Dark-field mid-infrared photothermal microscopy

A wide-field mid-infrared photothermal microscopy (MIP) system for analyzing a sample on a substrate using dark-field illumination, comprising:

• a mid-infrared optical source configured to generate a mid-infrared beam, the mid-infrared beam being directed through the substrate and to the sample from a first side of the sample to heat the sample;
• a visible light source for generating a light, the light illuminating the sample on the substrate from a second side of the sample, the second side of the sample opposite the first side of the sample, and creating a scattered field and a reflected field along a collection path of the system;
• an objective pupil within the collection path relayed to a unit magnification 4f system, wherein the reflected field is refocused at the objective pupil;
• and
• a camera positioned at an end of the collection path to collect the scattered field and generate a dark-field image of the sample,
• wherein the MIP system is configured to simultaneously heat the sample with the mid-infrared optical source while imaging the sample with the visible light source.