Progress towards a mid-infrared frequency standard using ultracold molecules

This thesis presents significant progress toward the development of a mid-infrared frequency standard using ultracold calcium monofluoride (CaF) molecules, as part of the QSNET project—a network of precision clocks designed to probe the temporal variation of fundamental constants. By comparing the frequency of the CaF clock with other clocks in the QSNET consortium, this work aims to measure potential variations in $\mu$ with unprecedented accuracy. The research includes three key experiments: Frequency characterization of a quantum cascade laser (QCL). Spectroscopy of CaF’s fundamental vibrational transition. Development of a Raman laser system. Further, we evaluated systematic uncertainties for the CaF lattice clock, identifying "magic wavelengths" (e.g., 694.5 nm) where ac-Stark shifts vanish. Projected uncertainties for key effects—lattice frequency, intensity, Zeeman shifts, and Doppler broadening—suggest a fractional uncertainty at the level of 10$^{-17}$, which is competitive as a molecular clock, and the clock will be possible to test the variation of $\mu$. This work bridges advanced molecular spectroscopy and precision frequency metrology, demonstrating the feasibility of a CaF-based optical lattice clock. Future efforts will focus on building and testing the CaF lattice clock, enabling new tests of fundamental physics.