Design and characterization of a large-area lens-coupled CCD detector for macromolecular crystallography

We have prototyped and characterized a very large format X-ray detector for macromolecular crystallography. The X-ray field strength is converted to visible light in a phosphor film. Light from the phosphor is focused onto a CCD imager by a lens specially designed for this detector, that has a very high numerical aperture. The CCD is very large (61 mm, 4,096 × 4,096 pixels), and employs a very low-noise on-chip preamplifier. Lens coupling between phosphor film and CCD avoids many of the optical imperfections of fiber optic coupling, but it remains a challenge to make a lens system with optical transfer efficiency matching or exceeding that of fiber optical systems. We have met this challenge by enhancing system gain in our detector through implementation of modern lens technologies and imaginative CCD design. At this point the system gain equals that of conventional CCD-based X-ray crystallography detectors, which couple the CCD to the phosphor through a fiber optic taper. Although many of our technical developments could also be used in fiber optic detectors, the overriding virtues of the lens-couple detector are simplicity, optical perfection, and cost.