Posted in | Monochromators

Grazing Incidence Monochromator - Model 248/310G from McPherson Inc

The McPherson Inc Model 248/310G Grazing Incidence Monochromator is suited to Soft X-ray and Extreme Ultraviolet applications.

Features of the Model 248/310G Grazing Incidence Monochromator include:

  • Scanning or Multichannel detection (interchangeable)
  • Broad Selection of Gratings
  • Variable Angle of Incidence
  • Precision Rowland circle accurate to ± 4 microns
  • Precision continuously variable Slits
  • Slits Equipped with Isolation Valves
  • Optional Integral Filter Slide
  • Rugged Construction, Compact Design, Operates in any Orientation

The most popular instrument for the 1 to 100-nm region is the 1m focal length grazing incidence spectrometer, McPherson Model 248/310. This instrument is packed with features simplifying measurement in the extreme ultraviolet (EUV, XUV) and soft x-ray spectrum. A similar version is available with a 2.2m focal length (Model 247.) Inquire for other focal lengths. The scanning monochromator selects wavelength by moving the exit slit along the Rowland circle, a circle equal to the grating radius.

The Model 248/310 is available as a scanning monochromator instrument, or as a multi channel spectrometer / spectrograph (using microchannel plate intensifier or CCD) and, when configured to operate in reverse, a variable source of XUV and soft x-ray emissions. All versions can be supplied with o-ring sealed vacuum or ultra high vacuum UHV all metal sealed compatibility. Equipped with microchannel plate or CCD this instrument is a powerful diagnostic tool used for fundamental plasma physics research (eg. at fusion / tokamak reactors or in high harmonic generation laser experiments.) With hollow cathode, Penning, or filament x-ray source this is a excellent source of calibration lines for detector, material or optic characterization.

When the Model 248/310G is used as a scanning monochromator best resolution and broadest wavelength coverage are achieved. The low profile exit slit assembly can scan within 50mm of the grating pole (center of the grating). Operating in these close confines, the user can scan spectra as short as 0.98nm using an 88degree angle of incidence.

A wide variety of gratings allow wavelength coverage from about 1nm to 310nm. With the coarse (133.6g/mm) grating calibration and alignment of this instrument can be completed at atmospheric pressure using ultraviolet emission lines (those from a Mercury light source, for example.) Kinematically mounted gratings insure that gratings repeat position when interchanged.

The grating chamber is stainless steel and equipped with a standard 4.5" metal sealed pump port. The grating chamber provides a kinematic grating mount, in vacuum adjustable focus micrometer to correct for slightly different radii of diffraction grating, aperture slide, entrance slit, exit bellows mounting port and flange and an optional filter insertion slide.

With the scanning system Model 789A-3 (36,000 steps /rev.) 0.0004" increments are made in chordal distance. This distance relates directly to wavelength and depends on the grating groove density and angle of incidence. The bilateral entrance slit (adjustable from 5 to 500um) is mounted to the wall of the grating chamber. An precision micrometer adjustment of slit position across the Rowland circle is provided. Ports are provided in the slit assembly for installing a vacuum gauge, air admittance valve and a roughing valve. To improve performance at wavelengths shorter than 30nm thin film metal filters block scatter from central image and longer wavelengths. To operate at the highest energies / lowest wavelengths VYNS type filters can be used.

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