# Electromagnetically-induced transparency, absorption, and microwave field sensing in a Rb vapor cell with a three-color all-infrared laser system

## TL;DR

This paper investigates three-photon electromagnetically-induced transparency and absorption in rubidium vapor using a three-color infrared laser system, modeling the phenomena and applying it for microwave field sensing via Rydberg states.

## Contribution

It provides a detailed experimental and theoretical analysis of three-photon EIT/EIA in rubidium and demonstrates microwave field sensing using Rydberg EIT with a three-color laser setup.

## Key findings

- Observation of EIT and EIA phenomena over various detunings.
- Numerical modeling of the phenomena using Lindblad equations.
- Application of Rydberg EIT for microwave field measurement at 100.633 GHz.

## Abstract

A comprehensive study of three-photon electromagnetically-induced transparency (EIT) and absorption (EIA) on the rubidium cascade $5S_{1/2} \rightarrow 5P_{3/2}$ (laser wavelength 780~nm), $5P_{3/2} \rightarrow 5D_{5/2}$ (776~nm), and $5D_{5/2}\rightarrow 28F_{7/2}$ (1260~nm) is performed. The 780-nm probe and 776-nm dressing beams are counter-aligned through a Rb room-temperature vapor cell, and the 1260-nm coupler beam is co- or counter-aligned with the probe beam. Several cases of EIT and EIA, measured over a range of detunings of the 776-nm beam, are studied. The observed phenomena are modeled by numerically solving the Lindblad equation, and the results are interpreted in terms of the probe-beam absorption behavior of velocity- and detuning-dependent dressed states. To explore the utility of three-photon Rydberg EIA/EIT for microwave electric-field diagnostics, a sub-THz field generated by a signal source and a frequency quadrupler is applied to the Rb cell. The 100.633-GHz field resonantly drives the $28F_{7/2}\leftrightarrow29D_{5/2}$ transition and causes Autler-Townes splittings in the Rydberg EIA/EIT spectra, which are measured and employed to characterize the performance of the microwave quadrupler.