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We performed the experiment of self-induced transparency in samarium atomic vapor under the condition of high temperature and high density. The sudden onset of the transmission, the maximum pulse delay and the pulse broadening were observed with π pulse. With this result we estimate the dipole moment of the transition line for 152Sm. The peak amplification, the pulse narrowing and the pulse breakup were observed when the pulse area was above 3π. These observations are strong evidences of self-induced transparency. Our result is the observation of self-induced transparency under the highest-temperature, highest-density condition and the first observation of this phenomenon in samarium vapor to our knowledge.

We design a high temperature oven for measuring the saturation intensity of the transition line $4f^ 6/6s^{2 7}7F_0 ↔ 4f^6/6s6p $^1$ P(J = 1)$ of the samarium atom. We first constructed a high temperature oven to generate the samarium vapor column and study the thermal characteristics of the oven. The oven is able to operate at a temperature up to about 1400 $^{\circ}C$ and the operation is tested by using several metals with high melting points. We describe two wave mixing experiment with the samarium vapor generated in the high temperature oven and obtain the saturation intensity by analyzing the first diffraction signal.

The two-photon absorption of a SiC photodiode was utilized to obtain autocorrelation signals of the pulses from a mode-locked Rh6G dye laser. The autocorrelation signals were in good agreement with those obtained by a conventional autocorrelator using a second harmonic crystal and photomultiplier tube. The sensitivity of the autocorrelator with the SiC photodiode was about $4{\times}10^3 {(mW)}^2$ . From these results it was demonstrated that the SiC photodiode is suitable as a nonlinear device for an autocorrelation measurement in the visible range.

The formation of spontaneous transverse optical patterns was investigated in a single feedback mirror system using nematic liquid crystals as nonlinear optical media. By varying the size of an input beam and the feedback distance, we obtained various interesting transverse optical patterns as well as the hexagonal pattern which are predicted theoretically assuming plane wave input. We can explain theoretically these characteristics of various pattern by introducing a ratio of the beam half width and spatial wavelength of the patterns. We have observed that as this ratio increased, the number of spot constituting the patterns also increased. Finally the patte군 evolved into the sucessive hexagon in the transverse plane.

We report on experimental investigations of nonlinear propagation of an array of first-order phase singularities with the same charges, which is lining up in a straight line, through a self-defocusing medium. The nonlinear rotation of the singularities depends on their density and is not uniform for each singularity pair. We discuss the non-uniform rotation considering singularity–singularity interaction.

The propagation properties of three-dimensional dark spatial solitons having odd ring formation is analyzed numerically in the frame of the (1 + 2)-dimensional nonlinear Schrodinger equation and compared with a pair of odd dark solitons. We discuss the experimental excitation condition of an odd ring dark soliton, which is superimposed on a finite-width background beam, with phase masks.

In the case of polarized light excitation, the atomic fluorescence which is affected by radiation trapping is partially polarized at the beginning. The time behavior for each polarization component of the fluorescence can be represented by a multiple scattering representation with the natural characteristic time of the sample. Some time after the excitation, the fluorescence is depolarized due to multiple scattering with random direction. In the collision dominant case, the collision makes the depolarization time shorter, which depends on the population transfer between the excited levels. We observed the time behavior of the polarization of fluorescence in an ytterbium-argon mixture and a short depolarization rate. We can interpret the time behavior by using a multiple scattering representation including the population transfer between the excited states due to the collision.

In a hybridly mode-locked continuous-wave dye laser with a Rh6G saturable gain and a 3,3′-diethyloxadicarbocyanine iodide saturable absorber, a pair of Brewster prisms were used to control the grou...

We present modulation of the vacuum field with a single mirror placed close to an unused port of a beam splitter. The electromagnetic field modes of the vacuum fluctuation near the mirror are modified with respect to those in free space, with their amplitudes having a sinusoidal spatial dependence upon the distance from the mirror. If we combine this spatially amplitude-modulated vacuum field mode and a coherent local oscillator with a beam splitter, we may obtain squeezed states of light in a homodyne detection scheme. We show that the amplitude fluctuation of the combined light can be reduced by a factor of\(\sqrt 2 \) below that of the coherent light and the fluctuations of the intensity difference of the two beams can be also reduced.

