High-Pressure Ultrafast Time-Resolved Far-Infrared Full-spectrum Spectroscopy with Air-Based Upconversion

Abstract

Abstract Most condensed materials exhibit characteristic excitations in the far-infrared range. The ultrafast dynamics of these excitations significantly influence the fundamental physical and chemical properties of the materials. Moreover, modulating the dynamics of these excitations through pressure variations is intriguing for unveiling the key microphysical processes involved and can offer dynamic experimental support for exploring novel materials. In this study, we demonstrate the first experimental elucidation and application of ultrafast time-resolved far-infrared full-spectrum spectroscopy combined with high-pressure diamond anvil cell (DAC) technology. The combination of an air-plasmon-based continuum and an air-based single-shot upconversion detection technique have been first employed in high-pressure time-resolved infrared spectroscopy. The air-plasmon-based ultrabroadband far-infrared continuum was directed into a DAC and the transmitted pulse was detected in a single shot form through four-wave mixing in the air to avoid the absorptions from phonon modes of the nonlinear medium. It allows the real-time capture of the spectrum spanning from < 50 to > 1800 cm− 1, with a few-cm− 1 spectral resolution. We investigate the pressure-dependent vibrational coupling dynamics of the complete set of vibrational fingerprint modes in microcrystalline octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) following mode-selective vibrational mode excitation. The results reveal that pressure enhances the vibrational coupling and energy transfer between the excited vibrational modes and doorway modes. The combination of high-pressure technology and time-resolved full-spectrum infrared spectroscopy opens up new perspectives for the study of the ultrafast phenomena in material science.