Uncertainty Estimation for the Brillouin Frequency Shift Measurement Using a Scanning Tandem Fabry–Pérot Interferometer

The expanded uncertainty of the measured Brillouin scattering shift frequencies is essential in assessing measurements parameters various materials. We describe general operation principles a light (BLS) spectrometer with high-power laser and scanning tandem Fabry–Pérot interferometer (TFPI) for material characterization. Various components have been analyzed BLS following Guide to Expression Uncertainty Measurement (GUM). relative frequency 15.70 GHz polymethyl methacrylate (PMMA) was estimated be 0.26%. calculated (based on properties PMMA) determined 15.44 2.13%. It shown that shifts PMMA agree within their uncertainties. TFPI-based can used measure longitudinal modulus materials an 1.9%, which smaller than ultrasonic velocity-based method (estimated 2.9%).