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Velocitas VMI Gate Module Velocitas VMI Gate Module

Velocitas VMI Gate Module

Photek's gate module enables gating of the MCP in a Vacuum Imaging Detector, allowing for mass gating, time resolved investigations and dc slicing in VMI experiments. The gate width can be varied from 8 ns up to a few microseconds. The GM-MCP is designed to work with the Velocitas VMI Vacuum Imaging Detectors, where the input trigger will supply a 500 V pulse to the rear MCP, bringing the MCP from almost no gain to full operation for a user-defined time window.


  • 8 ns FWHM minimum

  • Variable gate width

  • 500 V output pulse

  • 5 V trigger pulse

  • Up to 1 kHz repetition

  • Up to 3 kV offset voltage


  • Mass spectrometry

  • Velocity Map Imaging

  • Mass/isotope selectivity

  • dc slicing

  • Time resolved imaging

  • State-selected imaging

  • Detector protection from overload signal

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Above: Slice images from VMI of Br from photodissociation of IBr in VMI DOUBLE PRIME, with gate widths of 30 ns, 40 ns, 60 ns and 200 ns (full Newton sphere).

The image shows results from state selected, one colour photodissociation of IBr at 260.61 nm, where the gate window has been selected to image the 79Br isotope. The strongest signal comes from Br ions formed together with spin-orbit excited I, while a weaker, faster ring is attributed to the spin-orbit ground state products.

In VMI DOUBLE PRIME with Repeller at 4.5 kV, applying a 30 ns gate to the MCP images a central slice through the Newton Sphere. This offers much improved signal to noise compared to imaging the full Newton sphere (with gate = 200 ns) and negates the need for complex reconstruction algorithms (Abel inversion). The sliced data provides improved resolution compared to Abel inversion of the 200 ns pancake image.

With permission from University of Bristol.

Find out more about the Velocitas VMI Vacuum Imaging Detector  > Next: Pulsed Valve  >