Abstract: Mathieu-Gauss mode oscillations were observed in micro-grained isotropic Nd:YAG microchip ceramic lasers with azimuth laser diode pumping. The effect of fluorescence anisotropy thermal birefringence on these patter formations is discussed for several laser materials.
Abstract: We demonstrate vortex array-beam generations from a thin-slice, wide-aperture, solid-state laser with laser-diode end-pumping. Radial and rectangular vortex arrays were found to be formed in a controlled fashion with symmetric and asymmetric pump-beam profiles, respectively. Most of these vortices exhibited single-frequency oscillations arising from a spontaneous process of transverse mode locking of degenerate or nearly degenerate modes assisted by the laser nonlinearity. Single-frequency rectangular array beams consisting of a large number of vortices, e.g., closely packed 25, 36, or 46 vortex pixels, were generated, originating from Ince-Gaussian modes excited by the asymmetric pumping. (C) 2008 Optical Society of America
Abstract: We report successful real-time three-channel self-mixing laser-Doppler measurements with extreme optical sensitivity using a laser-diode-pumped thin-slice Nd:GdVO4 laser in the carrier-frequency-division-multiplexing scheme with three pairs of acoustic optical modulators (i.e., frequency shifters) and a three-channel FM-wave demodulation circuit. We demonstrate (1) simultaneous independent measurement of three different nanometer-vibrating targets, (2) simultaneous measurements of small particles in Brownian motion from three directions, and (3) identification of the velocity vector of small particles moving in water flowing in a small-diameter glass pipe. (C) 2009 Optical Society of America
Abstract: We present an analysis of the shoulder-shaped power spectrum observed in the modulated laser output due to feedback light scattered from dynamic changes in self-mobile phytoplankton with flagella in seawater performed using a self-mixing laser Doppler vibrometry system. The power spectrum occasionally has shoulder-shaped broad frequency components superimposed on a Lorentz-type spectrum. This reflects the translational motion of phytoplankton moving across the beam-focus area. The velocity of phytoplankton in the focus area can be obtained by applying a curve fitting procedure to the power spectrum. Moreover, the average velocity and the velocity distribution of phytoplankton can be determined from curve fitting of the long-term power spectrum. (C) 2009 Optical Society of America
Abstract: We have demonstrated self-mixing laser Doppler measurements using a laser-diode-pumped thin-slice Yb:Y3Al5O12 (Yb:YAG) ceramic laser whose optical sensitivity is two orders of magnitude higher than that of Nd-doped solid-state lasers, e.g., Nd:GdVO4. The pronounced optical sensitivity has been experimentally and theoretically shown to result from a longer fluorescence lifetime inherent in Yb atoms. The successful detection of nanometer-scale vibrations of a target embedded in large-amplitude environmental vibrations, which is desired in actual measurement circumstances, has been performed. (C) 2009 The Japan Society of Applied Physics DOI: 10.1143/JJAP.48.070212
Abstract: The overall dynamics of Brownian particles suspended in water were captured with high time resolution by using a self-mixing thin-slice solid-state laser. The net motion of an ensemble of many particles moving in the small imaging field observed at given time intervals was found to be represented by Brownian motions of an effective medium obeying the Ornstein-Uhlenbeck process, whose physical parameters have scaling relations with those of a real turbid medium. An approach toward measuring particle diffusion constants is described.
Abstract: An apparatus to achieve a single doughnut-like Laguerre-Gaussian (LG) mode with extremely high mode purity higher than 99.6% is reported. The proposed apparatus is a conceptual combination of a high-order HG mode selector and an astigmatic mode converter, which consists of only four simple and easily-made optical elements: three lens elements and one binary phase element. Theoretical simulations show that the apparatus has a good tolerance for both system production and alignment errors. With such high mode purity, the doughnut-like LG beam generated by the apparatus carrying an orbital angular momentum will be beneficial to numbers of studies including the trapping and rotating of micro and nano-particles, non-linear optics, and atom-light interaction. (C) 2007 Elsevier B.V. All rights reserved.
Abstract: We report selective excitations of higher-order Hermite-Gaussian and Ince-Gaussian (IG) modes in a laser-diode-pumped microchip solid-state laser and controlled generation of corresponding higher-order and multiple optical vortex beams of different shapes using an astigmatic mode converter (AMC). Simply changing the pump-beam diameter, shape, and lateral off-axis position of the tight pump beam focus on the laser crystal within a microchip semispherical cavity can produce the desired optical vortex beams in a well controlled manner. Pattern changes featuring different IG and HG modes obtained by rotating the AMC are also demonstrated. Numerical simulation shows that the vortex structure is changed by controlled off-axis laser diode pumping, which could lead toward precise optical manipulation of small particles. (C) 2008 Optical Society of America.
Abstract: Detailed polarization properties have been examined in laser-diode-pumped (LD-pumped) micro-grained ceramic Nd:YAG lasers in different microchip cavity configurations. Stable linearly-polarized single-frequency oscillations, whose polarization direction coincides with that of an LD pump light, were observed in an external cavity scheme. In the case of a thin-slice laser scheme with coated reflective ends, elliptically-polarized single-frequency operations took place in the low pump-power regime and dynamic modal instability appeared with increasing the pump power, featuring self-induced antiphase modulations among counter-rotating circularly-polarized modes having slightly different frequencies, with the total output being stabilized.
