1. 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

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

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

4. 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

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

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

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

8. 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)

9. 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, (2004)

10. 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

11. 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)

12. 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

13. 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

14. 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

15. 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

16. 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

17. 5 x 5 array of 20 μm diameter APD detectors (SensL, Cork)

18. 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