Lock-In Thermography Based on an Optical Chopper

The high power heat sources are very slow in response to the power modulation. Therefore such system is not used for applications with very high modulation frequency. A new thermography system is developed that combines an optical chopper with an infrared lamp array to realize higher frequency power modulation. This system not only has the benefit of broader modulation frequency range for lock-in thermography, but also can serve as a pulsed mode thermographic system with fast power cut off. Experiments are carried out to verify the system's capability. The results show that at 4 Hz lock-in frequency, it can effectively inspect thin solar wafer adhesion quality, and with 0.01 Hz lock-in frequency, it can furthermore detect defects of 4.7 mm depth.