Widefield Infrared Photothermal Imaging and Spectroscopy

Infrared Photothermal Heterodyne Imaging (IR-PHI) is now a well-established, chemical and morphological characterization technique widely applicable to environmental and material science applications. Examples include studying micro- and nanoplastics in spectrally complex, chemical environments as well as monitoring cation migration in hybrid lead halide perovskites. These successes portend future applications of IR-PHI to studying chemically heterogeneous processes such as those involved in catalytic reactions. Traditional IR-PHI possesses a spatial resolution of ~300 nm and works in a point-by-point scanning fashion. Time-expensive, single-point data acquisition limits image collection and subsequent chemical characterization. Consequently, we introduce here a widefield modality to IR-PHI where photothermal IR images are acquired using a high-speed CMOS camera. The approach parallelizes data collection and makes possible hyperspectral imaging of chemical specimens. Widefield image resolution and detection limits are established and compared with those of traditional IR-PHI.