Mid-infrared Energy Deposition Spectroscopy

TL;DR

This paper introduces mid-infrared energy deposition spectroscopy, a technique that achieves microsecond temporal and sub-micron spatial resolution for measuring light-matter interactions, overcoming previous speed limitations in photothermal microscopy.

Contribution

It presents a novel spectroscopic method that combines rapid infrared tuning with time-resolved energy deposition measurement, enabling high-speed, high-resolution vibrational spectroscopy.

Findings

Achieves microsecond temporal resolution in spectroscopy.

Provides sub-micron spatial resolution.

Increases detection bandwidth significantly.

Abstract

Photothermal microscopy is an emerging tool for measuring light-matter interactions with single-molecule sensitivity. It is generally believed that the spectral acquisition speed in photothermal microscopy is limited by the slow thermal diffusion process. Here, we demonstrate mid-infrared energy deposition (MIRED) spectroscopy, which offers both microsecond-scale temporal resolution and sub-micron spatial resolution. In this approach, the photothermal process is optically probed while the infrared pulses from a quantum cascade laser array are rapidly tuned. Based on Newton's law, the energy deposition corresponds to the first derivative of local temperature rise over time and provides the instantaneous infrared absorption. By employing time-resolved measurement of transient energy deposition, the upper limit for spectrum encoding shifts to the vibrational relaxation level, which occurs on the picosecond scale. This method significantly increases the detection bandwidth while maintaining the sensitivity and resolution advantages of photothermal detection.