THz Comb analysis with a subharmonic mixer

Ms. Alexandra Khabbaz1,2, Prof. Francis Hindle2, Dr. Jean-François Lampin1, Prof. Gael Mouret2
1Institut d’Electronique de Microélectronique et de Nanotechnologie (IEMN-CNRS), Lille, France. 2Laboratoire de Physico-Chimie de l’Atmosphère (LPCA), Université du Littoral Côte d’Opale, Dunkerque, France


Recent advancements in Terahertz spectroscopy, leveraging frequency combs (FC) generated by femtosecond lasers, have expanded the precision of metrology and spectroscopy in visible and mid-infrared spectral domains. Our study introduces an offset-free THz FC, produced through non-linear conversion of a frequency-doubled 1.55 µm femtosecond laser by a semiconductor photoconductor antenna. The repetition rate is synchronized to a reference synthesizer, allowing the selection of a spectral window via heterodyne mixing with a Local Oscillator (LO). The resulting Intermediate Frequency (IF) spectrum, recorded with exceptional resolution in the microwave band, reveals sharp peaks in the THz FC. Our setup is aimed to be used for high-resolution molecular spectroscopy.