Doppler-free heterodyne spectroscopy of Hα. measurement of the 2s12 collisional quenching in gas cell

By applying Doppler-free heterodyne spectroscopy techniques to the hydrogen Balmer-α line (λ = 656 nm), one observes a dramatic improvement in S/N ratios for large detection frequencies, δ. Short-noise limited signals are obtained for δ > 2 MHz. Signal phase shifts yield the first “in situ” measurement of the collisional quenching of the 2s_{$\text{1}\text{2}$} metastable state in gas discharges.