Document Type

Presentation

Date of Original Version

3-29-2025

Abstract

We present real-time measurements of ultrafast optical phonon decay in Barium Stannate (BaSnO3, BSO) using time-domain coherent Raman spectroscopy with < 120 fs time and ~0.1 cm⁻¹ spectral resolution. We traced phonon decay within multiple orders, with lifetimes ranging from 1.26 to 1.58 ps, and explained decay mechanisms via parametric phonon interactions. Objectives: BSO, a wide-bandgap semiconductor, exhibits high electron mobility, crucial for high-voltage transistors and other electronic applications. Carrier-phonon scattering impacts mobility, making phonon properties essential for understanding conductivity. Phonon decay times are inversely proportional to scattering rates. We used time-domain Coherent Anti-Stokes Raman Spectroscopy (td-CARS) to determine phonon decay times and linewidths due to its ability to detect weak phonon modes with high spatial and spectral resolution. Methods: We used two Optical Parametric Oscillators (OPOs) driven by ultrafast Ti:Sapphire laser pulses (120 fs, 76 MHz). The OPOs excited selected Raman-active vibrations in BSO, while a probe pulse tracked anti-Stokes signals to determine decay times. Experimental data was fitted with a theoretical model to extract decay constants (T₂), decay rates (Γ), and linewidths (Δν). Results & Conclusion: We measured decay times of 1.26 ps (LO2 at 465 cm⁻¹) and 1.47 ps (LO3 at 630 cm⁻¹), yielding linewidths of 8.25 and 7.22 cm⁻¹, respectively. DFT analysis identified phonon decay channels. The study provides high-precision phonon decay data critical for understanding electronic and optical properties, with td-CARS offering superior resolution over traditional Raman techniques.

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