Transcript Investigation of polarizing mirrors at 121.6 nm

1st SMESE Workshop, IAS Paris, 10-12 mars 2008
Investigation of polarizing mirrors at 121.6 nm
F. Bridou, M. Cuniot-Ponsard, J-M. Desvignes
Laboratoire Charles Fabry de l’Institut d’Optique
Palaiseau, France
Required specifications
Summary
From IAS team: A. Millard, F. Auchère, F. Rouesnel, J-C. Vial
The goal of this study is to demonstrate the feasibility of polarizing mirrors at l =
121.6 nm designed within the framework of the Lymana Lyot Coronograph Imager
project.
Parameters
Optical constants of the materials involved in the multilayers are determined
experimentally.
Reflectivity measurements in the VUV wavelength domain have been performed at
PTB (Synchrotron at BESSY II, Berlin).
Simulations, deposits, measurements and characterizations were made and first
experimental results are in good agreement with calculated predictions.
Spécifications
Justification
Incidence angle
30° à 70°
Limited dimensions of the
instrument
Angle of acceptance
2.6° (-/+ 1.3°)
Field of view of the
instrument
Rp/Rs
4. 10-3
Good rejection of the
perpendicular polarisation
Rs min
25%
Photometry condition
Polarizing mirror in the LYOT optical design
Fabrication and test of polarizing mirrors
In collaboration with PTB where Polarized reflectivity measurements were performed [5,6]
Present development
1
Ongoing development
1.0
Measurements
Rs
, Rp
Fit of measurements
Rs , Rp
Rs,Rp
0.6
0.4
Rp
PTB is working to install
the set-up on a new
dedicated VUV beam line:
the MLS
(Metrology Light Source).
Multilayer
1.0
0.8
Mesurements
0.8
Simulation
0.6
Al2O3 (<1 nm)
Rs
MgF2
Al
Experimental values
i= 69°
Rs = 0.71
Rp = 0.058
0.4
MgF2
0.2
0.2
0.0
0
20
40
60
80
Incidence angle (deg)
Measurement: i = 67°, Rs = 0.45, Rp = 0.023, Rp/Rs = 0.05
Fit :
i = 67°, Rs =0.45, Rp= 1. 10-4, Rp/Rs = 2.2 10-4
The precision of measurements at PTB is presently not
sufficient to give the value of the actual minimum of Rp
0.6
i = 62°
Rs = 0.75
-3
Rp = 1.6 10
0.4
0.2
Al
The precision of
measurements should be
increased.
(First measurements are
expected in the middle of
2008).
Réflectivity Rs, Rp
Mes
i = 67°
Rs= 0.45
Rp=0.023
Rs, Rp
Initial calculation
Rs, Rp
0.8
Al
With optimized thicknesses (calculation)
Rs
MgF2/float glass
MgF2
Ongoing development
Present development
2
Rp
0.0
0.0
20
40
60
80
0
20
i = 69° Rs = 0.71 Rp = 0.06 Rp/Rs = 0.085
40
60
80
Incidence angle (deg)
Incidence angle (deg)
i = 62° Rs = 0.75 Rp = 1.6 10-3 Rp/Rs = 2.1 10-3
CONCLUSION
A preliminary determination of indices in the wavelength range 80-140 nm was performed in order to select the materials and design of polarizing mirrors.
Two different designs of polarizing mirrors at l = 121.6 nm have been prepared and tested at PTB.
The first results show that each of these two designs allows to meet the requirements of the Lyman a Lyot Coronograph Imager project