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Phys Rev Letters Cover ! Detecting POAM with Arecibo • 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 ! Do it first at 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, ...) Astronomical potential of POAM • 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, & megamasers – Synchrotron emission with well-organized source geometry – propagation through a turbulent, ionized plasma – pulsars, quasars, SETI, ... How to produce (or detect) POAM (Thide etL=0 al. 2007) case How to produce (or detect) POAM L=0 case L = 0 case t=0 How to produce (or detect) POAM L=0 case L = 0 case t=0 t=0 How to produce (or detect) POAM L=0 case L = 0 case t=0 t=0 t=0 t=0 t=0 t=0 t=0 t=0 L=0 phase fronts L=0 beam pattern How to produce (or detect) POAM L=1 case L = 1 case t=0 How to produce (or detect) POAM L=1 case L = 1 case t=0 t = P/8 How to produce (or detect) POAM L=1 case L = 1 case t=0 t = P/8 t = P/4 How to produce (or detect) POAM L=1 case L = 1 case t=0 t = P/8 t = P/4 t = 3P/4 t = P/2 L=1 phase fronts L=1 beam pattern L=2 beam pattern How to detect POAM with a single radio telescope (DRS point of view - active discussion going on) • 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 POAM with a single radio telescope ... 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) !! Do it first at 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, ...)