Instrumental noise and detectivity analysis of photopyroelectric destructive thermal-wave interferometry

A complete noise analysis of a two-beam photopyroelectric ~thermal-wave! destructive interferometric sensor instrument is presented and compared to its single-beam, noninterferometric counterpart. The noise analysis is performed using a Green-function formalism applied to experimental observations. The instrumental background noise contribution from the detector and the amplifier is separated from the laser noise and the instrumental noise due to amplification associated with different sensitivity scales. The latter serves as the source of comparison between the two sensor configurations. It is found that the dc laser drift noise and low-frequency fluctuation noise, which are dominant in the single-beam mode, are greatly reduced to the same order of magnitude as the instrumental background noise in the two-beam mode. The system white noise resulting from the incident laser beam and from the sensitivity scale ~amplification! of the demodulating lock-in amplifier are also examined in light of the experimental data. It is found that the detectivity D* ~the inverse of the noise equivalent power!, of the instrument is enhanced by at least 1 order of magnitude in the interferometric mode. © 2000 American Institute of Physics. @S0034-6748~00!01305-8#