Grating Stretcher Research Articles

Coherent generation and control of tunable narrowband THz radiation from a laser-induced air-plasma filament.

We report on the proof-of-principle experiment of generating carrier-envelope phase (CEP)-controllable and frequency-tunable narrowband terahertz (THz) radiation from an air-plasma filament prescribed by the beat of a temporally stretched two-color laser pulse sequence. The pulse sequence was prepared by propagating the fundamental ultrafast laser pulse through a grating stretcher and Michelson interferometer with variable inter-arm delay. By partially frequency-doubling and focusing the pulse sequence, an air-plasma filament riding a beat note was created to radiate a THz wave with primary pulse characteristics (center frequency and CEP) under coherent control. To reproduce experimental results and elucidate complex nonlinear light-matter interaction, numerical simulation has been performed. This work demonstrates the feasibility of generating coherently controlled narrowband THz wave with high tunability in laser-induced air plasma.

Chirped pulse amplification based on praseodymium-doped fluoride fibers.

We have developed a chirped pulse amplification system for ultrashort 1300 nm pulses based on praseodymium-doped fluoride fibers (Pr:ZBLAN). The 1300 nm seed pulse is generated through soliton-dispersive wave coupling in a highly nonlinear fiber pumped by a pulse from an erbium-doped fiber laser. The seed pulse is stretched with a grating stretcher to ∼150 ps and amplified with a two-stage Pr:ZBLAN amplifier. The average power reaches ∼112 mW at the repetition rate of 40 MHz. The pulse is compressed to 225 fs by using a pair of gratings without serious phase distortion.

An All-Fiberized Chirped Pulse Amplification System Based on Chirped Fiber Bragg Grating Stretcher and Compressor

We report an all-fiberized chirped pulse amplification system without any bulk devices. The stretcher and compressor are chirped fiber Bragg gratings inscribed in a 6/125 μm single-mode fiber and a 30/250 μm large-mode-area fiber. The fabrication system of chirped fiber Bragg gratings was designed and built by ourselves. The width of the linear exposure spot was controlled according to the different fiber sizes to improve the fabrication quality, and the parameters of chirped fiber Bragg gratings were fine-tuned during the fabrication to achieve the overall system’s spectral matching. Two fiber circulators with the same fiber sizes as the chirped fiber Bragg gratings were employed to auxiliarily achieve the pulse stretching and compression. The dispersion accumulations provided by the stretcher and compressor are 129.8 ps and 90.8 ps. The power amplifiers were composed of the two-stage 10/130 μm fiber pre-amplifier and the 30/250 μm fiber main amplifier. The proposed chirped pulse amplification system with no spatial light is the true sense of an all-fiberized chirped pulse amplification structure and shows the main trend in development of ultrashort pulse fiber lasers.

Contrast ratio enhancement by spectral matching of a seed laser pulse and ASE in a Ti:sapphire laser system.

The ASE (amplified spontaneous emission) level in a laser system consisting of an oscillator and a regenerative amplifier is very important, for example, in the interaction of an intense laser pulse and a thin foil, so a lower ASE level is always required. In this paper, we propose a new method to achieve a lower ASE level, which can be obtained by spectral matching of the seed laser beam and the ASE in a CPA (chirped-pulse amplification) Ti:sapphire laser system. In this method, two baffles are used to control the seed pulse spectrum by blocking a portion of the seed beam in a grating stretcher and it was found that the spectral matching method can reduce the temporal contrast ratio (after the regenerative amplifier) by a factor of 10 in a few hundred picosecond scale. This kind of spectral matching method is simple and it can be easily employed for other CPA laser systems to enhance the contrast ratio.

Thin-disk ring amplifier for high pulse energy.

A CPA laser system for high pulse energy at high average power has been developed. The system is based on Yb:YAG thin-disk technology. It provides two laser beams with more than 500 mJ pulse energy each at 100 Hz repetition rate and 2 ps pulse duration. The system consists of a common oscillator, a grating stretcher and compressor and two identical amplifier chains that are both equipped with a regenerative amplifier and a ring amplifier. The compressor supports an individual alignment of the dispersion for the two laser channels.

