This thesis describes an experimental study of high intensity, pulsed, optically pumped, far-infrared (FIR) lasers. The work was motivated by the need for a radiation source for the measurement of the ion temperature in magnetically confined, high temperature plasmas (e.g. tokamak plasmas), using Thomson scattering. Constraints imposed by the plasma parameters, the scattering geometry and available detector sensitivities lead to the requirement of a radiation source wavelength between 30μm and 1mm and a source power . 1 MW in a bandwidth 60 MHz. Results are presented for a 496μm, 500 watt, methyl fluoride (CH<sub>3</sub>F) cavity laser, with a bandwidth of and < 30MHz, which was optically pumped by a 9.55μm CO<sub>2</sub> laser. Results are also presented for an optically excited mirrorless, super-radiant, CH<sub>3</sub>F laser, which generated over 0.6MW of FIR radiation within a bandwidth of about 300MHz. The performance of this laser has also been simulated by a computer model, which allows the optimum operating parameters to be predicted. An assembly constructed on the principle of the injection laser, in which low power narrow-band oscillator radiation is used to control the output of a super-radiant system, has been used to generate 250 kW of 496 andmu;m radiation, with a bandwidth of < 60 MHz. Investigations of the FIR output from heavy water vapour (D<sub>2</sub>O) in a super-radiant laser assembly, optically excited by several different CO<sub>2</sub> laser wavelengths, have resulted in the generation of 60 ns (FWHM) pulses of FIR radiation with average powers of 1.3, 9.2 and 15.8MW, at wavelengths of 385, 119 and 66μm, respectively. All these lasers were found to have a higher CO<sub>2</sub> to FIR photon conversion efficiency than the 496μm CH<sub>3</sub>F laser. In addition, the energy level spacing in D<sub>2</sub>O is such that the molecule can generate narrow bandwidth radiation more readily than the CH<sub>3</sub>F molecule. From this work it is concluded that an injection laser assembly, similar to that used with CH<sub>3</sub>F, but containing D<sub>2</sub>O vapour, optically pumped by a 9.26μm CO<sub>2</sub> laser and generating several megawatts of 385μm radiation, would satisfy the source requirements mentioned above.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:474656 |
| Date | January 1977 |
| Creators | Taylor, Gary |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:5cbbb21b-3d3a-4ca9-a6e5-3a172aa13653 |
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