Showing papers on "Laser published in 1982"

Injection locking properties of a semiconductor laser

Abstract: Injection locking properties of a semiconductor laser have been analyzed, taking into account the injected carrier density dependent refractive index in the active region. It has been found that this dependence significantly affects the injection locking properties, giving rise to a peculiar asymmetric tuning curve and dynamic instability. The instability originates from the intermode interaction via the modulation in the injected carrier density caused by intensity beat. The detuning dependence of the direct modulation response characteristics inside and outside of the locking range have also been examined.

Laser Deceleration of an Atomic Beam

Abstract: Deceleration and velocity bunching of Na atoms in an atomic beam have been observed. The deceleration, caused by absorption of counterpropagating resonant laser light, amounts to 40% of the initial thermal velocity, corresponding to about 15 000 absorptions. Atoms were kept in resonance with the laser by using a spatially varying magnetic field to provide a changing Zeeman shift to compensate for the changing Doppler shift as the atoms decelerated.

Direct frequency modulation in AlGaAs semiconductor lasers

Abstract: Direct frequency modulation characteristics in three different AlGaAs lasers-a channeled-substrate planar (CSP) laser, a buried-heterostructure (BH) laser, and a transverse-junction-stripe (TJS) laserare studied theoretically and experimentally. Experimental FM responses are measured by using the Fabry-Perot interferometer and birefringent optical filters in the 0-5.2 GHz modulation frequency region. Experimental FM response dependences on modulation frequency, dc bias level, and stripe structure are successfully explained by the theoretical analyses considering both the carrier density modulation effect and the temperature change effect. FM response in the low modulation frequency regin from 0 to 10 MHz, gradually decreasing with the modulation frequency, stems from the thermal effect. FM response in the high modulation frequency region from 10 MHz to 5.2 GHz is caused by the carrier effect. A flat FM response of several hundred MHz per 1 mA is observed in the CSP and TJS lasers, but a V-shaped FM response is obtained in the BH laser. Resonance peak due to relaxation oscillation and cutoff characteristics are observed in several gigahertz regions. Weak lateral mode confinement, strong vertical mode confinement, carrier injection outside the effective core region, and p-side down mounts are effective ways to achieve a flat and efficient FM response with a small spurious intensity modulation.

Growth of spontaneous periodic surface structures on solids during laser illumination

Abstract: Spontaneous periodic surface structures, or ripples, are frequently observed after illumination of metals, semiconductors, and dielectrics by intense laser pulses. We develop a theory which predicts the observed spacing, polarization, and growth properties of these ripples. In this model, one or several Fourier components of a random surface disturbance scatter light from the incident beam very nearly along the surface. The interference of this diffracted optical wave with the incident beam then gives rise to optical interference fringes which can reinforce the initial disturbance. Sinusoidal corrugations on either metallic or molten surfaces seem to provide strong positive feedback for ripple growth, whereas sinusoidal gratings in temperature, electron-hole density, or dielectric constant seem much less well correlated with observations.

Laser Induced Periodic Surface Structure

Abstract: Laser induced periodic surface structure can be understood as a universal phenomenon which occurs when high intensity pulses are absorbed near the surface of solids or liquids. The phenomenon occurs on metals, semiconductors and insulators because of the interference between the incident pulse and an induced “radiation remnant”. This scattered field may be enhanced by the existence of true surface modes such as surface plasmons or phonon-polaritons but this is not essential. The universality characteristics include beam polarization, since we show that circularly polarized light can induce surface ripples, with the damage structure showing a dependence on the sense of rotation. We also present time resolved results of the formation of the ripples to illustrate the essential dynamical processes that occur.

Laser-induced thermal lens effect: a new theoretical model.

Abstract: A theoretical model for the laser-induced thermal lens effect in weakly absorbing media is derived. The model predicts the intensity variation in the far field of the laser beam in the presence of the lensing medium and takes into account the aberrant nature of the thermal lens. Some experimental results which support the validity of this approach are presented.

Laser-Induced Periodic Surface Structure on Solids: A Universal Phenomenon

Abstract: Laser-induced periodic structure on solid surfaces can be understood as a universal phenomenon which occurs for a broad range of wavelengths and different laser polarization states in both polariton-active and -inactive media. Circularly polarized light has been used, for the first time, to generate periodic structures; these show an interesting dependence on the sense of rotation.

