Fuling Zhang

Recent progress in improving low-temperature stability of infrared thin-film interference filters

The degeneration of performance of an optical thin-film interference filter associated with the change of temperature is not acceptable. In this letter, we report a new progress in improving low-temperature performance of infrared narrow-band filters by using Pb(1-x)Ge(x)Te initial bulk alloy with appropriate Ge concentration x. It can be found that there exists a critical temperature for the investigated narrow-band filter, at which the temperature coefficient of filter is exactly zero. Therefore, by means of controlling the composition in (Pb(1-x)Ge(x))(1-y)Te(y) layers, the temperature coefficient of filter can be tunable at the designated low-temperature. In our present investigation, when temperature varies from 300 to 85 K, a shift of peak wavelength of 0.05935 nm.K-1 has been achieved.

Numerical simulations of the impact of wavefront phase distortions of pump on the beam quality of OPA

A numerical model of optical parametric amplification (OPA) is introduced to investigate the impact of wavefront phase distortion of pump on the beam quality of signal. Numerical results show that the unidentical walk-off directions of the pump and the idler waves are the main factors leading to the transfer of wavefront phase distortions of the pump to the signal, and by reducing the angle between the two directions, the beam quality factor (M2) can be greatly decreased and hence the good beam quality of the signal can be maintained.

Improving low-temperature performance of infrared thin-film interference filters utilizing the intrinsic properties of IV–VI narrow-gap semiconductors

Pb(1) (-x)Ge(x)Te is a pseudobinary alloy of IV-VI narrow-gap semiconductor, of which maximum refractive index corresponds to the ferroelectric phase transition. Since the temperature coefficient of refractive index can be tunable from negative to positive by changing the Ge composition, it is possible to utilize the intrinsic property in the fabrication of infrared thin-film interference filters. In this letter, we report a narrow-bandpass filter, in which Pb(0.94)Ge(0.06)Te was substituted for PbTe. It found that the low-temperature stability of the filter is obviously improved: in the temperature range of 80-300K, the shift of center wavelength with temperature is reduced from 0.48nm.K(-1) to 0.23nm K(-1); furthermore, the peak transmittance of filter fabricated with Pb(0.94)Ge(0.06)Te is ~3% over that fabricated with PbTe.

Diffraction grating single-shot correlation system for measurement of picosecond laser pulses

We study and experimentally demonstrate a sensitive single-shot correlation system in which only a diffraction grating is used to produce a transverse time delay (TTD) in the reference pulse. The mechanism of the TTD introduced by the grating and the formation of the relative time delay (RTD) in the noncollinear correlation system are analyzed in detail. By using our system, we successfully measured the temporal duration of picosecond laser pulses, and a time resolution of ~0.047 ps is obtained at 1047 nm. The impact of the grating dispersion and the second harmonic beam walk-off effect on the measurement are considered.

Contrast measurement of ultra-short laser pulses

The contrast measurements of ultra-short laser pulses from a typical Ti:Sapphire oscillator have been performed using homemade second- and third-order correlator respectively. The two correlators were all demonstrated a dynamic range of 108.

Spatial beam shaping by quartz crystal plano-convex lens

Based on the optical activity of quartz crystal, we proposed a scheme for shaping the spatial intensity distribution of a linearly polarized laser beam by utilizing a quartz crystal plano-convex lens in combination with a polarizer. The intensity profile of the shaped laser beam can be easily switched from one profile to another by controlling the polarization direction of the incident laser beam.