A Seeded Optical Parametric Generator/Amplifier (297)

A seeded optical parametric generator (OPG) has been developed at the University of Dayton in collaboration with Sandia National Laboratories. This device provides continuous and seamless tunable light in the mid-IR spectral region with a narrow bandwidth. As shown in Fig. 1, it consists of three stages: an OPG, a filter, and an optical parametric amplifier (OPA). The advantage of this source is that it provides efficient and simple conversion of a pulsed laser to new frequencies with single passes through two nonlinear optical crystals. This is contrasted with optical parametric oscillators, which are difficult to tune seamlessly owing to complications such as mode hopping.

Figure 1. A seeded optical parametric generator. This is a two-stage device that frequency converts a single pump laser to the mid-IR. The output is seamlessly and broadly tunable.

The basic principle behind the seeded OPG is simple. Optical parametric generation is a process where an input laser (the pump) is converted to two new frequencies (signal and idler) by passing the pump beam through a nonlinear optical crystal. The single-pass conversion efficiency of the pump to the signal and idler depends on many factors such as crystal nonlinearity, crystal length, and pump intensity. A new commercially available nonlinear crystal, periodically poled lithium niobate (PPLN), generates a high single-pass conversion to the signal and idler for nanosecond pump laser pulses.

The OPG signal and idler outputs are, in general, broad bandwidth. Injecting a narrow bandwidth beam  co-linear with the pump laser controls the output so that the bandwidth of the signal is the same as the seed bandwidth. The design shown in Figure 1 is unique in that it uses the filtered output of an OPG to generate seed light. This is a powerful technique since the frequencies where one can generate a seed beam is limited only by the nonlinear crystal. The tuning range for PPLN is 1.3 to 4.7 mm using a single nm pump laser.

For more information, please contact the Office for Technology Partnerships at 937-229-3515.

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