Use and development of a CW titanium sapphire laser for nonlinear optics
Abstract
A cw titanium sapphire laser pumped by an argon ion laser was used for
experiments both in second harmonic generation using a non-linear crystal and for sum-frequency
generation 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 was
frequency doubled over the range 860nm-905nm using an intracavity scheme. The
crystal was temperature tuned to achieve near non-critical phase-matching and powers
of up to 50mW were obtained, with a constant conversion efficiency per Watt over the
doubling range. The thermal properties of potassium niobate in frequency doubling
were examined and the effect of the crystal on the ring cavity during temperature tuning
was investigated.
The laser cavity was frequency stabilised using a 'side of fringe' locking scheme
with a confocal Fabry-Perot etalon as the reference discriminator. The cavity length
control 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 experimental
10GHz scan achieved. It was concluded that only dither and lock schemes are good
enough to achieve reliable 30GHz scans.
Using both a Ti:sapphire laser and a dye laser, two contrasting schemes for sum-frequency
generation in sodium vapour were investigated, in which a magnetic field
was used to break the symmetry of the medium. Using one of these resonantly
enhanced routes, powers of 17μW in the UV were obtained from a classically
'forbidden' quadrupole transition. The effects of phase-matching on each of the
transitions was examined in detail, and it was found that in general there are at least six
factors which affect the phase-matching behaviour of the frequency mixing scheme. It
was also found that on the route which had two sources of dispersion there was a
significant distortion of the output line profiles at high temperatures due to a variation
in phase-matching across the line profile itself.
Type
Thesis, PhD Doctor of Philosophy
Collections
Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.