Plane grating monochromator
Variable included angle monochromators, usualy refered to as plane grating monochromators (PGM), allow for a fixed focal length as a function of photon energy. PGMs combine ultra-high precision, repeatability and stability with a robust design for safe and reliable operation. Special attention is paid to the mirror and grating holders, which are designed to minimize deformations of the optical surfaces.
Mechanism
The mechanism of variable included angle monochromators use a deflection mirror close to the gratings to vary the included angle at the gratings. The position of the mirror rotation axis is optimised for constant position of beam incidence at the grating.
Options
- Up to five exchangeable gratings or crystal pairs and two exchangeable mirrors.
- Variable size, orientation and order of the optical elements.
- Passive, active or internal water cooling of the optical elements.
- Liquid nitrogen cooling.
- Piezo-actuated pitch rotations.
- Motion control system.
Performance parameters
Performance parameter values for individual projects may well exceed the values listed below.
Grating/mirror/crystal
pitch rotation
Range
35° (PGM), 70° (DCM)
Resolution
< 10 µrad /step
Scan speed
< 750 µrad /s
Repeatability
< 0.15 µrad
Stability
< 0.02 µrad
Grating/mirror/crystal
exchange
Range
< 270 mm
Resolution
< 0.25 µm
Repeatability
Pitch: < 0.15 µrad
Roll: < 0.50 µrad
Yaw: ≤ 1 µm
Performance Test Results
Grating pitch repeatability after pitch variation
Grating pitch repeatability after grating exchange
Long-time grating pitch stability
Pitch stability as a function of water flow rate
Grating pitch as a function of time
Grating pitch angle scan for 0.05 µrad step width
Application
Monochromators are essential components in most synchrotron radiation beamlines. They contain reflection gratings or crystals, which spatially disperse the soft X-ray radiation and filter the hard X-ray radiation as a function of the photon energy. Depending on the monochromator type deflecting and/or focusing mirror(s) are also integrated.
