Design of a compact, high-resolution velocity-map imaging spectrometer for attosecond spectroscopy.

We present the design of a VMI spectrometer optimized for attosecond spectroscopy in the 0-40 eV energy range. It is based on a compact three-electrode configuration where the lens shape, size, and material have been optimized using numerical simulations to improve the spectral resolution by a factor of ∼5 relative to the initial design [Eppink and Parker, Rev. Sci. Instrum. 68, 3477-3484 (1997)] while keeping a flat spectral response in the 10-40 eV range. The experimental performance is tested using an attosecond source based on high-order harmonic generation. A good agreement is observed between the measured and simulated spectral resolution. At low kinetic energy, the electrostatic lens remains the limiting factor, while the high energy range is mostly affected by the resolution of the camera objective.