d. dravins 1, c. barbieri 2 v. da deppo 3, d. faria 1, s. fornasier 2 r. a. e. fosbury 4, l....
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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
EXTREMELYHIGH-RESOLUTIONASTRONOMICALSPECTROSCOPY
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 interferometryIntensity interferometry
Narrabri stellar intensity interferomer circa 1970 (R.Hanbury Brown, R.Q.Twiss et al., University of Sydney)
Information content of lightInformation content of light
D.Dravins, ESO Messenger 78, 9
Top: Bunched (quantum-random) photons
Center: Independent (classically-random) photons
Bottom: Antibunched photons
After R. Loudon The Quantum Theory of Light (2000)
PHOTON STATISTICS
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)
S. Johansson & V.S. LetokhovAstrophysical lasers operating in optical Fe II lines in stellar ejecta of Eta CarinaeA&A 428, 497 (2004)
Lasers around Eta Carinae
Spectral resolution = 100,000,000 !
Spectral resolution = 100,000,000 !
o To resolve narrow optical laser emission (Δν 10 MHz) requires spectral resolution λ/Δλ 100,000,000
o Achievable by photon-correlation (“self-beating”) spectroscopy ! Resolved at delay time Δt 100 ns
o Method assumes Gaussian (thermal) photon statistics
Photon correlation spectroscopyPhoton correlation spectroscopy
E.R.Pike, in R.A.Smith, ed. Very High Resolution Spectroscopy, p.51 (1976)
LENGTH,TIME &FREQUENCYFORTWO-MODESPECTRUM
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 spectroscopyPhoton correlation spectroscopy
o Analogous to spatial informationfrom intensity interferometry,photon correlation spectroscopydoes not reconstruct the shape of
the source spectrum, but “only” gives linewidth information
Photon statistics of laser emissionPhoton statistics of laser emission
• (a) IfIf the light is non-Gaussian, photon statistics will be closer to stable wave(such as in laboratory lasers)
• (b) IfIf the light has been randomized andis close to Gaussian (thermal), photon correlation spectroscopy will reveal the narrowness of the laser light emission
Photon correlation spectroscopyPhoton correlation spectroscopy
o Advantage #1:Advantage #1: Photon correlations are insensitive to wavelength shifts due to local velocities in the laser source
o Advantage #2: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
Advantages of very large telescopes
Telescope diameter
Intensity <I> Second-order correlation <I2>
Fourth-order photon statistics <I4>
3.6 m 1 1 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
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