Erbium glass lasers and their applications

Abstract: In this paper results of experimental investigations into erbium glass lasers and their likely applications are discussed. Regularities of the inversion energy accumulation, also as channels of energy losses, are covered in detail. Different erbium lasers, both flashtube and neodymium laser-pumped, are compared. Parameters of some erbium laser glasses are presented, including the new LGS-E7, which requires a smaller pumping energy density (less than 100–200 J cm-2). Test data from experimental models are summarized.

Effective deep ultraviolet photoetching of polymethyl methacrylate by an excimer laser

Abstract: Photoetching of polymethyl methacrylate (PMMA) for pulsed high power UV light is demonstrated. As a high power UV light source, a KrF excimer laser was used. Etching depth obtained by deep UV light irradiation has not only energy dependence, but also power dependence. It increased abruptly by increasing the exposed power density for the same exposed energy density.These experimental results show that high power excimer lasers are the effective light source for UV photoetching of PMMA.

Coherent oscillation by self‐induced gratings in the photorefractive crystal BaTiO3

Abstract: We report here the demonstration of several new optical oscillator configurations including a unidirectional ring oscillator and a self‐pumped phase conjugate mirror. The gain medium is BaTiO3, pumped by a 632.8‐nm He‐Ne laser at power levels down to 50 μW.

Monoion oscillator as potential ultimate laser frequency standard

Abstract: An individual atomic ion localized in the center of a small Paul RF quadrupole trap has potential as an ultimate laser frequency standard because the ion may be brought to `a state of complete rest in free space' by sideband cooling As a consequence, all Doppler shifts vanish, `Free Space' is approximated in so far as the electric trapping field vanishes in the center of the trap and there is no Stark effect Neither need there be a Zeeman effect as magnetic fields may be controlled down to the microgauss range There is also no transit time broadening Minute laser powers provided by harmonic generators suffice for saturation of optical transitions as strongly focused beams may be used A million-fold atomic amplification of the single-ion fluorescence from a metastable level may bring resolutions of 1 part in 1018 within reach

Infrared Vibrational Predissociation Spectroscopy of Water Clusters by the Crossed Laser-molecular Beam Technique

Abstract: Water clusters formed in a molecular beam are predissociated by tunable, pulsed, infrared radiation in the frequency range 2900–3750 cm−1. Absorption spectra of the clusters are obtained by detecting the recoiling fragments off‐axis from the molecular beam as a function of laser frequency using a rotatable mass spectrometer. By carefully adjusting the expansion conditions of the molecular beam and monitoring the largest cluster observable, excessive contamination by clusters larger than the specific one of interest is avoided. It is found that the spectra of clusters containing three or more water molecules absorb over the same frequency range as the liquid. Dynamical information on the predissociation process is obtained from the measured angular and velocity distributions of the fragments. An upper limit to the excited vibrational state lifetime of ∼1 μs is observed for the results reported here. The most probable dissociation process concentrates the available excess energy into the internal motions of...

Extracavity laser band-shape and bandwidth modification

Abstract: A technique for modifying the laser power spectrum by use of an acousto-optic modulator is described. The theory of the power spectrum resulting from frequency modulation by Gaussian noise is reviewed, and several examples of broadened laser power spectra are presented.

Two-dimensional imaging of OH laser-induced fluorescence in a flame.

Abstract: A method for obtaining a two-dimensional image of laser-induced fluorescence of a naturally occurring flame radical is described. A tunable laser beam is focused by a cylindrical lens into a sheet that passes through the flame, exciting OH lying within the plane defined by the laser. The fluorescence at right angles is imaged onto an intensified vidicon tube, forming a map of the ground-state OH concentration within the flame. For a sheet 0.5 mm thick, up to 2800 counts/mm2 of flame area are obtained on a single laser pulse for an OH concentration of 700 parts in 106. The method holds considerable promise for imaging in time-varying systems, such as reactive turbulent combustion.

