Historically, the optical coating community has greatly improved the environmental stability of interference filters through the incorporation of energetic processes into the deposition chamber. This approach brought especially about a stabilization of their spectral features with respect to pressure changes, as occurring during the launching phase in space applications. The objective of our work was to quantify with a very high resolution (few picometers) the spectral shift under vacuum exposure of narrow bandpass filters manufactured by Dual Ion Beam Sputtering (DIBS).
We will give first a description of the structure of these filters completed by a presentation of their manufacturing procedure, then a detailed description of our experimental set-up, and at the end a presentation of the results of our measurements on these two specific narrow bandpass filters.
After two years of research and development under ESO support, LAM and Thales SESO present the results of their experiment for the fast and accurate polishing under stress of ELT 1.5 meter segments as well as the industrialization approach for mass production. Based on stress polishing, this manufacturing method requires the conception of a warping harness able to generate extremely accurate bending of the optical surface of the segments during the polishing. The conception of the warping harness is based on finite element analysis and allowed a fine tuning of each geometrical parameter of the system in order to fit an error budget of 25nm RMS over 300μm of bending peak to valley. The optimisation approach uses the simulated influence functions to extract the system eigenmodes and characterise the performance. The same approach is used for the full characterisation of the system itself. The warping harness has been manufactured, integrated and assembled with the Zerodur 1.5 meter segment on the LAM 2.5meter POLARIS polishing facility. The experiment consists in a cross check of optical and mechanical measurements of the mirrors bending in order to develop a blind process, ie to bypass the optical measurement during the final industrial process. This article describes the optical and mechanical measurements, the influence functions and eigenmodes of the system and the full performance characterisation of the warping harness.
The Laboratoire d'Astrophysique de Marseille (LAM) is involved in the prototyping of a full scale demonstrator for
stress polishing of segments for the European Extremely Large Telescope (E-ELT). Stress polishing method is developed
at LAM since more than 40 years, and this mature technology has recently been used with success for VLT instruments.
Stress polishing is now considered as a promising manufacturing method for mass production of large off axis mirrors,
specifically for ELT segments. This powerful method, based on elasticity theory, allows the generation of super-smooth
off-axis aspherics with a minimal amount of high spatial frequency ripples by spherically polishing a warped blank with
a full-sized tool. Thanks to the simple spherical polishing, the operation time can be strongly reduced compared to the
time-consuming sub-aperture tool methods of grinding and polishing. The goal is to rapidly converge to less than 1
micron RMS of optical quality on a circular blank which will be finally cut hexagonally and finished using Ion Beam
Finishing. In this paper we will present the status of the demonstrator and the design of the warping harness prototype
that must be able to precisely warp the circular blank.
In this article, a stitching Shack-Hartmann profilometric head is presented. This instrument has been developed to answer
improved needs for surface metrology in the domain of short-wavelength optics (X/EUV). It is composed of a highaccuracy
Shack-Hartmann wavefront sensor and an illumination platform. This profilometric head is mounted on a
translation stage to perform bidimensional mappings by stitching together successive sub-aperture acquisitions. This
method ensures the submicroradian accuracy of the system and allows the user to measure large surfaces with a submillimetric
We particularly emphasize on the calibration method of the head; this method is validated by characterizing a super-flat
reference mirror. Cross-checked tests with the Soleil's long-trace profiler are also performed. The high precision of
profilometric head has been validated with the characterization of a spherical mirror. We also emphasize on the large
curvature dynamic range of the instrument with the measurement of an X-ray toric mirror.
The instrument, which performs a complete diagnostic of the surface or wavefront under test, finds its main applications
in metrology (measurement of large optics/wafers, post-polishing control and local surface finishing for the industry,
spatial quality control of laser beam).
We report in this manuscript the study of solid-spaced Fabry-Perot filters. The use of high quality wafers as thick spacers and broadband dielectric mirrors with only few layers provides filters which have almost the same specifications as classical WDM interference filters. Multiple cavity filters, composed of single cavities of equal or different thick spacers are easy to manufacture and exhibit very low absorption and scattering losses. Experimental
results concerning simple and double cavity filters with thick spacers centered at 1.56 μm with a maximum transmission more than 98 % and a full-width at half-maximum (FWHM) of about 0.5 μm are exposed. We then propose different solutions for the extension to triple cavity filters with improved spectral properties.