Cesium active optical clock in four-level laser configuration

We propose an active optical clock scheme in four-level configuration with cesium atoms. The population inversion has been established experimentally between 7S
_1/2
state and 6P
_3/2
state in a thermal cesium cell with a 455.5 nm pumping laser. It can be used to generate active optical clock laser output in a bad cavity laser regime at the wavelength of 1469 nm.