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 1Σg(v′=1)–X3Σg(v″=0) forbidden absorption of oxygen near 689 nm.