The Mirrors & Metrology laboratory provides advice, support, research and development for reflective optical elements

The laboratory specialises in the surface characterisation of a variety of X-ray optical elements prior to their deployment at the ESRF and other light sources.

The Mirrors and Metrology laboratory develops mirror systems used at ESRF beamlines.

Based on the selected design and components, the mirror systems and associated optical coatings are specified by the X-ray Optics group. It then supervises the manufacture of the optical components, which is sub-contracted. The Mirrors and Metrology laboratory measures the performance of the systems relative to the specifications.

The laboratory develops nanofocusing reflective systems often implemented in the Kirkpatrick-Baez (KB) configuration. These systems, which are based on mirror benders designed in-house, rely on the laboratory for the integration of the optical components and their offline adjustment and characterisation prior to installation on beamlines.

The performance of the ESRF KB systems is considerably enhanced through the combination with multilayer coating technologies. Standard ESRF KB systems have been licensed and are commercially available.

The laboratory also performs surface characterisation of other optics (monochromator and analyser crystals).

Several instruments permit surface quality measurements at the highest level of accuracy, from the full length of the mirrors (up to 1.5 m) down to nanometre scale features. Optical figures as diverse as elliptical or toroidal surfaces can be measured.

The laboratory is located in a 56 m2 class 1000 clean room with temperature control to within 1°C.

The main characterisation capabilities are summarised in the description of the instruments:

  • Long trace profiler (LTP)
    A custom-built deflectometer measuring mirror surfaces using a scanned laser beam with an optoelectronics sensor. The instrument provides a lateral resolution of 2 mm over a range of 1.5 metres with a slope error precision better than 0.1 µradian rms. Specific software developments permit, for example, the automatic figuring of benders towards a programmed elliptical shape.

  • Veeco NT9300 Micro-interferometer
    Provides 3d surface measurements over small areas operating using either white-light or phase shifting interferometry. Its height resolution of 0.5 Ångström with lateral resolution better than one micron allows the evaluation of the roughness of the super-polished surfaces needed for X-ray optics. The instrument incorporates advanced stitching capabilities, allowing the mapping of surface topographies at the nm height scale with sub-micron lateral resolution over areas extending over tens or even hundreds of millimetres in length.

  • Zygo Verifire AT+ and XPZ Fizeau interferometers
    3d mapping of large radii surfaces with a precision of a few nanometres over a 150 mm area. The instruments are equipped with a variety of reference optics (transmission flats, transmission sphere, diverger). Measurements of larger aperture (>150mm) optics can be performed in the double pass configuration using oblique incidence and a reflexion flat.

  • Other instruments
    • Small Twymann-Green interferometer (FISBA DCI2): highly portable instrument allowing surface height mapping of shorter radius optics.
    • SIS atomic force microscope: study of surface topography with nanometre precision in 3 dimensions
    • Tactile profilometer (Bruker DektakXT) – stylus-based instrument with 2d scanning capability for measurement of highly curved or poorly reflecting surfaces.