Abstract: This study demonstrates successive higher-order Hermite-Gaussian (HG(0,m)) mode operations in a microchip solid-state laser with a controlled off-axis laser diode (LD) pumping and generation of the corresponding doughnutlike laser beam of tunable ring diameter and orbital angular momentum, by experimentally focusing a Hermite-Gaussian mode (HGM) lasing beam into an astigmatic mode converter (AMC) with a mode-matching lens. Based on the successful generation of stable doughnutlike vortex beams by combining the LD off-axis pumping of microchip lasers and an AMC, this study proposes a design for a compact, solid doughnutlike vortex laser beam generator that combines three elements (i.e., laser cavity, mode-matching lens, and AMC) into one practical device. The desired doughnutlike vortex beam with different orbital angular momentum is easily generated by simply controlling the lateral off-axis pump position and pump beam shape on the laser crystal by numerical simulation. (c) 2008 Optical Society of America.
Abstract: This paper proposes a new scheme for generating vortex laser beams from a laser. The proposed system consists of a Dove prism embedded in an unbalanced Mach-Zehnder interferometer configuration. This configuration allows controlled construction of p x p vortex array beams from Ince-Gaussian modes, IG(p,p)(e) modes. An incident IG(p,p)(e) laser beam of variety order p can easily be generated from an end-pumped solidstate laser system with an off-axis pumping mechanism. This study simulates this type of vortex array laser beam generation, analytically derives the vortex positions of the resulting vortex array laser beams, and discusses beam propagation effects. The resulting vortex array laser beam can be applied to optical tweezers and atom traps in the form of two-dimensional arrays, or used to study the transfer of angular momentum to micro particles or atoms (Bose-Einstein condensate). (C) 2008 Optical Society of America
Abstract: We observed self-formation of looped random lasing paths in a laser-diode-pumped wide-aperture thin-slice solid-state laser with imperfect reflective end surfaces. Observed lasing patterns, resulting from random scatterers on the surfaces, showed transverse intensity distributions possessing exponential spatial autocorrelation functions. It is shown that such a speckle type of lasing pattern formation takes place when the pump position is tuned such that the surface irregularity possesses an exponential autocorrelation function whose delay length is smaller than the lasing beam diameter.
Abstract: Dual-polarization oscillations (DPO) on different transitions have been observed for the first time in a mirror-coated thin-slice Nd:GdVO4 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. (c) 2007 Optical Society of America.
Abstract: We report on the experimental observations of chaos synchronizations among orthogonally polarized emissions in a dual-polarization laser. With a three-mode scheme with a single mode in one polarization and two modes in orthogonal polarizations, synchronization was achieved by the cross-saturation dynamics of population inversions when one of the dual-polarized emissions was subjected to external perturbations, i.e., self-mixing modulation or optical fiber feedback. In-phase synchronization or lag synchronization among orthogonally polarized emissions was achieved depending on the degree of cross saturation in the self-mixing modulation. Synchronization of random bursting was observed in the fiber feedback, in which two chaotic-spiking modes in one polarization with anticorrelated intensity variations synchronize the remaining mode in the orthogonal polarization cooperatively with their total intensity variation. Information sender-mediator-receiver relationships among modes, which represent the dynamical roles of individual modes for establishing the observed three types of collective synchronizations, were identified in terms of an information circulation analysis.
Abstract: The effect of average grain size on oscillation properties is studied in laser-diode-pumped miniature ceramic lasers. The inherent segregation of lasing patterns into local modes is found to be prevented in the case of ceramics with grains of micrometer size, resulting in linearly polarized TEM00 transverse-mode oscillations.
Abstract: 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-mu m red blood cells in a fluid flow were below 1 and 10 ppm, respectively, in the present self-mixing laser Doppler velocimeter system. (C) 2007 Optical Society of America
Abstract: This study proposes a three-lens configuration for generating a stable donutlike vortex laser beam with controlled Ince-Gaussian mode (IGM) operation in the model of laser-diode (LD)-pumped solid-state lasers. Simply controlling the lateral off-axis position of the pump beam's focus on the laser crystal can generate a desired donutlike vortex beam from the proposed simple and easily made three-lens configuration, a proposed astigmatic mode converter assembled into one body with a concave-convex laser cavity. (C) 2007 Optical Society of America.
Abstract: Detailed oscillation spectra and polarization properties have been examined in laser-diode-pumped (LD-pumped) microchip ceramic (i.e., polycrystalline) Nd:NAG 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.
Abstract: Various single-frequency Ince-Gaussian mode oscillations have been achieved in laser-diode-pumped microchip solid- state lasers, including LiNdP4O12 (LNP) and Nd: GdVO4, by adjusting the azimuthal symmetry of the short laser resonator. Ince-Gaussian modes formed by astigmatic pumping have been reproduced by numerical simulation.
Abstract: 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 LiNdP4O12 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. (c) 2006 Optical Society of America.
Abstract: 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.
