The production of intense tunable narrow bandwidth radiation is important in experiments for probing weak molecular resonances, saturating strong resonances, and probing the frequency dependence of multiphoton processes and in nonlinear optics applications. In the IR region of the spectrum, intense (10-100-mJ) pulses of tunable (1400-4000-nm) radiation have been produced by Nd:YAG pumped optical parametric oscillation (OPO) in lithium niobate. However, the Intrinsically broad gain bandwidth of the parametric process leads to an undesirably broadband (S-100-cm-1) signal and idler output radiation, limited only by phase matching restrictions. Frequency selective elements can be inserted into the optical cavity to narrow the output. Typically an etalon, beam expanding prism pair, and grating are used. Such elements raise the oscillation threshold by increasing cavity losses and the round trip time, which results in fewer amplifying passes occurring in the duration of the pump pulse. Despite these difficulties, single mode operation of an infrared OPO has recently been achieved with a reported signal linewidth of 0.001 cm−1.
© 1989 Optical Society of AmericaPDF Article