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Semiconductor lasers, first demonstrated in 1962, have spent a long time in development without finding many applications. (GaAl)As double heterostructure diode lasers with stripe structure have distinctive characteristics for cw operation with a pure mode, in addition to their compactness and ease of operation. Quick degradation of these lasers has been investigated and it was found that the degradation was caused by local crystalline defects produced by internal stresses and local weakness. Improvements based on the study have provided reliable lasers with an operating life of over several thousand hours. These new generation lasers will be useful for optical communications and other optical systems.

Photon loss coefficients in the active and passive regions of CdS electron-beam-pumped lasers were measured by a variable-length masking technique and found to be 140 and 230 cm-1, respectively. The results show there is little saturable absorption in Cd-rich CdS, and their marked difference from GaAs demonstrates that the absorption mechanisms are different in the two materials. A net gain of 45 cm-1was measured at an excitation of 8.2 kW/cm2using a nonresonant crystal configuration. This corresponds to an efficiency 700 times greater than that for optical excitation.

The factors responsible for the multimode emission of injection lasers are considered and a review is given of experimental investigations of this subject. Various methods of spatial and spectral selection of the oscillation modes are described, including particularly the use of external and composite resonators. The applications of single-mode injection lasers are discussed. It is reported that such lasers are used very widely in high-resolution infrared spectroscopy.

Quantum phase fluctuations in IR gas lasers, noting nearly Lorentzian power spectrum with bandwidth inversely proportional to output power

We present a quantum mechanical nonlinear treatment of the phase and amplitude flucutations of gas lasers, i.e. lasers with moving atoms, and of solid state lasers with an inhomogeneously broadened line. The atoms may possess an arbitrary number of levels. As in our preceding papers the noise due to the pump, incoherent decay, lattice vibrations or atomic collisions, as well as due to the thermal and zero point fluctuations of the cavity is completely taken into account.

The pulse modulation of DH-(GaAl)As lasers at a bit rate of 200 Mbits/s was examined. To reduce the variation of the lasing pulse peak and lasing delay time due to combinations of "1" and "0" bits, prepumping condition and the damped oscillation parameters are important. The spontaneous carrier life time of DH-(GaAl)As lasers was measured as 2-5 ns.

It is shown that the nonuniformity of excitation produced in circular cross-section solid-state lasers due to the focusing of pump power leads to a coupling of certain modes and reduction in their threshold of oscillation. These modes correspond in plane-wave representation to simple closed paths in the cavity. The off-axial radiation observed in the form of rings by Collins and Giordmaine and others is explained on the basis of the theory.

Time-resolved spectra of an internal Q -switching emission of electron-beam-excited GaAs lasers were measured. The spectra shifted to longer wavelengths at the rate of 5.63 A/ns at 85 K. Time-resolves spectra of a normal laser emission were also measured to be shifted to longer wavelengths at the rate of about 0.3 A/ns. This remarkable difference of the spectral shifts can be understood if the former shift is caused by the quasi-Fermi level in the conduction band and the latter shift is caused by thermal effects.

A review of p-n junction injection lasers is presented. The literature published up to November, 1963, is fairly completely covered as well as a number of preprints. Also, included in the end is a section covering "recent work."

A summory is presented of recent accomplishments and the state of the art of far-infrared (far-IR) molecular lasers. Problems of excitation, laser line assignments, relaxation, and absolute frequency measurements are discussed. Predictions of future far-IR developments are made.

Optical techniques have opened up new possibilities in air pollution monitoring because of their remote-sensing capability, very high specificity, and short observation time. Techniques involving the use of lasers include Raman scattering, emission either from resonantly excited or from hot gases, and resonant absorption. Unique advantages in these applications are provided by the recently developed tunable lasers, including organic dye lasers, parametric oscillators, spin-flip Raman lasers, and semiconductor lasers. The absorption technique which promises to have the widest range of application has been tested in the laboratory by using tunable diode lasers. High-resolution absorption spectra have been measured for SF6, NH3, and C2H4 at 10.6 ?m, SO2 at 8,6 ?m, CO at 4.7 ?m, and NO at 5.2 ?m, and the C2H4 (ethylene) content of automobile exhausts has been measured by means of a derivative technique. A sensitivity sufficient to detect one ppm of NH3 in air has been achieved in a 10-cm-long gas cell. The 50 to 100-kHz resolution achievable with diode lasers is about four orders of magnitude better than the resolution of conventional spectrometers and more than adequate to resolve Doppler broadened gas absorption lines which are on the order of 100 MHz wide.

A bibliography of commonly available literature concerning chemical laser devices is presented. The types of laser devices covered are restricted to the three major ones: 1) HF or DF lasers, 2) CO 2 chemical transfer lasers, and 3) CO lasers. These devices are also restricted to only those which have been shown to be vibrationally excited through chemical reactions. The bibliography contains 117 references and is intended to be complete as of June 1972. The references are also listed in tables along with pertinent information about the device obtained from that reference.

