Rapid scan absorption spectroscopy using a waveform-driven electro-optic phase modulator in the 1.6- 1.65 υm region
Kevin O. Douglass, Stephen E. Maxwell, Gar W. Truong, Roger D. van Zee, Joseph T. Hodges, David A. Long, David F. Plusquellic
A method is reported for performing fast optical frequency scans over a bandwidth of 36.9 GHz and at a sweep rate of 40 kHz using a single second-order sideband from an electro-optic phase modulator driven by an arbitrary waveform generator. Single sideband selection is accomplished using the resonator modes of a Fabry-Perot filter cavity having a finesse of ≅44 and a free-spectral range of 300 MHz. The finesse is sufficiently high to give 2 near 1602 nm and for CH4 lines near 1643 nm. Detection of ambient level concentrations of each of these gases is demonstrated in a 25 υs scan over a path length of 50 m at a sensitivity of ≅3 × 10−9 cm−1 Hz−1/2. The corresponding measurement uncertainties (k=1 or 1ς) in a (2-3) ms time period and a 1 km path length are 2 and 4. The arbitrary waveform control of the pulse sequence, repetition rate, and duty cycle provides for optimization of the light source for a variety of application areas that include path integrated differential absorption and differential absorption light detection and ranging.
Journal of the Optical Society of America B-Optical Physics