lasers

We have measured the pulse duration of gain-saturated 13.9 nm Ni-like Ag and 13.2 nm Ni-like Cd transient collisional lasers excited by grazing-incidence-pumping for several pumping conditions. High-resolution streak-camera measurements yielded FWHM pulse durations close to 5 ps for both lasers under optimum pumping conditions. The very high brightness and short pulse duration of these new high repetition tabletop soft x-ray lasers make them an attractive source for dynamic applications.     

掠入射低功率密度驱动Ni-like Ag X射线激光的理论研究

 用系列程序对掠入射方式驱动亚稳态类镍银的碰撞激发机制进行数值模拟。结果发现：与正入射方式相比,掠入射在1.2×10¹³ W·cm^-2低功率密度驱动时,驱动激光能量主要沉积在增益区附近,可以大幅度提高增益区的电子温度,也可以大幅度提高增益系数。通过对预主脉冲时间间隔和掠入射角的优化,采用10.5 ns延迟时间和16°的掠入射角,可使有效增益系数达到23.8 cm^-1,比正入射提高84％。用13 J驱动激光能量就可以获得增益长度积为23.8的深度饱和增益。     

A review of Ni-like X-ray laser experiments undertaken using the VULCAN laser at the Rutherford Appleton Laboratory

Recent progress using the VULCAN laser at the Rutherford Appleton Laboratory to pump X-ray lasing in nickel-like ions is reviewed. Double pulse pumping with ∼100 ps pulses has been shown to produce significantly greater X-ray laser output than single pulses of duration 0.1–1 ns. With double pulse pumping, the main pumping pulse interacts with a pre-formed plasma created by a pre-pulse. The efficiency of lasing increases as there is a reduced effect of refraction of the X-ray laser beam due to smaller density gradients and larger gain volumes, which enable propagation of the X-ray laser beam along the full length of the target. The record shortest wavelength saturated laser at 5.9 nm has been achieved in Ni-like dysprosium using double pulse pumping of 75 ps duration from the VULCAN laser. A variant of the double pulse pumping using a single ∼100 ps laser pulse and a superimposed short ∼1 ps pulse has been found to further increase the efficiency of lasing by reducing the effects of over-ionisation during the gain period. The record shortest wavelength saturated laser pumped by a short ∼1 ps pulse has been achieved in Ni-like samarium using the VULCAN laser operating in chirped pulse amplified (CPA) mode. Ni-like samarium lases at 7.3 nm.     

Saturated X-ray lasing in Ni-like Sn at 11.9 nm using the GRIP scheme

We report on gain-saturated operation of the 11.9 nm X-ray lasing line in Ni-like Sn using the grazing-incidence pumping scheme (GRIP). The experiments were done with 2-ps duration pump pulses and energies up to 5 J. Strong gain saturation with multi-microjoule output was measured for the Sn laser at a grazing angle of 30° and a pump pulse energy of 3 J. This was achieved with a 4.5%, 2-ps duration prepulse 2.4 ns ahead of the main pulse and also incident at grazing incidence. Increasing laser output was observed at GRIP angles up to 45°. At this angle, the minimum energy required for saturated lasing was determined as ∼2 J.     

Optimization of nickel-like collisional soft-X-ray lasers at low pump power

We report on the experimental demonstration of saturated X-ray laser output from collisionally pumped Ni-like Pd, Ag, and Sn at wavelengths of 14.7, 14.0, and 12.0 nm, respectively. Using a 100 ps drive pulse irradiation and a `twin-0.25%' prepulse configuration on flat slab targets, gain-length products >16 were obtained for the three elements. The drive power required for saturation was only 250 GW in a 100 ps pulse (25 J), corresponding to an irradiance of 10 TW/cm².     

双短脉冲驱动的瞬态电子碰撞激发类镍银13.9 nm X光激光

 研究了两个皮秒短脉冲驱动的瞬态电子碰撞激发类镍银13.9 nm X光激光,考察了脉宽分别为1,2,3 ps驱动的情况,分别给出了输出X光激光的角分布特性。模拟表明,(330 ps, 1 ps, 1 ps)驱动条件下,第二短脉冲延迟约500 ps,可以充分利用临界面附近的高增益。通过与相同长脉冲条件下单短脉冲驱动的结果相比较,分析了第一个短脉冲的作用及双脉冲驱动的优点。     

某些类氖离子和类镍离子等离子体状态对应关系的研究

利用一维拉格朗日流体动力学程序Med103详细研究了产生类镍Ag,Cd,In,Sn, Sb离子和类氖Fe,Co,Ni,Cu,Zn离子的等离子体状态.通过对电子温度、离子丰度、离子数密度等状态参量的分析比较，得到了这两类等离子体状态之间的对应关系.即类镍银的等离子体状态与类氖铁 的相近，类镍镉的与类氖钴的相近，依次类推.利用这一对应关系可以方便地由类氖机理x射线激光的等离子体状态来对相应元素的类镍x射线激光的等离子体状态进行判断. 关键词： 类氖 类镍 等离子体状态 x射线激光     

