Jing-Yuan Ko

Real-time nanometer-vibration measurement with a self-mixing microchip solid-state laser.

Nanometer vibration analysis of a target has been demonstrated by a self-aligned optical feedback vibrometry technique that uses a laser-diode-pumped microchip solid-state laser. The laser output waveform, which was modulated through interference between a lasing field and an extremely weak (<- 100-dB) frequency-modulated (FM) feedback field, was analyzed by the Hilbert transformation to yield the vibration waveform of the target. Experimental signal characteristics have been reproduced by numerical simulations. Real-time vibration measurement has also been achieved with a simple FM demodulation circuit.

Instability in a laser-diode-pumped microchip Nd: YAG laser in a Pi scheme

Dynamical instability, chaotic pulsations, and generalized bistability have been observed in a laser-diode-pumped microchip Nd:YAG laser operating in a double transition scheme in which lasing occurs on two transitions with overlapping gain profiles, F3/242→I11/243 and F3/241→I11/242, and simultaneously involves excited Nd atoms from different sublevels of the upper manifold. The modeling of the experimental results requires rate equations that include cross-gain coupling among oscillating modes that belong to different transitions whose population inversion densities are determined by the Boltzmann distribution.

Collective chaos synchronization of pairs of modes in a chaotic three-mode laser

We study chaos synchronization experimentally in a modulated globally coupled three-mode laser with different modal gains subjected to self-mixing Doppler-shifted feedback, which can apply the loss modulation to individual modes at Doppler-shift frequencies. Depending on the pump power, different forms of collective chaos synchronizations were found to appear when the laser was modulated at the highest relaxation oscillation frequency, reflecting the change in cross-saturation coefficient among modes. In the present experiment, each pair of modes exhibited phase, lag, or generalized synchronization collectively according to the inherent antiphase dynamics, where these types of synchronization have already been demonstrated in two coupled chaotic oscillators in different physical systems. Information flows among oscillating modes which are established in different forms of collective chaos synchronizations were characterized by information-circulation analysis of the experimental time series. (c) 2002 American Institute of Physics.

Nonstationary chaotic oscillations in lasers with frequency-shifted feedback

The nonlinear dynamics of lasers with frequency-shifted delayed feedback are investigated. Resonant excitation of sustained relaxation oscillations by harmonic resonance is demonstrated. Self-induced switching between sustained relaxation oscillation and spiking oscillation is observed as the feedback coefficient is increased. Observed instabilities are well reproduced by numerical simulations of proposed model equations. A statistical analysis of this switching phenomenon is carried out numerically, and the results indicate that an inverse-power relation with the feedback coefficient determines the periods over which the system dwells in its relaxation-oscillation state.

Pulsations induced by quantum interference in a microchip solid-state laser operating on a Λ transiton

Self-induced pulsations that are associated with atomic interference have been found in a laser-diode-pumped LiNdP(4)O(12) microchip laser with an intracavity KTP frequency-doubling crystal operating in a ? scheme. The instability and peculiar pulsations that were observed have been verified by a linear stability analysis and numerical simulation of two-mode laser equations, including nonlinear absorptions of a purely quantum nature and spontaneous-emission noise.

Modal Interference and Dynamical Instability in a Solid‐State Slice Laser with Asymmetric End‐Pumping

We observed complicated emission patterns consisting of many transverse modes and associated intensity pulsations at beat frequencies between some pairs of transverse eigenmodes in a solid‐state thin slice laser with laser‐diode asymmetric end‐pumping. The dependence of transverse patterns on pump power and crystal rotation has been demonstrated. The pump‐power dependent pulsation frequency and the resonant excitation of chaotic oscillation have been observed. The interference among non‐orthogonal transverse eigenmode fields, which are formed in a thin‐slice Fabry‐Perot cavity possessing an asymmetric gradient potential for optical waves, is shown to result in intensity modulations.

Self-induced high-speed modulation in microchip solid-state lasers with asymmetric end pumping

We applied laser-diode sheetlike end pumping to a multimode Nd:YVO(4) laser and observed high-speed (>400-MHz) modulation of the intensity of chaotic pulsation near 1 MHz. The frequencies of modulation were the beat frequencies for pairs of closely spaced lasing modes. Asymmetric optical confinement and the resultant modal interference are shown to lead to oval-hollow-mode operation in which modal beat notes induce high-speed modulation, the frequency range of which is 2 orders of magnitude higher than the intrinsic relaxation oscillation frequency. Good numerical reproduction of the observed chaotic pulsations and their high-speed modulation was obtained with model equations in which such effects as nonlinear gain coupling among modes and field interference between pairs of modes were included. High-speed pulsations in nonchaotic lasers were also demonstrated.

Stationary collective fluctuation in Brownian motions of particles within the limited field of vision

We report on our successful real‐time measurement of the dynamic frequency‐shift of light by particles in Brownian motion through self‐mixing laser spectroscopy with extreme optical sensitivity. We show that the changes over time in the non‐stationary random walks of small particles suspended in water result in different averaged 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 averaged motion which can be represented by the motion of a “virtual” single particle, whose velocity possesses a Gaussian‐white property, constitutes stationary fluctuations, featuring random sequences of the Lorentz‐type spectrum and double‐peaked probability distribution function for displacements.

Collective Chaos Synchronization among Modes in a Chaotic Three‐Mode Laser

We observed three types of collective chaos synchronization featuring phase, generalized and lag synchronization among pairs of modes for different pumping conditions in a three‐mode solid‐state laser subjected to self‐mixing modulations. The direction of information flow among modes formed in different collective synchronizations was characterized by information circulation analysis of the experimental time series. The combined effect of self‐mixing modulations and coherent delayed optical feedback has been investigated experimentally and random switching between stable and collective synchronization states has been demonstrated.

Pulsations induced by quantum interference in a microchip solid-state laser operating on a /spl Lambda/-transition

Summary form only given. Quantum interference in a three-level atomic system with two fields operating in a /spl Lambda/ or V scheme has attracted much attention as a mechanism for the mediation of interactions between light and matter. Amplification and even laser-behavior without a population inversion can be produced by such a system. Kozyreff and Pandel have recently shown analytically and numerically that atomic interference in a microchip laser with a population inversion operating on a /spl Lambda/-transition should result in antiphase pulsations in the vicinity of the Hopf bifurcation point. The phenomenon has been observed in a LiNdP/sub 4/O/sub 12/ (LNP) laser operating on a /spl Lambda/-scheme consisting of /sup 4/F/sub 3/2/(1)/spl rarr//sup 4/I/sub 11/2/(2,3) transitions in a limited pump power region. This paper outlines our demonstration of peculiar large-amplitude periodic pulsations in an intracavity frequency-doubled microchip LNP laser operating on a /spl Lambda/-transition and contains a theoretical confirmation of the mechanism for these pulsations.