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Phys Rev Letters Cover !
• Photon orbital angular momentum has never been detected from an astronomical source, but it holds great promise as a diagnostic tool.
• We now know how to do it with radio techniques.
• Arecibo is the right instrument for a first detection !
Detecting POAM with Arecibo
• the most sensitive single dish on the planet by a substantial margin
• the best user-accessible signal processing instrumentation in the world
• a long tradition of phase-coherent processing expertise: radar, ionospheric, pulsar (Hankins, ...)
Do it first at Arecibo!
• Martin Harwit in 2003: “POAM in Astrophysics” (ApJ, 597, 1266)
• Well established physics (it has revolutionized quantum optics in the last 10 years!)
• Astrophysics: wherever the orbital motion of source particles or vorticity matters (synchrotron radiation!) ...
Astronomical potential of POAM
• Some possible detection scenarios
– Masers: interstellar, circumstellar, & mega-masers
– Synchrotron emission with well-organized source geometry
– propagation through a turbulent, ionized plasma
– pulsars, quasars, SETI, ...
Astronomical potential of POAM ...
L=0 case How to produce (or detect) POAM(Thide et al. 2007)
L=0 case How to produce (or detect) POAM
L = 0 caset = 0
L=0 case How to produce (or detect) POAM
L = 0 caset = 0
t = 0
L=0 case How to produce (or detect) POAM
L = 0 caset = 0
t = 0
t = 0
t = 0
t = 0
t = 0
t = 0
t = 0
L=0 phase fronts
L=0 beam pattern
L=1 case How to produce (or detect) POAM
L = 1 caset = 0
L=1 case How to produce (or detect) POAM
L = 1 caset = 0
t = P/8
L=1 case How to produce (or detect) POAM
L = 1 caset = 0
t = P/8
t = P/4
L=1 case How to produce (or detect) POAM
L = 1 caset = 0
t = P/8
t = P/4
t = P/2
t = 3P/4
L=1 phase fronts
L=1 beam pattern
L=2 beam pattern
• construct a focal plane array with circular symmetry
• point the telescope off-axis by a prescribed amount for each L value (not restricted to integer L values)
• record the baseband signals from each of the detectors
• look for the helical winding of the signal characteristic of POAM
How to detect POAMwith a single radio telescope
(DRS point of view - active discussion going on)
MORE SPECULATIVE:
• detect the angular momentum content directly (torque as opposed to force on charge carriers)
– in optics (Curtis & Grier, 2003, PRL) this has been seen directly: imparting orbital motion to colloidal particles!
– E. Purcell “curlmeter” might be a radio technique
– or transfer the POAM to the ang. momentum of a quantum liquid (B-E condensate) !!
How to detect POAMwith a single radio telescope ...
• the most sensitive single dish on the planet by a substantial margin
• the best user-accessible signal processing instrumentation in the world
• a long tradition of phase-coherent processing expertise: radar, ionospheric, pulsar (Hankins, ...)
Do it first at Arecibo!
