Quantum efficiency measurements of a copper photocathode in an RF electron gun

Abstract

In most experiments, special consideration is given to the A 4.5 MeV photocathode RF Gun has been collection of all the charge produced by the injected photons.Since our goal is to create an electron beam, we measure the charge contained in the electron beam at the output of the rf gun and use it in the calculation of quantum efficiency. Therefore, this measurement defines an effective quantum efficiency of the photo-injected rf gun system which incorporates the collection efficiency of the beam.11. EXPERIMENTAL SETUP commissioned at UCLA. A photo-injector drive laser produces sub 2 ps pulses of UV (h=266 nm) light with up to 200 pJ/ pulse, and illuminates a copper cathode. The photoelectrons are accelerated to an energy of 3.5 MeV within the gun. The electron beam charge is measured as a function of laser energy using an integrating current transformer (ICT). We present measurements of qumtum efficiency as a function of laser polarization for injection angles of 2" and 70" with respect to the cathode normal. At 70" incidence a SO% enhancement in quantum efficiency ( > is observed for p-polarized light over s-polarized light.

Photocurrents obtained from a triple planar probe sensor for in situ extreme ultraviolet (EUV) radiation measurements on low Earth orbiting CubeSats

“…The estimated quantum efficiency of copper at UV wavelengths from 116 to 260 nm varies from 10 Ϫ2 to 10 Ϫ3 . Above 260 nm, its quantum efficiency is less than 10 Ϫ3 (Davis et al, 1993;Dowell et al, 2006).…”

Laser injection of ultra-short electron bursts for the diagnosis of Hall thruster plasma

“…One of the most developed was the injection of ultra-short bursts in RF accelerators. Such electron bursts have also been used in the eighties for diagnostics of RF plasma sheaths in 13.56 MHz capacitive low pressure discharges, where the injection time within an RF period revealed the time behaviour of the RF sheaths [21][22][23][24][25][26]. This section concerns the first step of the development of a similar tool for the diagnosis of the near exhaust plasma of a Hall thruster and presents a characterization of the production of photo induced electron bursts.…”

“…Space charge effects, as evidenced in other studies [19,21,22], can induce backward trajectories of emitted electrons towards the emitter surface and a collection efficiency η coll is defined as:…”

“…Such bursts can be produced with pulsed UV lasers inducing photoelectric emission at a convenient time scale. This method has already been used for other purposes concerning RF accelerators technologies [19] and diagnostics of RF (13.6 MHz) capacitive discharges [20][21][22]. In our case the electron burst production involves a quadrupled Nd-YAG laser as photon source and a tantalum plate as emitter.…”