Current Ground Experiments for Self-Guided Laser and Atomic Beam Space Propulsion

Author: Hayden Morgan

Background: Beamed energy space propulsion concepts must contend with beam divergence during propagation through space, resulting in reduced thrust during the later period of acceleration. A combination of a spatially overlapped laser beam and atomic beam shows capability for self-guiding and significantly reduces the detrimental impact of divergence. The laser light is guided through the higher refractive index in the atomic beam. In a corresponding way, the atoms are guided via an optical dipole trap that draws particles toward the regions of high laser intensity.

Objective: The research objective is to demonstrate and quantify a mutual self-guiding effect through the development of ground experiments that provide a reasonable space analogue environment. Methods: To characterize the propagation of the atomic beam, multiple laser diagnostic stations are installed along the propagation axis to extract the density and temperature cross-sections. Overlapped laser characterization is completed using a novel beam decoupler system that allows a camera to image the final state of the laser beam profile with and without the influence of the atomic beam.

Results: Data from the recent overlapped experiment is still being processed, however, from cursory evaluations it appears that a low intensity laser beam tuned closer atomic resonance exhibited some fluctuations in a spatial intensity profile that could indicate a light guiding behavior of the atomic beam. Additionally, by tuning the spatially overlapped laser across the atomic resonance, an axial velocity distribution of the atoms can be obtained. This absorption behavior of the atomic jet was seen in the experiment as laser intensity at the end of propagation changed with the laser tuning across the atomic resonance. Further analysis will identify if the atomic density distribution changed with the laser tuning parameters, or if the dipole force was too weak and further cooling of the atoms is necessary.

Conclusion: Demonstration of the self-guiding behavior and quantification of how it manifests for both constituents will provide key datasets for validation of computational models. These simulations can then be used to predict capabilities of proposed full-scale in-space infrastructure. This work will also identify areas for improvements with the design of the atomic beam, atomic cooling methods, and diagnostic capabilities.