Comb-Mode Resolved Lamb-Dip Spectroscopy

Absorption spectroscopy enables the non-destructive determination of gas composition or the detection of molecules. For this purpose, one exposes the sample to broadband light and observes which colors of the incident light are absorbed. This specific absorption fingerprint enables us to draw conclusions about the gases present or their molecular structure. The methodology described above has long been established in many scientific disciplines and works very well in the laboratory. A real challenge, however, is to provide absorption data over a broad spectrum with very high resolution in the kilohertz range. This is where established measurement methods reach their limits. This limit creates a problem as space missions to be launched in the next decade are equipped with spectroscopic instruments that measure absorption spectra over a wide range of wavelengths. These missions include the James Webb Space Telescope (launch date Dec. 24, 2021) and the Atmospheric Remote-Sensing Infrared Exoplanet Large-Survey (ARIEL), which operates in the 1.25-7.8 m wavelength window. Both missions aim to find characteristic molecular signatures in the atmosphere and on the surface of both solar system objects and exoplanets under extreme temperature and pressure conditions. To make these data useful, however, one needs very precise comparative data of the absorption properties of many gases. With the invention of the optical frequency comb it became possible to drastically increase the resolution of spectroscopic measurements. A frequency comb can be thought of as many different lasers of precisely defined colors. The well-defined color spectrum of the frequency comb allows to draw more precise conclusions about the absorbed light and thus to drastically increase the resolution and accuracy of the measurements. In this project we explore a novel approach to establish a new type of broadband precision spectroscopy. These measurements, using known samples in a well-controlled artificial environment, will aid in the creation of parameterized databases that will serve as input to numerical atmospheric simulations. In turn, the use of such simulations and numerical calculations help to understand measured spectra and to develop an accurate model of an object under study, such as an exoplanet.