1.       Utilisation of RRCAT-TGM beamline on Indus-1

(a)        Multiple ionization of Argon by photo absorption :

            A new experimental station for studying photo ionisation and related process in gaseous targets has been set up on RRCAT-TGM beamline of Indus-1 by Physical Research Laboratory, Ahmedabad in collaboration with RRCAT. In the first experiment, multiple ionization of Argon by the absorption of a single photon has been studied. Charge states as high as Ar⁴⁺ have been observed, and relative cross-sections for charge-states 1 to 4 have been measured over a photon energy range 120-280 eV. Comparison of present measurements with existing data shows an overall agreement of the relative cross-sections of all charge states, up to the threshold of the L2-shell. Some deviations are observed at higher energies.

(b)        Study of Ion Irradiation Effect in Float Glass and Silicon Substrates :

            Float glasses are used as base substrate for x-ray and neutron mirror deposition because of its ultra smooth surface. Earlier we had analyzed the soft x-ray optical constants of these substrates in the soft x-ray regime using Indus-1 synchrotron source [Applied Optics 42, 6939 (2003)]. Optical response of these surfaces may vary upon ion beam treatment. To analyze such effects the two surfaces of a float glass viz.tin and non-tin side surfaces are irradiated with 100 KeV Ar ions. Upon irradiation, morphological and density changes are analyzed by employing the grazing incidence x-ray reflectivity (GIXR) and atomic force microscopy techniques. Effects of irradiation are explained by the means of electron density profiles(EDP) obtained from GIXR data. EDP profiles of two respective surfaces of a virgin float glass sample are shown in Fig.1. Total reflection x-ray fluorescence technique is used to analyze the surface composition before and after irradiation. Irradiation caused a drastic change in density and surface roughness on tin side, whereas the other side (non-tin side surface) remained almost unaffected. Diffusion of tin inside the bulk is cause of major damage. Monte Carlo simulations are carried out to support the experimental results. Soft x-ray optical studies using Indus-1 are in progress.

Figure 1: Electron density profiles of tin and non-tin side surface of virgin float glass sample. The EDP has been derived using x-ray reflectivity data measured with l = 1.54Å. Regions marked by label ‘A’, ‘B’ and ‘C’ are corresponding to surface, transition and –substrate density regions.