Measurement of Methane Hyperfine Structure Using Laser Saturated Absorption

With optical resolution above 10¹⁰, we study hyperfine structure in the methane vibration-rotation line at 3.39 {μ}m. Doppler-generated crossing resonances were observed in addition to the resolved ΔF=0 and - 1 lines. Splittings in both ground and excited states were determined. Differential saturation of such hyperfine structure will lead to an intensity-dependent shift in many molecularly stabilized lasers.