Independent coherent control of phonon mode amplitudes in bismuth thin films via polarization and double-pulse manipulation

We demonstrate an approach for the selective modulation of the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi>A</a:mi> <a:mrow> <a:mn>1</a:mn> <a:mi mathvariant="normal">g</a:mi> </a:mrow> </a:msub> </a:math> and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:msup> <c:mrow/> <c:mn>1</c:mn> </c:msup> <c:msub> <c:mi>E</c:mi> <c:mi mathvariant="normal">g</c:mi> </c:msub> </c:mrow> </c:math> optical phonon amplitudes in bismuth thin films. Combining polarization-sensitive excitation with controlled pump-pulse delays, this is shown to enable the targeted manipulation of the reflectivity signals associated with distinct phonon modes. Employing an electro-optic detection scheme reveals that the observed changes arise from selective amplification or suppression of specific symmetry components within the detected signal. This combined excitation and detection strategy is broadly applicable to other material systems and may facilitate pathways for ultrafast phononic information processing and nanoscale thermal management, critical for next-generation optoelectronic technologies.