Transcript QuantEYE - Lund Observatory

D. Dravins 1, C. Barbieri 2
V. DaDeppo 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 !
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 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
o 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
o Advantage #1: Photon correlations are
insensitive to wavelength shifts due to
local velocities in the laser source
o 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 highspeed 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
1
1
8.2 m
5
27
720
21
430
185,000
50 m
193
37,000
1,385,000,000
100 m
770
595,000
355,000,000,000
4 x 8.2 m