Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002a%26a...384..350s&link_type=abstract
Astronomy and Astrophysics, v.384, p.350-363 (2002)
Astronomy and Astrophysics
Astrophysics
2
Atomic Processes, Radiation Mechanisms: Non-Thermal, Stars: Early Type, Stars: Individual: Hd 44179, Stars: Individual: Rr Tel, Ism: Lines And Bands
Scientific paper
The optical or far-UV (FUV) spectra of certain objects in Space are completely dominated by one or two spectrally narrow emission lines, strongly suggesting that laser action of some kind occurs in these objects. However, the electronic level structures of the atoms/ions producing these emissions preclude the possibility of maintaining population inversions on the electronic transitions involved. In lasers, gain is normally produced on an optical transition that is inverted, i.e. one that has more atoms maintained in the upper than in the lower state, so that stimulated emission can exceed stimulated absorption. However, as a result of discoveries made in quantum electronics over the past 30 years or so, one now knows that there are several ways to make stimulated emission occur on a transition that is not inverted, i.e. to realize a ``laser without inversion (LWI)''. This requires first making the atoms non-absorbing at the lasing frequency, i.e. setting up a condition of ``electromagnetically induced transparency (EIT)''. Some recently developed EIT techniques for three-level atoms are first reviewed. A simple model for a space LWI based upon a gas of two-level atoms is then proposed. In this model, transparency results from a form of EIT induced by the presence of an intense, monochromatic, continuous-wave, laser beam tuned to the frequency omega _o of the two-level-atom transition. Amplification of light at this same frequency occurs via resonant stimulated hyper-Raman scattering (SHRS) and four-wave mixing (FWM), with pumping energy provided by continuum starlight spectrally overlapping the two outer absorption sidebands (``Mollow bands'') induced by the presence of the beam at omega _o. Two specific examples of superintense line emission from Space are here considered. These are (a) the H(alpha ) emission line appearing as a dominant singularity in certain reddened, early-type stars, and (b) the powerful O VI (1032 Å, 1038 Å) emission doublet that dominates the FUV emission spectra of symbiotic stars such as RR Tel.
Glownia James H.
Sorokin Peter P.
No associations
LandOfFree
Lasers without inversion (LWI) in Space: A possible explanation for intense, narrow-band, emissions that dominate the visible and/or far-UV (FUV) spectra of certain astronomical objects does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Lasers without inversion (LWI) in Space: A possible explanation for intense, narrow-band, emissions that dominate the visible and/or far-UV (FUV) spectra of certain astronomical objects, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lasers without inversion (LWI) in Space: A possible explanation for intense, narrow-band, emissions that dominate the visible and/or far-UV (FUV) spectra of certain astronomical objects will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1407111