长波长激光驱动Ni-like Ag 13.9 nmX射线激光的理论研究

 为了进一步深入理解掠入射驱动碰撞机制的特点与长处，以基频光正入射驱动为参照，用系列程序研究了6 mm和3 mm激光正入射驱动类镍银碰撞激发机制。在波长6 mm的激光正入射驱动下，激光能量直接沉积到增益区，大大提高了增益区的电子温度；以5 J驱动能量，获得有效增益系数为20.7 cm^-1的高增益和有效增益长度积为41.4的深度饱和增益，与波长1.053 mm的正入射相比，以19%的驱动能量，使有效增益系数提高了60%。在波长3 mm的激光正入射驱动下，激光能量沉积到增益区附近，大大提高了增益区的电子温度；以15 J驱动能量，获得有效增益系数为21.2 cm^-1的高增益和有效增益长度积为42.4的深度饱和增益，与波长1.053 mm的正入射相比，以57%的驱动能量，使有效增益系数提高64%。     

掠入射驱动产生x射线激光的数值模拟

利用一维流体力学数值模拟程序MEDUSA和原子物理程序包，以类镍钼189nm x射线激光为例，对掠入射驱动x射线激光方案进行了研究.掠入射驱动x射线激光方案可以通过调整掠入射角来选择适合的增益区间.与正入射驱动方案相比，掠入射驱动方案加强了驱动激光在增益区内的吸收，提高了驱动激光向x射线激光的转换效率.模拟结果与实验结果符合较好. 关键词： x射线激光 掠入射辐照 激光等离子体     

Gain-saturated Ni-like antimony laser at 11.4 nm in grazing-incidence pumping geometry

We report on gain-saturated operation of the 4d → 4p, J = 0-1, 11.4 nm soft-X-ray laser line in Ni-like antimony (Sb) at a pump energy of only 2.5 J. The driving laser used was a 1054 nm Nd:glass CPA laser system with a pulse duration of 7 ps (FWHM). The pump beam was focused with a tilted on-axis parabolic mirror in a grazing-incidence (GRIP) pumping configuration at an incidence angle of 45°. A fraction of 2.8% of the pump energy (∼70 mJ) was used for the prepulse, which was propagated along the same beam line as the main pulse and arrived at the target 4.4 ns before the main pulse.     

Saturated 13.2 nm high-repetition-rate laser in nickellike cadmium

We report gain-saturated operation of a 13.2 nm table-top laser in Ni-like Cd at a 5 Hz repetition rate. A gain-length product G x L = 17.6 was obtained by heating a precreated plasma with 8 ps duration Ti:sapphire laser pulses with an energy of only 1 J impinging at a grazing angle of 23 degrees. With an average power of approximately 1 muW [corrected] this laser is an attractive coherent source for at-wavelength metrology of extreme UV lithography optics and other applications.     

Theoretical research on enhancement of gain for Ni-like Ag 13.9nm x-ray laser using a new two-layer target

For experiments such as on Ni-like Ag x-ray laser, driven by 1\omega laser, the gain region is only several~nm depth near the target surface, this paper proposes a new two-layer target, in which a thin layer (several nm depth) of silver is plated on the surface of some other materials. Furthermore, the Ni-like Ag 13.9~nm x-ray laser produced by three new kinds of two-layer target with CH, Al and Ge as foundation, was theoretically studied.     

Optimization toward a high-average-brightness soft-x-ray laser pumped at grazing incidence

We report the near-field imaging characterization of a 10 Hz Ni-like 18.9 nm molybdenum soft-x-ray laser pumped in a grazing incidence pumping (GRIP) geometry with a table-top laser driver. We investigate the effect of varying the GRIP angle on the spatial behavior of the soft-x-ray laser source. After multiparameter optimization, we were able to find conditions to generate routinely a high-repetition-rate soft-x-ray laser with an energy level of up to 3 microJ/pulse and to 6x10(17) photons/s/mm2/mrad2/(0.1% bandwidth) average brightness and 1x10(28) photons/s/mm2/mrad2/(0.1% bandwidth) peak brightness.     

数字全息形貌测量的基本特性分析

在对数字全息技术进行严格理论分析的基础上，本文指出随单个CCD像元的尺寸的减小可能被记录物体的横向尺寸将变大，所允许的纵向尺寸却变小；另一方面其系统误差和被测量值本身的大小成正比，和横向分辨率成反比。     

利用x射线激光干涉诊断等离子体电子密度

x射线激光探针干涉方法是诊断高温高密度激光等离子体电子密度等信息的重要工具.利用神光Ⅱ装置输出激光驱动的类镍-银x射线激光作为探针，成功地进行了马赫-曾德尔干涉法诊断实验，获得了清晰的包含等离子体信息的动态干涉条纹图像，并据此给出了待测C8H8等离子体临界面附近电子密度的空间分布. 关键词： 等离子体电子密度诊断 x射线激光 马赫-曾德尔干涉仪