High-resolution cavity enhanced absorption spectroscopy (CEAS) using a fast power-modulated laser with a phase-sensitive detection scheme has been adopted. A detailed investigation into the effects of laser chopping frequency and cavity modulation frequency (via a piezoelectric translator) on the sensitivity will be presented. The observed detection sensitivity has been improved by more than an order of magnitude after the implementation of phase sensitive detection. The observed single-scan sensitivity of the present setup is about 4.4 ppm Hz(-1/2) in fractional absorption using cavity mirrors with moderate reflectivity of similar to0.9997 and a ringdown cavity cell of 175 cm in length. (C) 2003 Elsevier Science B.V. All rights reserved.