Thermal noise further reduced ultrastable laser with frequency instability of 5൷10−16

We report on the progress of the thermal noise further reduced method via enlarging the equivalent beam size without increasing the cavity length in cavity-stabilized lasers at 1555 nm, which are built as the frequency source for a photonic microwave generation system. In addition, we perform an experiment to evaluate the effect of thermal noise reduced method via estimating the frequency instability of a synthesized new ultrastable laser. The relative frequency instability reaches 5∗10−16 at 1 s averaging time via reducing the thermal noise of the cavity.