16 May 2017
Wavefront aberrations are identified as a major limitation in quantum sensors. They are today the main contribution in the uncertainty budget of best cold atom interferometers based on two-photon laser beam splitters, and constitute an important limit for their long-term stability, impeding these instruments from reaching their full potential. Moreover, they will also remain a major obstacle in future experiments based on large momentum beam splitters. In this study, we have tackled this issue by using a deformable mirror to control actively the laser wavefronts in atom interferometry. In particular, we have demonstrated in an experimental proof of principle the efficient correction of wavefront aberrations in an atomic gravimeter.
- Laser wavefronts propagation.
- The laser beam enters the vacuum chamber from the top and exits through the bottom window. The descending wavefront is taken as flat (red). After being reflected by a standard mirror (left) or a deformable mirror (right), it re-enters the vacuum chamber (blue). Left: the ascending wavefront gets distorted by the aberrations of the bottom window, $\lambda$/4 plate and standard mirror. The laser phase difference then depends on the transverse position. It gets sampled differently at the three pulses depending on the ballistic trajectories of the atoms, which leads to a bias. Right: the ascending wavefront is corrected by properly shaping the deformable mirror. This leads to uniform laser phase differences and no bias.
The large dynamical range of the deformable mirror and its short response time would enable, at the same time, to suppress Coriolis acceleration (compensating Earth rotation by counter-rotating the mirror during the interferometer sequence) and reject ground vibration noise (by translating the mirror surface in real time or right before the last Raman pulse). These compensation techniques can be extended to other instruments based on atom interferometry, such as gravity gradiometers and gyroscopes. In particular, they would be relevant for large scale experiments, such as based on large momentum transfer beam splitters and/or long interferometer times. Indeed, in these experiments, the effect of wavefront aberrations scales as the effective momentum nħk imparted to the atoms, and the effect of high order aberrations onto the inertial measurement increases with the interferometer duration 2T.
S. Merlet, L. Volodimer, M. Lours, F. Pereira Dos Santos, "A simple laser system for atom interferometry", Appl. Phys. B 117, 749 (2014)
A. Trimeche, M. Langlois, S. Merlet, F. Pereira Dos Santos, "Active control of laser wavefronts in atom interferometers", Phys. Rev. Applied 7, 034016 (2017)