Simultaneous improvement of short- and long-term frequency stability of a diode laser

The long- and short-term frequency stability of a diode laser is simultaneously improved by using an external cavity whose resonance frequency is locked to the center of a Doppler-free spectrum of the 85Rb-D2 line without laser frequency modulation. The obtained linewidth of the diode lasers is less than 100 kHz and the long-term stability in terms of the square root of the Allan variance (sigma) monotonously decreases from 2 X 10-12 to 2 X 10-14 as the averaging time (tau) increases from 100 ms to 100 s.