Laser spectroscopy with a pulsed, narrowband infrared optical parametric oscillator system: a practical, modular approach

A pulsed optical parametric oscillator (OPO), based on bulk lithium niobate pumped at 1.064 mu m and injection-seeded at similar to 1.55 mu m by a single-mode tunable diode laser, has been developed to serve as a narrowband coherent infrared spectroscopic source. The OPO cavity com prises a slightly misaligned three-mirror ring that is operated passively, to provide continuous tunability of the signal (similar to 1.55 mu m) and idler (similar to 3.4 mu m) output radiation over several cm(-1) in a single scan. The potential of the OPO system for linear and nonlinear-optical spectroscopy is demonstrated by recording high-resolution photoacoustic absorption and coherent anti-Stokes Raman spectra of methane, as a gas and in a pulsed supersonic free jet. This narrowband tunable infrared source is shown to scan reliably with an optical bandwidth as small as 0.007 cm(-1) (210 MHz) full width half maximum (fwhm), close to the fourier-transform limit.