TUNABLE ATOMIC LINE MONOCHROMATORS FOR BRILLOUIN SPECTROSCOPY

Abstract

Brillouin microscopy, a non-contact, spatially-resolved imaging method, provides insights into the mechanical information of samples. The first generation of Brillouin microscopes combined confocal microscopes and etalon-based spectrometers. In this setup, a confocal microscope scans a laser across the sample pixel-by-pixel, while the etalon spectrometer measures the Brillouin shift frequency at each pixel. Despite the extended image acquisition times in biological samples (>20 ms/pixel), advancements have been made in the field to enhance the overall speed of Brillouin imaging. For example, line-scan Brillouin spectrometers use orthogonal detection to measure the Brillouin scattering at a row of pixels in a single shot. The pixel multiplexing in one-dimension (1D) improved the Brillouin imaging speeds 20-fold. Further multiplexing to two dimensions, or full-field spectroscopy, where the frequency domain is sequentially acquired but all the pixels in the field of view are simultaneously measured at each frequency, can further improve the average image acquisition time. However, there are currently no solutions for sub-picometer (sub-GHz) spectral resolution, two-dimensional (2D) multiplexing of Brillouin images.

Here, I use the laser induced circular dichroism (LICD) effect in atomic vapors to create monochromators for 2D multiplexing at high spectral resolutions. These atomic line monochromators possess spectral resolutions dependent on the linewidth of the atomic resonance (~MHz), and they are ideal for pixel multiplexing because they have spectral analysis capabilities that do not depend on the spatial separation of spectral components. First, I present a full characterization of a tunable atomic line monochromator. I measure the transmission, spectral resolution, and spectral tunability of the device, as well as demonstrate whole-image transmission through the atomic line monochromator. Next, for practical implementations of the device to Brillouin spectroscopy, I created an atomic line monochromator based on a ladder-type atomic transition. This iteration of the device suffers from less noise than the previous version, leading to the first Brillouin measurements with this device. Finally, I present the first full-field Brillouin microscope by demonstrating whole Brillouin imaging with orthogonal detection with an atomic line monochromator.