The master’s student will take part in forefront experiments dedicated to ultra-precise measurements of rovibrational molecular transitions to test a possible time variation of the proton-to-electron mass ratio (μ), a key constant of the Standard Model. Detecting such a drift would signal new physics and shed light on dark matter and dark energy. The approach relies on comparing astronomical molecular spectra with laboratory data. The experimental setup uses quantum cascade lasers (QCLs) stabilized to optical frequency combs traceable to primary standards, a technology pioneered at LPL that enables unprecedented precision in the mid-infrared. The internship centers on methanol (CH₃OH), whose transitions are especially sensitive to μ-variation. The student will install and stabilize a QCL in the relevant spectral region, aiming for sub-Doppler resolution and ~100 Hz frequency accuracy, necessary for astrophysical comparisons. This work is part of the ANR Ultiμos project with LKB and MONARIS, combining spectroscopy of methanol and other species such as ammonia to identify key transitions for Earth- and space-based campaigns. Partners including Vrije Universiteit Amsterdam and Onsala Space Observatory provide theory and astronomical input.