Ocean Optics S2000 - Manual (Page 93)

Transmission Experiments
Transmission is the percentage of energy passing through a system relative to the amount that passes through the
reference. Transmission Mode is also used to show the portion of light reflected from a sample. Transmission and
reflection measurements require the same mathematical calculations. The transmission is expressed as a percentage
(
%T λ ) relative to a standard substance (such as air). The software calculates %T (or %R λ ) by the following equation:
S
λλ
- D
λλ
%T
λλ
= x 100%
R
λλ
- D
λλ
where S is the sample intensity at wavelength
λ
, D is the dark intensity at wavelength
λ
, R is the
reference intensity at wavelength
λ
.
Common applications include measurement of transmission of light through solutions, optical filters, optical
coatings, and other optical elements such as lenses and fibers. To take a transmission measurement using
OOIBase32, our spectrometer operating software, follow these steps:
1.
Make sure you are in scope mode, by either clicking the scope mode icon on the toolbar, or selecting Spectrum
| Scope Mode from the menu. Make sure the signal is on scale. The peak intensity of the reference signal
should be about 3500 counts.
2. Take a reference spectrum by first making sure nothing is blocking the light path going to your sample. The
analyte you want to measure must be absent while taking a reference spectrum. Take the reference reading by
clicking the store reference spectrum icon on the toolbar or selecting Spectrum | Store Reference from the
menu. (This command merely stores a reference spectrum. You must select File | Save | Reference from the
menu to permanently save the spectrum to disk.) Storing a reference spectrum is requisite before the software
can calculate transmission spectra.
3. While still in scope mode, take a dark spectrum by first completely blocking the light path going to your
sample. (If possible, do not turn off the light source. If you must turn off your light source to store a dark
spectrum, make sure to allow enough time for the lamp to warm up before continuing your experiment.) Take
the dark reading by clicking the store dark spectrum icon on the toolbar or selecting Spectrum | Store Dark
from the menu. (This command merely stores a dark spectrum. You must use the Save Dark command to
permanently save the spectrum to disk.) Storing a dark spectrum is requisite before the software can calculate
transmission spectra.
4. Begin a transmission measurement by first making sure the sample is in place and nothing is blocking the light
going to your sample. Then choose the transmission mode icon on the toolbar or select Spectrum |
Transmission Mode from the menu. To save the spectrum, click the save icon on the toolbar or select File |
Save | Processed from the menu.
! !
If at any time any sampling variable changes -- including integration time, averaging, boxcar smoothing, distance
from light source to sample, etc. -- you must store a new reference and dark spectrum.
A typical configuration for a transmission experiment.
Experiment Tutorial: Transmission
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