Chai Lu

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.

Theoretical Study on a Cluster-Seven-Core Photonic Crystal Fiber with High Nonlinearity and High-Power Endurance

We present a novel cluster-seven-core photonic crystal fiber which possesses high nonlinearity and supports the high-power pumping. Its nonlinearity coefficient and effective mode area are calculated by the full vector multipole method. Compared with the single core PCF, the cluster-seven-core photonic crystal fiber can support high-power beam transmitting in the core, and simultaneously has high nonlinearity. This kind of photonic crystal fiber can be applied to the photoelectron-device field.

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.

Bifurcations and chaos in a circular Couette system

The techniques of the laser light scattering and the flow visualization are used to study the bifurcations and chaos in a circular Couette system. Two different routes to turbulence are observed. A physical understanding of the results is given based on the nonlinear interaction.

Design and manufacture of high dispersion mirror

The designed and manufactured high dispersion mirror combines the characteristics of chirped mirror and Gires-Tournois interferometer(GTI) mirror and provides high dispersion compensation with about -800fs 2 GDD in a wavelength range of 780-830 nm and about -2500fs 2 GDD in a wavelength range 1030-1050 nm, respectively. The dispersion mirror is manufactured by ion beam sputtering. The performance of the mirror has reached the designed values and can compensate the normal dispersion from ultrafst laser system effectively.

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.