Spectral characteristics of semiconductor lasers with optical feedback

Abstract: Optical feedback-induced changes in the output spectra of several GaAlAs lasers operating at 0.83 μm are described. The feedback radiation obtained from a mirror 60 cm away from the laser is controlled in intensity and phase. Spectral line narrowing or broadening is observed in each laser depending on the feedback conditions. Minimum linewidths observed with feedback are less than 100 kHz. Improved wavelength stability is also obtained with optical feedback resulting in 15 dB less phase noise. An analytical model for the three-mirror cavity is developed to explain these observations.

Atmospheric pressure monitoring of trace gases using tunable diode lasers

Abstract: High-sensitivity measurements of infrared absorptions due to isolated lines broadened by air at atmospheric pressure are reported. Tunable diode lasers and harmonic techniques were employed to detect absorptions as small as 0.01% over path lengths up to 250 m through the open air. The limiting noise source is caused by a base line signal which varies with the optical alignment. The reported sensitivity is not a fundamental limit. Techniques for further increasing sensitivity are discussed.

Quantitative measurements of laser-generated acoustic waveforms

Abstract: The generation of acoustic waves in metals by pulsed laser irradiation over a wide range of material conditions has been studied. Capacitance transducers have been used to obtain quantitative measurements of the amplitude of bulk acoustic waveforms where the laser beam was directed onto free metal surfaces in the presence and absence of surface plasmas, and onto modified metal surfaces. The application of acoustic wave propagation theory has allowed theoretical waveforms to be determined. By combining data for thermoelastic and normal force sources, waveforms have been produced that follow closely those measured experimentally.

Dynamics of Molecules in Condensed Phases: Picosecond Holographic Grating Experiments

Abstract: The development of laser equipment that can operate routinely in the subnanosecond (and more recently in the subpicosecond) time regimes has made possible the investigation of a wide variety of fast chemical, physical, and biophysical processes. Most of the successful picosecond time scale experiments, although very sophisticated in technique, have utilized the basic approaches that have been applied on slower time scales. One method involves monitoring time-resolved fluorescence following picosecond excitation (1-3). Since the time scale of interest is very short, techniques such as single photon counting, streak cameras, and fluorescence mixing have been employed to provide the necessary time resolution of the fluorescence. In many other experiments, the picosecond probe pulse technique has been used to examine changes in a systems absorption following picosecond optical excitation (4, 5). In this article I discuss a different approach to the application of subnanosecond laser pulses to the investigation of molecular and excited state dynamics. This involves the optical generation of a transient holographic diffraction grating in a sample, and the observation of various time and frequency dependent phenomena via subsequent Bragg diffraction from the induced grating. The basic experiment works in the manner illustrated in Figure 1. Two time coincident picosecond laser pulses of the same wavelength are crossed inside of the sample to set up an optical

Theoretical model of absorption of laser light by a plasma

Abstract: A simple model of laser light absorption is described. The absorption mechanism is mainly inverse bremsstrahlung, but a crude description of resonance absorption is also included. The intensity and the wavelength dependence are emphasized, but the model takes into account the target material composition, the laser pulse length, and the focal spot radius. Plane and spherical expansion are treated. Results range from short‐wavelength, low‐intensity regime, where inverse bremsstrahlung absorption is total, to long‐wavelength high‐intensity regime, where inverse bremsstrahlung absorption is negligible. Scaling laws concerning absorption, electron temperature, and electron kinetic pressure are given in the two limiting regimes. A characteristic flux Φ*, or, alternatively, a characteristic wavelength λ* is defined which separates the two regimes, the other parameters being held constant.

Surface ripples on silicon and gallium arsenide under picosecond laser illumination

Abstract: We report experimental results on spontaneous periodic surface structures or ripples which occur on the surface of crystalline or ion‐implanted semiconductors, using high‐power picosecond laser pulses. We suggest that these surface ripples develop as the result of an exponentially growing interaction between the incident laser wave front and a scattered surface optical wave.

Introduction to the Theory of Laser-Atom Interactions

Abstract: Basic Ideas. States in a Weak-Near-Resonant Field. More General States of an Atom in a Laser Field. Spontaneous Radiation by Atoms in Lasers. Deflection of Atoms in Laser Fields and External Fields. Potential Scattering of Charged Particles in a Laser Field. Multiphoton Ionization. Electron-Atom Scattering in a Laser Field. Atom-Atom Scattering in the Field of a Laser. Index.

