A new laser-based alignment method for the multi-slits VSANS in high precision

Abstract A multi-slit (MS) Very Small Angle Scattering (VSANS) instrument is now under construction on Beam Line 14 in China Spallation Neutron Source (CSNS). It is an upgrade of traditional SANS that extends the measurement length scale up to 1 micrometer. Success of the instrument depends on the precise alignment of the millimeter width MSs over more than 12 m. A prototype system has been built to rehearse the alignment of the 12 MSs. A traditional laser tracker is firstly chosen to align the 12 MSs coarsely to about ± 100 μ m, which is less than the required accuracy of ± 25 μ m. Then a laser-based non-contact alignment technique is used. When the expanded laser beam images MS directly to a high-resolution CCD, relative positions of each MS perpendicular to the beam line can be further aligned precisely. The transverse deviation of the 12 MSs can be kept within ± 5 μ m. High accuracy of the technique guarantees the success of the VSANS instrument, and can be applicable to other systems that need high lateral precision over long distance.