An optical beam (3) passes through an illuminator (18), a semiconductor device (70), and an imager (20) to form a test object image (17) on a camera (16). Intensity variations in the object image (17) correspond to carrier density and temperature gradients inside the semiconductor device (70)....http://www.google.com.au/patents/US6181416?utm_source=gb-gplus-sharePatent US6181416 - Schlieren method for imaging semiconductor device properties