We have studied the fatigue effect in unhydrogenated amorphous carbon ( a -C) films prepared by d.c. magnetron sputtering of graphite. At 12 K the fatifued photoluminescence spectra show neither a spectral shape change nor peak shift during illumination. The fatigued photoluminescence intensity at a fixed energy shows a t − b time process during illumination. The self-recovery of the fatigued photoluminescence in the dark requires much more time than hydrogenated amorphous silicon ( a -Si : H) and less than amorphous phosphorus ( a -P). The light induced defects in a -C films are in metastable states and explained to be π defects rather than dangling bonds (σ defects) as in a -Si : H or hydrogenated amorphous carbon ( a -C : H).

The authors have measured the quantum mechanical noise of a coherent light source and the fluctuation of the vacuum field simultaneously, using a balanced homodyne detector with an effective time delay. Without the conventional coaxial delay line, they have achieved a time delay by shifting the digitized data stored in a personal computer. With this method, they have obtained noise power spectra from the light from a laser diode and an Ar+ laser, without any distortion, comparable to those obtained with a coaxial delay line.

We have investigated the photorefractive properties of a fully functional polymer, 9-(2-Ethyl-hexyl)-3-[2-(4-methanesulfonyl-phenyl)vinyl]-9H-carbazole, using a multiline He-Ne laser. We measured the wavelength-dependent two-beam coupling coefficient, which exhibited a maximal value of 105 cm-1 at 609 nm under an applied electric field of 84 V/µm at room temperature.

We perform Raman amplification in a high-pressure methane cell seeded by a low-threshold liquid Raman oscillator. The Raman frequency of the oscillator medium, dimethyl sulfoxide (DMSO), is tuned when it is mixed with water to fit the Raman frequency of methane. The Raman gain in this configuration is not so sensitive to the methane pressure, and the conversion efficiency is high. Using this configuration, we measure the polarization dependence of the Raman amplifier. An experiment is performed for three typical polarization states. Complete gain suppression is expected in some polarization states, but there is a little gain because of the incompleteness of the polarization state. Theoretically the results are analyzed when the x and the y components of the scattered waves are coupled.

We experimentally explored the enhanced Raman scattering in pyridine (C 5 H 5 N) due to the excitation of long range surface plasmons (LRSP's) guided by a symmetrically bounded silver slab in the Sarid-type ATR (attenuated total reflection) configuration. We have observed that, with decreasing the metallic thickness, the absolute enhancement of the Raman cross section increases while the width of the polar angular distribution of the signal decreases. This observed dependence of the enhanced Raman intensity on the thickness of the thin Ag slab and the collecting solid angle is well explained by assuming that the Raman scattering is mediated by LRSP's. The observed maximum enhancement factor is 4 × 10 6 for the 140 A silver slab which agrees well with the theoretically predicted value of 6 × 10 6 .

9-(2-Ethyl-hexyl)-3-[2-(4-methanesulfonyl-phenyl)vinyl]-9H-carbazole (EHCS) was synthesized as a monolithic photorefractive molecule forming low Tg(∼25 °C) organic glass. It showed distinct photoconductivity due to the carbazole moiety and the optical nonlinearity by the push–pull structure. The EHCS glass showed excellent optical quality and great stability as the ethylhexyl group effectively suppressed the crystallization in the films. Also, the extremely simple structure of EHCS contributed to a very high chromophore concentration. This single-component photorefractive glass of EHCS showed large net gain (56.3 cm−1) and diffraction efficiency (12%). Photorefractivity of EHCS glass was greatly improved by doping with a small amount (

Lasing images from two merging ink-doped ethanol droplets (size ~37 microm), which were generated by modulation techniques and pumped by nanosecond laser pulses, were photographed through a microscope. By measuring the size difference of two adjacent droplets from the spectral shifts of lasing peaks, we confirmed that mass transfer occurred in the breakup process of the liquid jet. We observed lasing images from merging droplets in a variety of patterns. Noteworthy among these is the lasing from snowman-shaped droplets that are conjectured to stem from coupled modes with orbits around both droplets.

Spatial and dynamical properties of optical phonons in AlxGa1−xAs alloys and GaAs/AlxGa1−xAs quantum wells are studied. An isotopically disordered harmonic crystal model is developed to study spatial properties of optical phonons in AlxGa1−xAs alloys. In the GaAs/AlxGa1−xAs system, transmission of the GaAs optical phonons through an AlxGa1−xAs barrier is studied using three-dimensional lattice dynamical model, fully accounting for the random arrangement of Ga and Al atoms in the alloy barrier. In the AlxGa1−xAs alloy, a localized-to-extended transition is found as a function of x. In GaAs/AlxGa1−xAs quantum wells, the transmission coefficient of the GaAs LO phonons through the alloy barrier remains significant below x < 0.3. These results are in good qualitative agreement with the experimentally deduced coherence length of LO phonons from nonequilibrium hot phonon populations.

