26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Calibration and Optimisation of a VIPA-based Brillouin Spectrometer: The Steps Before Measurement

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Poster ANZOS | Photonics and Optics (ANZCOP)

Speaker

Nathan Falkner (University of Technology Sydney)

Description

Brillouin Microscopy is a contactless optical technique of measuring visco-elastic properties in a broad range of materials. Since the adoption of the Virtually-Imaged Phase Array (VIPA) spectrometer in the 2000s, Brillouin Microscopy applications have expanded into biological research and imaging living matter. Modern day Brillouin Microscopy systems commonly employ VIPA spectrometers with acquisition speeds of ~100 milliseconds per spectrum or less. Therefore, it is feasible to create a map of the mechanical properties of cells, organoids or tissues in under an hour, delineating stiff or soft regions in living matter.
Broadly, Brillouin light scattering is an interaction between incident photons and the acoustic phonons in materials from thermodynamic fluctuations of pressure. A transaction of energy occurs, with a photon either creating (Stokes) or absorbing (Anti-Stokes) a phonon, causing a GHz shift in light frequency. This shift, Brillouin Frequency Shift, is proportional to the speed of sound in a target material and is linked to a material's longitudinal modulus. VIPA-based spectrometers can resolve these GHz frequency shifts by recording and analysis the diffraction patterns produced by spatially dispersive VIPA etalons on a CCD or EMCCD array detector.
Due to the high sensitivity of VIPA-based Brillouin systems to environmental perturbations (temperature, vibration, laser amplitude and phase noise), a perfectly aligned VIPA system can still suffer symptoms of spectral instability and drifts, leading to erroneous results and consequently misleading interpretation of Brillouin data collected. This work highlights the correct procedure for calibration of VIPA spectrometers and also a necessary diagnostic protocol to ensure optimal instrument function, including diagnostics and reduction of long-term spectral drifts. Once implemented, these can lead to increased stability and higher spectral precision of a VIPA-based Brillouin Microscope, to the benefit of data quality and the impact of measurement results.