Widefield photothermal infrared spectroscopic imaging

A method for photothermal imaging of a sample, the method comprising:

• mounting the sample on a first surface of a multi-layer substrate, wherein the multi-layer substrate includes:
• a mechanical support layer, wherein the mechanical support layer is transparent to a range of probe wavelengths;
• a first reflective layer disposed between the mechanical support layer and the first surface, wherein the first reflective layer is partially reflective and partially transparent to the range of probe wavelengths;
• a first thermal spacer layer disposed between the first reflective layer and the first surface, wherein the first thermal spacer layer exhibits at least one of mechanical expansion or a change in refractive index at the range of probe wavelengths in response to heating;
• and
• a second reflective layer disposed between the first thermal spacer layer and the first surface, wherein the second reflective layer is reflective to the range of probe wavelengths and to a range of infrared pump wavelengths;
• illuminating the sample and the multi-layer substrate, from the first surface side of the multi-layer substrate, with infrared light at a first pump wavelength within the range of infrared pump wavelengths, thereby causing the first thermal spacer to exhibit at least one of mechanical expansion or a change in refractive index in a pattern corresponding to a pattern of absorption of the light at the first pump wavelength by the sample;
• illuminating the multi-layer substrate, from a second surface side of the multi-layer substrate that is opposite the first surface side, with light at the probe wavelength;
• and
• while illuminating the multi-layer substrate with light at the probe wavelength, imaging the second surface side of the multi-layer substrate at the probe wavelength to generate a first image.

A multi-layer substrate for photothermal imaging of a sample, wherein the substrate has a first surface on which the sample can be disposed for photothermal imaging thereof, the substrate comprising:

• a mechanical support layer, wherein the mechanical support layer is transparent to a range of probe wavelengths;
• a first reflective layer disposed between the mechanical support layer and the first surface, wherein the first reflective layer is partially reflective and partially transparent to the range of probe wavelengths;
• a first thermal spacer layer disposed between the first reflective layer and the first surface, wherein the first thermal spacer layer exhibits at least one of mechanical expansion or a change in refractive index at the range of probe wavelengths in response to heating;
• and
• a second reflective layer disposed between the first thermal spacer layer and the first surface, wherein the second reflective layer is reflective to the range of probe wavelengths and to a range of infrared pump wavelengths.