A Compact Pumping Laser at 459 nm with 10−15 Stability for Cs Four-Level Active Optical Clock

Utilizing the modulation transfer spectroscopy (MTS) technique, we realize a compact pumping laser at 459 nm based on cesium (Cs) 6
²
S
_1/2
F=4 to 7
²
p
_1/2
F'=3 transition with a stability of 1. 8 ×10
^-14
/√{τ} and decreasing to 8×10
^-15
at 60 s. The 459 nm pumping laser stabilized by MTS technique, achieves the stability by about 2 orders of magnitude better than that of the saturation absorption spectroscopy (SAS), which will contribute to the linewidth reduction of 1470 nm ultimate laser in Cs four-level active optical clock. The 1470 nm stimulated radiation can reach a power of 100 μW with the stabilized 459 nm pumping laser power being 6 mW. Such a stable laser not only can be used as the pumping laser in active optical clock system, but also a novel optical frequency standard for length and other applications.