Narrowband, tunable deep-UV diode-laser-based source detects gas species
Dahv Kliner from Harvard University (Cambridge, MA), with Jeff Koplow and Lew Goldberg from the Naval Research Laboratory (Washington, DC), demonstrated a narrow-bandwidth 215-nm ultraviolet (UV) source, tunable over many nanometers. The deep-UV (DUV) radiation was produced by frequency-quadrupling the 860-nm output of a high-power, pulsed gallium aluminum arsenide (GaAlAs) tapered amplifier seeded by an external-cavity diode laser. Pulsing the amplifier increased the 860- to 215-nm conversion efficiency by two orders of magnitude with respect to CW operation. The researchers generated enough DUV radiation to measure several absorption lines of nitric oxide (NO) and sulfur dioxide (SO2) by high- resolution absorption spectroscopy. Goldberg says these measurements represent an important "first" in the use of a compact UV source for gas detection.
Until now, UV-based gas detection has not been widely pursued for applications requiring compact instrumentation because of the lack of suitable narrowband, tunable UV sources. When compared with infrared (IR) absorption, the one to two orders-of-magnitude larger absorption cross section in the UV offers a significantly higher detection sensitivity for many species. Another important advantage of UV- versus IR-based detection is that relatively low-cost, low-noise detectors can be used that provide high sensitivity and operate at room temperature.