Synchrotron beamlines are extremely useful light sources across the electromagnetic spectrum for sensitive, broadband spectroscopy, in the far-IR or terahertz (1-10 THz) region which lacks bright, broadband laboratory sources. Far-IR synchrotron beamlines across the world are equipped with Fourier-transform infrared (FTIR) spectrometers. These instruments provide broadband spectra thanks to the powerful multiplex advantage of interferometry. However, they are also inherently limited in their maximum resolution, to around 20 MHz for the best available instruments. This resolution is in excess of an order of magnitude larger than typical THz molecular linewidths, and prevents the observation of many fine and hyperfine effects.

The goal of the HEROES (heterodyne receivers optimized for synchrotron sources) project is to unlock far-IR synchrotron sources for higher resolution spectroscopy, while simultaneously improving sensitivity and maintaining the broadband advantage of FTIR spectroscopy. Two new spectrometers are under development to achieve this goal. The first is an instrument based on the heterodyne mixing of the output of a QCL-pumped molecular laser with the far-IR continuum of the regular synchrotron radiation.¹ The second is a dual-comb spectrometer combining the THz frequency comb produced by the coherent synchrotron radiation mode of the synchrotron² with a comb produced from the incidence of a femtosecond laser onto a spiral antenna photomixer. The latest progresses on the development on these two spectrometers will be presented.

1. Lampin, J.-F. et al. Broadband terahertz heterodyne spectrometer exploiting synchrotron radiation at megahertz resolution. Opt. Lett. 44, 4985–4988 (2019).
2. Tammaro, S. et al. High density terahertz frequency comb produced by coherent synchrotron radiation. Nat. Commun. 6, 7733 (2015).