Speaker
Description
A coherent coupler for high-energy electron beams would enable quantum-optical experiments with electrons, in particular, the implementation of quantum metrology techniques in transmission electron microscopy (TEM). Bragg scattering of electrons by laser radiation is a promising candidate for realizing a coherent electron beamsplitter. The main challenge for achieving the Bragg regime with electron energies of 30 to 300 keV relevant to TEM is the need for a centimeter-scale interaction length at high continuous-wave laser intensities.
We are working toward realizing a Laser Bragg Beamsplitter for electron waves based on continuous-wave lasers. In our approach, electrons interact with a co-propagating volumetric optical lattice formed by two laser beams of different wavelengths, enhanced in a two-color resonator. This scheme allows the electron and laser beams to intersect at a low angle of about 10 mrad. This approach effectively yields an interaction length of a few centimeters, keeping the intensity requirements within reach of modern high-finesse cavities and enabling coupling of sub-relativistic electrons in the Bragg regime at achievable circulating power levels.
We have implemented an optical resonator with suitable geometry and demonstrated single-color operation with a continuous-wave circulating optical power of 300 kW, far exceeding the 16 kW that, according to our calculations, is necessary for $50/50$ splitting of a 31-keV electron beam. The interaction length was chosen to be $2.8$ cm, which is long enough to achieve the Bragg regime with losses to undesired diffraction orders below $1\%$.
The experimental realization of the device is well underway. The first electron-laser interaction in this system is expected next year.