Molecular iodine at 508 nm: hyperfine spectroscopy and operating regimes for optical frequency references

Kurzfassung

We investigated molecular iodine transitions near 508 nm as candidates for compact optical frequency references based on modulation transfer spectroscopy. Focusing on the R(41) 51-0 transition at 508.028 nm, we resolved and frequency-calibrated all 21 hyperfine components and determined their linewidths (Γ), signal-to-noise ratios (SNR), and figures of merit (SNR/Γ). We identified three particularly favorable components for laser frequency stabilization, a1, a2, and a3, which provide strong error signals suitable for robust locking. For these components, we systematically studied the dependence of linewidth, SNR, and SNR/Γ on iodine vapor pressure, pump and probe power densities, and modulation index. From the combined measurements we identified practical operating regimes that provide a robust compromise between signal contrast and narrow linewidth. From the measured linewidth and SNR, we estimate a short-term fractional frequency instability of 2.9 × 10-14 at 1 s. The resulting data set and working-point guidelines provide a quantitative basis for designing and optimizing iodine-stabilized frequency references at 508 nm and may serve as a useful starting point for neighboring transitions in this spectral region, supporting future metrology and space optical clock applications.