PHOTONIC FRONTIERS: FREQUENCY-SHIFTED DIODE LASERS: Shifting semiconductor laser wavelengths poses challenges

摘要

Nonlinear optics can generate new lines from semiconductor lasers by harmonic generation and frequency mixing, but it requires high power, good beam quality, and narrow linewidth. Nonlinear optics offer invaluable ways to fill gaps in the laser spectrum, from simple harmonic generation to more complex optical parametric oscillators (OPOs). Frequency doubling of diode-pumped neodymium (Nd) lasers has made green laser pointers cheap and compact, but why can't developers drop the diode pumping and directly double semiconductor laser output to produce hard-to-find wavelengths? It's been done for green light and is already reaching the market in pico-projectors from companies like MicroVision (Redmond, WA). But it's not easy. Nonlinear wavelength conversion requires not only raw power but also high beam quality and narrow-line emission. It's tough to combine all those features in a semiconductor laser. Yet progress is being made. The first products are on the market, and developers are reporting more encouraging results, including new laser designs, diode pumping of OPOs, and both harmonic generation and difference-frequency generation with quantum cascade lasers.