Nowadays degenerate four wave mixing (DFWM) with forward geometry (FDFWM) has found increasing usage, for example, in the gas phase detection. In the fields of theoretical development of DFWM, most of the studies have been concentrated on the understanding of phase-conjugated DFWM. However, few theories have dealt with FDFWM. These models calculated the signal directly from the off-diagonal element of the density matrix by assuming optically thin medium. In the paper we obtain a theoretical model for FDFWM in Doppler broadened two-level absorbers including propagation effect and discuss the Doppler effect on the signal intensity and lineshape. Assuming that probe and signal field amplitudes are small compared with those of the pump fields and pump field amplitudes are constant in the interaction volume, we obtain the following coupled equations from the Maxwell equation using the slowly varying envelope approximation and the paraxial approximation.

In our experiment conical emission (CE) has no wavelength shift and the same polarization as the original beam. Varying laser power, detuning, and atomic density, the images of CE were captured and analyzed. Typical far-field images are presented. Under the blue detuning condition, manifest CE patterns were observed, and under red detuning, original beam blurs due to not only to self-defocusing but also the conical pattern were observed. By comparing laser power and atomic density dependence of cone angle and theoretical curve, we could estimate spectroscopic data such as nonlinear refractive index. From the density dependence data, we get the fact that cone angle is proportional to atomic density which supports the self-phase-modulation (SPM) model. In conclusion, we observed and analyzed CE from near-resonant Sm vapor. With this simple setup, we could measure spectroscopic data.

We demonstrate the generation of 798 lines, flat amplitude multi-wavelength Brillouin/Rayleigh comb by employing dispersion compensating fiber both for efficient Brillouin Stokes generation and high Raman amplification. Multi-wavelength output of 798 Brillouin Stokes lines with average channel power of -17 dBm has been obtained with excellent flatness.

We study localization of atomic position when a three-level atom interacts with a quantized standing-wave field in the Ramsey interferometer setup. Both the field quadrature amplitude and the atomic internal state are measured to obtain the atomic position information. It is found that this dual measurement scheme produces an interference pattern superimposed on a diffraction-like pattern in the atomic position distribution, where the former pattern originates from the state-selective measurement and the latter from the field measurement. The present scheme results in a better resolution in the position localization than the field-alone measurement schemes. We also discuss the measurement-correlated mechanical action of the standing-wave field on the atom in the light of Popper's test., 6.5 pages and 5 figures

We report observation of lasing in the scarred modes in an asymmetrically deformed microcavity made of liquid jet. The observed scarred modes correspond to morphology-dependent resonance of radial mode order 3 with their Q values in the range of 10^6. Emission directionality is also observed, corresponding to a hexagonal unstable periodic orbit., 4 pages, 6 figures

We investigate the effect of laser pulse shape on the forward degenerate four-wave mixing(DFWM) in two-level media. Saturation behavior of the DFWM signal generated with the square top and Gaussian pulses are analyzed.

Highly selective photoionization of the ytterbium atom by coherent two-photon excitation was demonstrated experimentally. The Yb atom was excited by two single-mode lasers and ionized by a time-delayed broadband laser. The isotope ratio of the ions was analyzed by a time-of-flight mass spectrometer. The ion yield and the selectivity were recorded as a function of detuning of the first exciting laser. The maximum of ion yield was observed when the laser was detuned from resonance. The selectivity of $^{168}\mathrm{Yb}$ was increased higher than 20 000 when the laser was blue-detuned to the most efficient position. Also, numerical analysis was performed to explain the experimental results. \textcopyright{} 1996 The American Physical Society.

We investigate the dynamics of a novel multiwavelength generator in which cascaded-stimulated Brillouin scattering and Rayleigh scattering are automatically balanced to given an evenly spaced (9.4-GHz), highly flattened (

We investigate the effects of the input laser beam’s temporal pulse shape on a forward degenerate four-wave mixing (FDFWM) signal, assuming two-level saturable absorbers. Under conditions in which the coherence time is far shorter than the pulse-duration, we can calculate the signal easily in the time and frequency domains. From this result it is shown that, when the pulse duration is longer than ten times the population relaxation time, the calculated signal intensity is almost the same as that obtained by assuming a steady state throughout duration of the laser pulse. With this assumption, we obtain the signal by summing all the steady-state signals at each time-domain grid point during the pulse. The calculation is performed with three input beam temporal pulse shapes: square, Gaussian, and typical Q-switched pulses. After reaching a maximum, the signal intensity decreases. The rates of the signal increase and decrease depend strongly on the temporal shape of the input beam. For the same average power, the square-pulse input saturates the absorber faster than the other pulses. These results indicate that the weak part of the pulse input plays an important role in generating the signal, yielding differences in saturation behavior of the signal intensity and the spectral line shape. We compare the calculations with experiments by fitting the saturation curve of the FDFWM signal of argon atoms in a radio frequency inductively coupled plasma. Also, the spectral line shape of the DFWM signal is fitted with the calculation by use of published experimental data.

