Modeling polychromatic spontaneous emission of sodium in the mesosphere
Abstract
Adaptive optics systems correct the deformation of the wavefront caused by optical turbulence in the atmosphere. Absolute tip-tilt cannot be recovered in adaptive optics systems from laser guide stars and still limits the performance and sky coverage for adaptive optics systems. Normally a natural guide star is used for the tip-tilt sensing. Some techniques have been proposed to overcome the need for a natural guide star and to use laser guide stars for tip-tilt sensing. One of these techniques is the use of a polychromatic laser guide star, that generates light at several wavelengths in the mesosphere. Due to chromatic dispersion, different wavelengths show a differential tilt, and the absolute tip-tilt is recovered from the differential tilt between wavelengths. Two excitation schemes have been proposed for the generation of a polychromatic sodium laser guide star - a one-photon excitation at 330 nm and a two-photon excitation at 589 nm and 569 nm. We propose to numerically model the excitation of sodium atoms in the mesosphere at 330 nm and at 589 nm and 569 nm in a semi-classical approach by optical Bloch equations, and to model the propagation of the emitted light through the atmosphere by physical optics. The results will provide an expected number photons from spontaneous emission for each of the excitation schemes and estimates of the performance of polychromatic laser guide stars.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 06, 2025
- Source ID
- FA23862514008
Entities
People
- Joschua Hellemeier
Organizations
- Air Force Office of Scientific Research
- Australian National University
- United States Air Force