Photothermal refraction is a novel thermo-optical technique that measures absorbance from localized regions within larger samples. In this technique, a modulated pump laser beam and a coplanar continuous-wave probe laser beam cross at right angles within the sample. Absorbance of the pump laser beam generates a time-varying localized temperature rise within the sample. This heated region acts as a thermal cylindrical lens that periodically defocuses the probe beam and results in a change in the probe beam center intensity. Since the pump and probe beams interact only in their intersection volume, a localized measure of sample absorbance is produced. A high spatial resolution image of sample absorbance may be made by recording the photothermal refraction signal as the sample is scanned through the intersection of the laser beams.