title: Continuous adaptive beam pointing and tracking for laser power transmission.
abstract: The adaptive beam pointing concept has been revisited for the purpose of controlled transmission of laser energy from an optical transmitter to a target. After illumination, a bidirectional link is established by a retro-reflector on the target and an amplifier-phase conjugate mirror (A-PCM) on the transmitter. By setting the retro-reflector's aperture smaller than the diffraction limited spot size but big enough to provide sufficient amount of optical feedback, a stable link can be maintained and light that hits the retro-reflector's surrounded area can simultaneously be reconverted into usable electric energy. The phase conjugate feedback ensures that amplifier's distortions are compensated and the target tracked accurately.After deriving basic arithmetic expressions for the proposed system, a section is devoted for the motivation of free-space laser power transmission which is supposed to find varied applicability in space. As an example, power transmission from a satellite to the earth is described where recently proposed solar power generating structures on high-altitudes receive the power above the clouds to provide constant energy supply.In the experimental part, an A-PCM setup with reflectivity of about R(A-PCM) = 100 was realized using a semiconductor optical amplifier and a photorefractive self-pumped PCM. Simulation results show that a reflectivity of R(A-PCM)>1000 could be obtained by improving the self-pumped PCM's efficiency. That would lead to a transmission efficiency of eta>90%.
authors.affiliation: Space Communications Group, New Generation Wireless Communications Research Center, National Institute of Information and Communications Technology, Koganei, Tokyo, Japan. Schaefer@nict.go.jp
authors.forename: Christian A
authors.initials: CA
authors.lastname: Schäfer
mesh_terms: D001272:Atmosphere; D005336:Fiber Optic Technology / Q000379:methods*; D007834:Lasers; D008027:Light; D008962:Models, Theoretical; D011827:Radiation; D012993:Solar Energy; D018531:Spacecraft; D013472:Sunlight