Ls 785 spectrograph

The Low-Frequency Raman (LFR) measurements were carried out using a custom-built system [36 (link)] with an excitation source from a 785 nm laser module (Ondax Inc., Monrovia, CA, USA) that was filtered by BragGrate band pass filters (OptiGrate Corp., Oviedo, FL, USA) to remove amplified spontaneous emission before irradiating the sample. Backscattered light from the sample was collected and filtered through a set of volume Bragg gratings (Ondax Inc., Monrovia, CA, USA) and focused into a LS 785 spectrograph (Princeton Instruments, Trenton, NJ, USA) via a fiber-optic cable. The light was dispersed onto a CCD detector (PIXIS 100 BR CCD, Princeton Instruments, Trenton, NJ, USA) and the data were calibrated using a sulfur, 1,4 bis (2-methylstyryl) benzene (BMB), and a toluene and acetonitrile solvent (1:1) standards. Spectra were collected over the spectral window −360 to 2030 cm⁻¹ with a 5–7 cm⁻¹ resolution. Each spectrum was averaged from 60 scans with an integration time of 1 s, and the sample spot size was approximately 500 μm. Specific spectral range (900–1000 cm⁻¹) was used for the band analysis, and fitted peak positions were determined using the peak find function (default settings) in the SpectraGryph 1.2.14. software [37 ].