Bruce Dunham

Thermal emittance and response time measurements of negative electron affinity photocathodes

The thermal emittance and temporal response of a photocathode set an upper limit on the maximum achievable electron beam brightness from a photoemission electron source, or photoinjector. We present measurements of these parameters over a broad range of laser wavelength for two different negative electron affinity (NEA) photocathodes. The thermal emittance of NEA GaAs and GaAsP has been measured by two techniques—a measurement of the beam size downstream from a solenoid, whose strength was varied, and a double slit transmission measurement—for different laser spot sizes and shapes. The effect of space charge on the beam spot size allows a good estimation of the photoemission response time from these cathodes. Both cathodes show a subpicosecond response for laser wavelengths shorter than 520 nm.

Record high-average current from a high-brightness photoinjector

High-power, high-brightness electron beams are of interest for many applications, especially as drivers for free electron lasers and energy recovery linac light sources. For these particular applications, photoemission injectors are used in most cases, and the initial beam brightness from the injector sets a limit on the quality of the light generated at the end of the accelerator. At Cornell University, we have built such a high-power injector using a DC photoemission gun followed by a superconducting accelerating module. Recent results will be presented demonstrating record setting performance up to 65 mA average current with beam energies of 4–5 MeV.

Efficient temporal shaping of ultrashort pulses with birefringent crystals

A new and simple technique for temporal shaping of femtosecond and picosecond pulses with high efficiency is demonstrated. The pulse is divided into numerous pulses by a designed birefringent-crystal set. These divided pulses produce various shapes.

Thermal emittance measurements of a cesium potassium antimonide photocathode

Thermal emittance measurements of a CsK2Sb photocathode at several laser wavelengths are presented. The emittance is obtained with a solenoid scan technique using a high voltage dc photoemission gun. The thermal emittance is 0.56±0.03 mm mrad/mm(rms) at 532 nm wavelength. The results are compared with a simple photoemission model and found to be in a good agreement.

Thermal emittance and response time measurements of a GaN photocathode

We present the measurements of thermal emittance and response time for a GaN photocathode illuminated with 5 ps pulses at 260 nm wavelength. The thermal emittance was measured downstream of a 100 kV dc gun using a solenoid scan with a wire scanner and a beam viewscreen and was found to be 1.35±0.11 mm mrad normalized rms emittance per 1 mm rms of illuminated spot size. The response time of the photoemitted electrons was evaluated using a deflecting mode rf cavity synchronized to the laser pulses and was found to be prompt within the time resolution capability of our setup.

Cold electron beams from cryocooled, alkali antimonide photocathodes

In this paper we report on the generation of cold electron beams using a

Thermal emittance and response time of a cesium antimonide photocathode

{\mathrm{Cs}}_{3}\mathrm{Sb}

Benchmarking of 3D space charge codes using direct phase space measurements from photoemission high voltage DC gun

photocathode grown by codeposition of Sb and Cs. By cooling the photocathode to 90 K we demonstrate a significant reduction in the mean transverse energy validating the long-standing speculation that the lattice temperature contributes to limiting the mean transverse energy or intrinsic emittance near the photoemission threshold, opening new frontiers in generating ultrabright beams. At 90 K, we achieve a record low intrinsic emittance of

Generation of 110 W infrared and 65 W green power from a 1.3-GHz sub-picosecond fiber amplifier

0.2\text{ }\text{ }\ensuremath{\mu}\mathrm{m}

Performance of a very high voltage photoemission electron gun for a high brightness, high average current erl injector

(rms) per mm of laser spot diameter from an ultrafast (subpicosecond) photocathode with quantum efficiency greater than