An acousto-optic tunable filter instrument worked comparably to a CCD-based monochromator for a recent chemical warfare detection test, according to US military researchers. K. Ewing of the Naval Research Laboratory in Washington explained during a technical session at the Optical Society of America Annual Meeting that the lab has used Raman spectroscopy for several years to detect chemical warfare agents in the vapor phase. However, these instruments are too bulky and not rugged enough for military field use, so researchers tested a smaller solution: a collinear acousto-optic tunable filter device. Ewing said the research team used both Raman and acousto-optic instruments to examine nerve gas simulants and hydrocarbons. Both used argon-ion lasers at 488 nm. While the acousto-optic device required higher laser power (435 mW compared with only 75 mW for the CCD-based monochromator), he said the researchers believe they can reduce that power considerably. The team also is testing the instruments with a frequency-doubled Nd:YAG.