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Optional Components
This section provides theory and operating procedures regarding optional components to your
DRA-CA-3300.
Center Mount Sample Holders
A center mount sample holder offers two distinct advantages over the external sphere sample hold-
ers on the DRA-CA-3300. One advantage is the ability to vary the angle of incidence for reflec-
tance and transmittance measurements. The other advantage is the ability to measure the
transmittance and reflectance of a sample together. Simultaneous measurement of transmittance
and reflectance sometimes is called the transflectance of a sample.
Center mount sample holders, or variable angle sample holders (VASH), are available for all Lab-
sphere accessories with sphere diameters of 150 mm or greater. There are several basic Labsphere
center mount designs. One design resembles the celebrated Edwards attachment where the sample
and reference standard are mounted back-to-back. Another Labsphere design mounts only the
sample at the center of the integrating sphere. The sample mounting technique for this design can
be either a clip or a jaw style. Still a third center mount design features a fixed angle cuvette sam-
ple holder. If these standard sample holders do not conform to your application, Labsphere can
design a custom center mount sample holder to your specifications.
A variable angle center mount sample holder enables the sample reflectance and absorbance to be
studied at various beam incidence angles. The typical variable angle center-mount sample holder
utilizes a rotating dial to allow the user to very quickly set the desired incidence angle to the near-
est 1
°
increment. Depending on the sample size and the instrument beam characteristics, the user
can choose to perform measurements at beam incidence angles ranging from 0 - 60
°
. When you
receive your variable angle sample holder, you should load the device into the center mount port
and check for proper angle alignment to the sample beam - the beam should strike at normal inci-
dence when the dial is set at 0
°.
If it does not, rotate the dial until the angle is normal to the sample
beam, loosen the four screws along the perimeter of the dial and rotate the knob so it reads 0
°.
Ideally, the beam geometry for a reflectance accessory should be optimized for the application
concerned. For center mount sample measurements, the ideal configuration has the beam focused
on the front surface of the sample at the center of the sphere. Labsphere accessories, however, are
designed to accommodate the most general reflectance applications, such that the beam geometry
is not always ideal for all applications. In general, the accessory design has been optimized for
measuring samples at the sample reflectance port - not the center of the integrating sphere.
A solution to this problem is the placement of a lens into the sample beam path in order to focus