P.G. Kryukova,b aLebedev Physical Institute, Russian Academy of Sciences, Leninsky prosp. 53, Moscow, 119991, Russian Federation bProkhorov General Physics Institute of the Russian Academy of Sciences, Dianov Fiber Optics Research Center, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991, Russian Federation
Optical spectroscopy has been and remains an important feature of astrophysical research. Huge telescopes are being built to collect radiation from the most distant stars in the Universe for subsequently studying it with unique astronomical spectrographs. The fundamental problem one faces here is that of transferring the extremely weak radiation focused by the moving telescope to the entrance of the stationary spectrograph. The solution is connecting telescopes to spectrographs with a fiber-optical connection, and research and development of the system's necessary components is currently a major task in the field of fiber optics. A key problem in astronomical spectroscopy is the precision measurement of Doppler line shifts in the spectra of stars to determine the velocity of a star along the observation line (radial velocity, RV). A remarkable feature of Doppler spectroscopy is that a precision measurement of quite small RV variations (in fact, accelerations) can last for long periods of time. Such star RV variations can be due, for example, to a planet orbiting the star; the action of the planet causes periodical changes in the motion of the star, thus leading to a Doppler shift of the star's spectrum. The precise measurements of this shift has provided an indirect method for searching and discovering planets outside the Solar System (exoplanets). The important particular problem of searching for habitable earthlike exoplanets requires a spectral measurement accuracy sufficient to detect RV variations at the level of a few centimeters per second per year. Ten-fifteen years of such measurements would provide a direct estimate of the hypothetical accelerated expansion of the Universe. However, the accuracy required for this is more than the conventional spectroscopy techniques (iodine cell and spectral lamps) are capable of. This paper reviews approaches to radically improve Doppler spectroscopy techniques to achieve the required shift measurement accuracy. These approaches include the development of fiber optical systems for connecting the telescope with the spectrograph and the development of precision calibrators of astronomical spectrograph using laser physics and fiber optics advances.
Keywords: fiber-fed astronomical spectrographs, Doppler spectroscopy, optical frequency comb, exoplanets, dynamics of the Universe PACS:42.62.−b, 42.81.−i, 97.82.−j (all) DOI:10.3367/UFNe.2018.02.038331 URL: https://ufn.ru/en/articles/2018/11/c/ Citation: Kryukov P G "Lasers and fiber optics for astrophysics" Phys. Usp.61 1072–1078 (2018)