Abstract: 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.
Abstract: We observed self-formations of multiple lasing channels and two-dimensional lasing patterns consisting of composite local modes having different lasing frequencies in a laser-diode-pumped wide-aperture thin-slice solid-state laser with imperfect reflective end surfaces. Global patterns resembling higher-order Hermite-Gaussian modes or possessing N-fold rotational symmetries were experimentally shown to appear due to the standard polished surface roughness of closely spaced reflective ends and nonlinear modal interactions.
Abstract: We studied the dynamic behavior of laser-diode-pumped nonidentical thin-slice solid-state lasers, coupled face to face, with orthogonally polarized emissions. When such an incoherent mutual optical coupling was introduced, the coupled lasers exhibited slow fluctuations of transverse-mode patterns, and isolated lasers exhibited stable transverse-mode patterns. When one laser exhibited nonorthogonal multi-transverse-mode operations without coupling, simultaneous random bursts of chaotic relaxation oscillations took place in both lasers over time with coupling. A plausible physical interpretation is proposed in terms of the simultaneous excitation of chaotic relaxation oscillations in both lasers through resonances that stem from interference-induced modulation of one laser at a swept beat frequency of the fluctuating nonorthogonal mode pair. Observed instabilities were well reproduced by numerical simulation of the model equation. (C) 2005 Optical Society of America.
Abstract: 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.
Abstract: We demonstrate real-time two-channel self-mixing laser-Doppler measurement with extreme optical sensitivity using a laser-diode-pumped thin-slice LiNdP4O12 laser. Successful carrier-frequency-division-multiplexed two-channel operations are realized by using one laser, two sets of optical frequency shifters, and a two-channel frequency-modulated-wave demodulation circuit. Simultaneous independent measurements of vibrations of speakers and averaged motions of small Brownian particles in different scattering cells are demonstrated. Self-mixing photon correlation spectroscopy of particle size distributions is also discussed. (c) 2005 Optical Society of America.
Abstract: We found an abrupt transverse-mode transition from an irregular to a Gaussian lasing pattern or billiard-like lasing patterns with increasing the pump power in a laser-diode-pumped thin-slice Nd:GdVO4 laser with coated dielectric mirrors on both ends. A variety of irregular stationary lasing patterns were observed with a slight change in the pump position due to polished crystal surface roughness and ineffective lasing field confinement in transverse directions. A physical interpretation for observed irregular patterns was given in terms of wave formations in gradient refractive index lens with undulated reflective end surfaces. Intensity modulation of the laser, resulting from the interference of non-orthogonal transverse mode pairs embedded in the irregular lasing patterns, and associated rich chaotic pulsations were demonstrated. Observed nonlinear dynamics were well reproduced by numerical simulation. (c) 2005 Optical Society of America.
Abstract: We investigated self-induced pulsations in a globally-coupled microchip multimode solid-state laser operating on a Lambda transition. A variety of dynamic states, featuring locking of pulsation frequencies, multidimensional quasiperiodic, and chaotic pulsations, induced by nonlinear modal interactions were observed depending on the number of oscillating modes. The underlying modal interplay was characterized in terms of the dynamic statistical quantity of information circulations. Mode grouping and information sender-receiver-mediator relationships established among mode groups, i.e., "information networks," were identified. Observed dynamic states were reproduced by numerical simulation of a model equation and each dynamic state was shown to create its own information network.
Abstract: This work reports on a beam quality and dynamic behaviors of a mirror-coated highly-doped YAG (Y3Al5O12) 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. (C) 2004 Optical Society of America.
Abstract: We investigated chaotic dynamics in a microchip three-mode solid-state laser subjected to frequency-shifted optical feedback: When the frequency shift was tuned to harmonic frequencies of the relaxation oscillation, a bifurcation from a periodic sustained relaxation oscillation ("soft-mode") state to a chaotic spiking ("hard-mode") state via a chaotic itinerancy was observed as the feedback intensity was increased. Dynamic characterizations of modal interplay and self-induced switching between the soft- and hard-mode chaotic states over times (i.e., chaotic itinerancy) were carried out by the information circulation analysis and joint time-frequency analysis of long-term experimental time series., Drastic changes in information transfer rates among oscillating modes and occasional frequency locking among periodicities of two chaotic states associated with switchings were identified in chaotic itinerancy. Essential dynamical behaviors were reproduced by numerical simulation.
Abstract: This tutorial presents a detailed description of experiments, simulations, and characterizations of chaos synchronization phenomena in the model of a mutually coupled microchip solid-state laser array subjected to self-mixing feedback modulation. We demonstrate a transition to synchronized chaos by the method of 'phase squeezing' with increasing field overlap between the two lasers. This phenomenon is well reproduced by numerical simulation of model equations. It is also shown that low energy variation as well as high disorder are concurrently established in synchronized chaos in the present system. The deterministic random switching (i.e., chaotic itinerancy) among phase-squeezed states and synchronized chaos states is numerically demonstrated in a transition region from a phase-squeezed state to a synchronized state. We characterize observed behaviours; using such methods as singular value deposition (SVD), joint time-frequency analysis (JTFA) introducing a similarity function, and coarse-grained information transfer rate (CITR) analysis of long-term experimental or numerical time series, and discuss the physical significance of observed nonlinear dynamics in conjunction with chaos synchronization in mutually coupled lasers.
