Finding a cold needle in a warm haystack: infrared imaging applied to locating cryocooled crystals in loops

The use of infrared imaging to locate crystals mounted in cryoloops and cryopreserved in a nitrogen gas stream at 100 K is demonstrated. In the home laboratory, crystals are clearly seen in the infrared images with light transmitting through the sample while irradiating the crystal from behind, and with illumination from a direction perpendicular to the direction of view. The crystals transmit and reflect infrared radiation at different levels to the surrounding mother liquor and loop. Because of differences in contrast between crystals and their surrounding mother liquor, it is possible to identify the crystal position. At the synchrotron, with robotically mounted crystals, the small depth of field of the lens required the recording of multiple images at different focal points. Image processing techniques were then used to construct a clear image of the crystal. The resulting infrared images and intensity profiles show that infrared imaging can be a powerful complement to visual imaging in locating crystals in cryocooled loops.