A team from Los Gatos Research in Mountain View, Calif., has developed a modified version of ringdown spectroscopy that obtains information about a trace molecule's absorption spectrum over a large optical bandwidth with a single laser shot.

Ringdown spectroscopy measures the life-time of a photon in an optical cavity to determine the total intracavity loss, which can be used to derive a substance's absolute absorption intensities.

Most methods extract decay times by repeatedly scanning the narrowband-input laser over a range of frequencies.

As reported in the Dec. 20 issue of Applied Optics, the method, called ringdown spectral photography, simultaneously maps time and numerous frequency responses from a broadband source into orthogonal axes of an array detector with a rotating mirror and diffraction grating. This "single shot" technique should be several orders of magnitude faster than previous ringdown methods.