Abstract: Nanometre vibration measurement of an audio speaker and a highly sensitive sound reproduction experiment have been successfully demonstrated by a self-aligned optical feedback vibrometry technique using the self-mixing modulation effect in a laser-diode-pumped microchip solid-state laser. By applying nanometre vibrations to the speaker, which produced nearly inaudible music below 20 dB (200 muPa) sound pressure level, we could reproduce clear sound in real time by the use of a simple frequency modulated wave demodulation circuit with a -120 dB light-intensity feedback ratio.
Abstract: We studied the antiphase self-pulsation in a globally coupled three-mode laser operating in different optical spectrum configurations. We observed locking of modal pulsation frequencies, quasiperiodicity, clustering behaviors, and chaos, resulting from the nonlinear interaction among modes. The robustness of [p:q:r] three-frequency locking states and quasiperiodic oscillations against residual noise has been examined by using joint time-frequency analysis of long-term experimental time series. Two sharply antithetical types of switching behaviors among different dynamic states were observed during temporal evolutions; noise-driven switching and self-induced switching, which manifests itself in chaotic itinerancy. The modal interplay behind observed behaviors was studied by using the statistical dynamic quantity of the information circulation. Well-organized information flows among modes, which correspond to the number of degeneracies of modal pulsation frequencies, were found to be established in accordance with the inherent antiphase dynamics. Observed locking behaviors, quasiperiodic motions, and chaotic itinerancy were reproduced by numerical simulation of the model equations. (C) 2003 American Institute of Physics.
Abstract: Formation of complicated emission patterns consisting of many transverse modes and associated intensity pulsations at beat frequencies between some pairs of transverse eigenmodes in microchip solid-state lasers with laser-diode asymmetric end-pumping are reviewed. The dependence of billiard-like transverse patterns on pump power and crystal rotation (i.e. kaleidoscopic patterns) was demonstrated in a 0.3 mm thick thin-slice LiNdP4O12 laser with sheet-like end-pumping. Pump-power-dependent high-speed self-pulsations were observed. The asymmetric optical confinement resulted in the formation of transverse patterns which were totally different from normal Hermite-Gaussian resonator modes. The interference among pairs of non-orthogonal transverse eigenmode fields, whose energy levels exhibited avoided crossing with increasing pump power, was shown to result in high-speed intensity modulations. A good numerical reproduction of the observed high-speed modulations was obtained with model equations.
Abstract: We observed a highly efficient self-induced "oval hollow" mode operation in a Fabry-Perot microchip solid-state laser under strongly asymmetric "sheetlike" end-pumping. This new class of microresonator lasing mode features a hollow emission near-field pattern with a dark spot inside and a narrow unidirectional line-shape far-field pattern with a uniform intensity distribution.
Abstract: Relative intensity fluctuations in single-mode class B lasers, i.e., a laser diode (LD) and a microchip Nd:YVO4 solid-state laser (SSL), were examined. Experimental observations revealed significant difference in the characteristics of the LD and the SSL. A stochastic laser model and the Fokker-Planck equation approach were used, and reduced moment equations were developed, A close agreement was achieved between the theoretical and experimental results. As indicated by the theoretical analysis, the intrinsic parameter of the lasers; i.e., the time ratio between the lifetimes of the carrier density (population inversion) and the photons, is crucial to fluctuation dynamics. (C) 2002 Optical Society of America.
Abstract: Joint time-frequency analysis (JTFA) which expands signal in both time and frequency domain is widely used to study non-stationary time series. In this paper, a generalized JTFA is proposed to study the synchronization of chaos. A similarity function constructed from generalized time-frequency spectra was used to reveal phase portrait of synchronized chaos. This scheme is applied to analyze the experimental data sets of unsynchronized, phase-squeezed and synchronized chaos from a recent experiment with microchip solid-state laser array. When synchronized chaos established, a mirror symmetry appeared in the portrait together with power law distribution self-similar structure. Similar power law scaling is also found numerically for the Lorenz model.
Abstract: Stokes-like IR (1560-1600-nm) emissions, which have been observed in laser-diode- (LD-) pumped microchip Nd-doped lasers, are re-examined experimentally. Dependences of IR emissions on pump wavelengths, pump densities, and operating temperatures are studied. The response of IR emissions to coherent probe-beam injection is investigated by use of a tunable LD light source. Optical phonons emitted through Auger recombination processes that result from LD high-density pumping are proposed to induce resonant intracavity stimulated phonon-sideband emissions. (C) 2002 Optical Society of America.
Abstract: We applied laser-diode sheetlike end pumping to a multimode Nd:YVO4 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. (C) 2002 Optical Society of America.
Abstract: We examine higher-order photon statisitics of laser diodes (LDs) and microchip solid-state lasers (SSLs). When the lasers are operated above lasing threshold, significantly different features of fluctuations are exhibited, which are the result of the asymmetric non-Gaussian distribution characteristics that are always present in SSLs, whereas, in contrast, Gaussian fluctuation persists in LDs. It is found that the deterministic dynamic trajectory in phase space, which is controlled by the ratio between the fluorescence and the photon lifetimes, is crucial to the corresponding behavior of higher-order statistics. (C) 2002 Optical Society of America.
