Frequency stability measurement of laser by using two independent tunable lasers

We demonstrate a novel scheme to measure frequency stability of laser by using two independent tunable lasers with the exactly same parameters. Due to the square relationship between the Allan variance of the beating tone and two laser sources, the frequency stability of the measured laser can be obtained through two steps. Thus, an optical reference source which is significantly more stable than the laser under test can eliminate the need. The frequency stability of the laser is 2.96×10
^-9
.