Thermo-Optical Detection

If a high- energy laser beam is focussed onto a section of the capillary, heat is evolved and the refractive index changes causing a thermal lens to be produced. The lens can be made to cause the deflection of another laser beam passing through the window normal to the first laser beam. The second laser beam falls onto a photoelectric sensor that responds to the beam deflection. These types of detectors are only efficient if the substances to be detected adsorb strongly and so derivatization is often necessary. These types of detector can have sensitivities in the attomole range.