Abstract: 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. (C) 2002 Optical Society of America.
Abstract: 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.
Abstract: We observed complicated emission patterns consisting of different transverse modes and associated intensity pulsations at beat frequencies between pairs of transverse eigenmodes in a solid-state thin-slice Fabry-Perot laser with asymmetric end-pumping. The dependence of transverse patterns and pulsation frequencies on pump power has been demonstrated. The interference among nonorthogonal transverse eigenmodes, which are formed in a deformed Fabry-Perot microcavity possessing an asymmetric, gradient refractive-index potential for optical waves, is proposed for explaining observed instabilities. Intensity modulations have been remarkably reproduced by numerical simulations of model equations.
Abstract: A kind of chaotic oscillations featuring random switching between sustained relaxation oscillations (RO) and spiking oscillations (SO) has been demonstrated in lasers with frequency-shifted feedback. The presence of stochastic frequency locking between two periodicities of RO and SO motions and selective quantum-noise-induced ordering of chaotic spiking oscillations is demonstrated theoretically and experimentally.
Abstract: Self-induced pulsations that are associated with atomic interference have been found in a laser-diode-pumped LiNdP4O12 microchip laser with an intracavity KTP frequency-doubling crystal operating in a h 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. (C) 2001 Optical Society of America.
Abstract: 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, F-4(3/2)(2) --> I-4(11/2)(3) and F-4(3/2)(1) --> I-4(11/2)(2), 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. (C) 2001 Optical Society of America.
Abstract: A two-mode solid-state laser subjected to a delayed optical feedback is studied. Simultaneous random switchings between stable and chaotic antiphase spiking oscillations featuring the establishment of causal (drive response) relationships among modes have been demonstrated by a proposed information circulation analysis of an experimental time series. The observed phenomenon has been well reproduced by numerical simulations of two-mode laser equations with uncorrelated modal phase fluctuations.
Abstract: We report the instability behaviors of a single-mode microchip solid-state laser subjected to external feedback. Two kinds of instabilities, random chaotic burst generations and random sinusoidal burst generations, were observed experimentally in an LD-pumped microchip Nd:YVO4 single-mode solid-state laser with fiber feedback. These results are totally different form those observed in laser diodes with delay feedback systems, which have been widely studied in last decades. Main features were reproduced numerically by utilizing the Lang-Kobayashi equations with phase noise, indicating phase-noise-driven dynamic instabilities.
Abstract: This paper reviews our recent research on nonlinear dynamics of microchip solid-state lasers subjected to delayed optical feedback. Instabilities in two types of physical systems including multimode lasers with feedback and lasers with frequency-shifted feedback are discussed. Applications of microchip lasers with feedback to shot-noise-limited self-mixing optical sensing and imaging are summarized.
Abstract: Random chaotic burst generation was experimentally observed in a single-mode microchip Nd:YVO4 laser with fiber feedback. As the feedback strength was increased, a transition from stable relaxation oscillation state to unstable random chaotic burst state appeared. Furthermore, the non-stationary characteristic of probability association was experimentally identified at the transition of the two states while similar characteristics were reported only by numerical simulations of simple dynamical systems. This implies the general feature of non-stationary property of the dynamic switching between two states at transition. The observed chaotic burst generation and non-stationary nature were reproduced numerically based on the Lang-Kobayashi model.
Abstract: Synchronization of mutually coupled chaotic lasers has been demonstrated in a microchip LiNdP4O12 laser array with self-mixing feedback modulation. An abrupt transition to synchronized chaos by way of "phase squeezing" was observed when coupling between the two lasers was increased. This phenomenon is well reproduced by numerical calculations using model equations. It is also shown that low energy variation as well as high disorder are concurrently established in synchronized chaos.
Abstract: 1.5-mu m emissions from Nd:YAG, Nd:YVO4, and LiNdP4O12 microchip lasers pumped by laser diodes have been observed. These coherent emissions are attributed to the effect of high-energy modified lattice vibration owing to the existence of Nd ions as well as to stimulated intracavity Raman scattering enhanced by the microchip configuration. A four-wave mixing process involving two lasing fields and a Stokes field was identified as the generator of new adjacent 1.5-mu m emission. (C) 2000 Optical Society of America.
Abstract: We report on recent experimental results of the dynamics of a laser-diode-pumped free-running Nd:YVO4 laser operating in a two-mode regime. We observe intrinsic quasiperiodic and chaotic oscillations as well as a locking of pulsation frequencies. We perform an asymptotic analysis of model rate equations in which an intensity-dependent cross-gain (i.e., nonlinear gain) mechanism of direct mode-mode coupling is introduced in addition to the coupling mechanism via cross saturation of population inversions. We show that the intrinsic instability originates from the nonlinear gain mechanism. The observed locking of pulsation frequencies is successfully reproduced by simulations based on the proposed rate equations.
