Hiroaki Maekawa

Transverse-Mode Characteristics of InGaAs/GaAs Vertical-Cavity Surface-Emitting Lasers Considering Gain Offset

We have fabricated InGaAs/GaAs vertical-cavity surface-emitting lasers with modulation-doped graded distributed Bragg reflectors (DBRs) grown by metal-organic chemical vapor deposition (MOCVD). The threshold current was 3.2 mA. By observing the spontaneous emission through DBRs, we found that transverse mode behavior depends on gain characteristics. Single fundamental transverse-mode lasing is achieved at a negative gain offset and multiple transverse-mode lasing is achieved at a positive gain offset.

Spectral diffusion of the anti-symmetric stretching mode of azide ion in a reverse micelle studied by infrared three-pulse photon echo method

Fluctuation of the transition frequency of the anti-symmetric stretching mode of the azide ion in a nonionic reverse micelle was studied by infrared three-pulse photon echo method. The time correlation function of the frequency fluctuation has three components. It is found that the contribution of the static component is much larger than that in the bulk water, while the other two components with faster time constants are similar to those in the bulk.

Generation of 55 fs-Mid-Infrared Pulses with a 300 cm-1-Spectral Width and µJ-Pulse Energy

Optical pulses with a temporal duration of 55 fs, a spectral width of more than 300 cm-1, and an energy of 3 µJ/pulse are generated at around 3 µm with a repetition rate of 1 kHz by an optical parametric generation and amplification (OPG/OPA) system in which group-velocity dispersion is compensated. A silicon plate is used to compress the infrared pulses. A pulse energy as high as 5 µJ/pulse is obtained at around 3.5 µm.

Vibrational dynamics in liquids studied by non-linear infrared spectroscopy

Three-pulse photon echo experiments in the infrared region have been performed to study vibrational dephasing and transition frequency fluctuations in solutions. Time-integrated and frequency-resolved photon echo signals of the –N=C=N– anti-symmetric stretching mode of di-p-tolylcarbodiimide show an oscillatory behavior due to interference with a band nearby. Solvation dynamics or frequency fluctuations of several ions in hydrogen-bonding solvents have been studied and a couple of general trends of the time-correlation function of the frequency fluctuation on these systems have been observed.

All-solid-state femtosecond multi-kilohertz laser system based on a new cavity-dumped oscillator design

We have developed a compact Ti:sapphire laser system operating at variable repetition rates up to 40 kHz. Pulses of 13.2 fs from a cavity-dumped oscillator were amplified further by a seven-pass confocal amplifier, and after compression 23.8-fs pulses with a maximum pulse energy of 1.25 µJ at 10 kHz and more than 100 nJ at 25 kHz were generated. A new prismless cavity-dumping oscillator configuration was designed with the use of negatively chirped mirrors for dispersion compensation. Application of the developed laser system for nonlinear optical spectroscopy in condensed phase was demonstrated.

Carrier Transport in p-Type GaInAsP/InP Distributed Bragg Reflectors

The current-voltage characteristic of a p-type GaInAsP/InP distributed Bragg reflector (DBR) is theoretically and experimentally investigated. It is pointed out that the light hole tunneling current is dominant in the reverse bias condition. Highly selective p-doping in InP is effective to reduce the excess bias in the DBR. Experimentally, an excess bias of 0.5 V is observed for a five-pair GaInAsP (λ g=1.45 µ m)/ InP DBR grown by chemical beam epitaxy.

Development of two-dimensional Raman spectroscopy by higher-order optical nonlinear spectroscopy

Recent development of the optical two-dimensional spectroscopy is reviewed. This is an optical analogue of the two-dimensional magnetic resonance technique. We especially focus on the spectroscopy on the vibrational state in condensed phases and discuss about correlation of the vibrational modes which are anharmonically coupled.

Characteristics of High-Current Pulsed Arc Discharge

Characteristics of high-current arc discharge in H2, N2, air and SF6 have been investigated to develop a high-efficiency, high-repetition pulse power switch. The discharge parameter was typically 5–50 kV, 12–16 kA, with pulse duration around 600 ns. Energy transfer efficiencies and the recovery characteristics of breakdown voltage have been evaluated using a charge transfer circuit. The energy transfer efficiency was found to be much higher for H2. The recovery times required to obtain 50% of initial breakdown voltage are evaluated to be 0.5 ms, 2 ms, and 3 ms for H2, SF6 and air, respectively. The arc column was observed to expand with a supersonic velocity which produced a strong shock wave. The volume of hot gas remaining after the discharge was found to be much smaller for H2, as compared with SF6.

Vibrational Dynamics of the OH Stretching Mode of Water in Reverse Micelles Studied by Infrared Nonlinear Spectroscopy

Vibrational dynamics of the OH stretching mode of water in the water pool of reverse micelles (H 2 O/Aerosol OT (AOT)/isooctane) are studied by nonlinear infrared spectroscopy such as transient grating method and three-pulse photon echo peak shift measurements. The W 0 value (W 0 =[H 2 O]/[AOT]) is changed from 2 to 40, which corresponds to a water pool diameter of a few nm to about 20 nm. Polarization dependent transient grating experiments show rapid anisotropy decay of the OH stretching mode, which could be due to resonant intra and intermolecular energy transfer. From the three-pulse photon echo peak shift experiments, the spectral diffusion is found to be dependent on W 0 .

Recent developments of optical two-dimensional spectroscopy in liquids

Recent development of optical two-dimensional spectroscopy is reviewed. This is an optical analogue of the two-dimensional magnetic resonance technique. We especially focus on the spectroscopy on the vibrational state in condensed phases and discuss about correlation of the vibrational modes which are anharmonically coupled.