This application note demonstrates an easy-to-fabricate holder that is suitable for many small samples. In addition, it shows the measurement of absolute total reflectance using this sample holder.

1. Absolute Total Reflectance Spectra of
Very Small Objects Using The
ISR-2600Plus Integrating Sphere
Shimadzu Scientific Instruments, Columbia, Md.

2. Introduction
Often reflectance spectra of very small samples are required.
Typical sphere openings and sampling accessories are designed for samples in the
25mm X 25mm range with maximum thicknesses of 1 cm.
Consequently, correct positioning of such samples to acquire accurate spectra can be
very challenging.
This application note demonstrates an easy-to-fabricate holder that is suitable for
many small samples. In addition, it shows the measurement of absolute total
reflectance using this sample holder.
Small samples requiring special sampling
techniques

3. For accurate analysis of samples in the Shimadzu ISR-2600Plus integrating
sphere, the sample must be positioned level with the plane of the sphere. This
can be very challenging for small samples. Success has been demonstrated
by fabricating a small sample holder out of a white Compact Disk fiberboard
sleeve. The fiberboard sleeve offers three advantages.
1. There is a manufactured fold that aids in preparing a “binding” action for
small sample positioning.
2. The sleeve is white, which can mimic the sphere’s internal BaSO4 coating
and help to maintain a high S/N for measurements.
3. The thin nature of the fiberboard allows the positioning of the small sample
close to the plane of the sphere’s opening.
Sample Analysis
It is important that the sample be placed as close to the sphere opening as
possible as any depth can cause a tunnel effect which acts like a light trap and
can reduce overall S/N resulting in poorer quality spectra.

4. Sample cards ready for measurement
with samples attached
Small sample holder fabricated from
CD fiberboard sleeve
Sample Analysis

5. For small flat samples, the sample can be easily sandwiched between
the two sides of the sleeve. The sleeve can then be positioned against the
sphere using the sphere’s spring retaining arm for analysis.
For thicker samples, the sample can be fixed to the back side of the
sleeve and easily positioned on the sphere in a similar manner. A mark was
made on each card that could readily be used to reproducibly position the
modified holder so that the sample port was in the same position in the
sphere opening for each measurement.
For background measurements, a working (un-calibrated) mirror
was placed behind the modified sample holder so that the sampling port of
the holder was covered by the mirror. In a similar fashion, acquisition of the
spectrum of the calibrated reference mirror was accomplished by placing the
reference mirror behind the modified holder.
Sample Analysis

6. Alignment marks used to reproducibly align the
sample in the sphere port for analysis
Sample Analysis

7. Calibrated standard mirror in position for
measurement, behind the sample holder card
Sample Analysis

8. Spectra of typical small samples acquired with the modified small sampling
accessory card are shown. A blank spectrum (a scan of the working mirror
used for baseline acquisition) is shown below and demonstrates the
excellent linearity of the fiberboard sample holder throughout the full working
range of the sphere (1400 to 220 nm).
Blank of working mirror and new
fiberboard small sample holder
showing excellent linearity
throughout the full working
range of the instrument
Spectra

9. The graph below shows acquired relative reflectance spectra of typical small
samples. Notice that portions of two scans exceed 100% reflectance. This is
not uncommon as the resultant reflectance values are “relative” to the
working mirror used for background acquisition.
Acquired spectra of three typical
small samples: a glass optical
component (black), a plastic
lens (blue), and an optical filter
(magenta)
Spectra

10. Acquired spectrum of a
calibrated standard reference
mirror
The relative reflection data from the acquired spectra above can be converted to
absolute spectra values by acquiring the spectrum of a calibrated standard
reference sample and the following equation:
ρcorrected =((ρSample - ρ0) / (ρ100 - ρ0)) • ρReference
Spectra

11. In this example, the spectrum of the calibrated mirror becomes ρ100.
In theory, with highly specular samples, ρ0 is typically insignificant, and therefore
was not used in these measurement.
The Data Table feature of UVProbe was used to truncate the acquired scans to
match the 25nm pitch of the supplied reference mirror absolute reflectance data.
In addition, the Data Table allows for easy copying of the spectral data directly to
a spreadsheet program where the absolute (corrected) calculations were
performed, table 1.
Spectra

12. Table 1: Spreadsheet data for all scans
Spectral Data Table

13. Spectral Data Table
Table 1, continued

14. Acquired spectrum of a
calibrated standard reference
mirror
The final absolute results are shown in the graphic:
Spectra

15. Conclusion
With proper care to sampling holders and sample placement, the relative
reflectance of small samples can readily and accurately be measured using a
Shimadzu Integrating Sphere accessory.
In addition, with the Data Table features of the UVProbe software, Absolute
(corrected) reflectance spectra can be easily calculated with little extra effort.

16. Thank you for viewing this presentation. Should you have any
questions or require additional information about our research,
products or services, please visit our support page:
http://www.ssi.shimadzu.com/support/.
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