By: W. J. Alford, A. V. Smith, T. D. Raymond, and M. S. Bowers (Aculight Corporation)
SNLO Software | VECSEL | UV Source | OPO | OFM | Crystal Research | Supersonic Flight | Plasma Science & Technology | Information
Motivation
Optical Parametric Oscillators (OPOs) are optical devices pumped by a laser to produce two wavelengths, called the signal and idler, different from those of the pump laser. OPOs can be used to shift the wavelength of fixed-frequency lasers to a desired wavelength or to generate tunable light. When combined with rapidly developing pump laser technology, OPOs promise compact, tunable sources of coherent light. OPOs are more complicated than laser oscillators due to the nonlinear nature of the gain medium. Designs of compact, efficient OPOs requires models that properly describe this nonlinear behavior and can accurately predict the performance of real-world devices.
Accomplishment
We have developed state-of-the-art computer models for nanosecond duration pulsed OPOs.
These models include:
- the effects of light diffraction of the three interacting waves in the OPO cavity
- the effects of beam walkoff due to birefringence of the nonlinear mixing crystal
- strong exchange of energy among the three waves
We have also built a laboratory capability for building and characterizing OPOs.
A conventional ring OPO was thoroughly characterized in the lab and the results were accurately predicted by the computer models.
It should be pointed out that the model had no adjustable parameters in matching the experiments. We are using our computer model to explore new, compact OPO designs which have improved performance over conventional designs.
In particular, we are trying to obtain higher efficiency and better beam quality from OPOs that can be pumped by solid state lasers.
As an example, a promising design for an infrared OPO pumped by 1 micron light is shown in Figure 1. The OPO is monolithic with a cavity length of 3 mm. The short length and singly-resonant design minimize the unwanted effects of backconversion (the conversion of signal and idler back into pump).
Figure 1: Compact, MonolithicOPO using Periodically Poled Lithium Niobate (PPLN) as the gainmedium. Mirror coatings: HR = High Reflector, AR = AntiReflection coating, and PR = Partial Reflector.
Backconversion decreases OPO efficiency and degrades beam quality.
By designing this cavity to minimize backconversion, the model predicts outstanding efficiency and good beam quality as shown in Figure 2.
This OPO can easily be pumped by compact, diode-pumped solid-state lasers currently available, leading to a small overall system.
Figure 2: Efficiency of compact, monolithic PPLN OPO. Efficiencies as high as 50% are predicted by the OPO models.
The pump energies displayed are easily obtained with compact, diode-pumped solid-state lasers.
Significance
Development of compact, tunable laser sources will open up many opportunities in the areas of remote sensing, local sensing, and process control. For example, the OPO described above, when pumped by a compact, battery-powered micro-chip laser, could be part of a man-portable system to detect gases such as methane in industrial, commercial, and home environments.
Sponsors for various phases of this work include: DP
Point of Contact: Greg Hebner