Abstract: A simple laser vibrometer system (LVS) has been built around a laser-diode-pumped microchip LiNdP4O12 (LNP) laser combined with an acousto-optic frequency shifter, using an efficient self-mixing modulation arising from the interference between a laser field and a weak field that is fed back from a rough vibrating target. The LVS provides a 50 dB carrier-to-noise ratio for 3kHz bandwidth, even when monitoring parts that have extremely low reflectivity. Application to laser-Doppler-velocimetry (LDV) capable of discriminating the direction in which different targets are moving has been demonstrated. A remote-sensing experiment by optical fiber access to the target is described briefly.
Abstract: A self-mixing laser Doppler velocimetry (LDV) has been demonstrated with laser-diode-pumped microcavity LiNdP4O12 lasers. The feedback signal required for a usable measurement without using photon-correlation techniques was <1 photon per Doppler-beat cycle. an enhancement of LDV signals by resonant excitations of relaxation oscillations has been performed.
Abstract: In a LiNdP4O12 microchip laser pumped by a diode laser, atomic interference arise due to the simultaneous oscillation on two transitions forming a Lambda configuration. For a microchip laser, the low-frequency coherence is an important dynamical variable. It is coupled to the low spatial frequency of the population inversion grating. This results in modal intensities which are self-pulsing while the total intensity remains nearly constant. In addition, the modal power spectra display combinations of the relaxation oscillation frequencies which are absent in the power spectrum of the total output power.
Abstract: Simultaneous single-frequency oscillations on different transitions have been observed experimentally in a laser-diode-pumped microchip LiNdP4O12 laser. The peculiar modal input-output characteristics and the antiphase relaxation oscillation dynamics have been reproduced theoretically using rate equations, including the strong spatial localization of population inversions, cross saturation, and resonant reabsorption loss in an unpumped region brought about by the inherent high Nd concentrations.
Abstract: Brillouin scattering has been measured with a high degree of sensitivity by a system built around a laser-diode-pumped microchip LiNdP4O12 laser. An efficient self-mixing modulation effect that is due to the interference between a lasing field and a weak field fed back from an acousto-optic modulator by means of a phase-conjugate reflection was used. Laser-Doppler velocimetry that can discriminate the direction of motion has been demonstrated. (C) 1999 Optical. Society of America. OCIS codes: 140.3480, 140.3580, 280.3340, 290.5830, 190.2640, 190.5040.
Abstract: Random chaotic relaxation oscillation burst generations have been observed in laser-diode-pumped microchip multimode lasers coupled to a single-mode optical fiber. Dynamical characterizations have been carried out by the singular value decomposition method and the joint time-frequency analysis, and the observed instability has been identified to be a random switching between stable and chaotic operation. [S1050-2947(99)50511-8].
Abstract: Efficient simultaneous intracavity second-harmonic and sum-frequency generation that is free from irregular large amplitude fluctuations (the so-called green problem) is achieved with a laser-diode-pumped LiNdP4O12 (LNP) laser with a type II phase-matching KTiODPO4 crystal. Observed frequency-mixing operations result from the simultaneous single-frequency oscillations can different transitions that arise from the wide fluorescence linewidth in a stoichiometric LNP laser that possesses inherently high Nd concentrations. Sum-frequency generation has been shown to arise from the interaction of oscillating longitudinal modes that belong to different transitions. A promising application to coherent terahertz-wave radiation by use of photomixers is proposed. (C) 1999 Optical Society of America.
Abstract: Self-induced Q-switching-type spiking oscillations and associated instabilities have been observed in a free-running laser-diode-pumped microchip Nd:YVO4 laser operating in three-mode regimes, and dynamical characterizations of spiking pulsations have been demonstrated. Observed instabilities have been reproduced by numerical simulations of the model equations including intensity-dependent cross-gain coupling in three-mode lasers.
Abstract: Input-output characteristics and multimode oscillation properties have been investigated in laser-diode-pumped microchip LiNdP4O12 lasers under different pump-beam focusing conditions, using microscope objective lenses with varying magnifications. The lasing threshold and slope efficiency, as well as the number of oscillating modes, are shown to depend on the pump-beam radius. The results are explained in terms of the pump-radius-dependent thermal lens effect and the Auger recombination process in high-density pumping regimes.
Abstract: The dynamics of relaxation oscillations has been investigated in a free-running laser-diode-pumped microchip multimode Nd:YVO4 laser. The locking of relaxation oscillation frequencies, and quasi-periodic and chaotic oscillations have been observed in two-mode regimes. The cross-gain coupling among modes is proposed to explain the observed instabilities.
Abstract: Simultaneous single-mode oscillations on different transitions were observed in a laser-diode-pumped microchip LiNdP4O12 laser. The unusual modal-output characteristics of the laser were reproduced by multitransition-oscillation laser model equations that include cross saturation of population inversions with a strong spatial exponential decay and transition-dependent resonant reabsorption loss. (C) 1998 Optical Society of America.
