A CO₂ laser system delivering a 12 J pulse with a FWHM of 2 ns on target was developed to serve as a driver for studies of laser plasma interactions within a cylindrical cavity. The system consisted of a hybrid oscillator, followed by an amplifier chain, and it achieved its design goals of delivering an intense CO₂ pulse, Gaussian in time and space, with a high contrast ratio on a reliable basis. The targets in which the plasma was produced consisted of small rectangular plates of lucite, with holes drilled through one of the long axes. The holes were 350 μm to 600 μm in diameter, and 10 mm in length. These dimensions allowed the laser beam, focused at the entrance of the hole, to produce sufficient intensity on the inner walls of the cylindrical cavity for plasma formation, while allowing the beam, with a waist diameter of 100 μm at the focus to deliver most of its energy within the cavity. The beam propagated via multiple reflections from the plasma through the cavity. Diagnostics were performed on the beam transmitted through the target. Streak camera images were collected of the intensity of visible emission from the plasma along the axis of the target. Anomalous results were obtained with respect to the reproducible observation of maximum visible light emission from regions at the far end cavity from where the laser beam is injected. Another unforseen but interesting result was the small divergence of the beam transmitted through the cavity. Preliminary models were developed to attempt to explain the observations. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Thesis: M.S., Massachusetts Institute of Technology, Department of Physics, 1976 / Includes bibliographical references. / M.S. / M.S. Massachusetts Institute of Technology, Department of Physics

A novel design for a DC excited cw C02 metal waveguide laser has been developed in which a slotted hollow-cathode in a transverse discharge also doubles as a metal waveguide. This design has been implemented in a compact design that produces up to 1 watt of cw, 10.6 μm radiation. The discharge characteristics, laser gain and laser output has been studied as functions of various discharge parameters. The advantages of the new transverse discharge of the slotted hollow cathode geometry include low voltage, positive impedence and high optical gain. Overall efficiency is comparable with those of conventional longitudinal CO2 lasers. The output laser modes were very clean low order Gaussian modes.

The possibility of using sunlight to pump a CW carbon dioxide laser has been analyzed. Such a laser could be of interest for such applications as space communication and power transmission. In order to optically pump CO2 using sunlight, the intense vibrational-rotational absorption bands of CO2 in the 4.3 micron spectral region would have to be utilized. The total pumping power from sunlight can be calculated from the known data of the solar spectral irradiance outside the atmosphere and the infrared absorption by carbon dioxide at 4.3 microns. The pumping power is proportional to the collector area of the sunlight and is also dependent on the characteristics of the absorbing gas mixture, such as the gas composition, the gas temperature, the total pressure of the mixture, the partial pressure of CO2, and the absorption path length of the sunlight in the gas. To analyze the carbon dioxide laser system, a thermodynamic approach was used with a simplified CO2 chemical kinetic model. The gain and saturation intensity were obtained by solving a set of energy balance equations which describe the processes among the various vibrational modes. From those results, along with the estimated cavity losses, the output power was found.

Thesis. 1976. Sc.D.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / Microfiche copy available in Archives and Engineering. / Vita. / Includes bibliographical references. / Sc.D.

No description available.

An incoherent CO₂ laser radar, or lidar, system using a tunable CO₂ TEA laser has been developed, along with analytical techniques to permit the determination of atmospheric transmittance and aerosol backscatter from multi-angle lidar returns. This work has been motivated by the need for a more complete knowledge of the optical properties of the atmosphere in the 9 to 11 μm spectral region. Results of preliminary observations are discussed. CO₂ lidar systems have been used before to measure backscatter and transmittance. Here, a new analytic method is developed, applicable to the 8-12 μm window region in conditions of high visibility, when the aerosol component of extinction is negligible compared to the molecular component. In such cases the backscatter sensed by the system is due to the atmospheric aerosol while atmospheric transmittance is determined by molecular species such as carbon dioxide and water vapor. It is not possible to assume a functional relationship between backscatter and extinction, as required by many previous analytic techniques. Therefore, a new solution technique based on a weighted, non-linear least squares fit applied to multi-zenith angle lidar returns has been developed. It is shown how constraints may be applied to rule out solutions which are unlikely on a priori grounds. An error analysis and a discussion of proper weighting techniques are presented. A CO₂ lidar system capable of acquiring multi-angle returns was developed, which included a gain-switching amplifier to compress the dynamic range of the return signal. The entire system is operated under computer control and data acquisition and storage are fully automated. A laser pulse energy monitor allows sequential returns to be averaged to reduce signal fluctuations. Preliminary observations with the system have demonstrated the capability of acquiring and averaging hundreds of returns on a routine basis. The return signal was observed to have fluctuations of 20 to 50% from shot to shot, due to atmospheric fluctuations. This result indicates signal averaging will be necessary to reduce signal fluctuations to levels where the multi-angle solution method may be applied.

The objective of this thesis is to describe the development, construction and use of a new tool for optical coherent transient spectroscopy. The new tool is a frequency-switched CO₂ laser. A highly stable laser design was modified to include an intra cavity electro-optic modulator, which al lows the output of the laser to be frequency-switched. The frequency modulated output is used in spectroscopic experiments whose goals are the determination of decay rates for infrared moIecuIar transitions. The use of a frequency-switched laser is the most prom i sing means of making such measurements on nonpoIar molecules. The use of an electro-optic crystal inside a laser cavity introduces a number of fundamental problems which must be overcome before the instrument can be used to make useful spectroscopic measurements. These problems are brought about by the need for a stable laser amplitude and frequency output. The development of a novel stabilization technique to overcome these problems is documented in this thesis. Also included in this thesis is a description of the microcomputer and associated electronics necessary to integrate the laser into an experimental apparatus capable of performing signal averaging and background subtraction on raw time resolved data. The final chapters of this work describe experiments and results of measurements of the scattering cross sect ions of a nonpolar molecule with rare gas perturbers. The nonpolar molecule is SF₆ and the rare gas collision partners are Helium, Argon, and Xenon. The results indicate that the scattering cross section for state changing collisions displays a mass dependance predicted by classical collision theory. However, the measured cross sections for elastic velocity-changing collisions appears to be mass independent, which is at variance with theory.

Thesis. 1978. Sc.D.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERONAUTICS. / Includes bibliographical references. / Sc.D.

Made available in DSpace on 2014-10-09T12:44:49Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:50Z (GMT). No. of bitstreams: 1 07302.pdf: 3680134 bytes, checksum: 8ad9b39e352023c01b3fd610c63d0482 (MD5) / Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia) / IPEN/D-MPLO / Intituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP; Faculdade de Odontologia, Universidade de Sao Paulo