P.L. Kelley

Optimization of Q-switched lasers

The authors extend the standard rate equation analysis to obtain expressions for the maximum peak power, maximum pulse energy, and minimum pulsewidth of a single Q-switched output pulse; the maximum power efficiency of a repetitively Q-switched laser; and the corresponding cavity output couplings. Results are obtained analytically and numerically, and a comparison of the two sets of results is made. As a first step in this process the authors derive general expressions for the peak power, pulsewidth, pulse energy, and power efficiency. The authors next differentiate these expressions in order to find the maxima or minima that optimize the parameter of interest. Differentiation is done with respect to the cavity output coupling. >

THERMALLY SELF‐INDUCED PHASE MODULATION OF LASER BEAMS

Self‐phase modulation of laser beams by media which possess a temperature‐dependent refractive index gives rise to far‐field aberrational rings. Steady‐state aberration profiles were measured and quantitative agreement with theory was obtained. A simple qualitative explanation of the ring structure is given. A self‐induced frequency modulation of 1.5‐W argon laser pulses was also observed and chirping detected.

Collisional narrowing of infrared water‐vapor transitions

Water‐vapor absorption lines in the ν2 band involving transitions between states of high rotational energy have been found to undergo substantial collisional narrowing in the presence of buffer gases. Measurements were carried out near 5.35 μm, using tunable lead sulfide selenide semiconductor diode lasers.

Tunable diode laser measurements of water vapour absorption line parameters

Tunable diode laser measurements of water vapour lines in the 5 μm region have been extended to include oxygen as well as nitrogen broadening. Positive pressure shifts of line positions have been observed for the first time in the v 2 band. Absolute calibration of a line position using the CO laser as a reference has also been carried out.

Tunable laser measurements of water vapor transitions in the vicinity of 5 μm

Abstract The present results confirm earlier tunable laser observations that the atmospheric widths of high rotational energy transitions are considerably narrower than previously predicted. Intensities, self-broadening coefficients, nitrogen and air shifts, and relative positions have also been measured.

TIME DEPENDENCE IN THE THERMAL BLOOMING OF LASER BEAMS

The time dependence of the thermal defocusing of a laser beam has been studied. Under certain conditions the beam is found to expand linearly with time, under others it expands with a time dependence approaching t1/2.

SELF‐TRAPPING IN MEDIA WITH SATURATION OF THE NONLINEAR INDEX

Numerical solutions of the nonlinear wave equation show that the steady‐state self‐trapping of optical beams in molecular fluids exhibits new characteristics when the intensity‐dependent index (orientational Kerr effect) begins to saturate. The power dependence of the beam diameter and the radial electric field distribution are examined. Beam diameters less than the wavelength of light are predicted for CS2 in the saturation regime.

TRANSIENT AND STEADY STATE THERMAL SELF‐FOCUSING

Self‐focusing of a cw argon laser beam due to absorptive heating in glass is reported here, with particular emphasis on the time dependence.

Highly selective excitation of atoms and molecules using two-photon processes

Abstract Two-photon processes in gases can be enhanced and selectivity increased by choosing the relative direction between the photons so as to minimize the effect of the Doppler shift. The techniques considered can be important in the employment of lasers for isotope separation. Estimates are made of the degree of narrowing and enhancement obtainable as well as of the power levels required.

SELF‐INDUCED THERMAL LENS EFFECT IN CCl4 IN THE PRESENCE OF BEAM MOTION

The effect of transverse beam motion on the thermal lens effect in a liquid is studied. The beam intensity is found to peak as a function of speed of motion and to fall considerably below the value expected from linear optics for very slow speeds.