Xing Qi-Rong

Investigation of Cr4+:YAG passive mode-locking in a pulsed Nd:YAG laser

Abstract Passive mode-locking of a pulsed Nd:YAG laser using a Cr4+:YAG saturable absorber was realized for the first time in a nearly critical stable resonator containing an antiresonant ring structure. The output energy and pulse duration are 13.5 mJ and 180 ps, respectively. The recovery time and saturable intensity for excited-state absorption of Cr4+:YAG under the action of strong laser pulses were calculated from rate equations.

Observation of High-Order Femtosecond Solitons in a Self-Mode-Locked Ti:Sapphire Laser

The N = 3 femtosecond solitonlike pulses are observed directly in a self-mode-locked Ti:sapphire laser as well as even higher-order solitonlike pulses for the first time. When the laser is operating in a stable train of mode-locked pulses, the periodic pulse train appears by only varying the intracavity dispersion. The soliton period with N = 3 corresponds to a cavity round trip number of 164.

Phase Control of Few-Cycle Coherent Terahertz Radiation Pulses

We report a method to control the carrier-envelope phase shift in nearly single-cycle coherent terahertz (THz) radiation pulses, in which we used Kerr effect and two-photon absorption in the generated crystals due to the pump beam peak intensity. Dependence of relative carrier-envelope phase shift of THz pulses on the pump beam intensity in the ZnTe crystal was measured experimentally. Under our experimental condition, we measured that maximum relative phase shift is 0.29 radians.

Experimental Study of Optical Nonlinearities in a Broadband Semiconductor Saturable Absorber Mirror

The negative nonlinear index of a semiconductor saturable absorber mirror (SESAM) was investigated by using the reflection Z-scan technique. This is an experimental demonstration, for the first time to our knowledge, that the SESAM possesses comparable negative nonlinear index n2 = ?2.35?10?10?esu, which may have important implications in design and alignment of Kerr-lens mode-locking based on the self-focusing effect.

Multi-Slit Diffraction of Evanescent Electromagnetic Waves

The well-known Fraunhofer multi-slit diffraction is described as the multi-slit interference modulated by the single-slit diffraction, namely the multiplication between the single-slit diffraction factor and the multi-slit interference factor. By considering the simplified argument we show that the multi-slit diffraction of evanescent waves which are in the near-field region also has the interference and diffraction effects, and that this two-fold effect can be expressed as the convolution of the diffraction factor and the interference factor. Our conclusion could be helpful to understand the contribution of evanescent waves to the optical responses of sub-wavelength structures such as slits and grooves.

Transmission Properties of THz Radiation Pulses through Very Deep Zero-Order Metallic Gratings

Very deep zero-order metallic grating structures are processed to study the transmission properties of THz radiation pulses. The experiments have been performed with two samples. The delay of the THz pulses and the corresponding resonantly enhanced transmission spectra through the samples are observed. To explain the extraordinary transmission we have treated the samples as Fabry–Perot resonators through resonant excitation of the coupled surface plasmon polaritons filled in the cavities between the metal slats. The experimental results are in reasonable agreement with the numerical simulation. Our results show that THz-time-domain spectroscopy may be an effective technique for studying the optical properties of various THz microstructured devices.

Group-velocity dispersion in chirped-pulse amplifier

By using the pulse propagation equation in the nonlinear dispersive medium, the effects of second- and third-order group-velocity dispersion on pulse evolution in the stretching, amplification and compressing are studied when chirped pulse amplification is applied to the pulses of a width <30 fs, and the optimum dispersion-compensated conditions among the stretcher, amplifier and compressor are determined. From the standpoint of dispersion compensation and control and the compressor adjustment, it is proposed that low-groove-density gratings ( ≤ 800 line/mm) are the better choices for stretching and compressing the pulses of a width <30 fs in chirped-pulse amplification. It is also shown that, with a proper adjustment of the compressor incident angle and grating separation, an exact null in both second- and third-order dispersions can be achieved without any additional dispersion-compensated elements.