High pressure CO<sub>2</sub> lasers are good candidates for amplifying picosecond mid infrared pulses. High pressure CO<sub>2</sub> lasers are notorious for being unreliable and difficult to operate. In this paper a high pressure CO<sub>2</sub> laser is presented based on well developed LC-inversion type excitation circuit. The laser contains internal room temperature catalysts allowing closed loop or rare isotope operation. The laser was designed for 300Hz operation and could achieve this for short time periods and could be operated at up to 200Hz for extended time periods. Some of the design features and experimental results are presented in this paper.
A high power 1kW pulsed transversely excited atmospheric CO<sub>2</sub> laser that has been developed for the paint stripping of missiles was used to test paint stripping on several metallic and composite aircraft panels to determine the rate at which
this laser could remove paint from aircraft.
A theoretical and experimental study investigated beam perturbations on propagation through a MOPA chain, including both optical and medium influences. Analytical models are presented to explain the influence of thermal aberrations on the beam, and these effects are related directly to the change in M2 (quality factor) of the beam.
The development of a high repetition rate TEA-CO<SUB>2</SUB> laser chain has a number of difficulties that must be overcome. One of these difficulties is to predict the free space propagation of the beam. A low energy (approximately 100 mJ/pulse), high-quality, carbon-dioxide beam is amplified in a number of carbon-dioxide amplifiers to more than 1 J per pulse. On propagation through the amplifier chain the primary beam encounters several transmission optics. It was found that the beam parameters of the primary beam change dramatically for high repetition rate operation (greater than 100 Hz). The alteration in beam parameters is brought about by thermal expansion and refractive index variations known as thermal lensing. This phenomenon is caused by the thermal gradient introduced to an optic by absorption of a laser beam with a Gaussian profile. Thermal lensing caused by the aforementioned laser system in transmission optics was investigated. The influence of several types of transmission optics in the amplifier chain was studied and compared. It was found that the use of a specific substrate (KCl or ZnSe) is determined by the position in the chain. A marked increase in thermal lensing effects was observed with damaged or contaminated optics.
A CO<SUB>2</SUB> master oscillator power amplifier (MOPA) laser chain has been developed capable of producing approximately 2J per pulse at 2kHz. This leads to a unique combination of high peak and average power in a single laser system. As the laser is to be used in a process where it must be capable of prolonged periods of operation, a method had to be devised to allow constant monitoring of the beam profile and behavior of the optical components to ensure that the laser induced damage thresholds (LIDT) of the optical components are not exceeded. A photoacoustic detector (PAD), that allows determination of damage to optical components, and a M<SUP>2</SUP>, or beam quality detector for accurate calculation of beam profiles in the CO<SUB>2</SUB> laser chain have been developed. The results obtained with these detectors will be discussed.
A continuously tunable 3-atm mixed isotope CO<sub>2</sub> oscillator power amplifier (MOPA) chain is developed for a molecular laser isotope separation pilot plant. The characteristics of this laser such as tunability, bandwidth, and output energy are reported. A closed loop gas flow system with a catalyst is employed and its performance is reported.
To obtain economical extraction of <sup>235</sup>U in the molecular laser isotope separation (MLIS) process, 16-μm laser beams must be generated in a parahydrogen Raman cell with high repetition rates and sufficient intensity. Because the intensities of the 16-μm laser beams are dependent on the intensity of the incoming pump laser beams, the intensity of the CO<sub>2</sub> lasers must be kept as high as possible. The maximum intensity has, however, been found to be controlled by the onset of gas breakdown in the Raman cell at too low a level for efficient Raman conversion. Through tests, the origin of gas breakdown in a 2-kHz-repetition-rate Raman cell is identified as particle contamination. The effect of the degree of contamination is determined and compared with experimental results. Conditions are set and modifications implemented on the Raman cell to ensure efficient Raman conversion.