Precision Doppler thermometry in a portable optical frequency reference

High-precision laser spectroscopy is a key tool for probing fundamental physics and enabling quantum atom optics applications such as quantum sensing, precision thermometry, and metrology. We report a compact laser–spectroscopy module based on an additively manufactured opto-mechanical housing, designed for stable operation in both laboratory and outdoor environments. The system integrates a diode-laser module with a μ-metal-shielded ¹³³Cs vapor spectroscopy unit, providing a robust frequency reference and thermometric capability within a single modular footprint. The absorption spectra recorded over a range of vapor-cell temperatures and varying probe powers are analyzed to extract the Doppler linewidth, facilitating Doppler-broadened thermometry (DBT). Saturated-absorption spectroscopy performed in a controlled vapor-cell demonstrates reliable laser frequency stabilization to cesium atomic transitions using frequency-modulation spectroscopy. Long-term frequency-drift measurements show fluctuations below 400 kHz for over an hour. An overlapping Allan deviation of 3.06 ×10^-11 further indicates stable fractional frequency behavior against ambient magnetic-field and temperature fluctuations. The compact, plug-and-play architecture makes the module well-suited for portable quantum sensing and integration into field-deployable quantum atom- optics experiments.