arXiv subjects

Seiichi Sudo

Publications and source records attributed to Seiichi Sudo.

5 recordsLinked to original sources

arXiv2025

Harmonics-assisted optical phase amplification with a self-mixing thin-slice Nd:GdVO4 laser operating in the self-induced skew cosh Gaussian mode

Harmonic-assisted phase amplification was achieved in a 300-micrometer-thick Nd:GdVO4 laser in the self-mixing interference scheme. The key event is the self-induced skew cosh Gaussian (e.g., skew-chG) mode oscillation in a thin-slice solid-state laser with wide-aperture laser-diode pumping. The skew-chG mode was proved to be formed by the phase-locking of nearly frequency-degenerate TEM00 and annular fields. The resultant modal-interference-induced gain modulation at the beat frequency between the two modal fields, which is far above the relaxation oscillation frequency, increased experimental self-mixing modulation bandwidth accordingly. Fifty-fold phase amplification was achieved in a strong optical feedback regime.

physics.optics↗

arXiv2023

Spiking ruby revisited: self-induced periodic spiking oscillations leading to chaotic state in a Cr:Al2O3 laser with cw 532-nm pumping

This paper reexamines a 60 year old mystery of spiking behavior in ruby lasers with a cw 532 nm pump, paying special attention to mode matching between the pump and lasing beam within a ruby crystal placed in a semi-confocal laser cavity. Periodic spiking oscillations were observed in a limited pump power regime, where spikes obeying the generic asymmetric hyperbolic function appeared at a repetition rate around 50 kHz and with a 130-150 ns width and 0.1-0.6 microjoule energy depending on the pump power. The physics of the spiking behavior based on Kleinman's mechanical approach and a plausible interpretation for the periodic spiking oscillation in terms of self-induced mode matching between the pump and laser beams through the self-induced Kerr-lens effect are addressed. The statistical nature inherent to spiking and the associated self-organized critical behavior in quasi-periodic spiking oscillations as well as chaotic states occurring outside the periodic spiking regime are also explored from a nonlinear dynamics point of view.

physics.optics↗

arXiv2022

Self-mixing interference in a thin-slice solid-state laser with few feedback photons per observation period

Formation of a peculiar lasing pattern leading to a TEM00-like mode accompanied by a nonzero bright outer-ring emission (namely, a modified TEM00 mode) was observed in a 300-μm-thick LiNdP4O12 (LNP) laser with reflective flat end mirrors that was pumped with a laser diode whose focused spot size was larger than the lasing beam spot size determined by the thermal lens effect. The photon lifetimes of the laser oscillations were found to be greatly shortened to τ_{p} = 6.74 ps as compared with those in pure TEM00 mode operation, while the fluorescence lifetime was τ= 130 μs. The formation of the peculiar transverse mode was theoretically treated in terms of the pump-intensity-dependent thermal lens effect, which yields the lasing beam spot sizes in the resultant optical cavity. In addition, transverse spatial hole burning of population inversions due to the preceding transverse eigenmode intensity and the associated anti-guidance of the pure TEM00 field leading to formation of the TEM00 with an emergent outer ring emission was shown to appear with increasing pump power through the electric lens (i.e., population lens) effect, in which almost all of the population inversion contributes to lasing with a pronounced effective modal gain. Self-mixing laser Doppler velocimetry (LDV) experiments and numerical simulations revealed that spontaneous emission factors in the peculiar mode oscillations were greatly decreased in comparison with those in pure TEM00 mode operation. The present thin-slice solid-state laser possessing a large fluorescence-to-photon lifetime and decreased spontaneous emission factor enabled us to detect LDV signals in the regime of few feedback photons per observation period.

physics.optics↗

arXiv2021

Nonlinear dynamics of a self-mixing thin-slice solid-state laser subjected to Doppler shifted optical feedback

Chaotic oscillations of a linearly polarized single longitudinal-mode thin-slice Nd:GdVO4 laser placed in a self-mixing laser Doppler velocity scheme were dynamic characterized in terms the intensity probability distribution, joint time-frequency analysis and short-term Fourier transformation of temporal evolutions, and the degree of disorder in the amplitude and phase of the long-term temporal evolutions. The transition from chaotic relaxation oscillations (RO) to chaotic spiking oscillations (SO) was explored via the chaotic itinerancy (CI) regime by increasing the feedback ratio toward the laser from a rotating scattering object. The intensity probability distribution was found to change from an exponential decay in the RO regime to an inverse power law in the SO regime, which manifests itself in self-organized critical behavior, while stochastic subharmonic frequency locking among the two periodicities of RO and SO takes place in the CI regime featuring quantum-noise (spontaneous emission)-induced order in the amplitude and phase of the spiking oscillations. All of the experimental results were reproduced by numerical simulations of a model equation of a single-mode self-mixing solid-state laser subjected to Doppler-shifted optical feedback from a rotating scattering object.

physics.optics↗

arXiv2008

Brownian Motion Captured with a Self-Mixing Laser

We measured the overall motion of Brownian particles suspended in water by a self-mixing thin-slice solid-state laser with extreme optical sensitivity. From the demodulated signal of laser intensity fluctuations through self-mixing modulations by the interference between the lasing field and Doppler-shifted scattered fields from Brownian particles, it was found that the changes over time in random walks of small particles suspended in water result in different overall dynamics when the field of vision for particles seen by the laser beam (scale of the observation) is changed. At a small focal volume of the laser beam, in which the relevant diffusion broadening is observed, the overall motion which can be represented by the motion of a ''virtual'' single particle whose velocity obeys a double-peaked non-Gaussian distribution function. The fast motion of a virtual particle, featuring fractional Brownian motion, which leads to a pure random walk with increasing the observation time, has been characterized in terms of mean-square displacements of a virtual particle.

physics.optics↗