AQ-00275-000, Rev. 3
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When loading a sample into the clip sample holder, the sample should be held perfectly vertical by
the clip with the plane of the reflecting surface along the center of rotation of the dial. The sample
beam path will strike the sample at a point midway between the bottom tip of the clip and the baf-
fle. There is no need to use a diffuse reference standard with the clip style sample holder; the
sphere wall serves as the reference. If your are taking a specular measurement, you will need a
specular reflectance standard that fits snugly into the clip.
After loading the clip style VASH into the accessory, view the sample holder from the reference
port. Make sure the reference beam is not clipped by any part of the VASH or sample at the inci-
dence angle you require. When making angle adjustments to the device, see that the sample sur-
face is pointing away from the reference beam entrance port.
The jaw style VASH is a better alternative for holding large, bulky samples at sphere center. An
illustration of a jaw style sample holder is shown in Figure 13. The jaws easily will accommodate
sample sizes up to 1.5" in length and width. This is the size of a Labsphere SRS-99-010 diffuse
reflectance standard, however, the standard is mounted in a delrin casing with high absorption
characteristics. A clean disc of SRM-99O optical grade Spectralon material approximately 30 mm
in diameter will serve nicely as a reference standard.
The width limitation of the VASH depends on the thickness of your sample and the maximum
angle of incidence your application requires. The jaws protrude 12 mm from the frame of the sam-
ple holder. If possible, you should load the reference standard and reflectance sample such that the
reflecting surface is even with the front edge of the jaws. This will place the front surface at the
rotational axis of the sample holder. Tighten the jaws using the thumbscrew. Do not overtighten the
jaw mechanism as this could damage the sample. After loading the jaw style VASH into the acces-
sory, view the sample holder from the reference port. Make sure the reference beam is not clipped
Sample
Jaws
Baffle
Figure 13. Jaw type sample holder.