Grating Monochromators

PSL has built a number of SGM, CGM and VLS-PGM grating chambers over the years. These have normally included encoder & motor driver electronics in a cabinet, granite base on kinematic mounts, a full complement of grating holders with dummy gratings, and a PSL technician visiting the installation site to unlock the mechanism and check it operates properly upon delivery. However the chambers do not normally include a control computer, indexer, interface card, or software, which most synchrotrons prefer to standardize. The vacuum chamber is bellows decoupled from the mechanism so that barometric pressure changes do not affect the mechanism's accuracy. Documentation provided with the unit includes operating instructions, major subassembly drawings, calibration report, leak check certificate & bakeout history. Customization to customer requirements is common.

Features

Pictured here are two of the more recently built PSL grating chambers. The vertical axis chamber has porting to pass a closely neighboring beamline's light through its chamber. The horizontal axis chamber shown is part of a variable-line-space plane grating monochromator beamline. Both achieved well under their 0.5 arc second (2.5 microradian) peak grating pitch repeatability specification.

Options available at extra cost include motorized kinematic mounts, extra grating holders, and fiducial target holders surveyed onto the granite base top. Additional options available for rectangular chambers include counterweights, in-vacuum scan interferometer, scan zero reference, etc.

With in-vacuum scan interferometry, we have achieved below 0.02 arc second (0.1 microradian) standard deviation grating pitch repeatability. A typical rectangular chamber & electronics cabinet are shown below. One of the chambers was part of a beamline that has achieved experimental energy resolution of E/dE >100,000: Review of Scientific Instruments 77, 085102 (2006).

Earlier units made use of steel stands, which are lighter to ship but more expensive to build. Shown are a vertical with rectangular vacuum chamber, and an early model horizontal with small round chamber which was described in "An Ultrahigh-Vacuum Multiple Grating Chamber and Scan Drive with Improved Grating Change", Nuclear Instruments and Methods in Physics Research A291(1990) pp. 343-347.

Some earlier units have their own web pages.

Some factors that will help control costs are:

1. making as many features identical as possible,
2. ordering chambers at the same time for economies of scale,
3. adapting parameters where possible to our previous practice,
4. beamline design compatible with round chamber & no counterweights (either a vertical axis, or small grating rotation if a horizontal axis)
5. repeatability specifications that do not require in-vacuum interferometry or in-vacuum encoder

We'd welcome the opportunity to discuss your next beamline project's needs.