Hiroyuki Nagai

Ultrathin amorphous Si layer formation by femtosecond laser pulse irradiation

Formation of ultrathin amorphized Si layer by femtosecond laser irradiation is reported in this letter. Below the fluence of ablation threshold, femtosecond laser irradiation induced an amorphization of crystalline Si. The authors confirmed the thickness of amorphous Si layer by transmission electron microscope. The thickness of the amorphized layer was found to be quite uniform and did not depend on the number of irradiated laser pulses and fluence, which was related to the effective light penetration depth.

Generation of high-power femtosecond pulse and octave-spanning ultrabroad supercontinuum using all-fiber system

We present the all-fiber system for amplification of high peak power femtosecond pulses. The 260-fs pulses are generated in the passively mode-locked Er-doped fiber (EDF) laser and amplified using the EDF amplifier system. The average and peak powers of the generated pulses are 215 mW and 43.2 kW, respectively, and the pulsewidth is 42.3 fs. Then the amplified pulses are coupled into polarization-maintaining highly nonlinear dispersion-shifted fiber and octave-spanning supercontinuum is generated. The spectral range is widely expanded from 980 to 2570 nm. To the best of our knowledge, this bandwidth is the maximum one in this wavelength region.

Structural modification in fused silica by a femtosecond fiber laser at 1558 nm

We report on structural modification in fused silica by a novel commercial femtosecond fiber laser with a fundamental wavelength of 1558 nm. The refractive-index change was induced by laser pulses at a repetition rate of 173 kHz and pulse duration of 870 fs. The refractive index change with a magnitude of 1.2 x 10(-3) was estimated from the diffraction efficiencies of an internal grating.

Electronically controlled high-speed wavelength-tunable femtosecond soliton pulse generation using acoustooptic modulator

The compact system of electronically controlled high-speed wavelength-tunable femtosecond (fs) soliton pulse generation is realized for the first time using a passively mode-locked fs fiber laser, a polarization maintaining optical fiber, and an acoustooptic (A-O) modulator. The wavelength of the output pulses can be continuously tuned simply by controlling the input voltage into the A-O modulator. The wavelength of the soliton pulses can be changed at 2.5-/spl mu/s intervals. Wavelength stabilization, time division wavelength multiplexed soliton pulse generation, and a wavelength scanner have been demonstrated.

Giant Vesicle Fusion on Microelectrodes Fabricated by Femtosecond Laser Ablation Followed by Synchrotron Radiation Etching

We have developed a new technique for fabricating a hole (well) with a diameter of about 1 µm for a microelectrode on the surface of SiO2 (600 nm)/CoSi2 (10 nm)/Si substrate. This process enabled the fabrication of electrode holes while maintaining the original nanolevel flatness (Ra~0.8 nm) of the SiO2 surface. A lipid bilayer was formed by giant vesicle fusion on these microelectrodes. Fluorescence microscope, in situ atomic force microscope and electrical characteristics measurements showed that a single lipid bilayer of sufficiently high resistance (gigaohm seal) was successfully fabricated.

High-Peak-Power Ultrashort Pulse Generation Using All-Fiber Chirped Pulse Amplification System with Small Core Multimode Fiber

We present an all-fiber chirped pulse amplification system based on a single mode Er-doped fiber and a multimode fiber with 25 µm core diameter. The peak power of the output pulses amounts to 44 kW.

Investigation on Sub-20 fs Fiber-soliton Compression Performance of Dispersion-Flattened Fibers

Fiber-soliton compression capability of dispersion-flattened fibers into the sub-20 fs regime has been investigated through soliton order enlargement experiments and analyses of their results. The soliton order was boosted up by uses of a sub-nJ and sub-100 fs fiber-optic pulse source and a variety of dispersion characteristics in several anomalous-dispersion-flattened fibers (ADFFs). It has been found out that 75 fs pulses were successfully compressed down to 15.6 fs, which is the shortest fiber-optic soliton pulse width ever reported. Limiting factors for such an ultimate soliton compression regime have been studied experimentally and analytically, and it was clarified that the 15.6 fs compression is limited partly by an anomalous dispersion bandwidth given by the fourth-order dispersion nature of ADFF and partly by a limited value of the input pulse energy. In addition, a concept named as an effective value of second-order dispersion has been proposed, which is defined mainly by the fourth-order dispersion characteristics and was found out to be possibly applicable for the description of the sub-20 fs compression limitations.

Generation of Pedestal Free 22 fs Ultrashort Pulse with Single-Peak Spectrum Using All-Fiber Laser System

Almost pedestal free 22 fs ultrashort pulses with single-peak spectrum around 1.7 µm are generated in all-fiber laser system using highly nonlinear fiber and reverse dispersive fiber for the first time.

1.3-2.0 /spl mu/m widely wavelength tunable compact ultrashort pulse source using optical fibers

Summary form only given. Using two types of optical fibers and Er-doped fiber laser, widely wavelength tunable ultrashort pulses are generated from 1.32-2.03 /spl mu/m. In addition to the Stokes pulse, the anti-Stokes pulse which is shifted toward the shorter wavelength side is also generated. In the experiment, the passively modelocked Er-doped fiber laser (IMRA Femtolite 780 Model FA1550) is used as the pump light source. It generates 110 fs optical pulses at a wavelength of 1.56 /spl mu/m.

1.56-2.03 /spl mu/m widely wavelength tunable femtosecond soliton pulse generation using optical fibers

Using the high power ultrashort pulse fiber laser and optical fibers, the quite large wavelength shift of femtosecond soliton pulse from 1.56 to 2.03 /spl mu/m is successfully demonstrated. The ideal sech2 shaped pulse spectra is confirmed up to 2 /spl mu/m for the first time.