In LAMBDA, a pixelated sensor layer is connected face-to-face to the Medipix3 readout chip by a fine array of solder bumps. The readout chip provides sophisticated signal processing for each pixel, including photon counting, and the sensor layer can be independently optimized for different applications – for example, high-Z sensors for hard X-ray detection.
LAMBDA uses the Medipix3 readout chip, developed at CERN. Medipix3 not only allows photon-counting detection with a small pixel size, but also a wide variety of operating modes. For high-speed measurements, the chip allows deadtime-free readout at 2000 fps, while in experiments with polychromatic X-rays, energy binning can be used to achieve “colour” X-ray detection.
By counting individual X-ray photons hitting each pixel, LAMBDA achieves effectively noise-free detection, allowing optimal signal-to-noise performance. Each photon hit on each pixel is compared to one or more user-defined energy thresholds, making it possible to perform energy discrimination, for example to suppress background such as fluorescence.
How fast can LAMBDA go, what are the quickest dynamics you could image? Exposure time can be selected by the user to be any value all the way down to less than a 1 microsecond, making LAMBDA cameras sensitive to dynamics on the microsecond time scale and able to sample them at up to 24 kHz frequency, which is an excellent choice for a large class of XPCS and pump-probe type experiments!
LAMBDA allows noiseless imaging using dual thresholds. Conventional photon counters count every photon above the threshold regardless of its energy, but with the LAMBDA camera you can set the additional threshold such that you only count photons of an energy defined by the window between the two thresholds. In this way higher energy photons are ignored and do not contribute to the background!