Showing papers on "Quantum well published in 1972"

The Use of Lasers in Pollution Monitoring

Abstract: 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.

Filaments as optical waveguides in gallium-arsenide lasers

Abstract: Experimental evidence is given in support of a dielectric-waveguide model for filaments in gallium-arsenide lasers. Measurements of the variation with current of the spectral-mode frequencies of a single-heterojunction gallium-arsenide laser have been carried out both below and above threshold. It is suggested that the frequency shifts above threshold are due to the formation of filaments in the laser. Changes in the far-field pattern support this theory.

Mode configurations in second-order mode-locked lasers

Abstract: An analysis of the mode frequencies and phases of lasers that are self-pulsing due to second-order mode locking is presented. It is shown that locking can occur with the modes arranged in several different configurations with different pulsing frequencies corresponding to the beat notes between different combinations of longitudinal modes. The experimental observations of the transition between two of these configurations in a self-pulsing GaAs junction laser is reported.

Double‐heterostructure GaAs : Si diode lasers

Abstract: 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%.

Photon loss and gain in CdS electron-beam-pumped lasers

Abstract: 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.