Development of an IR tunable diode laser absorption spectrometer for trace humidity measurements at atmospheric pressure

Application of InAsSb/InAsSbP and lead chalcogenide infrared diode lasers for photoacoustic detection in the 3.2 and 5 microm region

An investigation of photoacoustic detection using 3.2-3.6 and 5 mum diode lasers is described. An inexpensive resonant photoacoustic system was developed based, on a simple glass cell and condenser and electret microphone (Brüel & Kjaer type 4144/Sennheiser type K6P). The system was tested on the single rotation-vibration lines of C(2)H(2), CO, COS, and NH(3) gases. The best detection limits obtained are 300 ppm V for C(2)H(2) and 20 ppm V for COS. Potential applications of infrared diode laser photoacoustic detection lie in the areas of analytical chemistry, atmospheric research, and investigation of the kinetics of reactive species.

Trace Moisture Detection Using Continuous-Wave Cavity Ring-Down Spectroscopy

We have developed an instrument to measure trace concentrations of small hydride species in gases using continuous-wave cavity ring-down spectroscopy with near-infrared diode laser excitation. An rms baseline equivalent absorbance of 9.2 x 10(-11) cm(-1)/square root(n) is found, where n is the number of ring-down transients. When the 1396.376-nm absorption line of water is used, this corresponds to a noise equivalent moisture concentration in nitrogen gas of 68 pptv/square root(n). Water vapor concentration is detected over a range extending from 3 to 1000 ppbv and found to depend linearly on the concentration as determined by a calibrated commercial moisture sensor.