We report results of quantum efficiency (QE) measurements carried out on a 150 nm thick nitrogen-incorporated ultrananocrystalline diamond terminated with hydrogen; abbreviated as (N)UNCD:H. (N)UNCD:H demonstrated a QE of $sim$10$^{-3}$ ($sim$0.1%) a
t 254 nm. Moreover, (N)UNCD:H was sensitive in visible light with a QE of $sim$5$times$10$^{-8}$ at 405 nm and $sim$5$times$10$^{-9}$ at 436 nm. After growth and prior to QE measurements, samples were exposed to air for about 2 hours for transfer and loading. Such design takes advantage of a key combination: 1) H-termination inducing negative electron affinity (NEA) on the (N)UNCD and stabilizies its surface against air exposure; and 2) N-incorporation inducing $n$-type conductivity in intrinsically insulating UNCD.
A 60 MeV beam at the BNL Accelerator Test Facility (ATF) was manipulated by a planar tunable de-chirper made out of two 10 cm long dielectric slabs with copper plated backs. While the gap was changed from 5.8 mm to 1 mm, the correlated energy chirp o
f the low charge electron bunch was reduced from approximately 330 keV/mm to zero. This result is in agreement with simulations. Calculations show that similar devices, properly scaled to account for the expected electron bunch charge and length, can be used to remove residual correlated energy spread at the end of the linacs used for free-electron lasers (FEL). Potentially, this technique could significantly simplify linac design and improve FEL performance.
We have directly measured THz wakefields induced by a subpicosecond, intense relativistic electron bunch in a diamond loaded accelerating structure via the wakefield acceleration method. We present here the beam test results from the first diamond ba
sed structure. Diamond has been chosen for its high breakdown threshold and unique thermoconductive properties. Fields produced by a leading (drive) beam were used to accelerate a trailing (witness) electron bunch which followed the drive bunch at a variable distance. The energy gain of a witness bunch as a function of its separation from the drive bunch describes the time structure of the generated wakefield.
We report observation of a strong wakefield induced energy modulation in an energy-chirped electron bunch passing through a dielectric-lined waveguide. This modulation can be effectively converted into a spatial modulation forming micro-bunches with
a periodicity of 0.5 - 1 picosecond, hence capable of driving coherent THz radiation. The experimental results agree well with theoretical predictions.
