Most X-ray imaging instruments never point a camera at X-rays directly. Instead, a scintillator or phosphor screen absorbs the X-rays and turns them into visible light, and a camera images that screen. This approach, called indirect detection, is common in X-ray crystallography, non-destructive testing, veterinary X-ray and streak tube readout. It lets a well-understood visible-light sensor do the hard work of measuring a very faint glow.
This post is for engineering teams building or refreshing those instruments. It covers how the camera couples to the screen, how format and pixel size follow from that choice, how to time a camera to a pulsed source, and the mechanical details that are easier to settle early. At Finger Lakes Instrumentation (FLI), the closest fits are our Aurora and Revelation cooled CMOS cameras, with our Kepler line where larger pixels help.
In an indirect system, the scintillator decides what the camera sees. Many common scintillators and phosphors emit in the visible range, often in the green, so the sensor's response in that band matters more than its peak specification. The screen's thickness also trades sensitivity against sharpness: a thicker screen stops more X-rays but spreads the light over a wider spot.
The camera's job is to collect as much of that light as possible and add as little noise as possible. Every photon lost between the screen and the sensor is signal you can't get back, which is why the coupling method is usually the first big design decision.
There are two main ways to get light from the screen to the sensor.
FLI cameras work well in lens-coupled designs as standard products. For fiber coupling, FLI can quote custom builds, including sensors coupled to a fiber-optic faceplate in a sealed chamber. These are engineering projects that our team scopes with you.
A larger sensor reduces the demagnification a lens-coupled system needs, which directly improves light collection. The Aurora line offers large back-illuminated Sony formats. The AR455 has a 36 x 24 mm sensor with 9568 x 6380 pixels, and the AR411 reaches 53.4 x 40 mm with 14192 x 10640 pixels, both with 3.76 µm pixels.
Small pixels give fine sampling, but the scintillator often sets the real resolution limit. If the light spot from each X-ray is larger than several pixels, you can combine pixels to gain signal. On Aurora cameras that binning is done digitally, because the Sony sensors don't support on-sensor binning. When you'd rather have larger native pixels, the Kepler KL4040 and KL6060 use 9 µm and 10 µm pixels. Our post on large-format cameras for national labs covers the bigger CCD and CMOS formats in more depth.
Many X-ray instruments use pulsed or flash sources, so the camera has to be exposing when the flash arrives. External trigger in and out is standard on Aurora cameras. In triggered global-reset mode, expect a row-reset delay of roughly 300 to 350 µs after the trigger. In practice, that means triggering the camera well before the X-ray flash and keeping exposures short, around 1 to 2 ms, to limit background.
Aurora cameras don't use a mechanical shutter, since CMOS sensors don't need one for exposure timing. For dark frames, plan on a blocked filter-wheel position or simply a frame with the source off. If several cameras must fire together, drive them all from an external sync or trigger signal rather than relying on independent timing.
Indirect X-ray signals can be very weak, and some measurements integrate for a long time. Cooling keeps dark current down so the faint glow from the screen stands out. Aurora and Revelation cameras are TEC-cooled to about 50 °C below ambient. Because that figure is relative to ambient, the air temperature inside your instrument sets how cold the sensor really runs. Our post on air versus liquid cooling for OEM cameras explains how to plan for heat inside an enclosure.
For compact instruments, the Revelation puts the same Sony sensors as Aurora in a thin, fin-less body that is shorter front to back and can be liquid-cooled. That makes it easier to fit behind a screen in a tight shielded housing.
X-ray instrument builders often need closer access to the sensor than an imaging customer does. A few points are worth knowing early:
If this is your first program with a camera supplier, our post on choosing an OEM camera partner walks through the wider process.
FLI has delivered over 10,000 cameras to OEMs, and X-ray crystallography and veterinary X-ray are among the applications. Every FLI camera is Made in USA, and our sensor chambers are assembled in our 1,000+ sq ft ISO Class 7 clean room. See how on our in-house manufacturing page.
Tell our sales team your screen, coupling method, source timing and enclosure limits, and we'll help you choose between a standard camera and a custom build. Request a quote or email sales@flicamera.com.
