A Novel Scheme of Doppler-Free Spectroscopy by Differential Detection

We propose and implement a differential detection scheme of Doppler-free spectroscopy. By setting the proper relative polarization direction between the linearly polarized probe and pump beam, which are spatially counter-propagated and overlapped, simultaneous enhanced absorption and transmission are observed by detecting the parallel and perpendicular polarization components of the transmitted probe beam. The differential signal with improved signal-to-noise ratio (SNR) is also obtained, which is desired for compact optical reference, high-resolution spectroscopy and so on.