The conditions for bistable operation of CW GaAs junction lasers are developed in terms of the previously published double-acceptor trap theory. The experimental CW operation of such devices is shown to agree well with the theoretical results. In addition the fabrication of these bistable lasers is described and several pulsed experiments are reported that indicate a significant increase in the number of trapping centers in the vicinity of the junction.

Experimental data are presented for multijunction GaAs lasers made by vapor-phase epitaxial growth in the form of p-n-p-n-p-n structures. The overall thickness of the four inside layers was 5 microns for the multilayer material for which experimental data are given. The diodes made from this material exhibited current-controlled negative-resistance characteristics. The emitted output beams of the multilayer lasers were extremely narrow, with the beam diverging only 0.5 degree in the direction transverse to the junction planes. The corresponding near-field patterns for these lasers have, in addition to the expected bright laser regions, almost fifty lines spaced about 1 micron apart and almost equally bright. The current thresholds at 77°K for the multijunction lasers are three to four times higher than single-junction laser thresholds and the incremental output quantum efficiencies of these lasers were more than unity, 1.1.

We developed a method which allows comparisons of the wavelengths emitted by two lasers with an accuracy of about 6·10−6.

The vibrational level populations in CO 2 lasers with mixtures of CO 2 , N 2 , CO, and He have been calculated using a method developed previously in [1] and [2]. A number of transition probabilities between the vibrational levels due to molecular collisions, the dependences of the population inversion upon various laser parameters (such as the total and partial pressures of the gases, electron density, and tube radius), and the radial profile of the laser gain are calculated in this paper. The calculations show that the CO molecules formed in the discharge play a significant role in the laser. The results given in this paper and in [2] allow us to explain all the main characteristics of both the pumped and the sealed-off CO 2 lasers.

Due to the high dispersion near the band gap, normal mode locking cannot occur in usual semiconductor lasers. According to the Paoli-Ripper model the pulse properties of such lasers can be explained in terms of second-order mode locking. We present an analytical quantitative treatment of the Paoli-Ripper model and apply the results to the GaAs laser diode. A rather good agreement between theory and experiment is achieved.

Processes are described for producing InAs diode lasers by liquid phase epitaxy. Measurements have been made on these lasers of wavelength of emission, power output, internal and external quantum efficiency, near- and far-field patterns and delay between current pulse and radiation output. We conclude that the efficiency of the lasers is low due partly to `spotty' emission and partly to a low non-radiative lifetime.

The influence of electron energy on the characteristics of electron-beam-pumped GaAs lasers is studied experimentally. Increases in the electron energy lead to increases in output power and decreases in beam divergence. Above radiation-damage threshold, a degradation of the laser output with time is observed due to bulk defects created by the beam. These defects are partially self-annealing if radiation is stopped.

RECENT investigation of the light emitted by gallium arsenide lasers1–3 when current pulses of widths in the tens of nanoseconds range are passed through the p–n junction have led to the observation in this laboratory that a certain charge must flow into the junction before laser action commences. For a given amplitude of the current pulse, there is a corresponding pulse width which will just induce laser action, the laser action commencing on the falling edge of the pulse. The converse is also true. As pulse-width is decreased, the pulse-amplitude must be increased if laser action is to be achieved. Statements that the laser threshold current density under pulse conditions is x amp/cm2 therefore become meaningless unless the pulse widths at which the measurements were made are also stated. Long time constants have also been observed in the light pulse emitted from the forward biased p–n junction.

The differential external quantum efficiency η ext of Fabry-Perot-type GaAs injection lasers has been measured as a function of the mean reflectivity R . By evaporation of antireflective films, R has been varied between 0.25 and 0.06. The observed increase of η ext with decreasing R is interpreted in terms of a simple model. Values for the optical losses α, the gain factor β, and the internal quantum efficiency at 77°K are obtained for individual diodes.

Additional excitation mechanisms, apparently overlooked in [1], but previously reported to be responsible for the selective excitation of the Hg II 7p 2 P_{3/2} upper state of the 6150-A laser line in mercury-helium lasers, are referenced and discussed. It is pointed out that asymmetric charge transfer and Penning-type ionization reactions can also account for the selective excitation of the Hg II 7p 2 P_{3/2} state as well as direct electron impact excitation from the Hg I ground state.

Laser action was observed for the first time in several new chemical systems in which HF was produced following a pulsed electrical discharge. The use of transverse multiple discharges enabled high pulse energies and peak powers to be obtained. It was possible to correlate the energy measurements and the spectroscopic output with the exothermicity of the reaction F + RH = HF + R.

Dissolved oxygen was found to dramatically influence the intensity of flashlamp-pumped organic-dye lasers. The relative energy per laser pulse was measured for nine new and 19 previously reported dye solutions in equilibrium with partial pressures of oxygen ranging from 0 to 1 atmosphere.

Double‐heterostructure diode lasers with Si‐doped active regions have exhibited laser action within the wavelength range 9100–9500 A under pulsed room‐temperature conditions. Threshold current densities are typically 4 × 103−1.1 × 104 A/cm2, and total power conversion efficiencies are ∼ 1–3%.

