Laser Induced Medium Perturbation Research Articles

Phase conjugation with CO 2 lasers

A TEA CO 2 laser was used for the investigation of four-wave mixing (4WM) processes in sulfur hexafluoride (SF 6), an organic solvent (toluene), and III/V semiconductor wafers (InSb, InAs). The relevant involved grating mechanisms were probed by the 4WM technique. It was found that the decay times of the corresponding built-up transient gratings in the various nonlinear media differ by approximately six orders of magnitude. Furthermore, simulations of a phase conjugates mirror (PCM) were carried out by solving the Kirchhoff-Fresnel integral equations by complex conjugating the spatial field distribution at the PCM. Applying this technique an efficient production of low divergence high energy CO 2 laser pulses generated from a 4WM master oscillator/power amplifier (MOPA) scheme was predictable. For the modelling a large volume e-beam controlled CO 2 amplifier was placed along the signal beam. The optical homogeneity of the laser gas was disturbed by shock waves and by the laser-induced medium perturbation (LIMP) effect. The disturbing influence of both effects on the optical quality of the output radiation will be shown.

Phase conjugation in long pulse CO 2 lasers

The laser induced medium perturbation (LIMP) effect for phase conjugation in CO 2 laser media is studied both experimentally and theoretically. The theory is developed to take account of acoustic wave propagation in the shorter term and thermal conductivity in the longer term. The experimental study demonstrates LIMP phase conjugation for the first time and that the reflectivity behaves substantially as predicted by the theory.

Laser-induced medium perturbation in a large CO2 laser

Laser-induced medium perturbation was investigated in a large ultraviolet-initiated CO2 laser using time-resolved interferometry and beam quality measurements. The beam quality was found to be severely degraded after about 3 μs, and analytical modeling was performed which predicts the onset time.

Chirp in pulsed, rf-excited CO2 waveguide lasers

An experimental investigation has been conducted to determine the frequency stability of a pulsed, rf-excited waveguide CO2 laser. Unlike transversely excited atmospheric CO2 lasers, for which the optical extraction of energy (laser-induced medium perturbation) is typically the dominant source of frequency instability, the driver in the long pulse (>30 μs) waveguide laser is the thermal heating of the gain medium due to the rf input energy. Modeling of the chirp in the pulsed waveguide laser is performed. Included are both finite V-T effects in the short term and heat conduction and particle migration out of the laser bore by the gaseous gain medium in the long term.

High Reflectivity Phase Conjugation at 10 μm

The laser-induced medium perturbation (LIMP) process is shown to be a very effective way of generating high reflectivity phase conjugate signals using four-wave mixing with a CO2 laser and amplifier.

Thermal defocusing (LIMP) in stable CO2 resonators

The effect on the output of an electron beam sustained CO2 laser due to LIMP (laser induced medium perturbation) is examined. An approximate theory is developed which leads to basic agreement with the experimental observations of beam spreading and temporal pulse structure.

A preliminary study of a retroreflective mirror resonator

The characteristics of the laser radiation emitted from a long pulse, electron beam sustained CO 2 laser employing a retroreflective mirror resonator have been studied. The minimum beam divergence is found to be determined by the retroreflective array imperfections. The effect of tilting both the output window and the array is studied and examination of the temporal behaviour of the laser output to determine both mode structure and the effect of the Laser Induced Medium Perturbation (LIMP) is reported for the first time.

LIMP in continuously coupled unstable resonators

The Laser Induced Medium Perturbation (LIMP) effect is shown to be a volumetric effect which plays a significant role in the beam quality obtainable from a CO2 laser employing a continuously coupled unstable resonator.

Laser induced medium perturbation in a pulsed CO 2 laser

Laser induced medium perturbation (LIMP) has been identified by time-resolved interferometry observations of the lasing/non-lasing boundaries in a pulsed, kilojoule CO 2 electron beam laser, working at atmospheric pressure. This fundamental effect destroys the quality of the laser output beam and therefore has serious implications in laser design.