Constructing an External Cavity Diode Laser for the Probing of Rydberg Excitons in Cu2O

Abstract

Cuprous oxide (Cu2O) is a direct bandgap semiconductor that presents a promising platform for the implementation of a solid state quantum simulator. This promise is in part due to the presence of excitons in the material which have the potential to become excited to Rydberg states, which are robust even in the presence of liquid nitrogen temperature thermal environments. The properties of the Rydberg excitons in Cu2O can be studied by the proxy of a series of P-exciton resonance peaks. For the study of peaks corresponding to principle quantum number n > 12 in the yellow P-series, high resolution spectroscopy methods are required due to the n^(-3) scaling of the width of each resonant peak. However, a tunable narrow linewidth light source, such as an external cavity diode laser, can be used to resolve these states by scanning the wavelength of the laser and measuring its transmission through a sample. Such a laser source can also be used in further experiments to probe and manipulate the excitonic state of the material, by for example inducing a Rydberg blockade.

A narrow line-width tunable laser system capable of generating the required wavelengths of light via cavity enhanced second harmonic generation to scan the yellow P-exciton spectrum is constructed, and a high resolution transmission scan is performed. The results of the scan show close agreement with previously and concurrently obtained white light transmission spectroscopy results. This close agreement is somewhat corroborated by further qualitative analysis performed by fitting an asymmetric Lorentzian function to visible exciton resonance spectral features, and comparing the extracted values of the function parameters between the white light and laser light data.