Nanosecond optical parametric oscillator

A typical experimental set-up for SHG is shown in Fig. 5.2. For excitation nowadays one usually uses either a mode locked Ti Sapphire laser, that delivers 100 fs pulses at a rate of about 80 MHz, or a pico or nanosecond Nd YAG laser, often in combination with an optical parametric oscillator (OPO). Whereas the first type of system gives a superior mode quality and stability but limited tunability, the second system is more convenient for SHG spectroscopy. 

T. Schroder, K.-J. Boiler, A. Fix, and R. Wallenstein, Spectral Properties and Numerical Modelling of a Critically Phase-Matched Nanosecond LiBsOs Optical Parametric Oscillator , Appl. Phys. B 58, 425 (1994). 

A variety of other pulsed laser light sources have been incorporated into optical emission spectrometer systems. The two most common ones are based on either a pulsed nitrogen laser or a frequency-upconverted pulsed Nd YAG laser as either a single line source (337 nm for the nitrogen laser, 266,355, or 532 nm for the Nd YAG laser) or used as a pump laser for a tunable secondary laser device such as a dye laser or an optical parametric oscillator (OPO). The ultimate wavelength tunabUity in such systems depends on the characteristics of the secondary laser and can be substantial in the case of the OPO, but at a substantial price in both cost and complexity of operation and maintenance. Nonetheless, these sources can have excellent temporal characteristics (sub-nanosecond pulse durations) and high per pulse energies. 

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