Masayuki Kakehata

Single-shot measurement of carrier-envelope phase changes by spectral interferometry.

We demonstrated single-shot measurements of spectral interference between a white-light continuum generated in a hollow-fiber and its second harmonic. The interference has information on the carrier-envelope phase of an input pulse to the fiber and the time delay of the blue wing of the continuum. By analyzing the observed spectral interference, we estimated shot-by-shot changes of the carrier-envelope phase. This method is useful for determining the carrier-envelope phase changes of a low-repetition-rate, high-intensity laser.

Carrier-envelope-phase stabilized chirped-pulse amplification system scalable to higher pulse energies

We have demonstrated a carrier-envelope phase (CEP) stabilized chirped-pulse amplification (CPA) system employing a grating-based pulse stretcher and compressor and a regenerative amplifier for the first time. In addition to stabilizing the carrier-envelope offset phase of a laser oscillator, a new pulse selection method referenced to the carrier-envelope offset beat signal was introduced. The pulse-selection method is more robust against the carrier-envelope offset phase fluctuations than a simple pulse-clock dividing method. We observed a stable fringe in a self-referencing spectrum interferometry of the amplified pulse, which implies that the CEP of amplified pulse is stabilized. We also measured the effect of the beam angle change on the CEP of amplified pulses. The result demonstrates that the CEP stabilized CPA is scalable to higher-pulse energies.

Direct measurement and analysis of the carrier-envelope phase in light pulses approaching the single-cycle regime

We demonstrate a solid-state device capable of providing direct information about the carrier-envelope (CE) phase of ultrashort (4 fs) laser pulses. The measurement is based on multi-photon-induced photoelectron emission from a gold surface. The amount of the charge emitted from the surface gives a clear indication of phase sensitivity, as predicted by our simulations and also by a simple intuitive model. This phenomenon was used to determine the CE phase value of each laser pulse in a mode-locked, unamplified, low-energy pulse train. The inability of the commonly used f -to-2f interferometric method to measure accurately extracavity drifts of the CE phase is discussed and contrasted with the direct phase measurement method proposed here. The evolution of the CE phase upon propagation of pulses comparable in duration to the optical cycle is analysed.

Laser-plasma scanning 3D display for putting digital contents in free space

We present a novel 3D display that can show any 3D contents in free space using laser-plasma scanning in the air. The laser-plasma technology can generate a point illumination at an arbitrary position in the free space. By scanning the position of the illumination, we can display a set of point illuminations in the space, which realizes 3D display in the space. This 3D display has been already presented in Emerging Technology of SIGGRAPH2006, which is the basic platform of our 3D display project. In this presentation, we would like to introduce history of the development of the laser-plasma scanning 3D display, and then describe recent development of the 3D contents analysis and processing technology for realizing an innovative media presentation in a free 3D space. The one of recent development is performed to give preferred 3D contents data to the 3D display in a very flexible manner. This means that we have a platform to develop an interactive 3D contents presentation system using the 3D display, such as an interactive art presentation using the 3D display. We would also like to present the future plan of this 3D display research project.

100- attosecond timing jitter between two-color mode-locked lasers by active–passive hybrid synchronization

We demonstrated a timing jitter as low as 83 as between passively-synchronized Ti:sapphire and Cr:forsterite mode-locked lasers from 10 mHz to 100 kHz in combination with a slow active extra-cavity feedback control by use of the balanced cross-correlator.

Ultralow-jitter passive timing stabilization of a mode-locked Er-doped fiber laser by injection of an optical pulse train

The pulse timing of a mode-locked Er-doped fiber laser was stabilized to a reference pulse train from a Cr:forsterite mode-locked laser by all-optical passive synchronization scheme. The reference pulses were injected into a ring cavity of the fiber laser by using a 1.3-1.5 mum wavelength-division multiplexer. The spectral shift induced by cross-phase modulation between copropagating two-color pulses realizes self-synchronization due to intracavity group-delay dispersion. The rms integration of timing jitter between the fiber laser pulse and the reference pulse was 3.7 fs in a Fourier frequency range from 1 Hz to 100 kHz.

Phase-coherent multicolor femtosecond pulse generation

We achieved phase-coherent multicolor femtosecond pulse generation by optical phase locking among the pump and its subharmonic signal and idler pulses in an optical parametric oscillator. The ability for coherent superposition of the multicolor pulses is demonstrated in a time-domain measurement. Clear interferometric fringes between two sum-frequency pulses, corresponding to phase stability among the subharmonics, were observed with phase locking.

Long-term optical phase locking between femtosecond Ti:sapphire and Cr:forsterite lasers.

Long-term optical phase-coherent two-color femtosecond pulses were generated by use of passively timing-synchronized Ti:sapphire and Cr:forsterite lasers. The relative carrier-envelope phase relation was fixed by an active feedback loop. The accumulated phase noise from 10 mHz to 1 MHz of the locked beat note was 0.43 rad, showing tight phase locking. The optical frequency fluctuation between two femtosecond combs was submillihertz, with a 1 s averaged counter measurement over 3400 s, leading to a long-term femtosecond frequency-comb connection.

Optical phase locking among femtosecond subharmonic pulses

We stabilized the relative carrier-envelope phase slip among the pump pulse and its subharmonic signal and idler pulses in a femtosecond optical parametric oscillator, resulting in long-term phasecoherence among the pulses. The stabilized beat signal corresponding to the relative carrier-envelope phase slip among subharmonic pulses had an accumulated phase error of 0.24 rad in the 1-mHz-1-MHz region. The fluctuation of the beat frequency measured by a 1-s-averaged counter was less than 1 mHz in a 1480-s measurement.

High-repetition-rate 12 fs pulse amplification by a Ti:sapphire regenerative amplifier system

We demonstrate the direct generation of 12 fs pulses from a Ti:sapphire regenerative amplifier system at a 1 kHz repetition rate utilizing properly designed broadband components for chirped-pulse amplification. Optimized designs of a regenerative amplifier with a multilayer gain-narrowing compensator and an adaptive dispersion compensator with a spatial light modulator contribute to the shorter pulse amplification.