Three-dimensional (3D) simulations and theoretical analyses on super-short pulse generated using freeelectron lasers (FELs) at perfect synchronism are carried out with the help of our 3D OSIFEL code. The evolution of longitudinal pulse width in the Japan Atomic Energy Research Institute (JAERI) experiment is simulated. The results show that the optical pulse is compressed on successive passes due to the slippage between the optical and electron beams, and an ultra-short 221-fs optical pulse is finally obtained, which agrees with the experiment. Furthermore, to shorten wavelength such as soft ultraviolet (SUV) spectrum range, an ultra-short pulse generated at perfect synchronism is analyzed and studied. Finally, the relationship between the optical pulse length compressed and the peak electron beam current is calculated. It shows that the higher the electron beam current, the shorter the output FEL width length, due to the higher gain.

An improved method for stabilizing a frequency-quadrupled 214.5-nm tunable diode laser system is reported. Improvements to the method include a homemade logic circuit and the use of a Fabry-Perot optical spectrum analyzer as a transfer cavity. Lasers locked with this method exhibit megahertz-level frequency stability measured with an optical frequency comb referenced to a cesium atomic standard. The laser can be locked for hours to days, depending on experiment requirements. Being relatively inexpensive, stable, and robust, the control method can be applied to stabilizing essentially all lasers of deep ultraviolet wavelengths.

Carrier-envelope phase effect of the monochromatic high frequency pulse generation from Thomson backscattering is investigated with an analytical model and verified by one dimensional particle in cell simulations. We show that the central frequency of the monochromatic light generated from Thomson backscattering is extremely sensitive to the carrier-envelope phase of the field driving the relativistic electron layers.

利用等离子体波导实现光场感应电离（OFI）X射线激光放大，一方面可以降低产生X射线激光的抽运激光阈值，从而提高由于自散焦而降低的有效激光功率密度；另一方面，由于等离子体中产生的大量电子被束缚在等离子体波导内，降低X光信号色散影响，可以大大提高激光增益长度，这是一种实现台上X射线激光新的抽运机制。详细介绍了光场感应电离X射线激光、强激光等离子体波导以及等离子体波导中光场感应电离X射线激光的研究进展。

Deep ultraviolet lasers have various applications in industries and scientific researches. For 266-nm ultraviolet (UV) laser generation, the good beam quality of 1064-nm laser and the elimination of gray-tracking effect of KTP crystal are two key factors. Using a dynamically stable resonator design, 1064-nm laser with an average power of 52 W is realized with repetition rate of 16 kHz. The measured M2 factor characterizing the beam quality is 1.5. By the elimination of gray-tracking effect of KTP crystal, an 18-W green laser is realized with the M2 factor of 1.6. Using a BBO crystal for the fourth harmonic generation, a 1.9-W 266-nm UV laser is achieved.

In a capillary discharge experiment for the neon-like argon lasing, we have proposed an experimental scheme to verify that the multi-spike of X-ray diode (XRD) signal is a multi-pulse laser or is a reflection of the laser pulse in the XRD. The ceramic capillary has an inner diameter of 3 mm and a length of 200 mm. At the gas pressure of 28 Pa and discharge current of 27 kA, stable lasing has been realized. The experimental results prove that the multi-spike of XRD signal is a reflection of the electromagnetic signal produced by the laser pulse in the XRD. The improved electrocircuit scheme of the XRD to minimize the reflection phenomena is also found.

瞬态碰撞激发X射线激光由于其所需驱动能量低、效率高和容易台式化等优点，极大地推动了X射线激光的发展。比较详细地总结了这一研究领域取得的突破性进展，并讨论了开展瞬态碰撞激发X射线激光的关键问题。