High-resolution spectroscopy of the ³⁹K transitions at 770 nm and ¹³C ₂H ₂ saturated lines by a solid-state laser at 1.54 μm: Toward an accurate frequency standard in the optical communication band

A novel and compact Er-Yb: glass laser was developed with single-frequency output power > 10 mW in a wavelength range from 1531 to 1547 nm. The laser output was efficiently frequency doubled at 770.1 nm in a single-pass periodically poled lithium niobate waveguide and a second harmonic power in excess of 15 μW was achieved, with an internal conversion efficiency of ∼ 220% W ^-1. This frequency-doubled beam was used for high-resolution saturated spectroscopy of the ³⁹K 4S _1/2-4P _1/2 absorption line. The best resolved crossover peak showed 16% line contrast and 10-MHz linewidth. In a second experiment, working at the fundamental frequency, saturation spectroscopy of ¹³C ₂H ₂ was achieved using a low-pressure gas cell inside a build-up cavity. The measured absorption dip has 3% line contrast and 1.2 MHz linewidth. Both the atomic and molecular saturated lines are very well suited for frequency locking in order to establish accurate frequency standards in the optical communication band.