Investigation of an all state synchronously pumped optical parametric oscillator
Investigation of an all state synchronously pumped optical parametric oscillator
This research was undertaken to demonstrate an all solid state source of a widely tunable continuous picosecond optical pulse train at high pulse repetition rates, for applications in ultrafast spectroscopy. The singly resonant optical parametric oscillator was identified as the most promising source. A laser-diode-pumped source was desired for ease of handling, reliability and longevity. The peak power requirements for continuous synchronous pumping of a singly resonant optical parametric oscillator were identified to be best met through the use of ultrashort pump pulses (im 1ps). The production of such short pulses required the use of passive rather than active mode-locking techniques. Steady state passive mode-locking of laser-diode-pumped Nd:YAG and Nd:YLF lasers was achieved utilising nonlinear feedback from an interferometrically stabilised coupled cavity, a technique known as self-starting additive-pulse mode-locking. With a 1W (3W) laser diode pump source, a continuous stable train of transform limited pulses of 2.0ps (2.4ps) duration was obtained in Nd:YAG (Nd:YLF), with a pulse peak power of 410W (1.7kW). By decreasing the wavelength of the pump laser, the achievable parametric gain can be raised, and the potential tuning range of the SPOPO improved if the conversion to the shorter wavelength can be done efficiently. Efficient second harmonic generation of the mode-locked oscillators was realised through the use of external resonant enhancement cavities. An interferometrically stabilised cavity allowed resonating of the fundamental pulse train to achieve efficient conversion to the second harmonic with an intracavity located MgO:LiNbO3 nonlinear crystal. For the Nd:YAG (Nd:YLF) laser, transform limited pulses of 2.0ps duration at a wavelength of 532nm (523nm) were achieved. An overall conversion efficiency of 56% (68%) was demonstrated, giving rise to a pulse peak power of 240W (1.3kW). Continuous synchronous pumping of an optical parametric oscillator was achieved using KTiOPO4 as the gain medium. KTP represented the best overall candidate after consideration of the various spatial and temporal limitations to achieving high parametric gain. An oscillation threshold average power at 523nm of 61mW was achieved, corresponding to a peak power of 230W, and a peak intensity of 57MWcm-2. An internal conversion efficiency as high as 78% yielded transform limited pulses of im 1ps duration tunable from 1.002 - 1.096μm with average powers of im 40mW. This research represented the first demonstration (to the author's knowledge) of continuous synchronous pumping of a singly resonant optical parametric oscillator with either a laser-diode-pumped mode-lock laser, or in an extracavity configuration. As such, it was a powerful and timely demonstration that the peak power requirements of such sources are now well within the capabilities of laser-diode-pumped lasers. Thus in the very near future, it is expected that sources similar to the one described here will prove to be a valuable addition to the experimental hardware in the field of ultrafast spectroscopy.
University of Southampton
1992
McCarthy, Matthew John
(1992)
Investigation of an all state synchronously pumped optical parametric oscillator.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
This research was undertaken to demonstrate an all solid state source of a widely tunable continuous picosecond optical pulse train at high pulse repetition rates, for applications in ultrafast spectroscopy. The singly resonant optical parametric oscillator was identified as the most promising source. A laser-diode-pumped source was desired for ease of handling, reliability and longevity. The peak power requirements for continuous synchronous pumping of a singly resonant optical parametric oscillator were identified to be best met through the use of ultrashort pump pulses (im 1ps). The production of such short pulses required the use of passive rather than active mode-locking techniques. Steady state passive mode-locking of laser-diode-pumped Nd:YAG and Nd:YLF lasers was achieved utilising nonlinear feedback from an interferometrically stabilised coupled cavity, a technique known as self-starting additive-pulse mode-locking. With a 1W (3W) laser diode pump source, a continuous stable train of transform limited pulses of 2.0ps (2.4ps) duration was obtained in Nd:YAG (Nd:YLF), with a pulse peak power of 410W (1.7kW). By decreasing the wavelength of the pump laser, the achievable parametric gain can be raised, and the potential tuning range of the SPOPO improved if the conversion to the shorter wavelength can be done efficiently. Efficient second harmonic generation of the mode-locked oscillators was realised through the use of external resonant enhancement cavities. An interferometrically stabilised cavity allowed resonating of the fundamental pulse train to achieve efficient conversion to the second harmonic with an intracavity located MgO:LiNbO3 nonlinear crystal. For the Nd:YAG (Nd:YLF) laser, transform limited pulses of 2.0ps duration at a wavelength of 532nm (523nm) were achieved. An overall conversion efficiency of 56% (68%) was demonstrated, giving rise to a pulse peak power of 240W (1.3kW). Continuous synchronous pumping of an optical parametric oscillator was achieved using KTiOPO4 as the gain medium. KTP represented the best overall candidate after consideration of the various spatial and temporal limitations to achieving high parametric gain. An oscillation threshold average power at 523nm of 61mW was achieved, corresponding to a peak power of 230W, and a peak intensity of 57MWcm-2. An internal conversion efficiency as high as 78% yielded transform limited pulses of im 1ps duration tunable from 1.002 - 1.096μm with average powers of im 40mW. This research represented the first demonstration (to the author's knowledge) of continuous synchronous pumping of a singly resonant optical parametric oscillator with either a laser-diode-pumped mode-lock laser, or in an extracavity configuration. As such, it was a powerful and timely demonstration that the peak power requirements of such sources are now well within the capabilities of laser-diode-pumped lasers. Thus in the very near future, it is expected that sources similar to the one described here will prove to be a valuable addition to the experimental hardware in the field of ultrafast spectroscopy.
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Published date: 1992
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Local EPrints ID: 461249
URI: http://eprints.soton.ac.uk/id/eprint/461249
PURE UUID: a8573809-10b2-4b08-893d-7f7163e76ce8
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Date deposited: 04 Jul 2022 18:41
Last modified: 04 Jul 2022 18:41
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Author:
Matthew John McCarthy
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