The Rb-D1 and D2 absorption lines and their spectroscopy systems are examined and discussed as a frequency standard for frequency stabilisation of a semiconductor laser. It is concluded that the Rb-D2 saturated absorption profile has large Doppler free spectra and is a good frequency standard.
We present and analyze a bichromatic version of the well-known saturation absorption spectroscopy technique used to stabilize lasers to atomic resonances without Doppler broadening. We show that the spectroscopic properties can be transferred between two transitions at very different wavelengths by spectral hole burning in a Doppler-broadened atomic ensemble. Specifically, we demonstrate that this technique can be used to stabilize a laser to the D1 line of Rb87 by obtaining a saturation absorption spectrum with a strong pump laser stabilized to the D2 line. This allows for more freedom in the choice of the probe laser frequency offsets compared to conventional saturation absorption spectroscopy. We compare our experimental results to an analytical model and numerical results based on rate equations.
The frequency of a GaAs semiconductor laser was locked to the hyperfine spectrum of the Rb D/sub 1/ line by saturation spectroscopy. A first GaAs laser was locked to one of the Doppler-free hyperfine lines using a source modulation method. The burnt hole modulated by the stabilized laser beam was detected by a second laser beam irradicated from the same or the opposite direction and was used as a frequency discriminator to stabilize the second laser. The characteristics of the double-resonance spectrum were measured. The frequency stability of the second laser, which was free from frequency modulation, was estimated to be on the order of 10/sup -9/.>
In recent years, much work has been done in experimental studies to frequency lock laser diodes to atomic or molecular resonances.1 By such techniques it is possible to improve greatly the laser frequency stability and to define precisely its nominal value. For laser sources operating in the 0.8-μm range, rubidium is the preferred specie and each isotope offers two resonance lines, one at 780 nm (D2 line) and one at 795 nm (D1 line). Both linear and saturated absorption have been used, and laser frequency charcteristics are published.2,3
We present a practical method to avoid the mis-locking phenomenon in the saturated-absorption-spectrum laser-frequency-locking system and set up a simple theoretical model to explain the abnormal saturated absorption spectrum. The method uses the normal and abnormal saturated absorption spectra of the same transition 5 2 S 1/2 , F = 2–5 2 P 3/2 , F ' = 3 saturated absorption of the 87 Rb D 2 resonance line. After subtracting these two signals with the help of electronics, we can obtain a spectrum with a single peak to lock the laser. In our experiment, we use the normal and inverse signals of the transitions 5 2 S 1/2 , F = 2–5 2 P 3/2 , F ' = 3 saturated absorption of the 87 Rb D 2 resonance line to lock a 780-nm distributed feedback (DFB) diode laser. This method improves the long-term locking performance and is suitable for other kinds of diode lasers.