Abstract

Ever since the invention of the laser, there has always been a great deal of interest in the development of continuously tunable coherent light sources. Such sources would have broad applications in research and industry. The development of tunable oscillators has been difficult because conventional lasers tend to be discrete-wavelength devices involving stimulated emission between quantized energy levels in the laser media. Only when these quantized energy levels are tunable or there are neighboring energy levels that are sufficiently broadened to merge into each other to form a continuous band can a continuously tunable laser be built. Even then, the tuning range tends to be limited. Optical parametric oscillators are powerful solid-state sources of coherent radiation with potentially very large continuous tuning ranges. For example, the recently developed pulsed β-barium borate (BBO) optical parametric oscillators can be tuned continuously from 415 nm to 2.5 μm with a single set of mirrors when pumped at 355 nm and from 300 nm to 2.5 μm with multiple sets of mirrors when pumped a 266 nm. The total conversion efficiency from the pump to useful OPO outputs can be well over 30% at pulsed output energy levels of millijoules to well above 100 millijoules depending on the device design and pump source. Although there is still a great deal of room for improvements, optical parametric oscillators have already been demonstrated to be versatile and practical broadly tunable coherent radiation sources.

© 1994 Optical Society of America