Abstract: Suppressing chaotic behavior by addition of a weak second periodic perturbation signal, which is nearly resonant to a subharmonic of the fundamental system frequency, is observed in a modulated microchip LiNdP4O12 multimode laser by a highly sensitive self-mixing modulation technique. The stabilization of the unstable period-2 orbit embedded in a chaotic attractor is demonstrated in a wide parameter region. The chaos-suppressing experiments are well reproduced by simulations of globally coupled modulated Tang-Statz-deMars [J. Appl. Phys. 34, 8289 (1963)] multimode laser equations, including a spatial hole-burning effect. (C) 1997 Optical Society of America.
Abstract: A nonlinear response of a laser-diode-pumped microchip LiNdP4O12 (LNP) multimode laser that is subjected to multiple-frequency modulations is investigated. Clustering and breathing motions featuring intermode parametric resonances are demonstrated when the LNP laser was modulated by rational frequencies chosen to be nearly resonant to multiple relaxation-oscillation frequencies inherent in multimode lasers, A simple correspondence between the modulation signal patterns and the total-output power-spectrum patterns is demonstrated. (C) 1997 Optical Society of America.
Abstract: Antiphase dynamics in globally coupled optical systems are investigated numerically in the model of intracavity second-harmonic generation in multimode lasers. Clustering, grouping of antiphase motions, and self-induced chaotic switching among a factorial number of coexisting grouping states, leading to antiphase periodic states, are found to occur when a pump parameter is increased. Dynamical characterization of grouping behavior and self-induced switching is carried out by global intensity circulation analysis. Nonreciprocal independence of intensity flow in grouping states and switching-path formation process among coexisting grouping states are presented. The controlled switching-path formation between different periodic grouping states by perturbation-pulse injections is demonstrated.
Abstract: We present an asymptotic study of a three-mode Fabry-Perot laser with arbitrary relative modal gains in the rate equation limit. Dynamical modes are defined as the eigenvectors of the stability or Jacobian matrix. The associated eigenvalues are the decay rates and the relaxation oscillation frequencies. We show that if the modal gains are not equal, the ratio of the relaxation oscillation frequencies may display rational ratios which will lead to resonances. We classify the various states of the modal field intensities as in-phase, partial and perfect antiphase and find universal relations between the peak heights in the power spectra of the total and of the modal intensities at each of the relaxation oscillation frequencies. Our theoretical results are confirmed by numerical computation using the full rate equations. Experimental results obtained for the noise spectrum of an LNP microchip laser fully support our theoretical results. We also conjecture some properties of lasers operating in an arbitrary N-mode regime.
Abstract: The effect of high-density pumping on lasing mode spectra is investigated in a laser-diode pumped microchip LiNdP4O12, (LNP) laser. Breakup of multimode oscillations, leading to single-mode oscillations, is observed experimentally. It is shown analytically that the enhanced Auger recombination process among excited Nd ion pairs results in a strong deformation of spatial hole-burning patterns, leading to a destabilization of the multimode laser output via a quadratic-to-quartic transition of the spatial distribution of population inversion. The destabilization threshold is shown to be given by a universal relation which reproduces experimental results quite well. A mode-partition instability is observed above the transition, whose properties are intimately related to the antiphase dynamics.
Abstract: We investigate the properties of power spectra of a two-mode laser and predict that universal relations among the peaks of the power and noise spectra for different modes but the same frequency hold for deterministic and stochastic perturbations. These results are confirmed experimentally.
Abstract: We propose a model for globally coupled lasers with intracavity second harmonic generation in which each laser gain is modulated separately. Suitable selection of the modulation phases can shift the resonance expected at the relaxation oscillation towards tower frequencies. This shift is accompanied by a reduction of the resonance width.
Abstract: Coexistence of periodic states with antiphase periodic states or with grouping states, which consist of qualitatively different motions, is predicted in the model of globally coupled modulated multimode lasers. It is shown that the injection seeding can switch the system from periodic states to antiphase periodic states or to grouping states, which are composed of a large-amplitude periodic (chaotic) antiphase spiking mode group and a small-amplitude periodic (chaotic) mode group. A switching process between different states is investigated and the inverse power-law relation for seeding assignment is demonstrated. A class of synchronized chaos, in which two modes exhibit a small-amplitude synchronized chaotic motion while other modes show a large-amplitude antiphase chaotic motion, is found in the grouping state. Characterization of grouping phenomena is provided by Lyapunov spectrum calculation, phase-space trajectories, return map, and circulation analysis. A grouping is found to occur so as to satisfy the self-organized vanishing-gain-circulation rule, which is the strong constraint which governs globally coupled multimode laser dynamics. Synchronized chaos is shown to take place being accompanied with the cooperative power flow from the antiphase chaotic merle group to the synchronized chaotic mode group.
Abstract: Highly sensitive laser Doppler velocimetry featuring the simultaneous measurement of light-scattering objects moving at different velocities and vibration sensing based on Doppler-shifted light-injection-induced intensity modulation in an externally pumped microchip solid-state laser is demonstrated.
Abstract: The underlying physical processes inherent in self-organized antiphase dynamics in multi-longitudinal-mode lasers are explored in terms of gain circulation, a new physical quantity. Transverse effects on antiphase dynamics in multi-longitudinal-mode lasers are investigated, and three-dimensional self-organization is shown to result from the cross-saturation dynamics in the longitudinal and transverse directions.
