@article{158,
  author = {Jun Ye and John Hall},
  title = {Cavity ringdown heterodyne spectroscopy: High sensitivity with microwatt light power},
  abstract = {We present an ac heterodyne technique in cavity ringdown spectroscopy that permits 1x10-10 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.},
  year = {2000},
  journal = {Physical Review A},
  volume = {61},
  month = {2000-05},
  issn = {1050-2947},
  doi = {10.1103/PhysRevA.61.061802},
}