Optimizing modulation transfer spectroscopy signals for frequency locking in the presence of depleted saturating fields

A theoretical model of modulation transfer spectroscopy (MTS) that includes pump beam depletion is presented and experimentally verified with data covering visible iodine transitions at 532, 543, and 612 nm. This model is used to determine the values for pressure, interaction length, and saturation intensity that yield maximum MTS signals for frequency locking to iodine transitions. The approach is demonstrated for iodine transitions at 532, 633, and 778 nm, with the results showing that theoretically the frequency instability scales inversely to the absorption coefficient. OCIS codes: 140.0140, 140.3425, 120.0120, 120.3930, 120.3940, 300.6190.