Yuxin Leng

Polarization-dependent two-color dispersion wave generation and evolution in polarization-maintaining photonic crystal fiber

We investigate the effect of the polarization state of the input pulses on the visible emissions in the anomalous dispersion region of polarization-maintaining photonic crystal fiber (PM-PCF), by using ∼100 fs pump pulses whose central wavelength (1064 nm) is close to the second zero dispersion wavelength (1100 nm) of the fiber, where the soliton fission mechanisms play an important role. The experimental results show that the phase-matching two-color dispersive wave emission, one at 582 nm and the other at 600 nm, is polarization-dependent and frequency shift results from the different dispersion characteristics along the two orthogonal principal axes of PM-PCF. Furthermore, it is observed for the first time that the variation of the linear input polarization angles in 45° region almost has no influence on the output spectral profiles, and the break variation of the output spectrum exists when the angle between the polarization of the linear incident pulse and the fast-axis or the slow-axis of PM-PCF is 45°, which are attributed to the coupling between the two polarization modes in high birefringent PM-PCF.

Broadband optical gain in the normally dispersive region of a high-birefringence photonic crystal fiber

Based on a designed high-birefringence photonic crystal fiber (HB-PCF) with two zero-dispersion wavelengths (ZDWs), the effect of pump parameters and Raman scattering on the modulation instability (MI) gain is comprehensively analyzed in this paper. An interesting result is found, in that only when the pump wavelength lies within an approximately 10xa0nm range of the zero-dispersion points in the normal dispersion region of the HB-PCF does a broadband gain characteristic appear. The Raman effect results in a combination of the gain spectra from the Stokes and anti-Stokes band, which finally promotes the formation of broadband amplification. Moreover, there exist an optimal pump wavelength and a suitable pump power along the fast axis or the slow axis of the fiber. With these optimal pump parameters, the total MI gain bandwidth finally reaches 159xa0nm for the fiber fast axis and 162xa0nm for the fiber slow axis.

Broadband modulation instability gain in a high-birefringence photonic crystal fiber with two zero-dispersion wavelengths

Based on a designed high-birefringence photonic crystal fiber with two zero-dispersion wavelengths (ZDWs), the effect of fiber dispersion, pump power and pump wavelength on the modulation instability (MI) gain in the anomalous dispersion region is comprehensively analyzed in this paper. An asymmetric and broadband MI gain spectrum appears at the anti-Stokes band due to the different ZDWs along the fiber slow- and fast-axes. An optimal MI gain can be obtained when the pump wavelength (1675 nm) is slightly shorter than the second ZDW (1683 nm) and the pump power is 280 W. The optimal MI gain bandwidth finally reaches 152 nm and the gain profile is smoother.

Improvement of the large aperture Ti:sapphire amplifiers in the petawatt femtosecond laser system at SIOM

We report the recent improvement on the petawatt (PW) femtosecond Ti:sapphire chirped pulse amplification (CPA) laser system at Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences. By enlarging the sizes of the pump and signal beams in the large aperture Ti:sapphire amplifiers and optimizing the whole laser system, the output laser energy before the pulse compressor is upgraded to 42.6 J. Accordingly, the peak power of the laser system exceeds 1 PW. The shot-to-shot instability of the output laser energy at about 40 J is less than ?%.

Extremely short pulse compression in bulk materials: a scheme for generating few cycle intense laser pulse

We investigate experimentally the self-compression behavior of high-power femtosecond pulses in normally dispersive solid bulk media with un-chirped laser pulses and negatively chirped laser pulses. It is demonstrated that high-power femtosecond laser pulses can be compressed by the nonlinear propagation in the transparent bulk media, and the temporal and spectral characteristics of resulted pulses were found to be significantly affected by the input laser intensity, with higher intensity corresponding to shorter compressed pulses. By the propagation in a piece of thin BK7 glass plate, a self-compression from 50fs to 20fs was achieved, with a compression factor of about 2.5. However, the output laser pulse was observed to be split into two peaks when the input laser intensity is high enough to generate supercontinuum and conical emission. When the input laser pulse is negatively chirped, the spectra of the pulse is reshaped and narrowed due to strong self-action effects, and the temporal pulse duration is found to be self-compressed, instead of broadening. With the increase in the input pulse intensity, the resulted self-compressed pulses became even shorter than the input laser pulse, and also shorter than sech2 transform-limited pulse according to the corresponding spectra. The self-compression scheme is simple and robust, and it is promising as a new pulse compression method to achieve intense laser pulses of few cycles.

High contrast research in the Nd:glass laser system based on optical parametric amplification temporal cleaning device

We demonstrate high amplified spontaneous emission (ASE) contrast pulses in a Nd:glass laser system based on the hybrid double chirped pulse amplification (double CPA) scheme. By an OPA temporal cleaning device, ~100 uJ/46 fs/ 1011 clean pulses are generated and amplified in the next Nd:glass laser. After compressor, >150 mJ/~0.5 ps/1 Hz pulses can be obtained. The ASE temporal contrast of amplified pulses is ~1011 with energy gain ~2.5×104 in the Nd:glass amplifiers.

High amplified spontaneous emission contrast of 1011 in a Nd:glass laser based on a hybrid double chirped pulse amplification scheme

By using a Ti:sapphire-Nd:glass hybrid double chirped pulse amplification scheme and a pulse cleaner based on optical parametric amplification and second harmonic generation, we demonstrate high amplified spontaneous emission (ASE) contrast at 1053u2009nm. The optimized ASE temporal contrast of the output pulse is about 1011 at about 160u2009ps before the main peak with an output of 140u2009mJ/500u2009fs. And the potential of 10u2009J level output with high ASE contrast is demonstrated in a laser system with attenuated injection.

Broadband spectral shaping in a Ti:sapphire regenerative amplifier

A 0.34-mm thick quartz plate is used in a Ti:sapphire regenerative amplifier for spectral shaping, the bandwidth of the amplified pulse is increased from /spl sim/18 nm to /spl sim/35 nm, and the amplified pulse is compressed to /spl sim/35 fs.