A classical experimental configuration for a photothermal radiometry1 setup is depicted in Fig. 6.1. A laser is directed to a sample that is to be measured. The laser intensity is modulated mechanically using a chopper wheel. A signal derived from this chopper wheel serves as the reference signal for the lock-in amplifier.
The lens images the surface of the sample onto a detector. This allows for remote measurement of the sample temperature, which is modulated by the incident laser radiation. Lock-in amplification provides information on the amplitude and phase of this variation in temperature. The specimen under test is mounted on a translation stage so that different points on the surface of the sample can be measured in subsequent steps.