Sensing the Invisible World

The human eye has a very limited spectral response and is completely insensitive to ir radiation. Objects at or near earth ambient temperatures of 300 K emit ir radiation. In order to sense this long wavelength ir radiation, a variety of image translation devices have been developed. This introductory article describes the important characteristics of some of these image translation devices. It also briefly mentions a few of their very many applications in the field of nondestructive examination and testing. Further details of the image translation scanners and of related instruments and techniques, as well as of their multifold applications, are given in the following papers that constitute the feature of the September 1968 issue of APPLIED OPTICS.