Ultrafast Laser Laboratory

Ultrafast detection of relativistic particles

It is well known that the response time of the polarizability of optical crystals is in the femtosecond regime. If the electric field produced by the relativistic charged particles, both positive and negative charged particles, can be probed by such crystals, the passage of these particles could be detected with unprecedented temporal resolution, limited only by the bandwidth of the associated electronics. This scheme also has an added benefit of removing the detector from the vicinity of the interaction region, reducing the real space required near the beam line.

Experiments are done using the electron beam at the Accelerator Test Facility to examine the temporal shape of the electron induced polarization. A short 7 ps duration, 50 MeV electron beam passes at the vicinity of an electro-optical crystal, thereby induce a large polarization field on the crystal. The perturbed field induced by the electron beam will be probed with a highly polarized optical beam. After converting the optical phase change into light intensity variation, the transient electric field can be measured during the passage of the electron beam.

In one verison of the apparatus, the light field propagates at 45 degree to the principle axis of the crystal. The electron beam induced signal is measured to be less than 1 ns limited by the bandwidth of the photoreceiver.

In another verison of the apparatus, a free space Mach Zehnder interferometer is employed to probe the electron induced phase change. The electro-optical signal is sent to a streak camera. Less than 40 ps fast optical transient is measured.

Several variations of the apparatus are planned to lower the temporaal resolution to the femtosecond regime. Upon the success of these initial experiments, the project may be expanded to the construction of a real detector. If successful, this idea could lead to the development of particle detectors with temporal resolution in the femtoseconds and spatial resolution of a few microns which would be highly useful in both hadron and lepton colliders.

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For more information or preprint request contact Thomas Y. F. Tsang

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Last Modified: Wednesday, 06-Feb-2013 22:33:56 EST