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Section I. General Description
1.1 Description
The Princeton Instruments Model VM-502 is a nominal 0.2 meter vacuum scanning
monochromator, with an optimum wavelength range in the vacuum ultraviolet region.
However, with other gratings and coatings, the instrument is useful from the extreme UV to
the infrared.
The Model VM-502 is designed to use an aberration-corrected concave holographic grating,
which provides and aperture ratio of f/4.5.
The Model VM-502 is set up as specified in the conventional “V” configuration (Model VM-502-
V), in a straight through configuration (Model VM-502-S), or a combination of both
(Model VM-502).
1.2 Specifications
Specifications are with standard 1200 G/mm gratings unless otherwise noted.
Focal Length: Nominal 0.2 meters
Optical System: Aberration-corrected concave holographic grating
Aperture Ratio: Nominal f/4.5
Reciprocal Linear Dispersion: Nominally 4.0 nm/mm, with 1200 G/mm grating in the first
order
Wavelength Range: Mechanical scanning range is zero order to 546.1 nm, with a 1200
G/mm grating. Low wavelength limit is dependent upon light source and detector; typically
less than 30 nm
Grating Coating: Standard coating is Princeton Instruments #1200 VUV Aluminum and MgF2,
with reflectance of 80% typical at 121.6 nm. Iridium coatings are optional for the extreme UV,
and are supplied if specified
Grating Holder: The grating holder is kinematically mounted in the instrument, allowing
gratings to be interchanged without requiring realignment. Each grating holder contains the
classical grating adjustments for initial alignment of the grating to the instrument
Scanning Mechanism: A sine drive mechanism provides a linear wavelength change with the
rotation of a precision lead screw. A Model SD3 controller is provided for scanning drive
control using a computer (customer provided).
Slits: Standard bilateral slits are supplied and are adjustable from 5 micrometers to 3
millimeters. A precision micrometer provides for slit adjustment under vacuum conditions, and
is graduated in 10 micrometer increments. The slit height is adjustable from 0 to 20 mm.