Use and development of a CW titanium sapphire laser for nonlinear optics

Lasers;

Shepherd, Sara ; Sinclair, B. D. (Bruce D.) ; Sinclair, B. D. (Bruce D.)

University:University of St Andrews

Department:Physics & Astronomy (School of)

关键词: Lasers;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/9931/SaraShepherdPhDThesis.pdf?sequence=2&isAllowed=y

来源: DR-NTU

【 摘 要 】

A cw titanium sapphire laser pumped by an argon ion laser was used forexperiments both in second harmonic generation using a non-linear crystal and for sum-frequencygeneration in an atomic vapour. In addition the laser was stabilised to sub-MHz levels.Using a crystal of potassium niobate (KNbO₃), the Ti:sapphire laser wasfrequency doubled over the range 860nm-905nm using an intracavity scheme. Thecrystal was temperature tuned to achieve near non-critical phase-matching and powersof up to 50mW were obtained, with a constant conversion efficiency per Watt over thedoubling range. The thermal properties of potassium niobate in frequency doublingwere examined and the effect of the crystal on the ring cavity during temperature tuningwas investigated.The laser cavity was frequency stabilised using a 'side of fringe' locking schemewith a confocal Fabry-Perot etalon as the reference discriminator. The cavity lengthcontrol elements were two Brewster-angled tilt plates and a piezo mounted mirror.Using this scheme the frequency noise was reduced from tens of MHz to 550kHz.Methods of obtaining a 30GHz frequency scan were also evaluated and an experimental10GHz scan achieved. It was concluded that only dither and lock schemes are goodenough to achieve reliable 30GHz scans.Using both a Ti:sapphire laser and a dye laser, two contrasting schemes for sum-frequencygeneration in sodium vapour were investigated, in which a magnetic fieldwas used to break the symmetry of the medium. Using one of these resonantlyenhanced routes, powers of 17μW in the UV were obtained from a classically'forbidden' quadrupole transition. The effects of phase-matching on each of thetransitions was examined in detail, and it was found that in general there are at least sixfactors which affect the phase-matching behaviour of the frequency mixing scheme. Itwas also found that on the route which had two sources of dispersion there was asignificant distortion of the output line profiles at high temperatures due to a variationin phase-matching across the line profile itself.