The current photoacoustic instrument uses a laptop data acquistion system and a small equipment rack (left). The acoustical resonator and laser, optics, etc, that comprise the photoacoustic instrument are in the enclosure on the right. Two lasers are now in use, the usual one at 532 nm that requires use of an optical chopper, and another one at 1047 nm that can be electronically modulated (no chopper necessary). The 1047 nm instrument is particularly useful for monitoring the black carbon content of vehicle exhaust. Laser alignment is now easily accomplished with 4 knobs, and feedback on alignment progess is provided by 2 miniature video cameras located in the enclosure.