Characteristics of a resonant opto-acoustic gas concentration detector

Brewster window and windowless resonant spectrophones for intracavity operation

“…For most efficient excitation of the j1th mode, it is ' * irable that the integrand (and hence Pj) have the same sign throughout that rather small portion the cell volume in which I(r) differs significantly from zero. Brewster1s angle~the ratio of cell radius R to length L must be (2) where a Ol = 1.2197 is the fi zero of dJo(TIa)/da, 6 01 = 0.7655 is the first zero Jo(TIS), and n is the ve index of the window material.…”

“…Our spectrophone was designed for use with NaCl Brewster windows, having refractive index 1.491 at wavelength 10~m; thus (2) gives R/L = 1.188. (Our actual R/l was 1.190.)…”

Determination of nitrogen dioxide by visible photoacoustic spectroscopy

“…The resurgent interest in photoacoustiic spectroscopy fostered by the development of versatile lasers was rapidly directed toward practical applications such as the quantitative detection of atmospheric pollutants (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14), particularly N02…”

Photoacoustic spectroscopy in gases based on wavelength modulation

“…A differential cell design in principle can compensate for the background (10), but it is very difficult to match the reference and the sample chambers, both in magnitude and in the phase of the background signal. A resonant cell can be built to create standing acoustic waves inside, such that the windows are at well-defined nodes (11). The nature of the resonance obviously depends on the exact composition of the gas inside and may not be easily controlled from one sample to the next.…”