Upconversion use for viewing and recording infrared images

The upconversion of 1.54-microm radiation to shorter wavelengths has been studied in CaF(2) crystals doped with Er(3+) ions. Experimental measurements of the intensity dependence and temporal behavior of the upconverted radiation give results in good qualitative agreement with a simple model of a cooperative luminescence process. Measurements with a silicon diode matrix array (DMA) of the spatial distribution of the luminescence from screens of CaF(2) doped with Er(3+), which were irradiated with an Er laser, showed that the resolution is not limited by the cooperative luminescent process but is determined by the granularity and/or thickness of the screens. Good results on 1.54-microm beam profiles were obtained with a computer-based image recording system incorporating the screen-DMA combination. A linear dependence on intensity without saturation of the DMA was achieved by interposing neutral density filters between the screen and the DMA.