Magnesium Fluoride (MgF ) Optics for Infra- Red

Magnesium Fluoride (MgF2) Optics for InfraRed Systems
Knight Optical can offer Magnesium Fluoride (MgF2) Optics for Infra-red systems over the
waveband of 0.12 to 6µm. We offer MgF2 optics for UV, visible, NIR (0.7-1.5), and MWIR (3 to
5µm) Imaging Systems. MgF2 has a good transmission in the MWIR band, and can be used
with Silicon or Zinc Selenide, given its refractive index range is lower than the two of them,
to form corrected doublets and lens systems. These systems include, for example, Forward
Looking Infra-Red (FLIR) systems, and thermography.
MgF2 has a range of refractive indices from 1.628no and
1.632ne at 0.120µm, 1.1.373no and 1.385ne at 1µm, to
1.314no and 1.321ne at 6µm. MgF2 is birefringent and it
is usual to cut the glass with the optic axis perpendicular
to the faces, this is to minimise the affect of the
birefringence upon the ray paths as they will be the same.
This glass will produce a well corrected lens system
using other IR glasses, such as Silicon, Zinc Selenide, or
Calcium Fluoride, provided the birefringence is taken into
account.
Magnesium Fluoride make excellent Rochon Polarizers
with a waveband of, for example, 0.13 to 7µm. The
separation angle, which is the angle between the ordinary
and extraordinary rays, is about 10° at 1.55µm. The
extinction ratio is about 10,000:1 with an output aperture
of about 10mm (Crystal size dictates). Figure x shows
the Rochon polarizers form and mode of operation.
The figure shows an image of MgF2 as it would be
combined with other IR glasses to provide a wavelength
corrected lens for use in a Fourier Transform Infra-Red
(FTIR) spectroscope. When combined with the KRS-5
ATR prism, the wavelength range is from 0.1 to 6µm. Its
performance is inferior to Barium Fluoride and Calcium
Fluoride even though it is the hardest of the Fluoride
glasses.
Magnesium Fluoride (MgF2) Optics for InfraRed Systems
The input beam, which is collimated by a mirror, that comes from the scattered light of the sample is directed toward the
dispersive prism. If the prism for the FTIR is a dispersive type, it fans the light beam out such that each wavelength has
its own angle, then it is best for the apex angle to be between 60° and 72°.
The output beams, which are focused by a mirror, as there is no wavelength dispersion to introduce errors compared to
a lens, at a slit. The slit has the width that defines the wavelength bandwidth. At this image plane is a linear detector,
composed of many individual detection sites.
Each wavelength is detected by its relative position in
the image plane, and this is electronically processed to
provide a display of intensity versus wavelength as is
dispersed by the prism. Each angle is at a wavelength
that corresponds to particular mineral and thus the
unique composition of the sample is determined. This is
the fingerprint for the organic and in-organic material. By
changing the prism, and detector, other wavelengths can
be measured.
Contact our multilingual technical sales team and
discover how Knight Optical’s high quality Magnesium
Fluoride optics and superior service can improve your
instrumentation and supply chain experience.
Tel +44 (0)1622 859 444