The PCI technique, a modification of photothermal spectroscopy, has become a powerful tool for testing various low absorptive optical materials and components. The current state of the technique and recent progress in extending its capabilities toward the mid-infrared region is presented. A 3.39 μm probe was used for testing and studying various semiconductor materials, such as p-doped GaAs, that can exhibit non-thermal response to the pump beam in addition to the thermal one. A simple theoretical model of the PCI method is shown to describe adequately the experimental data, making it possible to calibrate the setup without using a calibration standard.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.