Shian Zhou

Compensation of nonlinear phase shifts with third-order dispersion in short-pulse fiber amplifiers

We show that nonlinear phase shifts and third-order dispersion can compensate each other in short-pulse fiber amplifiers. This compen-sation can be exploited in any implementation of chirped-pulse amplification, with stretching and compression accomplished with diffraction gratings, single-mode fiber, microstructure fiber, fiber Bragg gratings, etc. In particular, we consider chirped-pulse fiber amplifiers at wavelengths for which the fiber dispersion is normal. The nonlinear phase shift accumulated in the amplifier can be compensated by the third-order dispersion of the combination of a fiber stretcher and grating compressor. A numerical model is used to predict the compensation, and experimental results that exhibit the main features of the calculations are presented. In the presence of third-order dispersion, an optimal nonlinear phase shift reduces the pulse duration, and enhances the peak power and pulse contrast compared to the pulse produced in linear propagation. Contrary to common belief, fiber stretchers can perform as well or better than grating stretchers in fiber amplifiers, while offering the major practical advantages of a waveguide medium.

Divided-pulse amplification of ultrashort pulses

We demonstrate an approach to avoid nonlinear effects in amplification. The initial pulse is divided into a sequence of lower-energy identical pulses. The low-intensity pulses are amplified and recombined to create a final pulse.

Stabilization of high-energy femtosecond ytterbium fiber lasers by use of a frequency filter

The performance of a femtosecond Yb fiber laser is investigated in the limit of high pulse energy (>10 nJ) and short pulse duration (<100 fs). By reducing the strength of nonlinear polarization rotation and introducing amplitude modulation through an intracavity frequency filter, pulses with unprecedented peak powers can be generated. The laser emits stable 13 nJ pulses that are dechirped to 55 fs duration and are capable of providing 130 kW peak power.

Efficient temporal shaping of ultrashort pulses with birefringent crystals

A new and simple technique for temporal shaping of femtosecond and picosecond pulses with high efficiency is demonstrated. The pulse is divided into numerous pulses by a designed birefringent-crystal set. These divided pulses produce various shapes.

Divided-Pulse Amplification of Ultrashort Pulses

We demonstrate an approach to avoid nonlinear effects in the amplification. The initial pulse is divided into a sequence of lower-energy identical pulses. The low-intensity pulses are amplified and recombined to create a final pulse. Article not available.

Generation of 400-fs solitons with 2-MHz repetition rate by a Yb-fiber laser

We study the minimum repetition rate achievable with a Yb fiber laser. We find that a cavity with large anomalous dispersion generates 400-fs, near-transform-limited pulses at repetition rate of 2 MHz

All polarization-maintaining fiber chirped-pulse amplification system for microjoule femtosecond pulses

A femtosecond fiber system based on nonlinear chirped-pulse amplification is investigated. It is the first investigation on pulse properties from all-normal-dispersion fiber laser after amplification. Nonlinearities due to fibers are carefully managed. The system generates up to 5-μJ pulses, and delivers near diffraction-limit beam (M2 < 1.1), polarization extinction ratio (40 dB) and polarization extinction ratio (36 dB).

The laser system for the ERL electron source at Cornell University

A master oscillator-power amplifier (MOPA) laser system has been developed to meet the requirements of the Cornell ERL high brightness electron photoinjector. The system is comprised of a Yb-fiber laser oscillator, a single-mode fiber pre-amplifier and a double-clad, large mode area fiber amplifier. The system provides 5 watts average infrared power in a train of 3-ps pulses at 50 MHz. These pulses are efficiently frequency-doubled to produce 2-ps pulses at 520 nm with more than 40 nJ energy per pulse. We demonstrate an efficient longitudinal pulse shaping technique that allows us to achieve 20- to 40-ps-long, nearly flat-top pulses with sharp rise and fall times. We characterize the noise properties of the fiber oscillator and discuss the route to upgrade the system to achieve 130-watt average infrared power and a repetition rate of 1.3 GHz.

Divided-pulse Amplification of Ultrashort Pulses

We demonstrate an approach to avoid nonlinear effects in amplification. The initial pulse is divided into a sequence of lower-energy identical pulses. The low-intensity pulses are amplified and recombined to create a final pulse.

Exploitation of stimulated Raman scattering in short-pulse fiber amplifiers.

Stimulated Raman scattering (SRS) generally limits the performance of short-pulse fiber amplifiers. We present the results of experiments that show that, under some conditions, SRS can extend the performance of amplifiers limited by nonlinear phase accumulation. The Stokes spectrum can be free of distortions arising from self-phase modulation and can circumvent the gain-narrowing limit of the amplifier. The generation of 1 microJ and 90 fs pulses from a single-mode fiber amplifier illustrates the potential of the process.