Document Type

Article

Publication Date

Spring 5-17-2000

Publication Title

Physical Review A

ISSN

1050-2947

Volume

61

Issue

6

First Page

061802-1

Last Page

061802-4

DOI

10.1103/PhysRevA.61.061802

Abstract

We present an ac heterodyne technique in cavity ringdown spectroscopy that permits 1×10−10 absorption sensitivity with microwatt-level light power. Two cavity modes, one probing the empty cavity and the other probing intracavity absorption, are excited simultaneously but with their intensities temporally out of phase, with one mode decaying and the other rising. Heterodyne detection between the two modes reveals the dynamic time constants associated with the empty cavity and the additional intracavity gas absorption. The method offers a quick comparison between the on- and off-resonance information, a prerequisite to reaching the fundamental shot-noise limit. This simple and yet important improvement of cavity ringdown spectroscopy should lead to the enhanced performance of a wide range of applications.

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