Peter G. Crowell

A simplified analytic model for gain saturation and power extraction in the flowing chemical oxygen-iodine laser

This paper describes the development of a simplified saturation model (SSM) for predicting power extraction from a chemical oxygen-iodine laser (COIL). Using the Fabry-Perot gain saturation assumption, analytic expressions for COIL extraction efficiency are presented for both constant-density and variable-density cavity conditions. The model treats mirror scattering, nonsaturable distributed losses, and diffractive losses from the mode-limiting aperture and is shown to be in excellent agreement with experimental COIL power extraction data. A comparison of the model with the Rigrod power extraction model is presented showing that the Rigrod model accurately predicts COIL extraction efficiency only in the limit that the COIL device no longer behaves as a transfer laser.

Experimental investigation of an optically pumped mid-infrared carbon monoxide laser

Results from a dual experimental/theoretical investigation of an optically pumped room-temperature carbon monoxide (CO) laser are discussed. Ro-vibrational transitions in the (2, 0) overtone of CO at 2.3 /spl mu/m were pumped with an optical parametric oscillator to generate lasing on (2, 1) band transitions near 4.7 /spl mu/m. During the build-up of the laser pulse, only rotational redistribution of the initial optically pumped population was observed in the resolved CO spectra. Calculations describing the CO laser pulse dynamics and collisional relaxation rates support this observation. The addition of helium and argon bath gases enhanced the rotational relaxation process. A pressure dependent loss mechanism that degrades optical efficiency has been identified and possible causes are discussed.

Demonstration of a repetitively pulsed magnetically gain-switched chemical oxygen iodine laser

Abstract Experimental results are presented for the power output of a gain-switched chemical oxygen iodine laser using a magnetic switch based on the Zeeman effect. Switching is achieved using rapid field nulling of a permanent de magnetic field. A peak-to-average power enhancement factor of 12.7 has been demonstrated at a rep rate of 500 Hz. Numerical and analytic models are developed to calculate the output spike and are compared with experimental results.

630-W average-power Q-switched chemical oxygen iodine laser

The Zeeman effect is used here to demonstrate a gas-phase, self-healing Q-switch for a kwatt-class chemical oxygen-iodine laser. Enhancement ratios of pulse power over CW power of 16 to 1 are achieved with extraction efficiencies of 75 percent. The flows of each type of chemical are presented, and the laser configurations are shown.

Tunable diode laser gain measurements on the HF(2-0) overtone transistions in a small-scale HF laser

A tunable diode laser was used to probe the overtone gain medium of a small-scale HF laser. Two-dimensional, spatially resolved small signal gain and temperature maps were generated for the P(3) ro-vibrational transition in the first HF overtone band.

The chemical oxygen iodine laser in the presence of a magnetic field. II. Frequency tuning behavior

For pt.I, see ibid., vol.29, no.3, p.933-43 (1993). Results are presented from an experimental/theoretical investigation of the frequency shifting and tuning behavior of a chemical oxygen-iodine laser in the presence of an applied magnetic field. Frequency shifting measurements are presented for both P and S polarization over a range of magnetic field strength from 0 to 3000 G, in a pressure regime (3 torr) where the line shape is Doppler broadened. Theoretical predictions of the location and magnitude of the frequency shifts are shown to be in good agreement with both the present measurements and a previous investigation in the pressure broadened regime. >

Comparison of subsonic and supersonic mixing mechanisms for the chemical oxygen-iodine laser (COIL) using computational fluid dynamic (CFD) simulations

Simulation of chemical lasers such as the chemical oxygen-iodine laser (COIL) laser is of timely interest due to ongoing commercial and military development programs. Accurate models of the gas dynamics and chemistry within a COIL have been developed using Computational Fluid Dynamics (CFD) codes, matching data from experiments designed to probe these physics. This work details the use of these codes to investigate the supersonic injection of molecular I2 and atomic I into the supersonic region of the O2(1?) flow in the COIL, and compare these results with a simulation of sonic injection of I2 into the subsonic region of the O2(1?) flow. The performance of each of these injection mechanisms is characterized by the theoretical power extracted from a Fabry-Perot resonator model, which then serves as the primary basis for comparison. Additional quantities such as power available and chemical efficiency are used to compare and contrast the performance of each concept. Based on these comparisons, the supersonic-supersonic injection methods demonstrate a performance increase over the traditional subsonic methods, with supersonic injection of I atoms providing the greatest performance increase.

Chemical oxygen-iodine laser (COIL) beam quality predictions using 3D Navier-Stokes (MINT) and wave optics (OCELOT) codes

This paper describes a series of analyses using the 3-d MINT Navier-Stokes and OCELOT wave optics codes to calculate beam quality in a COIL laser cavity. To make this analysis tractable, the problem was broken into two contributions to the medium quality; that associated with microscale disturbances primarily from the transverse iodine injectors, and that associated with the macroscale including boundary layers and shock-like effects. Results for both microscale and macroscale medium quality are presented for the baseline layer operating point in terms of single pass wavefront error. These results show that the microscale optical path difference effects are 1D in nature and of low spatial order. The COIL medium quality is shown to be dominated by macroscale effects; primarily pressure waves generated from flow/boundary layer interactions on the cavity shrouds.

Tunable diode laser gain measurements of the HF(2-0) overtone transitions in a small-scale HF laser

A tunable diode laser was used to probe the overtone gain medium of a small-scale HF laser. 2D, spatially resolved small signal gain and temperature maps were generated for the P(3) ro-vibrational transition in the first HF overtone band.

Frequency-tunable optically pumped carbon monoxide laser

Single-line frequency-tunable lasing was observed in an optically pumped, repetitively pulsed, room-temperature CO laser for the first time. The R(0) and R(7) ro-vibrational transitions in the (2,0) overtone of CO at 2.3 /spl mu/m were optically pumped with a high-energy optical parametric oscillator. Single-line lasing was observed on (2,1) P(2)-P(17) transitions and R(0)-R(11) transitions (covering wavelengths within the range 4.6-4.9 /spl mu/m) when using a diffraction grating as the spectrally selective reflector of the laser resonator. The observed CO laser pulse lengths were /spl sim/10/sup -7/ s with peak power up to 10/sup 4/ W. The influence of CO pressure, the addition of buffer gas (He, Ar), Q-factor of the laser resonator, and the pump pulse energy on CO laser pulse temporal characteristics and output energy spectral distribution was studied experimentally.