Vogt, F. P. A., Kerber, F., Mehner, A., Yu, S. S., Pfrommer, T., Lo Curto, G., Figueira, P., Parraguez, D., Pepe, F. A., Megevand, D., Riva, M., Di Marcantonio, P., Lovis, C., Amate, M., Molaro, P., Cabral, A., Osorio, M. R. Z. 2019. Rotational and Rotational-Vibrational Raman Spectroscopy of Air to Characterize Astronomical Spectrographs. Physical Review Letters 123, 6 DOI: 10.1103/PhysRevLett.123.061101
Raman scattering enables unforeseen uses for the laser guide-star system of the Very Large Telescope. Here, we present the observation of one up-link sodium laser beam acquired with the ESPRESSO spectrograph at a resolution lambda/Delta lambda similar to 140 000. In 900 s on source, we detect the pure rotational Raman lines of O-16(2), N-14(2), and (NN)-N-14-N-15 (tentatively) up to rotational quantum numbers J of 27, 24, and 9, respectively. We detect the O-16(2) fine-structure lines induced by the interaction of the electronic spin S and end-over-end rotational angular momentum N in the electronic ground state of this molecule up to N = 9. The same spectrum also reveals the nu(1 <- 0) rotational-vibrational Q-branch for O-16(2) and N-14(2). These observations demonstrate the potential of using laser guide-star systems as accurate calibration sources for characterizing new astronomical spectrographs.