在大功率激光系统的评价与分析中，激光器的光束品质是系统光束品质的决定性因素，也是激光器验收、鉴定的重要指标，其中束散角是判别激光光束质量的重要参数。本系统测试激光波长的范围比较宽，一般在0.532 μm~10.6 μm之间，没有合适的探测器能够覆盖整个波段，所以采用了一种新的方法来解决宽波段束散角的测量问题。选用CCD成像和扫描狭缝相结合的方法来实现宽波段激光光束束散角的测量，可见光和近红外波段（0.532 μm~1.2 μm）激光光束采用CCD法测量激光束散角，中红外波段（1.2 μm~10.6 μm）激光光束采用扫描狭缝法测量激光束散角。两种方法的结合可以较为精确地测量出不同波段的激光束散角。

针对切伦科夫辐射特点，采用厚度尽量小的石英薄片作为转换靶，并将电子束以切伦科夫辐射角入射转换靶的形式构成一种电子束发散角分布的测量布局，并基于焦平面成像原理，研制了相应的电子束发散角光学测量系统。在强流脉冲直线感应加速器上完成了装置研制和测试工作，显示了电子束发散角分布测量系统可以获得电子束一定方向上的散角分布概况，测量结果具有一定的可信度，具有装置结构简单、数据处理难度低及速度快等特点。

利用切伦科夫辐射方向性极好的特性进行电子束发散角的测量是一个比较有希望的方法，但转换靶材料对电子的库伦作用力等因素又使得电子束散角展宽，对发散角的测量产生影响。在将转换靶划分成多重薄片并以串联的形式构建了靶模型，考虑了库仑力、多重散射、轫致辐射、电离等全物理过程作用效果的情况下，利用蒙特卡罗模拟软件相关程序对电子在靶材料中的发散过程进行了仿真。基于电子束散角分布与切伦科夫辐射光子分布相对应的原理，完成了对电子束发散角测量技术的模拟，获得了转换靶材料及其厚度、电子束能散、测量系统光学带宽等对电子束发散角测量的影响规律，为测量系统的设计及数据反演处理工作提供了指导性的建议。模拟结果显示，基于切伦科夫辐射进行电子束发散角测量的方法具有可行性，具有一定的对电子束发散角分布进行测量的能力。

We design a 645 nm laser diode (LD) with a narrow vertical beam divergence angle based on the mode expansion layer. The vertical beam divergence of 10.94° at full width at half-maximum is realized under 1.5 A continuous-wave operation, which is the smallest vertical beam divergence for such an LD based on the mode expansion layer, to the best of our knowledge. The threshold current and output power are 1.07 A and 0.94 W, limited by the thermal rollover for the 100 µm wide and 1500 µm long broad area laser, and the slope efficiency is 0.71 W/A. The low coherence device is fabricated with the speckle contrast of 3.6% and good directional emission. Such 645 nm LDs have promising applications in laser display.

In this Letter, we firstly, to the best of our knowledge, demonstrated the influence of pre-pulse current and delay time on the intensity of a discharge pumped Ne-like Ar soft X-ray laser operating at 46.9 nm by employing an alumina capillary having an inner diameter of 4.8 mm. Specifically, the delay time was changed from 8 to 520 μs in small intervals. The pre-discharge current was increased from 25 A to 250 A through small steps, while keeping the main discharge current constant. Usually, a small pre-discharge current is applied to an Ar-filled capillary to attain a plasma column having sufficient pre-ionization before the injection of the main current. The pre-discharge current of 140 A was declared the best current to obtain lasing with a 4.8 mm diameter capillary. The laser spots were captured at best time delays for the pre-discharge currents of 25, 45, 80, 140, and 250 A, which support the experimental results. We observed that by applying the pre-discharge current of 140 A, the laser spot exhibits small divergence, higher symmetry, and uniformity, which is clear evidence of strong amplification. The laser spot obtained at 140 A is cylindrically symmetric and has a better structure than those reported by all other groups in the literature. Hence, the laser spot indicates that the laser beam is highly focusable and beneficial for the applications of the 46.9 nm laser. Results of this Letter might open a new way to enhance applications of a 46.9 nm capillary discharge soft X-ray laser.