Velocity-map imaging for emittance characterization of multiphoton-emitted electrons from a gold surface

A velocity-map-imaging spectrometer is demonstrated to characterize the normalized transverse emittance of photoemitted electron bunches. The two-dimensional (2D) projected velocity distribution images of photoemitted electrons are recorded by the detection system and analyzed to obtain the normalized transverse emittance. With the presented distribution function of the electron photoemission angles a mathematical method is implemented to reconstruct the three-dimensional (3D) velocity distribution curve. As a first example, multiphoton emission from a planar Au surface is studied via irradiation at a glancing angle by intense 45 fs laser pulses at a central wavelength of 800 nm. The reconstructed energy distribution agrees very well with the Berglund-Spicer theory of photoemission. The normalized transverse emittance of the intrinsic electron bunch is characterized to be 0.52 and 0.05 $\pi \cdot mm \cdot mrad$ in $X$- and $Y$-directions, respectively.