Yoshihiko Miyasaka

Quick and easy measurement of particle size of Brownian particles and plankton in water using a self-mixing laser

We describe a method for quickly and easily measuring the size of small particles in suspensions. This method uses a self-mixing laser Doppler measurement with a laser-diode-pumped, thin-slice LiNdP(4)O(12) laser with extremely high optical sensitivity. The average size of the particles in Brownian motion is determined by a Lorentz fitting of the measured power spectrum of the modulated self-mixing laser light resulting from the motion. The dependence of the measured power spectra on particle size and concentration was quantitatively identified from the results of a systematic investigation of small polystyrene latex particles with different diameters and concentrations. The sizes and ratios of particles with different diameters mixed in water were accurately measured. An application of this self-mixing laser method for estimation of the average size of plankton in seawater showed that it is a practical method for characterizing biological species.

Detection of small particles in fluid flow using a self-mixing laser

We describe a highly sensitive, real-time method of detecting small particles in a fluid flow by self-mixing laser Doppler measurement with a laser-diode-pumped, thin-slice solid-state laser with extremely high optical sensitivity. Asymmetric power spectra of the laser output modulated by the re-injected scattered light from the small particles moving in a dilute sample-flow, through a small-diameter glass pipe, were observed. The observed power spectra are shown to reflect the velocity distribution of the fluid flow, which obeys Poiseuille’s law. Quick measurements of flow rate and kinetic viscosities of water-glycerol mixtures were also performed successfully. Measurable low-concentration limits for 262-nm polystyrene latex spheres and 3-μm red blood cells in a fluid flow were below 1 and 10 ppm, respectively, in the present self-mixing laser Doppler velocimeter system.

Oscillation spectra and dynamic effects in a highly-doped microchip Nd:YAG ceramic laser.

This work reports on a beam quality and dynamic behaviors of a mirror-coated highly-doped YAG (Y(3)Al(5)O(12)) microchip ceramic laser possessing an increased number of grain boundaries. The degradation of beam quality factor in transverse patterns due to spatial inhomogeneity across the beam, multiple split-mode operations, violation of antiphase dynamics and high-speed intensity modulations due to the interference between non-orthogonal transverse modes were observed in a laser-diode end-pumping scheme.

Polarization properties of laser-diode-pumped microchip Nd:YAG ceramic lasers

Detailed oscillation spectra and polarization properties of laser-diode-pumped ceramic Nd:YAG lasers were examined. Inherent segregation of lasing patterns into local modes possessing different polarization states and oscillation frequencies was observed. Single-frequency, linearly polarized stable oscillations were achieved by forcing the laser into Ince-Gaussian mode operation by adjusting azimuthal cavity symmetry.

Microanalysis of Brownian Particles and Real-Time Nanometer Vibrometry with a Laser-Diode-Pumped Self-Mixing Thin-Slice Solid-State Laser

Doppler particle sizing by self-mixing laser was demonstrated by using a laser-diode-pumped thin-slice Nd:GdVO4 laser with extreme optical sensitivity. A substantial improvement of optical frequency shifters led to quick and accurate sizing of Brownian particles with concentration as low as 50 parts per billion (ppb) for 262-nm polystyren latex spheres in water. A successful real-time measurement of sub-nanometer vibrations was also demonstrated with the present self-mixing laser.

Nonlinear dynamics in thin-slice Nd : YAG ceramic lasers: Coupled local-mode laser model

The authors propose a coupled spatially distributed local-mode laser model for understanding self-induced high-speed modulations in Nd:YAG ceramic lasers with laser-diode end pumping, which critically depend on pump positions. In addition to complicated high-speed modulations, quasiperiodic and chaotic relaxation oscillations have been demonstrated experimentally and reproduced by numerical simulation of the model of coupled local-mode lasers. Q-switching-like periodic spiking pulsations have been also observed and reproduced numerically by assuming saturable absorber type of inclusions in grain boundaries.

Linearly Polarized Single-Frequency Oscillations of Laser-Diode-Pumped Microchip Ceramic Nd:YAG Lasers with Forced Ince–Gaussian Mode Operations

Detailed oscillation spectra and polarization properties have been examined in laser-diode-pumped (LD-pumped) microchip ceramic (i.e., polycrystalline) Nd:YAG lasers and the inherent segregation of lasing patterns into local modes possessing different polarization states was observed. Single-frequency linearly-polarized stable oscillations were realized by forcing the laser to Ince–Gaussian mode operations by adjusting azimuthal cavity symmetry.

Detection of small particles in fluid flow with a self-mixing laser

Highly sensitive, real-time detection of small particles in fluid flow has been demonstrated by using a laser-diode-pumped, self-mixing thin-slice Nd:GdVO4 laser. Power spectra of modulated laser output, reflecting the velocity distribution of liquid flow, due to the scattered light from small particles in fluid flow were observed.

Self-Induced Instabilities in Nd:Y3Al5O12 Ceramic Lasers

We systematically studied dynamic effects in Nd-doped Y3Al5O12 (YAG) ceramic lasers having different Nd concentrations. A variety of dynamic instabilities, including square wave periodic pulsations, were found to take place due to the increased grain boundaries in highly-doped samples.

Experimental observations of dual-polarization oscillations in laser-diode-pumped wide-aperture thin-slice Nd:GdVO 4 lasers

Dual-polarization oscillations (DPO) on different transitions have been observed for the first time in a mirror-coated thin-slice Nd:GdVO(4) laser possessing a large fluorescence anisotropy with laser-diode (LD) pumping. Oscillation spectra, input-output characteristics, pump-dependent pattern formations and noise power spectra are studied experimentally. Simultaneous oscillations of orthogonally-polarized different (higher-order) transverse modes and the resultant violation of inherent antiphase dynamics in multimode lasers have been demonstrated. The experimental results have been explained in terms of the reduced three-dimensional cross-saturation of population inversions among orthogonally-polarized modes peculiar to LD-pumped wide-aperture anisotropic lasers, in which a pumped area is larger than a lasing beam diameter.