The imaging of fast processes with nanosecond-scale timing resolution is becoming a necessity in many applications such as imaging mass spectrometry, velocity mapping ion imaging, coincidence and covariance imaging, neutron time-of-flight imaging and others. Here we describe the concept of the counting and time stamping of optical photons, and present recent results on Tpx3Cam, a fast optical imager. The camera is a hybrid pixel detector: an optical sensor with high quantum efficiency (QE) , bump-bonded to a Timepix3 ASIC . The design of the silicon sensor, in particular its entrance window, which should be transparent for 400 nm photons was inspired by the fully depleted astronomical CCDs used in LSST, while the readout chip is a product of the Medipix collaboration at CERN employing technologies developed for the LHC experiments. Timepix3 has 256x256 pixels, 1.5 ns time resolution and data-driven readout with multi-hit capabilities, which is able to process 80 Mpixel/sec. The intensified version of the camera is coupled to an image intensifier, a vacuum device with a photocathode followed by MCP and fast scintillator, which ensures single photon sensitivity.
The camera has been used for a variety of applications for single photon and ion imaging in TOF mass spectrometry. In the latter case the image intensifier is not required as ions impinge a micro-channel plate producing light flashes in fast phosphor behind the MCP. This approach is popular with coincidence velocity map imaging (VMI), an essential tool in the study of reaction dynamics and strong field laser-matter interactions. VMI projects the transverse momenta of charged particles to positions on a 2D detector such that for a given particle species, its distance to the center of the detector is proportional to its initial transverse velocity. The time of flight measurement in the camera allows to do it for all ion fragments simultaneously.
|Title||Fast imager with 1.5 ns time stamping of optical photons|
Time-of-flight mass spectrum of CH₂IBr recorded with the fast camera after strong-field ionization with an intense laser pulse along with the camera images for each of the peaks in the TOF spectrum
Brookhaven National Lab, Upton NY, USA
|Session||16. Sensors and photonics I|
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