Lamb-dips and Lamb-peaks in the saturation spectrum of HD

TL;DR

This paper investigates the complex line shape in the saturation spectrum of HD's R(1) transition, explaining the Lamb-dip and Lamb-peak features through hyperfine cross-over resonances, and accurately determining the transition frequency.

Contribution

It introduces a density-matrix model explaining the composite line shape caused by hyperfine effects in HD's saturation spectrum, resolving previous frequency discrepancies.

Findings

Identified Lamb-dip and Lamb-peak features in HD spectrum

Quantitative explanation based on hyperfine cross-over resonances

Precise measurement of the R(1) transition frequency at 217105181901(50) kHz

Abstract

The saturation spectrum of the R(1) transition in the (2-0) band in HD is found to exhibit a composite line shape, involving a Lamb-dip and a Lamb-peak. We propose an explanation for such behavior based on the effects of cross-over resonances in the hyperfine substructure, which is made quantitative in a density-matrix calculation. This resolves an outstanding discrepancy on the rovibrational R(1) transition frequency, which is now determined at 217 105 181 901 (50) kHz and in agreement with current theoretical calculations.