Trace Chemical Vapor Detection by Photothermal Interferometry

Photothermal interferometry has been demonstrated for detection of vapors with extremely high sensitivity (parts-per-trillion). Our present research uses a photothermal detection scheme that incorporates tunable sources and a modified Jamin interferometric design to provide high selectivity and sensitivity for organo-phosphate vapor detection. Phase shifts on microradian levels have been detected. Trace chemical vapor detection is accomplished by introducing the tunable excitation laser along the path of one interferometer beam providing a phase shift due to absorptive heating. Preliminary results indicated parts-per-billion detection of both DMMP and DIMP using ~400mW of CO2 laser power at appropriate wavelengths.