Atomic force microscopy-infrared (AFM-IR) is an AFM based technique that measures mid-IR absorption spectra at nanometre spatial resolution. One of the most attractive advantages of AFM-IR for chemical spectroscopist is that it provides spectra which compare well to conventional FTIR absorption spectra [1]. The technique of AFM-IR relies on the detection of the pulsed wavelength tuneable IR laser induced thermal expansion of the sample area underneath the AFM tip. While this mode of signal generation sounds simple enough it is still not fully understood. In this work, we present a theoretical investigation of the laser heating induced thermal expansion process and model it as a point spread function (PSF). This approach draws parallels to super resolution microscopy where the PSF is used to determine spatial resolution and to resolve features below the diffraction limit [2]. The biggest challenge in determining the PSF of AFM-IR is fact that it relies on the thermal diffusion process and depends on material and sample properties in addition to the time / frequency. Our approach is comprised of finite element simulations, and theoretical considerations which are verified experimentally using confocal microscopy and AFM-IR experiments. We investigate the influence of material properties, IR laser properties, sample thickness, vertical positions of the samples well as laser repetition rate and pulse length on the AFM-IR spatial resolution.