Optical Design of Angle Resolved Photoelectron Spectroscopy Beamline at Indus-1 Synchrotron Radiation Source

In this paper we have discussed the optical design principle and imaging characteristics of the angle resolved photoelectron spectroscopy (ARPES) beamline which have been recently commissioned at the Indus-1 synchrotron radiation source, Centre for Advanced Technology (CAT), Indore. The heart of the beamline is the 1.4 meter focal length Toroidal Grating Monochromator (TGM-1400) supplied by M/S. Jobin-Yvon, France. The monochromator uses three interchangeable aberration corrected toroidal holographic gratings having groove densities of 1800g/mm, 600g/mm and 200g/mm and it covers the spectral region of 40 A to 1000A with an average spectral resolution of 0.4A. A toroidal mirror focuses the light originating from the tangent point of the synchrotron source onto the entrance slit of the monochromator and a second toroidal mirror focuses the light emerging from the exit slit of the monochromator at the experimental sample position. All the three optical components are coated with platinum. After optimising the geometrical parameters of the beamline, extensive ray tracing work has been performed to evaluate the imaging properties of the beamline.