All-fiber stimulated Brillouin ring laser with submilliwatt pump threshold.

Abstract: An all-fiber ring resonator, constructed from a single strand of single-mode optical fiber and a directional coupler, is shown to have a low threshold for stimulated Brillouin laser action. The 10-m-perimeter fiber ring resonator has a low round-trip loss of under 3.5% and an inherent pump-power enhancement of approximately 30. Lasing threshold for the 4.0-microm-core fiber occurred with a pump power of 0.56 mW at lambda = 6328 A and 1.74 mW at lambda = 5145 A.

Laser-induced local heating of multilayers

Abstract: For a multilayer structure illuminated by a laser beam, absorption of optical energy in the absorptive layers and the diffusion of the resultant heat throughout the structure are studied. Analytical and numerical procedures for this study are described, and, as a specific example, the profiles of temperature distribution during recording on a magnetooptical disk are presented. The technique is also expected to be of value for studies of thermal marking and laser annealing.

Chemical dynamics via molecular beam and laser techniques

Abstract: Based on the author's Hinshelwood Lectures at Oxford in 1980. ...a masterly overview of this field that will be useful to everyone from beginning student to expert.'___ Physics Today .

Stimulated Surface-Plasma-Wave Scattering and Growth of a Periodic Structure in Laser-Photodeposited Metal Films

Abstract: Ripple morphologies of submicrometer spatial period are observed on metal films grown by UV laser photolysis of adsorbed organometallic molecules. This structure develops from surface roughness by coupling of the incident UV field to a surface-plasma wave. The intensity variation due to interference between the incident laser field and the surface-plasma wave modulates the film growth rate which in turn enhances the scattering of the incident field into the surface-plasma wave; an exponentially growing instability results.

Observation of Ramsey Fringes Using a Stimulated, Resonance Raman Transition in a Sodium Atomic Beam

Abstract: Ramsey fringes have been observed using a stimulated, resonance Raman transition at 1772 MHz excited by two dye lasers in a sodium atomic beam. The width of the central fringe is 650 Hz (half width at half maximum), corresponding to a 30-cm interaction-region separation. The fringes are free from laser jitter because the jitters in both laser beams are correlated. Applications to frequency standards as well as to high-resolution spectroscopy in the microwave to far-ir regions are discussed.

The effective index method and its application to semiconductor lasers

Abstract: By the effective index method a two-dimensional field problem is transformed to a problem for a one-dimensional effective waveguide. This method is applied to semiconductor lasers having a gradual lateral variation in the complex permittivity. For the special case of a parabolic variation, analytical formulas for the required gain in the center and the half width of the intensity distribution are derived. The results are compared with a numerical method and very good agreement is found except in some cases where convergence problems occur for the numerical method. This agreement is taken as evidence for the validity of results obtained using the effective index method for analysis of semiconductor laser structures.

Longitudinal mode self‐stabilization in semiconductor lasers

Abstract: A general mechanism of self‐stabilization of longitudinal modes in semiconductor lasers is presented. The stabilization is due to the modulation of the inverted population by the beating of the fields of lasing and nonlasing modes, thereby modulating the rate of stimulated emission. This leads to two optical nonlinearities: one causing gain suppression of nonlasing modes and the other causing coupling of pairs of nonlasing modes that are equally separated from the laser line. The two nonlinearities nearly cancel, but their net effect is a weak suppression of the nonlasing modes and stabilization of the lasing mode. Buried optical guide lasers were stabilized in a single longitudinal mode for currents greater than 6mA above threshold. The mode intensity spectra of the lasers were measured over 5 decades and converted to gain spectra, which could be compared with the theory. The gain spectrum is parabolic at threshold. At 20 mA above threshold it remains continuous at the laser line but narrows and becomes structured. The structure is characterized by a dip in the gain and in the mode intensities occurring about 3 modes from the laser line. The laser line also causes a pronounced dip in the gain spectra of the nonlasing first order transverse modes. All of these features can be approximately accounted for by the theory.