Narrow linewidth laser system used for the intercombination transition spectrum measurement

Abstract

We observe the intercombination transition spectrum of alkaline-earth strontium, using a stable narrow 689 nm laser which is locked to a high fineness ultralow expansion reference cavity. The finesse is measured using cavity ring down techniques in different transverse modes of the cavity. Additionally, the response time of optical switch and PD monitor are taken into consideration in the measurement. Using a fiber-based optical frequency comb, the Allan deviation calculated from the counter value of the beat frequency shows a stability of 2.8× 10-13 in a 1 s averaging time. The saturation spectrum is measured with a minimum sub-Doppler width of 55 kHz. The high resolution intercombination transition spectrum can be used for absolute frequency stabilization.