Takumi Okada

Transverse Mode Characteristics of a DBR-Surface Emitting Laser with Buried Heterostructure

Distributed Bragg reflector (DBR)-surface emitting lasers (SELs) with buried heterostructure (BH) are fabricated with the combination of metal-organic chemical vapor deposition (MOCVD), electron cyclotron resonance (ECR) dry-etching and liquid phase epitaxial (LPE) regrowth techniques. Low threshold and stable fundamental lateral-mode characteristics are realized by the optimum design of the cavity diameter and refractive indices. Other important characteristics such as polarization characteristics, series resistance and thermal resistance are also discussed.

Coherent Control of Exciton in a Single Quantum Dot Using High-Resolution Michelson Interferometer

We developed a high-resolution Michelson interferometer with a He–Ne two-frequency laser positioning system, and measured the coherent carrier dynamics of a single InAs self-assembled quantum dot (SAQD) using a micro-spectroscopy system. The phase-locked double pulses were stabilized, with the maximum deviation being below 10 nm during the long measurement time of 1 h. Using this system, coherent control of an exciton in an InAs SAQD with very fine phase stabilization was demonstrated. The dephasing time of the single quantum dots was 9.5 ps which is close to that estimated from the homogeneous linewidth in the photoluminescence excitation (PLE) spectrum.

Ultrafast Coherent Control of Excitons and Exciton-Polaritons in Quantum Nanostructure

We have demonstrated ultrafast coherent control of excitons and exciton-polaritons in semiconductor quantum nanostructures. An InGaAs/AlGaAs multi-quantum-well Bragg structure and an AlGaAs/GaAs crescent-shaped quantum wire structure were used as samples for the control of the exciton-polariton and excitons in the nanostructure. In the multi-quantum-well Bragg sample, a two-stage decay due to the super-radiant exciton-polariton mode is clearly observed under the resonance conditions. Highly sensitive coherent control measurement enables us to observe the dephasing characteristics in the crescent-shaped quantum wire sample, and a very fast dephasing time T-2 of between 200 fs and 300 fs with powder dependence was observed.

Development of high resolution Michelson interferometer for stable phase-locked ultrashort pulse pair generation

We developed a high resolution Michelson interferometer with a two-frequency He-Ne laser positioning system in order to stabilize the relative phase of a pulse pair. The control resolution corresponded to a 12 as time resolution or a phase of 1.5 degrees at 900 nm. This high resolution Michelson interferometer can generate a phase-locked pulse pair either with a specific relative phase such as 0 or pi radians or with an arbitrary phase. Coherent control of an InAs self-assembled quantum dot was demonstrated using the high resolution Michelson interferometer with a microspectroscopy system.

Electrodeposition of Diamond-like Carbon Films on Silicon Substrates Using N,N-Dimethylformamid

Diamond-like carbon (DLC) films were synthesized by an electrodeposition technique on silicon (Si) substrates using liquid N,N-dimethylformamid (DMF). The electrodeposition was performed in the temperature range from 40 to 80°C and the applied voltage range from -1 kV to -5 kV. The structures of the films were characterized by Raman spectroscopy. The films with the electrical resistivity of about 1010 Ωcm can be deposited using the liquid DMF under the liquid temperature of 80°C and the applied voltage of -2 kV. Moreover, the current density has an important role in the deposition of the films.

Coherent control of exiton in a single quantum dot using a high-resolution Michelson interferometer

Tokai University Junior College, Department of Communications Engineering 2-3-23, Takanawa, Minato-ku, Tokyo 108-8619, Japan Phone: +81-3-3441-1171, E-mail: takumi@ttc.u-tokai.ac.jp National Institute of Advanced Industrial Science and Technology (AIST) 1-1-1, Umezono, Ibaraki 305-8568, Japan CREST, Japan Science and Technology Corporation (JST) 4-1-8, Honcyou, Kawaguchi, Saitama 332-0012, Japan University of Tsukuba, Institute of Applied Physics 1-1-1, Tennoudai, Ibaraki 305-8573, Japan