Transmission experiments – Ocean Optics S1024DW Install User Manual

Page 56

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 (

) relative to a standard substance (such as air). The software calculates %T

(or

) by the following equation:

- D

x 100%

where S is the sample intensity at wavelength

, D is the dark intensity at wavelength

, R is the

reference intensity at wavelength

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:
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. 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.

2. 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. Take the dark reading by clicking the store
dark spectrum icon on the toolbar or selecting Spectrum | Store Dark from the menu.

3. 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.