AQ-00275-000, Rev. 3
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sphere or provide a means of mounting a sample into a beam path. Additionally, a large center
mount port is provided on top of the sphere assembly for internal access and for mounting the
optional center mount sample holder. The illustration in Figure 6 shows the DRA-CA-3300 inte-
grating sphere along with the detachable transmittance sample holder and aperture plate. The aper-
ture plate is used to reduce flare around the reference port and should be installed for all
measurements.
The reflectance sample holders, mounted either at the reference or sample reflectance port on the
outside of the accessory enclosure, clamp the reflectance standard or sample against the respective
port. Two wedges are provided with the accessory for mounting a sample either at 0° or 8° angles
of incidence.
The sphere detector is a standard R928 photomultiplier tube (PMT) installed at the detector port at
the bottom of the integrating sphere. Access to the detector can be obtained through a removable
panel underneath the accessory enclosure. The R928 PMT is a common side-on detector used for
spectroscopy applications. The detector covers a nominal 185-900 nm spectral range and features
nine stages of amplification. Detailed information on the R928 PMT is provided in Appendix A.
The detector cable from the accessory is located inside the sphere compartment where it is perma-
nently wired to a Labsphere designed socket. The connector at the opposite end of the cable plugs
into the instrument detector connection in the bottom well of the sample compartment. When the
cable is plugged in correctly, the instrument will recognize the presence of the DRA-CA-3300
accessory during initialization.
Optical Chamber
The optical chamber houses the transfer optics of the DRA-CA-3300 accessory that direct the
spectrophotometer reference and sample beams to their respective ports on the integrating sphere.
The sample beam is the rear beam in the accessory. As shown in Figure 5, mirrors labeled M1, M2
and M3 guide the sample beam through the sample transmittance port and onto the sample reflec-
tance port at normal incidence. Mirrors M4 and M5 direct the reference beam into the reference
beam entrance port onto the reference port.
Mirror M3 is a spherical mirror that condenses the sample beam onto the target sample. The mirror
can be mounted at any of three different positions on the base plate of the accessory. These posi-
tions correspond to the transmittance port, center mount sample holder and sample reflectance
port, and are labeled "T", "C" and "R" respectively. If you move M3 to a different position, you
will need to realign the transfer optics.
The accessory is shipped from Labsphere with a protective metal dust cover installed over the opti-
cal chamber. You should reinstall the cover when the accessory is not installed in the instrument.
Loading the Sample Reflectance Port
The sample reflectance port is a one-inch hole in the front panel of the accessory enclosure. The
reflectance sample holder fits over a dovetail extension located underneath the port. The clamp on
the sample holder has two ends - one for 0° incidence and one end for 8° incidence. To mount a
sample at 0°, flip the clamp so the flat end of the cylinder holds the sample securely against the