The creation of photonic orbital angular momentum in electromagnetic waves propagating through turbulence⋆,⋆⋆,⋆⋆⋆
1 Air Force Research Laboratory, Directed Energy Directorate, Kirtland AFB, New Mexico, USA
2 Science Applications International Corporation, Albuquerque, New Mexico, USA
Received: 26 June 2012
Accepted: 12 May 2013
Context. We have recently shown that the phenomenon known as “branch points” in AO are markers for photons carrying orbital angular momentum (OAM). In doing so, we have demonstrated that atmospheric turbulence creates well defined OAM states in beams propagating through it.
Aims. In this paper, we extend our previous research to include any astrophysical turbulent assemblage of molecules or atoms (TAMA), demonstrating that these clouds, similar to Earth’s atmosphere, also create photonic orbital angular momentum (POAM) in electromagnetic waves propagating through them. A TAMA is any gaseous cloud with a varying density and therefore variation in its index of refraction, which includes but is not limited to stellar envelopes, circumstellar disks, molecular clouds, planetary atmospheres, and the interstellar medium.
Methods. We applied our previous theoretical, simulation, and laboratory results to astrophysical TAMAs. Additionally, we demonstrated how sensors designed for AO can be used to measure this POAM flux.
Results. Our results apply to light propagating through any TAMA. Since TAMA are ubiquitous in the cosmos, steady, long lasting POAM fluxes will be ubiquitous as well.
Conclusions. Our results, which include theory, benchtop laboratory data, and wave optic simulation, indicate that, under the right conditions, POAM fluxes can reach over 50% of the total photon flux. An initial set of on-sky experimental observations appear to corroborate the laboratory results with two of the five stars, HR 1529 and HR 1577, showing POAM fluxes of 3% ± 1% and 2% ± 1% of the total flux, and a third, HR 1895, with a PAOM flux of up to 17% ± 2% of the total flux.
Key words: instrumentation: adaptive optics / turbulence / waves / radiation mechanisms: general / ISM: clouds
We express our gratitude to the Air Force Office of Scientific Research for their support of this research.
Appendices are available in electronic form at http://www.aanda.org
Data referred to in measurements are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/556/A130
© ESO, 2013