Doctoral Degrees (Physics)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/3640

Browse

Browsing Doctoral Degrees (Physics) by browse.metadata.advisor "Esser, M. J. Daniel"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Middle-infrared laser sources
    (Stellenbosch : Stellenbosch University, 2016-03) Koen, Wayne Sean; Esser, M. J. Daniel; Rohwer, Erich G.; Strauss, Hencharl J.; Stellenbosch University. Faculty of Science. Dept. of Physics
    ENGLISH ABSTRACT : Both bulk solid-state mid-infrared lasers and amplifier systems based on Tm3+ and Ho3+, as well as mid-infrared optically pumped molecular gas lasers based on HBr were developed and studied. An efficient high-power Ho:YLF laser which was end-pumped by a commercially available Tm:fibre laser was designed and demonstrated. The holmium laser delivered 45.1 W of average power in a near diffraction-limited beam when pumped with 84.7 W, resulting in a record optical-to-optical efficiency of 53 %. A compact 60.2 W Ho:YLF master oscillator power amplifier system pumped by two unpolarised Tm:fibre lasers was subsequently developed. The seed laser delivered a maximum average output power of 24 W with a beam quality factor (M²) equal to 1.06. The two-crystal, single-pass amplifier delivered a gain of 2.5 and M² of 1.09. The amplifier utilised the transmitted pump from the seed lasers’ single fibre laser in addition to a second fibre laser, resulting in an optical-to-optical efficiency of 55.5 %. Under Q-switched operation, laser pulse lengths of between 43 and 113 ns at pulse repetition rates from 15 to 40 kHz were measured. An optical pump source for molecular HBr lasers was developed collaboratively, which comprised of a double-pass, single-frequency Ho:YLF slab amplifier that delivered 350 ns long pulses of up to 330 mJ at 2064 nm, with a maximum M² of 1.5 at 50 Hz. It was end-pumped with an in-house developed diode-pumped Tm:YLF slab laser and seeded with up to 50 mJ of single-frequency laser pulses from an injection-seeded, single-frequency Ho:YLF ring-laser. Subsequently an optically end-pumped HBr master oscillator power amplifier was demonstrated for the first time. It produced a record output energy of up to 10.3 mJ, operating simultaneously at 4.20 and 4.34 μm when pumped with the single-frequency Ho:YLF slab amplifier. Wavelength selection with the use of an intra-cavity CO² absorption cell was also demonstrated, forcing the oscillator to emit at 3.89, 4.13 and 4.16 μm simultaneously, with a maximum output energy of 6.5 mJ per pulse after amplification. Lastly, an optically pumped tuneable HBr molecular laser was demonstrated for the first time. Laser oscillation was demonstrated on nineteen molecular transition lines including both the R-branch (3870 nm to 4015 nm) and the P-branch (4070 nm to 4453 nm) by the use of an intra-cavity diffraction grating. This was also the first time laser operation on the R-branch of HBr was demonstrated. The highest output energy from the laser was 2.4 mJ at 4134 nm.