We studied the conical emission in samarium (Sm) vapor under the near-resonant condition. The incident dye laser was tuned to the transition line, 4f66s2 7F→4f6(7F)6s6p(1P0)(λ=562.601 nm), of the Sm atom. Using a high-temperature oven, we could obtain the atomic density of 8×1014 atoms/cm3, large enough to observe the conical emission. We observed one to three rings around the original laser beam, and the number of the rings depended on the laser intensity, the laser wavelength, and the atomic density. These results are attributed to the self-phase modulation of the laser beam interacting with the near-resonant atomic medium. We give a simple expression that describes the dependence of the locations of the rings on the laser intensity. We compare the experimental results with this expression quantitatively and then estimate the nonlinear susceptibility of Sm vapor.

A GaAs based semiconductor saturable absorber mirror (SESAM) has been fabricated using molecular beam epitaxy and applied to a hybridly modelocked Rh6G dye laser. The generated pulse was as short as 56 fs at the centre wavelength of 580 nm, which shows the shortest centre wavelength in these kinds of dye laser.

A theoretical description for a forward degenerate four-wave mixing process in homogeneously broadened two-level absorbers with arbitrary intensities of all four beams is presented. Assuming no pump absorption and depletion, we obtain an analytical solution of forward degenerate four-wave mixing signal intensity in the limit of the strong pumps and weak probe and signal. In the case of low absorption or large detuning, this solution is shown to become equivalent to that of the phase-conjugate degenerate four-wave mixing derived by Abrams and Lind [Opt. Lett.2, 94 (1978)]. For arbitrary beam intensities and absorption parameters, the signal intensity is numerically calculated by solution of the coupled equations of complex wave amplitudes. Comparing the results of the numerical calculation with those of the analytical solution, we discuss the validity of using the analytical solution in practical experiments and show the saturation behavior that is due to the strong probe beam. The line shapes under the various ratios among the input beams and absorption parameters are also obtained and discussed.

The dynamic behavior in the angular distribution of emission was measured from an asymmetrically distorted liquid jet which was induced by laterally flowing gas. We observed that the intensity pattern was restricted to around φ∼90°, above 2% of the distortion parameter η. The fine structure of the intensity pattern was also restricted to φ∼90°, which is evidence of the directional emission of MDR (morphology-dependent resonance) lights. As η increases, the intensity profile narrows down to φ∼90° and then broadens at η≥5%. We found that a broad peak shifts continuously with a linear relationship to η, which should be related to the detailed shape of deformation. Broad split peaks were observed when the intensity of emission was substantially enhanced for efficient coupling, which is not expected from the ray-optics model for an ideal elliptical microcavity.

Spectral changes in fluorescence and lasing spectra were observed from a noncircularly deformed ink-doped ethanol jet, which was induced by a lateral gas flow. The distortion parameter was determined from the analysis of diffraction patterns to be as much as ~10%. Q -spoiling effects were clearly observed in the appearance of high- Q (~10(7)) modes in fluorescence and their disappearance in lasing. From the behavior of resonance modes, we concluded that the effective Q does not decrease so rapidly as predicted by the relation obtained from the ray-optics model. We also found that the signals leak out, with a wide angular spreading, mainly from near the boundary of the major axis, even for a large distortion parameter.

We present simple methods to produce optical vortices on the axis of beam propagation with nonspiral phase plates. We show that a phase plate that provides linear phase retardation on one half of a laser beam produces optical vortices, which is demonstrated experimentally by use of a thickness-varying glass platelet. We also demonstrate and explain that mixed dislocations of a bent edge dislocation transform into a pair of vortices with opposing topological charges.

Scattering patterns captured at two different directions from ink-doped ethanol droplets containing submicrometer-sized particles, which had been pumped by nanosecond pulses, were obtained simultaneously. By use of ray optics we interpreted the various scattering patterns of the lasing in droplets. The scattering image of one side and the spectral image of the opposite side were also detected simultaneously. We observed that particles scatter with similar output couplings among modes of the same order. We also found that a single particle could react to modes of different orders with different output couplings.

