Electrical detection of Rydberg interactions in nitric oxide at room temperature

Abstract

In this work I will present measurements of Rydberg states in nitric oxide (NO) at room temperature. The detection of the Rydberg states is realized by measuring the current of free charges resulting from collisions of the excited molecules. All measurements are performed using continuous-wave (cw) lasers in a sub-Doppler configuration, which together with a stabilization setup yield a frequency error of only 2𝜋 × 2.5 MHz. The full width at half maximum (FWHM) of a typical Rydberg state is only about 2𝜋 × 130 MHz. We take a look at the necessary theory of diatomic molecules first. Afterward, a thorough walkthrough of the experimental setup is given. The heart of our setup is a custom-designed measurement cell, which features readout electronics based on a transimpedance amplifier (TIA). As such I will also give an overview on the basics of operational amplifiers (OpAmps). When all prerequisites are introduced, we will take an in-depth look on the Stark effect in Rydberg states. To our knowledge, the presented resolution is unmatched, and may enable us to give a more precise value to the g–quantum defect in NO in the future. In a final experimental section I show the collisional broadening and shift of Rydberg states of NO due to an increasing background gas density. Such measurements have a long history in alkalis, yet to our knowledge, no such measurements in NO exist. The overall experiment is performed in the context of a trace-gas sensor for NO in a medical application. This work gives suitable density and electric field ranges for such a sensor.