Cs 455 nm Nonlinear Spectroscopy with Ultra-narrow Linewidth

Nonlinear spectroscopy has become a useful tool in laser cooling, frequency stabilization and so on. We use the 455.5 nm light beam output of an external cavity diode laser to perform the saturation spectroscopy signal and polarization spectroscopy signal on the 6S 1/2 → 7P 3/2 transition in cesium. The measured linewidth of the F4 → 4, 5 transition is as narrow as 1.40 MHz and that of the F3 → 2,3 transition is 1.67 MHz. Both of them are very close to the natural linewidth of about 1.2 MHz. Our result is the narrowest measured linewidth of Cs 455 nm saturation spectroscopy signal to our knowledge.