Laser stabilization to an atomic transition using an optically generated dispersive line shape

Abstract

We report a simple and robust technique to generate a dispersive signal which serves as an error signal to electronically stabilize a monomode continuous-wave laser emitting around an atomic resonance. We explore nonlinear effects in the laser beam propagation through a resonant vapor by way of spatial filtering. The performance of this technique is validated by locking semiconductor lasers to the cesium and rubidium D 2 lines and observing long-term reduction of the emission frequency drifts, making the lasers well adapted for many atomic physics applications.

Two-beam nonlinear Kerr effect to stabilize laser frequency with sub-Doppler resolution

“…The signal of ℜ(χ (3) ) changes across the atomic resonance, giving rise to a sign change of n 2 and of the self-lensing effect, which passes from self-defocusing (red detuned) to self-focusing (blue detuned). Detection of the laser beam after an aperture past a hot resonant atomic vapor thus results in a Doppler-broadened dispersive lineshape, used in the ANGELLS technique to lock the laser frequency [8].…”

“…Differently from [8], a second counter-propagating pump beam is introduced to produce a sharp dispersive lineshape. It velocity-selectively saturates the vapor and modifies the medium seen by the detected probe beam.…”

“…The scheme of the electronic circuit that produces the electronic feedback is detailed elsewhere [8] and will be described here in a simplified way: the photodetector signal has a dispersive-like shape with a non-zero voltage average value, corresponding to the off-resonance aperture transmission. We obtain an error signal centered at zero by subtracting a controlled reference voltage from the photodetector signal.…”

“…Alkali vapors are very interesting nonlinear systems since the third-order susceptibility (χ (3) ) can be easily modified by changing the field amplitude or by finely tuning the laser frequency across the resonance [9]. The dependence of χ (3) with the detuning is the key element of the ANGELLS technique we have developed to lock the laser frequency with Doppler resolution [8]. Moreover, the χ (3) term can be drastically modified by the introduction of a second laser beam permitting sub-Doppler resolution.…”

Stabilization of a laser on a large-detuned atomic-reference frequency by resonant interferometry

“…Many different techniques generate a reference signal to stabilize the laser frequency around the atomic resonance, within a range that is of the order of the Doppler width. Examples of such techniques are modulation of a linear absorption signal [1], DAVLL [2] and ANGELLS [3,4]. However, in some experiments it is desirable to stabilize the laser frequency up to a few GHz from the line-center.…”