The spectral changes of stimulated Raman scattering (SRS) from a micrometer-sized sinusoidally modulated water jet (radius, ∼14.5µm) have been observed. The pumping pulses of a frequency-doubled Q-switched Nd:YAG laser were synchronized to the modulation wave on the water jet. Before conducting SRS experiments, we measured the modulation amplitudes of the water jet from the diffraction patterns. The spectral changes of SRS exhibited the peak's shifts, the narrowing down of the SRS spectral range, and the reduction of the SRS peak. From the estimation of the mode orders of the SRS peaks with the cylinder modes, we found that the cylinder modes are not sufficient to explain the observed SRS peaks at small modulation amplitude, which are thought to be caused by the appearance of new modes in the modulated jet. We have interpreted the spectral changes as the reduction of the effective quality factor in the modulated cylinder.

We discuss a few examples of cases in which the widely used mean-field approaches to alloys and alloy superlattices may not give complete solutions. These examples include the anomalously large Stokes and anti-Stokes real space-charge transfer over thick alloy barriers and the spatial extent of optical phonons in alloys and alloy superlattices, which have remained unsolved or controversial. We argue, both theoretically and experimentally, that approaches that fully account for inhomogeneities, partial ordering, and disorder effects in the alloys as well as the proper understanding of coupled quantum-mechanical systems do give answers to these important puzzles.

We report the dependence of Raman gain on the correlation between the pump and the Stokes waves in a broadband Raman amplifier. Experimentally, the Raman correlation function is obtained by measurement of the Stokes output energy as a function of pump delay. When the Stokes wave precedes the pump, the Stokes output is larger than in the opposite case. The correlation function becomes more asymmetric as the pump energy increases. We propose that this asymmetry is caused by the nonlinear Raman dispersion. Using a multimode model, we perform numerical simulations to confirm this idea. The results of the simulations agree well with the experimental data.

We obtain information about the amplitude fluctuations of both signal and idler beams from a doubly resonant optical parametric oscillator (DRO) without an optical isolator or a frequency stabilizer. To get a total noise power spectrum, we digitized the photocurrents of the cross-polarized twin beams from the DRO and calculated the noise spectra of the two beams from the digitized data; we also calculated the sum and the difference of the two beams. We fabricated a DRO with a KTiOPO4 (KTP) crystal pumped by a single-mode Ar+ laser (514.5 nm). The experimental results of the quantum-mechanical correlations of the twin beams are well fitted by a theoretical prediction [ J. Opt. Soc. Am. B4, 1520 ( 1987)].

We have produced amplitude-squeezed light whose noise is reduced by ~10 dB below the quantum noise limit in four different feedback systems. In our experimental method we have directly compared the noise power spectrum of the laser diode with the quantum noise limit in the low-frequency region, where the classical noise is stronger than the quantum noise. In addition to the well-known methods for extracting the out-loop beams from the feedback system by use of a 50:50 beam splitter, a polarizing beam splitter, or the leakage light from the rear side of a laser diode, we also have tried to use the spatial coherence of the laser light. We also have examined the vacuum fluctuations that prohibited the out-loop beam from being amplitude squeezed. In all these systems we have verified that the noise power spectrum for the in-loop beam is reduced below the quantum noise limit but not that for the out-loop beam; the difference arises mainly because vacuum fluctuations enter each system differently.

An optical bleaching effect in a BiI3 microcluster colloidal system in the visible region was observed. We find that this effect can be adequately explained by a two-level model with inhomogeneous broadening. By measuring the intensity dependence of the saturated absorption coefficient, we evaluated the third- and fifth-order effective nonlinear-optical susceptibilities of the BiI3 microcluster colloidal system to be approximately 10−10 and 10−15 esu, respectively. By applying the effective-medium approximation, we find that the third-order nonlinear-optical susceptibility of BiI3 microclusters is approximately 5 × 10−6 esu.

A multiple object-beam holography is proposed, where a two-dimensional rectangular amplitude grating and a phase plate of matrix form placed at the frequency plane of the grating constitute the main parts of a speckle-free periodic illumination system of continuous tone transparencies. Demonstration experiments are made, where the number of diffracted orders of the grating, the ratio of the widths of transparent and opaque zones of the grating, the retardation of each matrix zone of the phase plate and the distance between planes of the image of the grating and a transparency are taken as variables.

We demonstrate a novel laser structure which enables efficient utilization of the laser gain profile and recirculation of Brillouin shifted signals inside the cavity. Multi-wavelength operation of more than 53 Stokes lines has been obtained with excellent flatness and stability. Procedures for optimum operation conditions will be described.