Several pulsed optical oscillators (OPOs) based on periodically poled lithium niobate (PPLN) and pumped by single longitudinal mode Ti:sapphire lasers have been developed. These OPOs provide access to important spectroscopic regions in the 1 - 5.5 [mu]m region and can be rapidly turned by varying the pump wavelength. Previously many of the OPOs developed to take advantage of PPLN relied on a combination of period selection and temperature tuning and as a result were slow and cumbersome to tune. This problem my be avoided by using tunable pump sources or acoustically induced strain waves.
Several candidate OPO pump sources were characterised. These pump sources with themselves pumped by lasers operating at repetition reates of either 1.5 kHz (high repetition rate) or 10Hz (low repetition rate). High repetition rate systems include: a Ti-sapphire laser, injection seeded by a single longitudinal mode diode laser, several coupled cavity Ti:sapphire lasers with bandwidths less than 100 Ghz and Cr:forsterite lasers narrowed by prisms and eĢtalons. The low repetition rate systems were all coupled cavity Ti:sapphire lasers one of which was single and double pass amplified. Of these it was found that only the high repetition rate injection seeded laser and the low repetition Ti:sapphire lasers were suitable as OPO pump sources.
OPOs were characterised at high and low repetition rates. The high repetition rate system exhibited a low threshold of oscillation (18.7 [mu]J) and a low overall efficiency (25%) which was thought to be due to the pulse to pulse variability of the Ti:sapphire bandwidth. The tuning range of the OPO was 932 to 1310 nm (signal) and 1.989 [mu]m to 5.281 [mu]m (idler) using multiple poling periods and only 15 nm of pump tuning. OPO oscillation on two separate signals simultaneously was observed. Two separate low repetition rate systems were investigated; the first was tuned from 1200 to 1600 nm (signal) and from 1600 to 2400 nm (idler) on a single poling period with a high absolute efficiency of 35% and a threshold of 180 [mu]J. The second OPO was tuned from 940 to 1220 nm (signal) and 2.2 to 4.3 [mu]m (idler) on a single poling period. The absolute efficiency of the system was 25% and the threshold was 200 [mu]J. OPO oscillation on two separate signals was investigated using an OPO based on grazing incidence configured cavity. It was found that the signals coupled together through Raman transitions present in lithium niobate and that coupling reduced the efficiency of the device as a whole.
The affect of an acoustically induced strain field on the optical nonlinearity of tetragonal ferroelectric materials was investigated. It was found that the optical nonlinear coefficient varies linearly with the cell displacement and as the square root of the acoustic power. A crystal designed to implement a quasi phase matched interaction based on this variation is proposed.
| Identifer | oai:union.ndltd.org:ADTP/217475 |
| Date | January 2005 |
| Creators | Lee, Chris J., n/a |
| Publisher | University of Otago. Department of Physics |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Chris J. Lee |
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