How fast is fast? Sampling microsecond dynamics with a high frame rate camera
LAMBDA cameras are capable of taking 2,000 fps continuously without time
gap in between images, making them the fastest large format imaging
cameras currently available. But is this the limit? How fast can LAMBDA go,
what are the quickest dynamics you could image?
To answer these questions, we need to dive into several of the unique
features of the chip. The Medipix3RX chip has two counters in each pixel,
which can either be combined for a high dynamic range of 24 bits or used in
continuous read/write mode, where one counter is being used for counting
while the other one is read out. Switching the counters is easy and happens
instantaneously (i.e., in much less than 1 microsecond). The detector can
also be “gated”, i.e., it counts only when an external signal is provided, for
applications that require special acquisition modes.
Continuous read/write mode
In continuous read/write mode reading the detector out takes 0.5 ms to read
12 bits per pixel. But that's not the limit, we are currently developing faster
readout for lower counter depths. So if 6 bit counter depth is sufficient for
you, you can run the camera at 4,000 fps without time gap. Certain
application may even be possible with 1 bit readout (>= 1 photon or no
photons during counting time), which can run at up to 24 kHz.
24 bit mode
In 24 bit mode, there is one counter of 24 bit, which can be read out in 1 ms
- the dead time between two frames taken in this mode.
However the counting time can be selected by the user to be any value all
the way down to less than a 1 microsecond, at which point the shaping time
of the preamplifier limits further reduction of the counting time. Choosing
such a short shutter time will not give you more than 1 frame every millisecond (since the detector still needs to be read), but will allow
you to have very brief counting periods. These extremely brief counting periods can be advantageous for certain types of applications.
One example would be XPCS, where a long counting time would smear out the coherent properties of the system, resulting in reduced
contrast. Another example are certain pump-probe experiments where a repeatable quick response of the system is externally
triggered. Sweeping the delay between system and camera trigger the entire response dynamics can be sampled down to the
Gating is a feature that allows multiple (usually very short) exposures that are added up within one frame. The advantage of this
approach is that starting and stopping of the counter is much faster than the 1 ms needed to read out the detector, this feature is also
sometimes called an “electronic shutter”. This mode allows you to take data exclusively during defined time windows, which can be
synchronized to your source or an experimental trigger, thereby suppressing background photons that are arriving outside of your time
LAMBDA cameras are sensitive to dynamics on the microsecond time scale and offer multiple acquisition modes enabling up to 24 kHz
sampling frequency, making LAMBDA an excellent choice for a large class of XPCS and pump-probe type experiments.
© Copyright X-Spectrum GmbH 2014-2017
about the detector
using the detector
Video with high-Z
Imaging at 2000 fps
Imaging with high-Z
Diamond Anvil Cell