Motoki Yonemura

An array-grating compressor for high-power chirped-pulse amplification lasers

Abstract We propose and discuss an array-grating compressor that can be used in high-power large-scale chirped-pulse amplification Nd:glass laser systems. Theoretical models including various angular errors are derived for the optical design of the array-grating compressor. With a criterion that the stretch in the pulse duration due to alignment errors of the array grating must be kept below 25%, we carried out the optical design for 0.5 ps pulse duration and 1 m beam diameter. Some limitations due to groove-width difference, parallelism, planar error, and tilt angular error are discussed.

Wavelength-change characteristics of semiconductor lasers and their application to holographic contouring

The dependence of double-heterostructure AlGaAs semiconductor laser wavelength on injection current and temperature was investigated by means of a Michelson interferometer. The lasers operated in a single longitudinal mode at 790 nm, permitting them to be applied to two-wavelength holographic contouring. Continuous change and discontinuous change by mode hopping were observed. The wavelength was continuously tunable by variation of injection current and temperature at rates of 0.0045 nm/mA and 0.070 mm/ degrees C, respectively. Discontinuties in wavelength change were observed to be integer multiples of the longitudinal mode spacing. Holographic contour fringes were interpreted given the measured variation in wavelength.

Endoscopic hologram interferometry using fiber optics.

Basic and practical problems on the formation of fringes in endoscopic hologram interferometry using fiber optics have been studied in connection with medical diagnosis of living body cavities, nondestructive testing of inner parts of machines, etc. It is pointed out that fiber bundles instead of single fibers can be used to transmit high power laser light for object illumination to prevent the light path break induced by the high power density of concentrated laser light. The effects of extended source illumination by the fiber bundle, image transmission through the ordered fiber bundle, and fiber bundle movement on the fringe visibility were investigated.

Holographic contour generation by spatial frequency modulation

A contouring method by spatial frequency modulation using hologram interferometry is presented. The principle is that Youngs fringes produced by tilting the illumination ray are modulated by the object shape and demodulated by tilting the observation ray to generate depth contours. The problems of fringe localization and visibility in the arrangements of Fresnel holography and Fourier transform holography are studied. This method has the advantages that the sensitivity and the standard plane orientation are continuously variable, and high sensitivity and large measurable depth can be achieved for diffuse surface objects.

A Simulation Code for Tempo-Spatial Analysis of Three-Wave Interaction with Ultrashort- and Ultrahigh-Intensity Laser Pulses

We have developed a simulation code that can be used for tempo-spatial analysis of three-wave interaction with ultrashort- and ultrahigh-intensity laser pulses. The code can be used to estimate conversion efficiency, tempo-spatial and spectral profiles and many transverse effects including diffraction, walk-off, phase modulations and self-focusing through the third-order nonlinear process. An application example of the code to second-harmonic generation is given in this short note.

Pulse Shaping of Ultrashort Laser Pulses with Nonlinear Optical Crystals

We present a detailed description of the pulse shaping of ultrashort laser pulses with nonlinear optical crystals by introducing a time delay between two fundamental pulses. We demonstrate that the frequency reconversion process from a second-harmonic pulse to fundamental pulses will play an important role in fundamental pulse compression and train pulse generation. A collinear type II potassium dihydrogen phosphate (KDP) crystal can be used to achieve complete pulse shaping for a 1053 nm wavelength. Under conditions of a 50 GW/cm2 fundamental intensity, a 1.0 ps fundamental pulse duration and a 0.7 ps delay time, the second-harmonic pulse can be compressed to 0.14 ps. In addition, the fundamental pulse can be compressed to 0.3 ps by introducing an intensity unbalance into the two fundamental pulses. Furthermore, the train pulse can be generated by increasing the fundamental intensity over 20 GW/cm2. A train pulse with three 0.1 ps individual pulses with a 2.5 THz frequency interval can be generated for a 100 GW/cm2 fundamental intensity. We also demonstrate that pulse shaping with a noncollinear type I BBO crystal can be achieved at wavelengths near 800 nm.

MULTIPASS MICHELSON INTERFEROMETER WITH THE USE OF A WAVELENGTH-MODULATED LASER DIODE

An improved multipass Michelson interferometer is implemented. This technique uses the fact that the wavelength of a laser diode varies in proportion to the diodes injection current. With this method the sensitivity augmentation is accomplished by inserting a beam splitter into one arm of the interferometer, resulting in multiple reflections between the end mirror and the beam splitter. In addition, the interference of laser beams reflected from two arms can be accomplished with unequal arms in the condition of a short coherence length. The sensitivity increase of interference fringes and the compensation of the short coherence length have been demonstrated in experiments.

Pulse Compression with a Noncollinear Type I Frequency Doubling Crystal

We propose a new scheme to generate a compressed second-harmonic pulse with a noncollinear type I frequency doubling crystal. Theoretical calculations predict that a 25 fs second-harmonic pulse could be generated from a 100 fs fundamental pulse with the proposed scheme.

Efficient type I second-harmonic generation of subpicosecond laser pulses with a series of alternating nonlinear and delay crystals

We propose a novel configuration of efficient type I second-harmonic generation (SHG) with ultrashort laser pulses by group-velocity compensation. The configuration is composed of a type I SHG crystal and a series of alternating time-delay and type I SHG crystals. The numerical calculations show that the conversion efficiency can be increased to almost 100% by using crystal pairs in series, and the duration of the second-harmonic pulse is almost the same as that of the fundamental pulse.

Optical design of an array-grating compressor for high-power laser pulses

In this paper, we propose and discuss an array-grating compressor that is used in high power chirped-pulse amplification Nd:glass laser systems. Theoretical models including various angular errors are developed for the optical design of the array-grating compressor. With a criterion that the stretch in the duration of the compressed pulse due to the combining imperfection must be kept below 25%, we carry out the optical design of the array-grating compressor for a 0.5 ps pulse duration and a 1-m laser-beam diameter. The limitations to groove-width difference, parallelism, and planar are also discussed.