Optimization of pulse compression in a fiber chirped pulse amplification system by adjusting dispersion parameters of a temperature-tuned chirped fiber Bragg grating stretcher

In this work, we present a femtosecond fiber chirped pulse amplification (FCPA) system with a temperature-tuned chirped fiber Bragg grating (CFBG) stretcher for uncompensated higher-order spectral phase reduction. An improvement in pulse compression through the optimization of temperature distribution along a CFBG stretcher is predicted numerically and verified experimentally by using a CFBG stretcher with four independent thermoelectric cooler (TEC) elements.

Carrier-envelope phase stabilization of a multi-millijoule, regenerative-amplifier-based chirped-pulse smplifier dystem

This article reports on the successful stabilization of the carrier-envelope phase of a 1-kHz laser system that includes a large grating stretcher, a regenerative amplifier, a multipass amplifier and a grating compressor. Phase stability for pulse energies up to 6 mJ is demonstrated using electronic feedback to the oscillator locking electronics as well as feedback via an acousto-optic programmable dispersive filter.

Ultrafast thulium-doped fiber-oscillator with pulse energy of 43 nJ

A femtosecond fiber laser based on thulium-doped double-clad silica fiber with an internal dispersion compensation is presented that generates pulses at a center wavelength of 1976 nm with an energy of 4.3 nJ and a duration of 1.2 ps. The dechirped pulse duration is 294 fs. The pulse energy is more than 2 orders of magnitude above the pulse energy demonstrated previously. Mode locking is achieved using additive pulse mode locking, and dispersion compensation is facilitated by a grating stretcher arrangement.

KHz 반복률에서의 Ti:sapphire 이득 스위칭 레이저 발진과 펨토초 처프펄스 재생 증폭

1kHz 반복률의 펨토초 펄스를 방출하는 안정된 Ti:sapphire 처프펄스 재생 증폭 시스템의 자체제작 및 최적화를 위해 시스템을 구성하는 각 요소들의 특성을 세부적으로 분석하였다. 사용된 증폭 공진기를 kHz 영역에서 반복률 변환 가능한 이득스위칭 레이저 구조로 변환하여 펄스 생성시간, 펌프출력에 따른 방출출력 특성 및 파괴여부, 펄스의 길이 및 파장가변 영역 등의 다양한 발진특성을 측정 분석하고, 이 결과를 기반으로 증폭 공진기를 설계하였으며, 내부에 설치된 포켈셀의 작동시간, 증폭 시 펄스의 공진횟수 등을 고려하여 증폭단을 최적화하였다. 증폭기의 종자펄스로는 자체제작된 커 렌즈 모드잠금 Ti:sapphire 레이저로부터 방출되는 50fs 펄스가 사용되었다. 종자펄스는 3개의 거울로 구성된 재생 증폭공진기에 입사되기 전에 펄스늘림기를 통해 120ps로 확대되었으며, 증폭 후 펄스길이의 재압축을 통해 815nm 영역에서 85fs, <TEX>$320{\mu}J$</TEX>의 극초단 펄스를 방출하는 1kHz 처프펄스 재생 증폭기를 제작하였다. We present a comprehensive study of a chirped pulse Ti:sapphire regenerative amplifier system operating at 1 kHz. Main constituents of the system are described in detail. The amplifier stage was first converted to a repetition rate-tunable kHz gain-switched nanosecond Ti:sapphire laser. Operation characteristics at different repetition rates such as build-up times of laser pulses, pump power-dependent output powers and pulse durations, damage thresholds, and tunability ranges were studied. Based on the results achieved, the switching time of the Pocket's cell used and the round trip numbers in the regenerative amplifier were optimized at 1 kHz. The output pulses with a pulse width of 50fs from a home-made Ken lens mode-locked Ti:sapphire oscillator were used as seed pulses. The pulses were expanded to 120ps in a grating stretcher prior to coupling into the 3-mirror amplifier cavity. After amplification and recompression, a stable 1kHz Ti:sapphire regenerative amplifier system, which delivers 85-fs, <TEX>$320-{\mu}J$</TEX> pulses, was fully constructed.

Single-shot sonogram generation for femtosecond laser pulse diagnostics by use of two-photon absorption in a silicon CCD camera

We present an experimental technique capable of single-shot recording of an ultrashort laser pulse sonogram by use of two-photon absorption in a conventional silicon CCD camera. The quadratic spectral phase, introduced into a 100-fs pulse by a grating stretcher, was measured and found to be in good agreement with the analytically calculated value. The nonlinear response of silicon allows sonogram characterization in a wavelength range from 1 to 2 mum .