A compact, short pulse photolytic iodine laser (PIL) system designed for use as a source in Raman conversion experiments is described. The single-shot, flashlamp-pumped laser outputs 10 Joules in a 3 microsecond(s) FWHM pulse at a wavelength of 1.315 micrometer and uses n-C<SUB>3</SUB>F<SUB>7</SUB>I as the renewable laser fuel. Laser design and performance characteristics are presented.
We have investigated rotational Raman conversion experiments in hydrogen using a single-shot photolytic iodine laser (PIL) at 1.315 micrometer as a pump laser. The total output energy of the PIL is between 5 - 7 J per pulse distributed in a train of approximately 120 pulses each with a FWHM of 6 or 9 nsec and a temporal spacing of 33 nsec. The energy distribution within the pulse train is characterized by high energy pulses in the gain switched spike followed by lower energy pulses in the tail of the laser pulse. Stimulated Raman scattering (SRS) experiments were performed with (1) a focused beam geometry in a single Raman cell, (2) two Raman cells, whereby the pump focus was reimaged into a second Raman cell, and (3) a Stokes resonator specifically suited for an annular pump beam. Thermal distortions in the laser beam made it necessary to lower the peak intensity of the pump laser beam by adjusting the focusing conditions. With a long focus mirror we demonstrated (1) a conversion efficiency of up to 70% for the high-energy pulses of the gain switched spike of the PIL micropulses and (2) lowering of the threshold with a Stokes resonator.
We report the operation of a short pulse photolytic iodine laser (PIL) using an unstable resonator under long-pulse and injection seeded operation. The laser is designed as a surrogate source to replicate the output from a q-switched chemical oxygen iodine laser (COIL). Under long pulse conditions the single shot laser produces up to 10 Joules in a 3 microsecond(s) pulse. When seeded with the output from a narrow pulse (10 ns) broadband KTP Optical Parametric Oscillator (OPO), the temporal output is composed of a train of 10 ns pulses separated by the round trip time of the cavity. The enhanced peak power in the individual pulses is more attractive for subsequent efficient Raman conversion. A description of the laser performance with the unstable resonator and with seeding is presented.