Abstract: The response of an N-mode solid-state laser when the output field is reinjected in the cavity after N frequency shifts is analyzed. The results obtained with up to four modes are described and it is tried to infer general rules. The emphasis is on comparing the dynamics of the partial and the total mode intensities.
Abstract: 2N-1 different periodic oscillations are obtained experimentally in a microchip N-mode laser by different combinations of modulations at multiple relaxation oscillation frequencies that appear on the basis of antiphase dynamics among lasing modes. Application of mode-dependent periodic oscillations to generation of dynamic spatial patterns is demonstrated using a shear plate interferometer.
Abstract: We analyze temporal variations in local Lyapunov exponents for chaotic spiking lasers in terms of standard deviation and Allan variance as a function of integral time tau. We show that standard deviations for local Lyapunov exponents become saturated in short tau regimes. The calculated Allan variance and power spectrum analysis suggest that the transition between stationary and nonstationary chaos takes place around the relaxation oscillation period of lasers, and that local Lyapunov exponents become nonstationary in time in the short tau regime.
Abstract: A minimal model for a laser with delayed feedback is analyzed. The model is motivated by two independent studies of a laser controlled by a fully optical feedback [Otsuka and Chem, Opt. Lett. 16, 1759 (1991)] and a laser with an optoelectronic feedback [Loiko and Samson, Opt. Commun. 93, 66 (1992)]. By reformulating the original laser equations in terms of dimensionless quantities, we obtain a simpler problem which is valid for both lasers. We then investigate the limit of small-amplitude feedback and small damping and determine a bifurcation equation for all periodic solutions. We analyze this condition in terms of increasing values of the delay time and show that each branch of solutions emerges from the basic state and becomes isolated as the delay time is progressively increased. The overlap of bifurcating and isolated branches of solutions explains the coexistence of nearly harmonic and pulsating solutions. Pulsating solutions may change stability through period-doubling bifurcation. We determine a simple approximation for this bifurcation point and study its validity numerically.
Abstract: We analyze a two-mode laser; described by rate equations, whose gain is periodically modulated. The nature of the response varies significantly with the modulation amplitude. We study both the small modulation in which the pump parameter remains always above the lasing threshold for the second mode, and the deep modulation in which the pump parameter is located during part of the,cycle between the single-mode and the two-mode thresholds. Apart from the strong McCumber nonlinear resonance at the relaxation oscillation frequency, we describe a rich variety of nonlinear properties such as multistability among periodic and quasi-periodic solutions, and small resonances in the vicinity of the second (and lower) internal frequency. We also identify domains that suggest the occurrence of the traditional routes to chaos.
Abstract: We derive a set of multimode rate equations which couple the complex fields to the mean number of amplifiers. We show that in the case of semiconductor lasers, phase-sensitive interactions must be retained. The resulting equations are studied and bifurcation diagrams are presented that display the steady, periodic, and quasiperiodic solutions.
Abstract: Antiphase periodic oscillatlons and clustering in a modulated microchip multimode solid-state laser have been demonstrated experimentally. Chaotic relaxation oscillations featuring intermode statistical non-independence that result from cross-saturation dynamics among oscillating modes have been observed.
Abstract: Transverse effects on antiphase dynamics in a multi-longitudinal-mode solid-state laser are investigated experimentally We show a three-dimensional self-organization resulting from the cross saturation dynamics in the longitudinal and transverse directions, in which the intensity noise spectrum of partial output within the beam cross-section possesses the antiphase relaxation oscillation components inherent in multi-longitudinal-mode lasers and the noise spectrum changes along transverse direction, while these antiphase components vanish completely for the entire beam. Modulation dynamics in a multi-transverse-mode laser featuring transverse synchronization and clustering is also demonstrated.
Abstract: The two-mode rate equations for a laser in a Fabry-Perot cavity are studied, taking into account the dynamics of spatial hole-burning. We prove analytically that each mode intensity has a transient behavior characterized by two damped oscillation frequencies, while the total intensity displays a domain where only the largest oscillation frequency remains; this domain appears to display antiphase dynamics. These results are generalized to N lasing modes. We then analyze the response of the two-mode laser to a periodic pump modulation. For small modulation depth, the two oscillation frequencies are clearly displayed as resonances on the response curve. For deeper modulation depth, the beating of the modulation frequency and the largest internal oscillation frequency produces a subharmonic sequence to chaos. This chaotic domain disappears in a crisis when it collides with the branch of stable periodic oscillations associated with the smaller oscillation frequency which coexists with the subharmonic cascade.
Abstract: We apply information theory to the study of chaotic itinerancy in a globally coupled multimode laser model. Structure changes are found in the self-information flow, corresponding to switching among destabilized clustered states. The inhomogeneity in the self-information flows among modes shows that different information transport structures are created by cluster switching in chaotic itinerancy.
Abstract: A novel method for producing high-speed picosecond optical pulses from semiconductor laser diodes that uses incoherent optical feedback is proposed. The incoherent optical feedback provides a successive pulselike modulation in carrier density and drives the system to a self-sustained pulsation state whose repetition rate is determined by relaxation oscillations.
