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.

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.