Interferometric measurements on mirrors Idoia Freijo Martin X-Ray Optics and Beam Transport, WP-73 TDR review meeting, Hamburg, 14th Sep. 2012 How to edit the title slide Upper area: Title of your talk, max. 2 rows of the defined size (55 pt) Lower area (subtitle): Conference/meeting/workshop, location, date, your name and affiliation, max. 4 rows of the defined size (32 pt) Change the partner logos or add others in the last row.

Introduction Interferometric measurements system to characterize the prototype and perform corrections in the mirrors. Goal: accuracy 10nm / 10nrad (in positions / angles) Pitch angle changes interferometer measures angles Operational range for the mirrors: - SASE1 and SASE2: 2.5 mrad - SASE3: 14 mrad Distribution mirrors: - Angular range in pitch is enough. - Tilt of the mirrors and interferometer head vertically Foreseen set-up for the mirror chamber 14 Sep. 2012, TDR review meeting. Idoia Freijo Martin, WP-73

Test set-up Current set-up in the lab Mirror dummy Interferometer heads Cooling plate Rotation stage Translation stage Interferometer head The laser beam is generated in a central He-Ne laser and split into two parts, which are guided by optical fibers to two interferometer heads. Each head consists of a double pass interferometer and a detector. 14 Sep. 2012, TDR review meeting. Idoia Freijo Martin, WP-73

Measurement method Δ(α) : distance measured by the interferometer Aim: to find the angular acceptance of our set-up before losing the beam Mirror Mirror at 96mm distance from interferometer head Δ(α) : distance measured by the interferometer Each rotation stage is moved in steps of 0.01 and 0.1 deg (left and right direction) Theoretically: interferometer head rotated out of perpendicular position, distance to mirror increases (positive parabola) Experimentally: parabola is negative cos α = D / (D + Δ(α) ) Δ(α) = D/cos α - D 14 Sep. 2012, TDR review meeting. Idoia Freijo Martin, WP-73

Measurements’ results Rotation of each interferometer head at the time Observed negative distance change: due to measurement principle. Slopes of parabolas: 1nm/(0.01°)2, so, a precision of 0.01° is enough for the goniometers to obtain 1 nm accuracy ( < 2nrad angular accuracy ) Deviations from parabolas:  50 nm, due to temperature fluctuation, and no backlash compensation of motors controller. Eccentricity of goniometers contribution: 50 nrad 14 Sep. 2012, TDR review meeting. Idoia Freijo Martin, WP-73

Long-term measurements Set-up enclosed by a Styrofoam cover, aluminum frame is temperature stabilized with a water chiller Results of a 7 days measurement: -Room temperature variation:  0.2K -Temp. inside the enclosure:  0.1K -Linear drift by one head:  0.5 μm -Drift in differential signal: 50nm (vendor specifications: for the laser unit, 50 nm/°C and for the interferometer heads, 100 nm/°C) Observed drifts caused most likely by relaxation motions of aluminum frames or interferometer mounts. 14 Sep. 2012, TDR review meeting. Idoia Freijo Martin, WP-73

Conclusions and outlook The observed precision levels of the test setup are in the range of 50 nm  accuracy of an angle determination of about 60 nrad for an 800 mm long mirror. With a granite support, better temperature and motion control this number is likely to improve. However, with a stability level of 60 nrad, the chamber deformations of 0.6 μrad should be easily detectable. Optimization of the set-up using a granite support and an improvement of the temperature and motion control. To perform similar tests with an autocollimator and compare both results. Thank you for your attention 14 Sep. 2012, TDR review meeting. Idoia Freijo Martin, WP-73

END 14 Sep. 2012, TDR review meeting. Idoia Freijo Martin, WP-73

Drifts caused mainly by: -Relaxation motions of the aluminum frame and of the interferometer mounts -Temperature and pressure changes 14 Sep. 2012, TDR review meeting. Idoia Freijo Martin, WP-73

Extra slide L= 96 mm is the distance between the mirror and the center of rotation d=0.1mm is what I supposed that I am apart from the COR. X2= L – d*sin (α) D(α) = L/ cos(α) – d *tan(α) D(0)= L = 96 mm If we are in the COR, then d=0 ­ D(α) = L/ cos(α) , D(α) = L + Δ(α) Δ(α) = L/ cos(α) - L 14 Sep. 2012, TDR review meeting. Idoia Freijo Martin, WP-73

Extra slide 14 Sep. 2012, TDR review meeting. Idoia Freijo Martin, WP-73

14 Sep. 2012, TDR review meeting. Idoia Freijo Martin, WP-73