Frequency stabilization of lasers by locking to an atomic isoclinic point

To overcome the temperature sensitivity of lasers locked to Doppler-broadened transitions, we propose a scheme in which the laser is locked to an isoclinic point of the atom's spectrum: a frequency at which the first derivative of the absorption spectrum does not change upon a physical change of the sample. Here, we demonstrate that an isoclinic point exists in the Rb
⁸⁷
D
₁
spectrum at 795 nm, and that it is located midway between the F
_g
=2 → F
_e
=1 and F
_g
=2 → Fe=2 transitions. Locking a VCSEL diode laser to this isoclinic point, we have been able to demonstrate a very low sensitivity of the locked laser's frequency to temperature variations of the atomic vapor.