photographic materials (plates and films) that are sensitive not only to the rays of visible light but also to infrared radiation. Photographic emulsions containing silver halide exhibit so-called intrinsic sensitivity in the blue-violet region of the visible spectrum; they are virtually insensitive to yellow, green, red, and infrared rays. To make photographic materials sensitive in additional spectral regions, special additives consisting of sensitizing dyes that absorb radiation of the appropriate wavelength are introduced into the emulsion. The sensitivity caused by the additives is called additional or sensitized sensitivity. Infrachromatic materials are sensitized to infrared radiation mainly by the use of cyanine dyes.
Most infrachromatic materials have sensitized sensitivity in a relatively narrow spectral band. They are graded according to the spectral position of their maximum sensitivity (in nanometers [nm]): I–720, I–760, I–810, and so on. An increase in the wavelength at which the maximum occurs is usually accompanied by a decrease in the magnitude of the maximum. Infrachromatic materials are sometimes sensitized to a wide range of wavelengths by introducing into the emulsion several sensitizers that absorb radiation in various spectral regions. Materials that are simultaneously sensitized to the red and infrared regions are called paninfrachromatic materials.
Infrachromatic materials are distinguished by a rapid drop in sensitivity during storage; the magnitude of the drop increases with an increase in the wavelength of maximum sensitivity. Therefore, the emulsion for infrachromatic materials with a far sensitivity threshold (above 900 nm) is prepared immediately before usage. The maximum limit for infrared sensitizing in the longwave region is 1200 to 1300 nm.
Infrachromatic materials are used for the recording and determination of the field properties of the infrared radiation of lasers, particularly those operating in the pulsed mode.