High-resolution laser spectroscopy based on polarisation-modulated optical phase conjugation in a demountable cathode discharge

Abstract

Doppler-free laser spectroscopy based on polarisation-modulated optical phase conjugation in a demountable hollow-cathode discharge is a sensitive analytical method, as a visible coherent laser beam is generated as the signal. Because the conjugate signal beam is a time-reversed replica of the probe beam, the optical signal can be detected conveniently and efficiently. Spectral resolution is excellent as both Doppler and Lorentzian broadenings are negligible. Taking advantage of the polarisation properties of the phase-conjugate wavefront, we demonstrate a novel polarisation-modulated detection scheme in this spectroscopic method using a relatively low-power continuous-wave laser and the hyperfine structure of the sodium 3s ²S_1/2 to 3p ²P_3/2 transition. Some advantages of the polarisation-modulated degenerate four-wave mixing are discussed.