Knowledge Bank

High quality semiconductor lasers that operate at room temperature, in the red and near-IR spectral region, are beginning to play a significant role in $spectroscopy.a,b$ Our group at NIST, is one of many, that are developing and applying diode laser technology to scientific and technical problems. With some modification to the commercial laser devices it is possible to construct compact, efficient, broadly tunable (coarse tuning ~30 nm), single-frequency narrow-linewidth laser systems. Output powers of these tunable lasers range from ~1 to 100 mW with a good spatial beam quality. The spectral coverage of the diode lasers can be extended to the blue, UV, IR and even Far-IR by utilizing the modern techniques of nonlinear $optics.c,d,e$ These methods work very well in some spectral regions and are more challenging in other regions. A good-case example is the use of second harmonic generation in $KNbO3$ to produce light near 425 nm, where it is fairly straight forward to produce 10#### of milliwatts of usable output power. Access to much of the IR and far-IR can be achieved with difference frequency $mixing.d,e$ Recent advances in the rapidly changing semiconductor laser technology include: commercialization of grating-tuned external cavity lasers, and high power semiconductor amplifiers that can boost output powers to ~500 $mW.f$ Combining these system with the new nonlinear mixing materials (such as periodically-poled lithium niobate, and GaAs photomixers) opens up a variety of new research opportunities. In addition, many previous applications become more feasible with diode laser sources because the lasers are more efficient, compact and lower cost. The capabilities and limitations of these systems will be illustrated with examples taken from spectroscopic experiments.