Kenji Torizuka

Sub-100-fs timing jitter of mode-locked laser

Timing stabilization of mode-locked femtosecond laser is reported. Timing fluctuations of mode-locked laser come from the change in gain medium, and the change in cavity length via mechanical vibrations and environmental disturbances. To suppress the gain change, a low noise all-solid-state pump source was used. And the cavity optical length was controlled to be stable with a PZT and a motor driven translation stage. The timing jitter was reduced to be 77 fs.

Timing stabilized regenerative amplifier with spectral-resolved cross-correlation technique

We modified a conventional cross-correlation technique for the timing fluctuation measurement of the pulses generated from a 1-kHz regenerative amplifier. By actively controlling the amplifier cavity length, we suppressed the rms timing jitter of the regenerative amplifier into the sub-femtosecond region.

Arbitrary shaping of amplified femtosecond pulses with phase-only filters

Summary form only given. Fourier-transform synthesis of femtosecond laser pulses is opening up new application fields including mode-selective excitation of coherent phonons and generation of THz radiation from a semiconductor quantum well. Some applications, such as the coherent control of chemical reactions and the efficient generation of electrons in an RF-gun, need amplified and arbitrarily shaped femtosecond laser pulses. When we want such pulses, we should place a pulse shaping apparatus, which consists of a modulating devise, a grating pair, and a lens pair, between an oscillator and an amplifier to avoid damages to a modulation device. In order to obtain arbitrarily shaped femtosecond laser pulses, we may use amplitude-phase filters or a phase-only filter. Amplitude modulation of laser pulses before the chirped pulse amplification may cause damages of optical elements in a regenerative amplifier especially for a longer shaped pulse. Hence, in this presentation, we show the results with a phase-only filter, which does not cause damages in a process of the chirped pulse amplification.

Measurement of the timing jitter in a kilohertz regenerative amplifier system

The timing jitter measurement scheme for low repetition rate pulse train is proposed. Measuring a spectrum of upconverted light generated from frequency mixing with a transform limited reference pulse and a linear-chirped amplified pulse, a relative time lag between two pulses can be obtained. The measurable range and resolution with this method are discussed.

Development of diode-pumped Yb:S-FAP laser system for laser-Compton X-ray generation

We are developing a diode-pumped Yb:S-FAP laser system for laser-Compton X-ray generations. We obtained the amplified pulse energy up to 210-mJ at 50-Hz after the double-pass preamplifier of the Yb:S-FAP laser system in preliminary experiments.

Evaluation of in-situ feedback control algorithms for a femtosecond pulse shaping

In-situ feedback controlled pulse shaping has demonstrated when a pulse shaping apparatus is placed before the amplifier. For the efficient and rapid control, we evaluated optimization algorithms and parameters.

Accurate pulse timing control between independent two mode-locked lasers with a novel phase-locked loop

A novel phase-locked loop was developed for synchronization between two mode-locked lasers. The up-converted signal was used to detect phase difference. The relative timing jitter was reduced to less than 500 fs for 30 minutes.

Stable terawatt Ti:sapphire laser system operating at 50 Hz for a compact laser synchrotron X-ray source

We present operational results of a terawatt Ti:sapphire laser system operating at a repetition rate of 50 Hz, which is designed to be stable for thermal lensing in the amplifiers.

Generation of amplified square shaped picosecond pulses with phase-only filters for an efficient electron generation in an RF-gun

Applications, such as the coherent control of chemical reactions and the efficient generation of electrons in an RF-gun, need amplified and arbitrarily shaped femtosecond laser pulses. We are constructing an RF-gun system which is used to generate electrons to seed into an accelerator. We shape femtosecond pulses to square shaped picosecond pulses with a phase-only filter, which does not cause damages in a process of the chirped pulse amplification.