Filamentary and other nonuniform emission characteristics have been observed from electron-beam-pumped dislocation-free GaAs lasers. X-ray topographs taken before and after bombardment showed relatively few dislocations present in the as-grown material and no dislocation introduced at the power levels used for electron-beam excitation.

Lasing characteristics of GaAs-Ga1-xAlxAs double-heterostructure distributed feedback diode lasers are investigated at 80-100 K under electrical pumping. The main subjects studied here are the spectrum and mode of the distributed feedback laser and its temperature characteristics. Single longitudinal mode oscillation is observed at wavelengths which are determined by the corrugation period. The temperature dependence of the wavelength is about 1/3 that of the cleaved Fabry-Perot laser made from the same wafer.

Mode-locked oscillation is a major bottleneck in the generation of short, high-power laser pulses, for application in laser fusion, communications, or radar. The objective has been to attain a comprehensive understanding of the mode locking of lasers with specific application to high-pressure CO2 TEA lasers. Toward this end work has proceeded along both theoretical and experimental lines. A new theoretical approach was developed, applicable to both active and passive mode locking. Experiments on high-pressure CO2 lasers are in progress to substantiate the theoretical predictions. Results are summarized.

Molecular association lasers are characterized by laser molecules having a repulsive ground state with stable excited states formed by association of the constituent atoms. These lasers have the potential for high power operation with high efficiency in the visible and shorter wavelength region. The recent achievement of a xenon molecular laser has demonstrated the feasibility of this class of lasers.

A new capillary structure for ion lasers has led to greatly improved operating reliability and lifetime. This paper traces the development of this structure from the original suggestion for a segmented metal capillary to its present form. The major goals of this development have been increased reliability and operating lifetime. Experimental results at various stages of development are presented to illustrate the effect of improvements in design. The result of this development, a high reliability, two-watt argon ion laser, is described and its operating characteristics compared to those of more conventional ion lasers.

The author derives, from first principles, an explicit result for the perpendicular conductivity of superlattice solar cells by means of the generalized Kubo-Greenwood formulas and the Green's function. The advantage of superlattice based solar cells, when compared to their bulk counterparts is that quantization of energy levels takes place within the quantum wells leading to enhancement of conductivity. These energy levels form minibands that allow the carriers to tunnel through the barriers. >

The topics of power and energy output from lasers are treated. Both three- and four-level lasers are considered in the pulsed and continuous modes of operation. The theoretical power and energy estimates are compared, when possible, with experimental data.

The report describes some of the advances in the design and performance of stable gas lasers. The construction and output characteristics of highly reproducible, stable, selectable single transition grating-controlled CO2 and CO lasers are described. Experiments on short-term stability, standing wave saturation resonances, pressure and power broadening, pressure shift and long-term stabilization of CO2 lasers are discussed.

In the realistic EuS/PbS/EuS quantum well system with strong material parameter contrasts in heteroboundaries (MPCH) a collective plasmon-phonon excitation spectrum for a weakly polar quasi-two-dimensional electron gas interacting with the longitudinal optical phonons is investigated. The calculations are carried out within the framework of the random-phase approximation by use of exactly calculated dielectric function of an electron gas. The analytical and numerical deviations from the results when MPCH is absent are established. The mode coupling due to MPCH for typical moderate low in-plane densities ( 3.5.1011 cm-2 ) is presented. It is shown, that in this realistic structure a low plasmon-like coupled mode is deeply suppressed and high phonon-like mode weakly depends from the transverse optical frequency due to the lead salt material features.© (1899) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We performed a low temperature photoluminescence study of ultra thin single Si/SiO/sub 2/ quantum wells. We observe a strong quantum confinement effect and a high increase in the internal quantum efficiency in the thinnest wells.

An infrared hot-electron transistor with a thin (300 AA) InGaAs base layer is constructed. The transistor structure increases the detectivity of a state-of-the art quantum well infrared photoconductor (QWIP) by a factor of two at 77 K, provides a photovoltage gain of 9.7 and a power gain of 3.2, reduces the noise equivalent temperature difference of a detector array by a factor of 36, and can be used for quasi-photovoltaic operation. Using the transistor structure as an analytical tool, the photoelectron transport properties of a QWIP can be extracted, based on which a quantitative theory for the photoconductive gain can be established. >

In the practical application of pulsed injection lasers it is necessary to distinguish between the power and energy spectra. Most workers never distinguish or identify spectra. When the terms are used, power and energy spectra have been used interchangeably with the resultant confusion. Due to the closer spacing between modes in gas and insulator-type lasers, this distinction is not nearly so important as it is for injection lasers.

The effect of interdiffusion on hydrogen-like donor impurity binding energy in a multiple quantum well structure composed of 9 wells and 8 barriers is investigated. The effect of external magnetic field along the growth direction is taken into account as well. The obtained results show that the simultaneous effect of interdiffusion and the external magnetic field give a great opportunity of purposeful manipulation of binding energy and the character of the diffusion effect on binding energy strongly depends on the position of impurity center.