Design of Highly Directive Ni-Like Ag X-Ray Laser at 13.9nm

We theoretically investigate a 13.9nm Ni-like Ag x-ray laser using a one-dimensional hydrodynamic code coupled with an atomic physics data package. The population inversion is transiently pumped by a grazing incident 0.5ps main pulse irradiating into an optimized plasma, which is generated by a normal incidence 300ps pulse and a subsequent grazing incidence 300ps pulse. The effect of the grazing-incidence angle on the source position of the output x-ray laser is investigated. Near zero deflecting angle is found for the peak output intensity of the Ni-like Ag x-ray lasers, with a small FWHM divergence of 5mrad. It is predicted that saturation can be achieved with a total pump energy of 165mJ.     

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。     

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.     

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.     

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.     

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     

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.     

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.     

A superpowerful source of far-ultraviolet monochromatic radiation

In several independent experiments investigating the interaction between the optical field of an intense laser pulse and a xenon cluster beam, we recorded an anomalously high quantum yield of the plasma radiation in the region 10–15 nm. In several cases, the conversion efficiency into the hemisphere reached 10% of the pumping pulse energy. The nature of this phenomenon has not yet been adequately explained. A high conversion efficiency is shown to be possible when producing a plasma with optimal parameters for the amplification of spontaneous radiation on Ni-like xenon transitions to be generated. In a collisional-radiative model, we performed detailed atomic-kinetic calculations of the gains and radiation spectra on the transitions with λ ≈ 4, 10, and 11.3 nm and in the region 13–13.9 nm. For each transition, we determined the time dependences of the gains on plasma parameters. The theoretical and experimental values of the optimal plasma parameters and energy yields of the radiation are in close agreement. Using a theoretical model, we propose possible plasma pumping schemes to achieve the maximum yield of the intense, narrowly beamed soft X-ray radiation. At a pumping pulse repetition rate of 10⁴ Hz, the output power for various Ni-like xenon transitions ranges from 100 to 5 × 10³ W.     

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     

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.     

Demonstration of a 100 Hz repetition rate gain-saturated diode-pumped table-top soft x-ray laser

We demonstrate the operation of a gain-saturated table-top soft x-ray laser at 100?Hz repetition rate. The laser generates an average power of 0.15?mW at λ=18.9 nm, the highest laser power reported to date from a sub-20-nm wavelength compact source. Picosecond laser pulses of 1.5?μJ energy were produced at λ=18.9 nm by amplification in a Mo plasma created by tailoring the temporal intensity profile of single pump pulses with 1?J energy produced by a diode-pumped chirped pulse amplification Yb:YAG laser. Lasing was also obtained in the 13.9?nm line of Ni-like Ag. These results increase by an order of magnitude the repetition rate of plasma-based soft x-ray lasers opening the path to milliwatt average power table-top lasers at sub-20?nm wavelengths.     

Development of a saturated transient X-ray laser at 13.9 nm in LSAI

We summarise the progress achieved at LSAI in the understanding and optimisation of the transient collisional pumping of X-ray lasers using an ultra-short sub-ps heating pulse. The effect of travelling-wave irradiation on the lasing signal on the 4d¹S₀→4p¹P₁ Ni-like Ag line at 13.9 nm is studied in detail. Under specific irradiation conditions strong laser emission is also obtained on another spectral line at 16.05 nm, which is identified as the 4f¹P₁–4d¹P₁ transition in Ni-like Ag.     

Diagnostics of laser-induced plasma with soft X-ray (13.9 nm) bi-mirror interference microscopy

X-ray interference microscopy diagnostics of a nanosecond-pulse pumped Al (Z=13) plasma are presented. A transient picosecond Ni-like Ag X-ray laser (13.9 nm) is used as the probe beam and a wavefront division bi-mirror interferometer is adopted as the diagnosis tool. From the fringe shifts, the two-dimensional plasma density profile at 1 ns after the peak of the heating pulse is deduced. Opposite fringe shifts during the plasma development are observed and possible explanations for this behavior are discussed. This study will contribute to the validation of 1D and 2D hydrodynamic codes as well as to the better understanding of the physics during the development of laser produced plasmas. PACS 41.50.+h; 41.85.Ew; 42.55.Vc     

X射线激光对激光烧蚀薄片靶的阴影成像研究

长脉冲激光辐照烧蚀薄片靶会加速物质进而在靶后表面产生凹坑现象,通过凹坑的实验诊断,配合相关的理论模拟,对理解相关物理过程,校验理论程序的相关参数具有很好的参考价值.利用波长13.9 nm的类镍银X射线激光作为探针,诊断了纳秒倍频激光辐照C₈H₈平面薄片靶产生的等离子体以及加速物质产生的凹坑现象,并利用XRL2D程序对实验现象进行了细致的模拟,电子热传导限流因子选取为0.03时的模拟结果与实验符合比较好.模拟给出凹坑宽度和深度(即薄片加速距离)与实验观测数据定量符     

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     

软X射线双频光栅干涉诊断等离子体

针对高温稠密激光等离子体临界密度附近电子密度的诊断需求,发展了基于软X射线激光的软X射线双频光栅干涉诊断技术。利用波长13.9nm的类镍银软X射线激光作为探针,掠入射式的双频光栅作为分光干涉元件,对激光辐照金平面靶产生的等离子体进行诊断尝试。实验获得了清晰的干涉条纹图像,充分表明该技术的实用性。但结果中存在靶面不清晰等问题,为此,提出了初步的解决方案。     

Investigation on the hydrodynamics of slab x-ray laser plasma by nonuiform line focused laser irradiation

Based on the two-dimensional model,this paper compares the hydrodynamics of slab x-ray laser plasma produced by different nonuniform line focused irradiations.It finds that the average intensity and the duration of laser pulse and the overall shape of the intensity distribution in the focal line have different influences on the plasma.Calculations show that the evolution of temperature variation is more sensitive to the pulse duration and the electron density variation is more sensitive to the pulse intensity.Pulses with duration of 200 ps to 500 ps and with intensity of 0.2 TW/cm 2 to 1.0 TW/cm 2 are proved acceptable in slab x-ray lasers.     

Single-pulse coherent diffraction imaging using soft x-ray laser

We report a coherent diffraction imaging (CDI) using a single 8 ps soft x-ray laser pulse at a wavelength of 13.9 nm. The soft x-ray pulse was generated by a laboratory-scale intense pumping laser providing coherent x-ray pulses up to the level of 10(11) photons/pulse. A spatial resolution below 194 nm was achieved with a single pulse, and it was shown that a resolution below 55 nm is feasible with improved detector capability. The single-pulse CDI might provide a way to investigate dynamics of nanoscale molecules or particles.     

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.