InnovaTIve hiGh-resolution THz spectrometER (TIGER) – TIGER

Spectroscopy is an extremely powerful tool that is used in many fundamental and applied fields. Among the different spectral domains and despite the advances of recent years, the TeraHertz domain (THz) is much less mature than millimeter waves, infrared or ultraviolet. It is sometimes known as the "spectral gap". To date, one of the most successful applications of THz waves remains the study of atmospheres (terrestrial, planetary or cometary) and the interstellar medium. If the observation and its associated instrumentation has made enormous progress, we have to maintain a significant effort for laboratory studies penalized by a lack of solutions to cover the frequency range between 1-4 THz with very high-resolution instrumentation. This spectral region is also considered as fundamental for the determination of structural parameters. Most of investigation below 1.1 THz use spectrometer based on amplifier / multiplier chains that that does not require excessive budgets. But, this technique requires major financial and technical constraints beyond this frequency. Furthermore, it is impossible to cover the full target spectral range (100 - 4000 GHz) with a single instrument. It should be stressed that the spectral band between 2000 and 3500 GHz is not fully covered (at least with commercial elements). Only dedicated spectral bands around target frequencies are available (but with very limited diffusion). To date, components able to work above 1 THz are almost a US exclusively and the distribution of which is subject to control by its administration.
We propose in this project an alternative that uses the advantages of various fields, such as optics, optoelectronics and electronics for the design of a unique THz spectrometer with unprecedented capabilities based on a high performance heterodyne detection.
The objective is to design a single spectrometer able to work between 500 and 4000 GHz associated with excellent spectral resolution (<50 kHz) and frequency metrology (<50 kHz). Such characteristics will make it an unrivaled instrument for high resolution studies in such a wide spectral band. To achieve this goal, we propose to use a new generation of THz source as a local oscillator, patented by one of the partners of this project (IEMN). This is a new type of molecular laser that uses strong advances of quantum cascade lasers oscillating around 10 microns.
A special attention will be focused on the development of an optical frequency comb oscillating directly at 780 nm wavelength along with a high repetition rate (> 1 GHz) to boost the sensitivity of the future spectrometer. For this, we must harness the skills and resources of each partners for the design of a new generation of a high contrast saturable absorber and a hybrid active and passive mode locking technique. Such an optical FC can be considered as outstanding progress considering the lack of FC based onto fiber technologies with repetition rate greater than GHz, and potential applications far exceeds that of THz spectroscopy. This laser could be used in the generation of high spectral purity local oscillators, in signal processing as analog to digital conversion or in telecommunications and time/frequency applications to cite a few.
TIGER instrument will be validated by various spectroscopic studies, most of which are still almost inaccessible with existing spectrometers, on key molecules for atmospheric physic or planetology.