Control and acquisition systems for new scanning transmission x-ray microscopes at Advanced Light Source (abstract)

Abstract

Two new scanning x-ray transmission microscopes are being built at beamline 5.3.2 and beamline 7.0 of the Advanced Light Source that have novel aspects in their control and acquisition systems. Both microscopes use multiaxis laser interferometry to improve the precision of pixel location during imaging and energy scans as well as to remove image distortions. Beam line 5.3.2 is a new beam line where the new microscope will be dedicated to studies of polymers in the 250–600 eV energy range. Since this is a bending magnet beam line with lower x-ray brightness than undulator beam lines, special attention is given to the design not only to minimize distortions and vibrations but also to optimize the controls and acquisition to improve data collection efficiency. 5.3.2 microscope control and acquisition is based on a PC computer running WINDOWS 2000. All mechanical stages are moved by stepper motors with rack mounted controllers. A dedicated counter board is used for counting and timing and a multi-input/output board is used for analog acquisition and control of the focusing mirror. A three axis differential laser interferometer is being used to improve stability and precision by careful tracking of the relative positions of the sample and zone plate. Each axis measures the relative distance between a mirror placed on the sample stage and a mirror attached to the zone plate holder. Agilent Technologies HP 10889A servo-axis interferometer boards are used. While they were designed to control servo motors, our tests show that they can be used to directly control the piezo stage. The use of the interferometer servo-axis boards provides excellent point stability for spectral measurements. The interferometric feedback also provides active vibration isolation which reduces deleterious impact of mechanical vibrations up to 20–30 Hz. It also can improve the speed and precision of image scans. Custom C++ software has been written to provide user friendly control of the microscope and integration with visual light microscopy indexing of the samples. The beam line 7.0 microscope upgrade is a new design which will replace the existing microscope. The design is similar to that of beam line 5.3.2, including interferometric position encoding. However the acquisition and control is based on VXI systems, a Sun computer, and LABVIEW™ software. The main objective of the BL 7.0 microscope upgrade is to achieve precise image scans at very high speed (pixel dwells as short as 10 μs) to take full advantage of the high brightness of the 7.0 undulator beamline. Results of tests and a discussion of the benefits of our scanning microscope designs will be presented.