Ultra-cold atoms in an optical cavity: two-mode laser locking to the cavity avoiding radiation pressure

Abstract

The combination of ultra-cold atomic clouds with the light fields of optical cavities provides a powerful model system for the development of new types of laser cooling and for studying cooperative phenomena. These experiments critically depend on the precise tuning of an incident pump laser with respect to a cavity resonance. Here, we present a simple and reliable experimental tuning scheme based on a two-mode laser spectrometer. The scheme uses a first laser for probing higher-order transversal modes of the cavity having an intensity minimum near the cavity's optical axis, where the atoms are confined by a magnetic trap. In this way the cavity resonance is observed without exposing the atoms to unwanted radiation pressure. A second laser, which is phase-locked to the first one and tuned close to a fundamental cavity mode drives the coherent atom-field dynamics.

Observation of Subradiant Atomic Momentum States with Bose-Einstein Condensates in a Recoil Resolving Optical Ring Resonator

“…The pump light is generated by an amplified external cavity diode laser which is locked to a transverse mode of the cavity (TEM 10 ) with an uncertainty of better than 200 Hz. This reference mode has very little spatial overlap with the atoms and thus does not interact with the atoms [19]. The frequency of the pump light is red detuned relative to the frequency ω 0 of the D1 transition (5s, F = 2, m F = 2 to 5p 1/2 , F = 2, m F = 2) by ∆ a = ω − ω 0 = −100 GHz.…”

Pinning Transition of Bose-Einstein Condensates in Optical Ring Resonators

“…The s-polarized forward propagating TEM 00 mode ("pump mode") is longitudinally pumped from one side with up to 6 mW from an amplified diode laser system at a frequency ω detuned by ∆ a = ω − ω 0 =−60 GHz relative to the atomic transition frequency ω 0 (D1 Line: 5s 1/2 , F = 2 to 5p 1/2 , F = 2). Part of the laser output is used to electronically stabilize the laser to the reverse propagating p-polarized TEM 10 mode [16] with a precision of about 2π×200 Hz. Frequency and amplitude of the pump light is controlled by an acousto-optical modulator.…”

Cavity-Controlled Collective Scattering at the Recoil Limit

“…We minimize the impact of this reference light on the atomic cloud by two measures. Firstly, the reference light is injected with low power on a TEM 11 -mode of the cavity exhibiting an intensity minimum near the optical axis, where the atomic cloud is located [10]. The pump beam frequency is shifted from the reference light by means of an acousto-optic modulator (AOM) in order to lie close to a TEM 00 -resonance.…”