X-ray reflectivity is a non destructive tool for study of surfaces and interfaces in thin films and multilayers. Soft x-ray resonant reflectivity is a powerful tool to study buried interfaces due to its increased sensitivity around the absorption edges of the constituent materials. Measurement of accurate optical constants is an important need to model and predict the actual performance of x-ray optical elements. Various detectors and spectrometers are generally required to be calibrated in Vacuum Ultra Violet (VUV) and soft x-ray regions. A medium resolution of ~ 2000 is sufficient to perform such experiments. A Varied Line Spacing Plane Grating Monochromator based soft x-ray beam line has been designed on bending magnet of Indus-2 to cater the above experimental needs in the extended soft x-ray energy range from 50eV to 1500 eV. This beamline will cover the K-edges of light elements like C, N and O and the L- and M-edges of transition elements. The beamline will be set up at the bending magnet port BL-3 and a reflectometer will be installed as an experimental station
Optical layout
The first optical element of the beamline is a horizontally deflecting and vertically mounted toroidal mirror, TM1, which accepts 2 mrad (horizontal) and 3 mrad (vertical) of the emitted bending magnet radiation. TM1 focuses the light vertically on to the entrance slit, S1, and horizontally on to the exit slit, S2. The second mirror is a spherical mirror, SM, which is vertically deflecting and forms a convergent beam for the plane grating. After SM, the white light is diffracted by plane grating and the required wavelength is focused on S2. Three interchangeable gratings, G1, G2 and G3, of line densities 1200, 400 and 150 lines/mm are used to efficiently cover the whole energy region. The monochromatized light is focused on to the sample by horizontally deflecting and vertically mounted toroidal mirror, TM2. An order suppression system will be placed after the TM2. The remaining parameters of all the beamline optical elements are given in
Beamline specifications
| Energy range |
50-1500 eV |
| Photon Flux |
109-1011 ph/sec |
| Spectral resolution |
1000 – 6000 |
| Beam size at experimental station |
0.5 mm (H) Χ 0.05 mm (V) |
Details of Optical elements
Parameters of the beamline optical elements |
Optical Element |
TM1 |
SM |
TM2 |
G1 |
G2 |
G3 |
Deflection |
Horizontal |
Vertical |
Horizontal |
Vertical |
Vertical |
Vertical |
Size (mm2) |
900×50 |
300×20 |
270×25 |
180×20 |
180×20 |
180×20 |
Coating |
Au |
Au |
Au |
Au |
Au |
Au |
Meridional Radius (m) |
413087.7 |
152745.2 |
85961.1 |
-- |
-- |
-- |
Sagittal Radius (m) |
279.99 |
152745.2 |
104.70 |
-- |
-- |
-- |
mer. slope error (arc sec) |
1.0 |
0.1 |
1.0 |
0.16 |
0.16 |
0.16 |
sag. slope error (arc sec) |
3.0 |
0.2 |
3.0 |
0.2 |
0.2 |
0.2 |
Included angle (deg) |
176 |
177 |
176 |
174.5 |
174.5 |
174.5 |
Groove density (l/mm) |
-- |
-- |
-- |
1200 |
400 |
150 |
Energy range (eV) |
-- |
-- |
-- |
400-1500 |
150-600 |
50-225 |
Present status
The beamline is planned to be completed till end of 2011. Presently, the design, procurement and fabrication of various key components are underway.
