Fiber-based angular filtering for high-resolution Brillouin spectroscopy in the 20-300 GHz frequency range

TL;DR

This paper introduces a fiber-based angular filtering method for high-resolution Brillouin spectroscopy, enabling broadband acoustic phonon detection from 20 to 300 GHz with improved filtering and spectral resolution.

Contribution

It presents a practical experimental setup integrating fibered angular filtering with spectral filtering for broadband Brillouin spectroscopy.

Findings

Achieved high spectral resolution in the 20-300 GHz range.

Enhanced angular filtering improves detection of low-frequency phonons.

The setup is suitable for cavity optomechanics and stimulated Brillouin scattering studies.

Abstract

Brillouin spectroscopy emerges as a promising non-invasive tool for nanoscale imaging and sensing. One-dimensional semiconductor superlattice structures are eminently used for selectively enhancing the generation or detection of phonons at few GHz. While commercially available Brillouin spectrometers provide high-resolution spectra, they consist of complex experimental techniques and are not suitable for semiconductor cavities operating at a wide range of optical wavelengths. We develop a pragmatic experimental approach for conventional Brillouin spectroscopy integrating a widely tunable excitation-source. Our setup combines a fibered-based angular filtering and a spectral filtering based on a single etalon and a double grating spectrometer. This configuration allows probing confined acoustic phonon modes in the 20-300 GHz frequency range with excellent laser rejection and high spectral resolution. Remarkably, our scheme based on the excitation and collection of the enhanced Brillouin scattering signals through the optical cavity, allows for better angular filtering for low phonon frequency. It can be implemented for the study of cavity optomechanics and stimulated Brillouin scattering over broadband optical and acoustic frequency ranges.