Leng Yu-Xin

Anti-Stokes Frequency Shift and Evolution in Polarization-Maintaining Photonic Crystal Fiber with Two-Zero Dispersion Wavelengths

Using the tunable pump pulses with about 100 fs pulse duration and 1064 nm central wavelength; the polarization-, wavelength- and power-dependent anti-Stokes lines are generated and modulated simultaneously in a polarization-maintaining photonic crystal fiber (PM-PCF) with two zero-dispersion wavelengths. By accurately controlling the polarization directions, the wavelength and the power of the pump pulse in the fiber anomalous region close to the second zero-dispersion wavelength of the PM-PCF, the output anti-Stokes pulse spectra can be tuned between 563 nm and 603 nm, which is in good agreement with the theoretical simulation. The color conversion of the mode image from yellow to orange is also observed with the different polarization pump pulses. These results can be attributed to the combined interaction between the fiber birefringence (including linear- and nonlinear-birefringence) and dispersion, and are attributed to phase-matching parametric four-wave mixing.

Efficient Spherical Wavefront Correction near the Focus for the 0.89 PW/29.0 fs Ti:Sapphire Laser Beam

We demonstrate a new loop system of the spherical wavefront (SW) correction near the beam focus to effectively improve the focusability of 0.89 PW/29.0 fs Ti:sapphire chirped pulse amplification laser. After wavefront correction, the Strehl ratio is improved to reach 0.91, and the focal spot size using the f/4 off-axis parabola is reduced to 6.34 ? 6.94 ?m2 (corresponding to 1.63 ? 1.78 times diffraction limitation). With full peak power of 0.89 PW, the peak intensity of 2.59 ? 1021 W/cm2 is obtained. The experimental results show that the SW correction scheme near the beam focus is comparatively simple, economic and high-efficient.

Pulse Temporal Cleaner Based on Nonlinear Ellipse Rotation by Using BK7 Glass Plate

We report a new pulse cleaning technique to enhance the contrast ratio of intense ultra-short laser pulses. A pulse temporal cleaner based on nonlinear ellipse rotation by using BK7 glass plate is developed, and a contrast ratio improvement of two orders of magnitude for the milli-joule level femtosecond input pulses is demonstrated, the total transmission efficiency of the pulse cleaner is 16.7%.

Propagation of Intense Femtosecond Laser Pulses in Deuterated Methane and Deuterium Cluster Jets

Propagation of intense femtosecond laser pulses (60 fs, 800 nm, 120 mJ, 6 × 1017 W/cm2 in vacuum) in supersonic (CD4)N and (D2)N cluster jets at different backing pressures was studied. Pump-probe interferometry is employed to investigate the propagation of laser beams in dense cluster jets by examining the electron density distribution of plasma channels. It was found that propagation effects, including ionization-induced defocusing and laser attenuation of incident pulses, are very different in the (CD4)N and (D2)N cluster jets. Different ionization states of CD4 and D2 molecules were observed by analyzing the transverse electron density profiles of the plasma channels and should be considered as a major reason for the differences in the propagation effects. Numerical simulations of the nonlinear propagation of femtosecond laser pulses in (CD4)N and (D2)N cluster jets were performed, and the results indicated a good reproduction of the experimental data.

Tunable phase-stabilized infrared parametric laser source

This paper reports that the tunable self-phase-stabilized infrared laser pulses have been generated from a two-stage optical parametric amplifier. With an 800 nm pump source, the output idler pulses are tunable from 1.3μm to 2.3μm, and the maximum output energy of the idler pulses is higher than 1 mJ at 1.6μm by using 6 mJ pump laser. A carrier-envelope phase fluctuation of ~0.15 rad (rms) for the idler pulses is measured for longer than one hour by using a home build f-to-2f interferometer.This paper reports that the tunable self-phase-stabilized infrared laser pulses have been generated from a two-stage optical parametric amplifier. With an 800 nm pump source, the output idler pulses are tunable from 1.3 mu m to 2.3 mu m, and the maximum output energy of the idler pulses is higher than 1 mJ at 1.6 mu m by using 6 mJ pump laser. A carrier-envelope phase fluctuation of similar to 0.15 rad (rms) for the idler pulses is measured for longer than one hour by using a home build f-to-2f interferometer.

Femtosecond parabolic pulse nonlinear compression with gas-filled hollow-core fiber

We study theoretically the spectral intensity evolutions of the femtosecond Gaussian and parabolic pulses with different initial pulse energies and compare the nonlinear compressions of these pulses based on a meter-long hollow-core fiber filled with neon for different initial pulse durations. The pulses are first coupled into gas-filled hollow-core fiber for spectrum broadening, then compressed by the optimal chirp compensation. The parabolic pulse possesses a shorter pulse duration, larger peak power, and cleaner wings than Gaussian pulse. The properties are useful for compressing the pulses and thus generating the high-energy, short-duration pulses.

High and Stable Conversion Efficiency Obtaining in Single-Stage Multi-Crystal Optical Parametric Chirped Pulse Amplification System

An optical parametric chirped-pulse amplification system is demonstrated to provide 32.9% pump-to-signal conversion efficiency . Special techniques are used to make the signal and pump pulses match with each other in both spectral and temporal domains. The broadband 9.5-mJ pulses are produced at the repetition rate of 1 Hz with the gain of over 1.9 x 10(8). The output energy fluctuation of 7.8% is achieved for the saturated amplification process against the pump fluctuation of 10%.

Frontiers in ultrafast optics and ultra-intense laser technology

Ultrafast optics and ultra-intense laser technology, which are important frontiers in the fields of optics and lasers, are expected to promote fundamental science discoveries and high-technology developments. In this paper, the current status and future trends of ultrafast optics and ultra-intense laser technology are introduced briefly, including the applications of ultrafast and ultra-intense lasers in particle acceleration, attosecond science, ultrafast nonlinear optics, micro/nano-fabrication, broadband optical frequency combs, etc. The future prospects and key techniques for generating ultra-intense and ultra-short laser pulses with higher performance are also described.

High-Conversion-Efficiency and Broadband Tunable Femtosecond Noncollinear Optical Parametric Amplifier

We build a compact high-conversion-efficiency and broadband tunable noncollinear optical parametric amplifier (OPA) in the infra-red (IR) pumped by a femtosecond Ti:sapphire CPA laser. The OPA consists of an internal seed of white-light continuum generator (WLG) and two noncollinear optical parametric amplifiers. The tunable wavelength range is from 1.2 μm to 2.4 μm for both signal and idle pulses. The total OPA efficiency in the last OPA stage reaches about 40% in a wider tunable spectral range (from 1.3 μm to 1.7 μm for signal pulse, from 1.5 μm to 2.0 μm for idle pulse respectively).

Compression of Intense Laser Pulse through Filamentation in an Argon-Filled Cell

We demonstrate a pulse compression technique through filamentation in an argon-filled cell. By using a pair of chirped mirrors for dispersion compensation, we have successfully compressed the 53 fs pulse to 15 fs with good spatial qualities and good pulse stability. The total transmitted efficiency is more than 75%. The influence of the experiment parameters to the compressed pulses is also studied experimentally.