Dear Editor,

please find enclosed a manuscript on the use of temporal correlation spectroscopy as tool to measure the line width of very narrow spectral features. We demonstrate the ability of identifying a line width on the order of 10 MHz, which could be useful to shed some light on some very narrow optical lines that are sometimes suspected to be caused by natural lasing mechanisms. Apart from measuring a coherence function of a thermal source, the presented method also allows distinguishing thermal sources from laser-like coherent sources.
We showcase the method on a laboratory experiment, where a Doppler-broadened laser light source is used instead of a stellar light source. However, since our technique does not require the high spatial coherence of other high resolution spectroscopy techniques like heterodyne spectroscopy, we feel it may be of sufficient interest to the astronomical community.

We hope our manuscript fits the scope of the Monthly Notices of the Royal Astronomical Society, and look forward for you reply.

With Best Regards,

Christian Kurtsiefer and Peng Kian Tan