Output Intensity Distribution Research Articles

Stochastic-master-equation description of an optical bistability: A comparison with the microscopic theory

We consider a gas of homogeneously broadened two-level atoms in a Fabry-Perot cavity injected with a coherent resonant electric field. Adopting a macroscopic birth-death description, we construct a stochastic master equation for the output intensity distribution. From this starting point we find the steady-state distribution and show it to be bimodal in the region of the optical bistability. We compare our results for the mean and variance with the microscopic results of Bonifacio, Gronchi, and Lugiato as a test of the stochastic-master-equation approach.

Output power and intensity distribution of a transverse-flow CO2 laser

We have measured the intensity distribution of a transverse-flow CO2 laser along the flow direction and the dependence of its output power on the cavity width. The experiments were performed with a transverse-flow CO2:N2 laser chemically excited by the reaction of nitric oxide with atomic nitrogen. The intensity distribution is found to be of a multimode structure, fairly symmetrical about the optical axis. The overall output power for a given flow velocity and gas mixture is found to increase with increasing cavity width, up to a maximum value, and then it diminishes with any further increase of the cavity width. These results do not agree with those expected from a simple geometric-ray model. On the ohter hand, our results conform qualitatively with those expected from a coupled multimode approach. The main differences between the two approaches are discussed, and simple arguments are presented to illustrate the limitations of these two approaches.

Beam Characteristics of a Lidar System

The variations in four-beam characteristics of a high repetition rate, giant pulse, ruby laser Lidar system were investigated as functions of five controllable laser parameters. The beam characteristics investigated were divergence, intensity distribution, directivity, and consistency of output energy. The variations in the laser beam characteristics were monitored as functions of ruby rod temperature, ruby rod quality, pumping repetition rate, cavity loss, and pumping energy. The resulting requirements on the pumping repetition rate in order to obtain minimums in laser beam divergence and deviation in the laser output energy were mutually exclusive. The results indicate that a laser oscillator-amplifier system with automatically controllable cavity mirrors would give more consistency in output energy and intensity distribution than lasers presently used in Lidar systems.

Optical 3rd-order autocorrelator

The correlator is simply composed of a diffused light source, a slit, a condenser lens and three identical transparencies ƒ(x). Output intensity distribution Θ(τ 1, τ 2) is proportional to the 3rd-order autocorrelation function of ƒ(x); that is, Θ(τ 1, τ 2) ∝ lim T→∞ ( 1 2T ) ∫ −T T ƒ(x)ƒ(x+τ 1)ƒ(x+τ 2) dx . The square of the modulus of the bi-spectrum of ƒ(x) is also easily obtained from the output by a coherent optical system.

Method for laser-beam cleaning

A simple method for removing irregularities in laser output-intensity distributions caused by internal reflections in the output mirror is described. The design equations for a lens and iris combination are given, and experimental results for one type of laser are shown.

Interferometric Method of Measuring the Spectral Slit Width of Spectrometers*

The spectral slit width of a monochromator is defined as the half-intensity band width of frequencies passed by the exit slit. This paper discusses its measurement using methods similar to those used to measure the frequency transmission of electrical networks. A Fabry-Perot interferometer, used as a sinusoidal signal generator, produces interference fringes constantly spaced in wave numbers at a known amplitude input to the monochromator. It can be shown that the attenuation of the fringe pattern as the spacing is changed is a function of the exit-slit output-intensity distribution function. From this information the spectral slit width in any spectral region can be measured and the exit-slit function indicated.The sensitivity of measurement is limited by the fringe amplitude obtainable from the interferometer, which is a function of the reflectivity of the interferometer plates and their adjustment. Rays passing through the interferometer at other than normal incidence tend also to damp the fringe pattern.