Middle-infrared laser sources

Journal Title
Journal ISSN
Volume Title
Stellenbosch : Stellenbosch University
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.
AFRIKAANSE OPSOMMING : Beide vastetoestand mid-infrarooi laser- en versterker-stelsels gebaseer op Tm3+ en Ho3+, sowel as mid-infrarooi opties-gepompte molekulêre gas lasers gebaseer op HBr, is ontwikkel en bestudeer. 'n Doeltreffende hoë-energie Ho:YLF laser, wat ge-entpomp is deur 'n kommersieel beskikbare Tm:vesel laser is ontwerp en gedemonstreer. Die holmium laser het tot 45.1 W se gemiddelde krag gelewer in 'n diffraksie-beperkte laser-bundel wanneer dit gepomp is met 84.7 W. Die ontwerp het gelei tot 'n rekord optiese-tot-optiese doeltreffendheid van 53%. 'n Kompakte 60.2 W Ho:YLF meester ossillator en versterker-stelsel gepomp deur twee ongepolariseerde Tm:vesel lasers is daarna ontwikkel. Die ossillator het 'n maksimum gemiddelde uitsetkrag van 24 W gelewer, met 'n laser-bundel gehalte-faktor (M²) gelyk aan 1.06. Die twee-kristal, enkel-gang versterker het 'n versterkingsfaktor van 2.5 en M² van 1.09 gehad. Die versterker het die ongeabsorbeerde pomplig van die ossillator se enkele vesel-laser in kombinasie met die pomplig van ‘n tweede vesel-laser gebruik. Die pomp skema het gelei tot 'n optiese-tot-optiese doeltreffendheid van 55.5%. Onder Q-skakeling is laser pulslengtes van tussen 43 en 113 ns vir puls repetisie frekwensies van 15 tot 40 kHz gemeet. 'n Optiese pomp bron vir molekulêre HBr lasers is gesamentlik ontwikkel. Dit het bestaan uit 'n dubbel-gang, enkel-frekwensie Ho:YLF versterker wat 350 ns lang pulse van tot 330 mJ per puls gelewer het by 2064 nm, met 'n maksimum M² van 1.5 teen ‘n repetisie tempo van 50 Hz. Dit is gepomp met 'n Tm:YLF blad laser. Daarna is 'n opties ge-entpompte molekulêre HBr meester-ossillator drywingsversterker vir die eerste keer gedemonstreer. Dit het 'n rekord uitset energie van tot 10.3 mJ gelewer, en gelyktydig ossilleer by 4.20 en 4.34 μm. Die HBr stelsel is gepomp met die enkel-frekwensie Ho:YLF blad versterker. Golflengte-seleksie met die gebruik van 'n CO² absorbsie-sel is ook gedemonstreer, wat die laser gedwing het om gelyktydig uit te straal by 3.89, 4.13 en 4.16 μm, met 'n maksimum uitset energie van 6.5 mJ per puls na versterking. Laastens is 'n opties gepompte, golflentge-verstelbare HBr molekulêre laser vir die eerste keer gedemonstreer. Laser ossillasie is gedemonstreer op negentien oorgange, insluitende beide die R-transisies (3870 nm tot 4015 nm) sowel die P-transisies (4070 nm tot 4453 nm) deur die gebruik van 'n diffraksierooster. Dit is die eerste keer wat laser-emissie op die R-transisies van HBr gedemonstreer is. Die hoogste uitset energie van die laser was 2.4 mJ per puls by 4134 nm.
Thesis (PhD)--Stellenbosch University, 2016
Lasers, Laser amplifiers, Mid-infrared lasers, Ho:YLF lasers (Holmium:Yttrium Lithium Fluoride lasers), Tm:YLF lasers (Thulium:Yttrium Lithium Fluoride lasers), HBr lasers (Hydrogen Bromide lasers)