Modulation-Free Laser Systems for Frequency Domain and Atom Interferometry Experiments*

We discuss the characterization and specifications of a home-built external cavity diode laser (ECDL) system that is suitable for frequency-domain cold-atom velocimetry and measurements of gravitational acceleration [Randhawa, et. al., Rev. Sci. Instrum. 96, 123204 (2025)]. The laser system is frequency stabilized using the modulation-free technique of Doppler-Free Dichroic Atomic Vapor Laser Lock (DF DAVLL). We find that this laser lowers the temperature of a magneto-optical trap (MOT) in comparison with a MOT realized using a laser that relies on lock-in spectroscopy. The laser system also incorporates a feedback loop involving an acousto-optic modulator (AOM) for intensity stabilization, which reduces the effect of low frequency vibrations. By integrating this laser with a home-built, dual-output radio frequency synthesizer, we are able to derive two laser beams with a precisely controlled relative detuning for frequency domain interferometry using laser-cooled atoms. The detuning can range from the mHz to the MHz level with a stability of 10 μHz. We compare the performance of the DF DAVLL-stabilized ECDL to another modulation-free source stabilized by an AOM in a side arm.