V. Da Deppo 3, D. Faria 1, S. Fornasier 2 D. Dravins 1, C. Barbieri 2 V. Da Deppo 3, D. Faria 1, S. Fornasier 2 R. A. E. Fosbury 4, L. Lindegren 1 G. Naletto 3, R. Nilsson 1, T. Occhipinti 3 F. Tamburini 2, H. Uthas 1, L. Zampieri 5 (1) Lund Observatory (2) Dept. of Astronomy, Univ. of Padova (3) Dept. of Information Engineering, Univ. of Padova (4) ST-ECF, ESO Garching (5) Astronomical Observatory of Padova

EXTREMELY HIGH-RESOLUTION ASTRONOMICAL SPECTROSCOPY λ/Δλ ≳ 100,000,000

HIGHEST TIME RESOLUTION, REACHING QUANTUM OPTICS Other instruments cover seconds and milliseconds QUANTEYE will cover milli-, micro-, and nanoseconds, down to the quantum limit !

SPECTRAL RESOLUTION Resolving power λ/Δλ ≳ 100,000,000 First “extreme-resolution” optical spectroscopy in astrophysics Required to resolve laser lines with expected intrinsic widths ≈ 10 MHz Realized through photon-counting digital intensity-correlation spectroscopy

Intensity interferometry Narrabri stellar intensity interferomer circa 1970 (R.Hanbury Brown, R.Q.Twiss et al., University of Sydney)

Information content of light D.Dravins, ESO Messenger 78, 9

PHOTON STATISTICS Top: Bunched (quantum-random) photons Center: Independent (classically-random) photons Bottom: Antibunched photons After R. Loudon The Quantum Theory of Light (2000)

CO2 lasers on Mars Spectra of Martian CO2 emission line as a function of frequency difference from line center (in MHz). Blue profile is the total emergent intensity in the absence of laser emission. Red profile is Gaussian fit to laser emission line. Radiation is from a 1.7 arc second beam (half-power width) centered on Chryse Planitia. The emission peak is visible at resolutions R > 1,000,000. (Mumma et al., 1981)

Lasers around Eta Carinae S. Johansson & V.S. Letokhov Astrophysical lasers operating in optical Fe II lines in stellar ejecta of Eta Carinae A&A 428, 497 (2004)

Spectral resolution = 100,000,000 ! To resolve narrow optical laser emission (Δν  10 MHz) requires spectral resolution λ/Δλ  100,000,000 Achievable by photon-correlation (“self-beating”) spectroscopy ! Resolved at delay time Δt  100 ns Method assumes Gaussian (thermal) photon statistics

Photon correlation spectroscopy LENGTH, TIME & FREQUENCY FOR TWO-MODE SPECTRUM E.R.Pike, in R.A.Smith, ed. Very High Resolution Spectroscopy, p.51 (1976)

Spectral resolution R Length Time 100,000 5 cm 200 ps 1,000,000 50 cm 2 ns 10,000,000 5 m 20 ns 100,000,000 50 m 200 ns 1,000,000,000 500 m 2 s

Photon correlation spectroscopy Analogous to spatial information from intensity interferometry, photon correlation spectroscopy does not reconstruct the shape of the source spectrum, but “only” gives linewidth information

Photon statistics of laser emission (a) If the light is non-Gaussian, photon statistics will be closer to stable wave (such as in laboratory lasers) (b) If the light has been randomized and is close to Gaussian (thermal), photon correlation spectroscopy will reveal the narrowness of the laser light emission

Photon correlation spectroscopy Advantage #1: Photon correlations are insensitive to wavelength shifts due to local velocities in the laser source Advantage #2: Narrow emission components have high brightness temperatures, giving higher S/N ratios in correlation spectroscopy

ROLE OF LARGE TELESCOPES VLT’s & ELT’s permit enormously more sensitive searches for high-speed phenomena in astrophysics Statistical functions of arriving photon stream increase with at least the square of the intensity

5 x 5 array of 20 μm diameter APD detectors (SensL, Cork)

Advantages of very large telescopes Telescope diameter Intensity <I> Second-order  correlation  <I2> Fourth-order photon  statistics  <I4> 3.6 m 1 8.2 m 5 27 720 4 x 8.2 m 21 430 185,000 50 m 193 37,000 1,385,000,000 100 m 770 595,000 355,000,000,000