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Title: Development of an intense optically pumped laser of narrow bandwidth in the far infrared
Author: Taylor, Gary
ISNI:       0000 0001 2409 5225
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1977
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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 (CH3F) cavity laser, with a bandwidth of and < 30MHz, which was optically pumped by a 9.55μm CO2 laser. Results are also presented for an optically excited mirrorless, super-radiant, CH3F 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 (D2O) in a super-radiant laser assembly, optically excited by several different CO2 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 CO2 to FIR photon conversion efficiency than the 496μm CH3F laser. In addition, the energy level spacing in D2O is such that the molecule can generate narrow bandwidth radiation more readily than the CH3F molecule. From this work it is concluded that an injection laser assembly, similar to that used with CH3F, but containing D2O vapour, optically pumped by a 9.26μm CO2 laser and generating several megawatts of 385μm radiation, would satisfy the source requirements mentioned above.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Vacuum ultraviolet spectroscopy ; Far infrared lasers ; Tokamaks