Using the fringing fields of a hemispherical spectrograph to improve its energy resolution

Abstract

The energy resolution of a hemispherical deflector analyser (HDA) can be substantially improved by using its entry fringing fields advantageously, rather than trying to eliminate them—the traditional approach. The intrinsic lensing properties of these fringing fields, as shown in simulations, are able to not only restore, but even improve first-order focusing at the 180° deflection plane in a controlled way, without the use of any additional field correction electrodes. This is accomplished by changing the entry radius R0 and bias from their conventional values of , the mean radius and to new values with or with . An HDA with , ΔR = R2 − R1 = 58.4 mm and maximum entry angle αmax = 2° demonstrates the impressive resolution gains that can be attained, 34 for a point entry (Δr0 = 0) and 4.2 for an aperture diameter of Δr0 = 1 mm, over corresponding conventional entry conditions.