A typical AFM-IR setup consists of a pulsed laser focused onto a sample at the location of the tip of an AFM cantilever (see Figure ). In general, the working principle of this technique is described by focusing on the change of the sample's density, which induces a localized sample expansion. The partial or total absorption of light from the pulsed laser by molecules distributed in the sample results in a local temperature increase affecting the density and refractive index of the sample at the place of absorption. A train of laser pulses will thus generate a modulated temperature change in the sample leading to photothermal and photoacoustic waves that propagate within the sample. AFM-IR employs the the spatially resolved detection of the photothermal expansion of the sample by the AFM's cantilever upon illumination with a pulsed light source (see Figure ). Absorption of light from the laser pulse leads to local temperature increase and concurrent thermal expansion (Figure ). As the heat is redistributed within the sample this local expansion subsides.