claudio germanà and dainis dravins inaf observatory of padua lund observatory
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1. Laser Emission in astrophysical sources
2. Photon-Correlation Spectroscopy: Resolving narrow spectral lines
3. Signal – to – Noise ratio
Medium acts as an amplifier
”Light amplification by stimulated emission of radiation” LASER
Population inversion
Lasers may be observed if:
1) Population inversion is feasible
2) Pumping mechanism for population inversion
3) Structures allow amplification (e.g., clouds)
...laser emission might be observed in:
Fe II and O I lines in η Carinae (Johansson & Letokhov 2004, 2005)
Wolf-Rayet starsHe II He I lines(Varshni & Nasser 1975,1986)
Mass – loosing stars
S. Johansson & V.S. LetokhovAstrophysical lasers operating in optical Fe II lines in stellar ejecta of Eta CarinaeAstron.Astrophys. 428, 497 (2004)
Model of a compact gas condensation near η Car with its Strömgren boundarybetween photoionized (H II) and neutral (H I) regions
S. Johansson & V. S. LetokhovLaser Action in a Gas Condensation in the Vicinity of a Hot StarJETP Lett. 75, 495 (2002) = Pis’ma Zh.Eksp.Teor.Fiz. 75, 591 (2002)
S. Johansson & V.S. LetokhovAstrophysical lasers and nonlinear optical effects in space New Astron. Rev. 51, 443 (2007)
A microsecond “bottle-neck” creates a population inversion in the 3 → 2 transition of Fe II
at 9997 Å
...how to confirm Laser emission?
Expected extremely narrow linewidth < 1 mÅ (0.1 pm)(Johansson & Letokhov 2004)
Spectral resolution 100 million!!
by Dravins et al. 2007
What about a spectral line?
Electric field emitted from one atom which undergoes collisions:
E n(t)= E0 cos(ω0t + φn (t))
φn (t) is a Gaussian (chaotic process)
a(t) is a Gaussian
Total electric field from the system of n atoms (Loudon 1973):
exp(iωt)Fourier component
... signal in Fourier’s notation...
E(t)TOT thermal light a(t) ≠ cost (Gaussian)
E(t)TOT laser light a(t) ≈ cost
Intensity interferometryIntensity interferometry
Narrabri stellar intensity interferomter (R.Hanbury Brown, R.Q.Twiss et al., University of Sydney)
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