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Double Crystal Monochromator
A double crystal monochromator is an instrument that extracts light of a specific wavelength using crystal diffraction. Light of various wavelengths can be extracted by changing the incident angle to the crystal. We have designed a structure and assembly precision that assures maximum light intensity and a fixed exit beam position even when the wavelength is changed. To keep the crystal surface as clean as possible, all the monochromators have a structure that can maintain a pressure of approximately 10-4 (Pa) or less. Some examples of our double crystal monochromators with different structures are presented below.
Common Rotary Table System
The common rotary table type operates with a rotary table that carries adjustment mechanics of both crystals The movement of the rotary table is transmitted from the atmosphere side through a ferro-fluid seal into the vacuum chamber.
Calculation and Combination Type
The positions of the two crystals in the instrument above are controlled to follow the orbit calculated by a computer. Multiple stages are used for position adjustment so that fine adjustment of Bragg angle and horizontal position adjustment of the beam are possible. Also the crystals are cooled with liquid nitrogen to withstand the thermal load of the beam. This instrument was installed at the Advanced Photon Source (APS) of the Argonne National Laboratory in the USA.
Although this instrument has the same structure as the calculation and coupling type double crystal monochromator described previously, this instrument has a structure in which silicon crystals and multilayers are arranged along the optical axis. For a diffraction experiment that requires high resolution, silicons is used, and for a small-angle scattering experiment that requires brightness, multilayers are used. This instrument was installed at the Advanced Light Source (ALS) in Berkeley, California.
Single-Cam Type
The instrument shown on the left is designed to obtain the optimum distance between two crystal planes by using a cam. To prevent deterioration of the precision caused by large variations of moment load applied to the main spindle when the Bragg angle is changed, this instrument is equipped with a cancellation mechanism (patent number 2782397) that cancels the force by means of an air cylinder. At the SPring-8 (Super Photon ring-8 GeV) synchrotron radiation facility in Japan, 27 of these instruments are now in standard service.
Double-Cam Type
The instrument shown on the left is designed to optimize the distance between double crystal planes and the distance between the double crystal centers at the same time by using double cams. The use of double cams enables the number of motors used in the vacuum to be reduced, the control to be facilitated, and the wavelength to be changed at high speed. This instrument was installed at Beijing Synchrotron Radiation Facility (BSRF) in China.
Independent Rotation Table System
In the independent Rotation table system, crystals are mounted on independent Rotation stages. This type of monochromator is used to obtain high resolution or to distribute a beam to multiple locations.
The instrument shown on the left is manufactured to distribute a beam to multiple locations. The white light that enters from the lower left is separated by the first diamond crystal in the cylindrical chamber, reaches the right chamber, is diffracted by the second crystal, and is extracted. Light that passes through the first crystal is used also by another instrument. This system is called a troika system, and a beam line can be used by multiple groups without time sharing. This instrument was installed in the SPring-8 (Super Photon ring-8 GeV) BL24XU hatch of the synchrotron radiation facility in Japan.
Downloadable Documentation
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Adobe PDF | 93 KB | |
Adobe PDF | 535 KB |