Selective Infrared Phonon Stimulation to Tune Thermal Transport

The recent developments in high power optical sources at far-to-mid infrared (IR) frequencies (0.1 to 100 THz) have provided the means to investigate and control material properties in solid-state and condensed matter systems under nonequilibrium conditions¹. In particular, in energetic materials where phonons are the primary carriers of heat, optical heating, and ultrafast spectroscopy have enabled the investigation of shock-induced chemistry², and ignition modulation³. In this work⁴, we determine the degree to which material properties such as thermal diffusivity and conductivity can be modulated via a selective nonequilibrium infrared stimulation of phonons. Using the molecular crystal RDX, we use detailed momentum-dependent coupling information across the entire Brillouin zone and the phonon gas model to show that selective stimulation of certain low and mid frequency phonons can have a substantial positive/negative effect on the overall thermal transport properties. Specifically in the case of RDX, stimulating modes at ~22.74 cm^-1 over a linewidth of 1 cm^-1 can lead to enhanced scattering rates that reduce the overall thermal diffusivity and conductivity by 15.58% and 12.46%, respectively, from their equilibrium values. In contrast, stimulating the modes near ~1140.67 cm^-1 over a similar bandwidth can produce an increase in the thermal diffusivity and conductivity by 55.73% and 144.07%, respectively. The large changes suggest a mechanism to evoke substantially modulated thermal transport properties through light matter interaction.<br/><br/>(1) Nicoletti, D.; Cavalleri, A. <i>Advances in Optics and Photonics</i> <b>2016</b>, <i>8</i>, 401.<br/>(2) Powell, M. S.; Sakano, M. N.; Cawkwell, M. J.; Bowlan, P. R.; Brown, K. E.; Bolme, C. A.; Moore, D. S.; Son, S. F.; Strachan, A.; McGrane, S. D. <i>Journal of Physical Chemistry A</i> <b>2020</b>, <i>124</i>, 7031–7046.<br/>(3) Alibay, Z.; Olsen, D.; Biswas, P.; England, C.; Xu, F.; Ghildiyal, P.; Zhou, M.; Zachariah, M. R. <i>ACS Applied Nano Materials</i> <b>2022</b>, acsanm.1c04157.<br/>(4) Kumar, G.; Chung, P. W. <i>ACS Omega</i> <b>2022</b>, <i>7</i>, 12787–12794.