OWL Instrument Concept Design Quantum OWL ! INSTRUMENT CONCEPT IDEAS Dainis Dravins Lund Observatory, Sweden

OWLS NEED QUANTUM EYES…

Quantum OWL OWL instrument design study 2005 ESO Garching; Lund Observatory; University of Padua

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

SECONDS & MILLISECONDS Lunar & planetary-ring occultations Rotation of cometary nuclei Pulsations from X-ray pulsars Cataclysmic variable stars Pulsating white dwarfs Optical variability around black holes Flickering of high-luminosity stars X-ray binaries Optical pulsars Gamma-ray burst afterglows (partially listed from pre-launch program for HSP on HST)

MILLI-, MICRO- & NANOSECONDS Millisecond pulsars ? Variability near black holes ? Surface convection on white dwarfs ? Non-radial oscillations in neutron stars ? Surface structures on neutron-stars ? Photon bubbles in accretion flows ? Free-electron lasers around magnetars ? Astrophysical laser-line emission ? Spectral resolutions reaching R = 100 million ? Quantum statistics of photon arrival times ?

MAIN PREVIOUS LIMITATIONS CCD-like detectors: Fastest practical frame rates: ms Photon-counting detectors: Limited photon-count rates: ≳ 100 kHz

DESIRED INSTRUMENT PROPERTIES Temporal resolution limited by astrophysics, not detector: ≈ 1 ns – 100 ps Photon-counting detectors: Sustained photon-count rates ≈ 100 MHz Quantum efficiency ≲ 100% from near-UV to near-IR

INSTRUMENT DESIGN ISSUES Challenges are primarily in detectors & data handling Imaging optics may be “ordinary” (more or less similar to those of imaging cameras)

4-Dimensional detector system 2D spatial + 1D spectral & polarization + 1D temporal 1024 x 1024 imaging elements (possibly in sections to include calibration objects) Each imaging element with spectral & polarization channels Spectral resolving power λ/Δλ ≈ 100,000,000 (digital intensity correlation spectroscopy)

INSTRUMENT DESIGN ISSUES Possible detector layout (only APD arrays appear to match requirements) Detector filling factor ≪ 100% (probably requires microlens imaging)

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

32x32 Single Photon Silicon Avalanche Diode Array Quantum Architecture Group, L'Ecole Polytechnique Fédérale de Lausanne

Four 32x32 Single Photon Silicon Avalanche Diode Arrays Quantum Architecture Group L'Ecole Polytechnique Fédérale de Lausanne

SUSS MicroOptics Neuchâtel

Photonics and Optoelectronics, Edith Cowan University, Perth, WA

Microlens array Fraunhofer-Institut für Siliziumtechnologie (ISIT), Itzehoe

“ULTIMATE” DATA RATES * 1024 x 1024 imaging 100 spectral & polarization channels * Each channel 10 MHz, 1 ns time resolution * photon time-tags per second = 1 PB/s (Petabyte, B) = some EB/h (Exabyte = B)

“REALISTIC” DATA RATES * 1024 x 1024 imaging elements one wavelength channel at a time * Each channel 10 MHz with 1 ns time resolution * photon time-tags per second = 10 TB/s (Terabyte, B) ≈ 1 PB/min (Petabyte, B) ≈ 1 EB/few nights (Exabyte = B)

HANDLING HIGH DATA RATES Digital correlator integrated onto each detector channel (or pair of channels), outputting 1024 points on correlation functions Sampling correlation function once per second ”compresses” data a factor 10 4 Real-time system identifies the 100 most interesting spatial channels; reduces data another factor 10 4 Original data rate 10 TB/s thus reduced to 100 kB/s

INSTRUMENT DESIGN ISSUES How to separate spectral & polarization channels ? (dichroic and/or variable filters ? grisms ?) How to realize spatial sampling ? (integral-field fiber-optics bundles ? different detector segments ?)

INSTRUMENT DESIGN ISSUES Incorporate measurements of photon orbital angular momentum ? (or does this not specifically require ELT’s ??)

INSTRUMENT DESIGN ISSUES Telescope mechanical stability ? (small and well-defined vibrations, etc.) Temporal structure of stray light ? (scattered light may arrive with systematic timelags) Atmospheric intensity scintillation? (is OWL larger than outer scale of turbulence?)

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

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

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

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

Photon correlation spectroscopy E.R.Pike, in R.A.Smith, ed. Very High Resolution Spectroscopy, p.51 (1976)

Photon correlation spectroscopy E.R.Pike, in R.A.Smith, ed. Very High Resolution Spectroscopy, p.51 (1976) LENGTH & TIME FOR SPECTROMETERS OF DIFFERENT RESOLVING POWER

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

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

Information content of light D.Dravins, ESO Messenger 78, 9 (1994)

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

Intensity interferometry R.Hanbury Brown, J.Davis, L.R.Allen, MNRAS 137, 375 (1967)

Intensity interferometry LABORATORY EXPERIMENT Artificial star (pinhole illuminated by white-light arc lamp) Two “telescopes” observe “star” with APD ≳ 5 MHz photon counts Digital cross 1.6 ns resolution (monitored as baseline between telescopes is changed) Ricky Nilsson & Helena Uthas, Lund Observatory (2005)

S.Johansson & V.S.Letokhov Possibility of Measuring the Width of Narrow Fe II Astrophysical Laser Lines in the Vicinity of Eta Carinae by means of Brown-Twiss-Townes Heterodyne Correlation Interferometry astro-ph/ , New Astron. 10, 361 (2005)

S.Johansson & V.S.Letokhov Possibility of Measuring the Width of Narrow Fe II Astrophysical Laser Lines in the Vicinity of Eta Carinae by means of Brown-Twiss-Townes Heterodyne Correlation Interferometry astro-ph/ , New Astron. 10, 361 (2005) Expected dependence of the correlation signal as function of (a) heterodyne frequency detuning and (b) spacing of telescopes d

Photon statistics of laser emission If(a) If the light is non-Gaussian, photon statistics will be closer to stable wave (such as in laboratory lasers) If(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

Information content of light D.Dravins, ESO Messenger 78, 9 (1994)

R. Loudon The Quantum Theory of Light (2000) QUANTUM OPTICS

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

Advantages of very large telescopes Telescope diameterIntensity Second-order correlation Fourth-order photon statistics 3.6 m m x 8.2 m , m19337,0001,385,000, m770595,000355,000,000,000

Quantum OWL ! [Almost] all our knowledge of the Universe arrives through photons Both individual photons and photon streams are more complex than has been generally appreciated

Quantum OWL ! Quantum optics may open a fundamentally new information channel to the Universe ! ELT’s will bring non-linear optics into astronomy !

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