| 摘要 |
Infrared and visible light energies are directed through a container (14) onto a CCD camera (28) that is responsive to both the visible and infrared light energy. Crossed polarizers (22, 24) are positioned on opposed sides of the container (14), and operate on the visible light energy in such a way as to block transmission of visible light to the camera (28) in the absence of stress variations in the container, which after polarization of the visible light energy traveling through the container. On the other hand, the polarizers (22, 24) have little or no effect on the infrared light energy, which creates a normally gray intensity of background light at the camera. In this way, incidence of visible light on the camera (28) due to stress variations in the container appears as a bright signal against a normally gray background, while blockage of infrared light due to opaque variations in the container appears as a dark signal against the normally gray background. <IMAGE> |
