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