Possibility of measuring the width of narrow Fe II astrophysical laser lines in the vicinity of η Carinae by means of Brown–Twiss–Townes heterodyne correlation interferometry

Abstract

We consider the possibility of measuring the true width of the narrow Fe II optical lines observed in spectra of the Weigelt blobs in the vicinity of η Carinae. The lines originate as a result of stimulated amplification of spontaneous emission of radiation in quantum transitions between energy levels showing inverted population [Johansson, S., Letokhov, V., 2002. JETP Lett. 75 (10) 495; Johansson, S., Letokhov, V., 2003. Phys. Rev. Lett. 90 (1) 01110-1; Johansson, S., Letokhov, V., 2004. A&A 428,497]. The lines should have a subDoppler spectral width of 30–100MHz, depending on the geometry of the lasing volume. To make measurements with a spectral resolution of R>107 and an angular resolution better than 0.1″, we suggest the use of the Brown–Twiss–Townes optical heterodyne intensity correlation interferometry. The estimates made of the S/N ratio for the optical heterodyne astrophysical laser experiment imply that it is feasible.