Integrated cavity output analysis of ultra-weak absorption

It is demonstrated that direct absorption optical measurements with sensitivities of better than 1 part in a million can be made using pulsed light sources and employing a simple cavity optical configuration. A model is presented which demonstrates that the integrated absorption signal provides a quantitative total attenuation measurement if the absorption cavity mirror reflectivities are known. This approach to making absorption measurement provides a sensitivity comparable to that realized using the time-domain cavity ringdown approach with a significant reduction in complexity. The approach is demonstrated using the weak b(1)Sigma(g(upsilon'=1))-X(3)Sigma(g(upsilon "=0)) forbidden absorption of oxygen near 689 nm. (C) 1998 Elsevier Science B.V. All rights reserved.