Ocean Optics Overture - Manual (Page 17)

Chapter 2: Overture Software Icons and Menus
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Integration Time
Integration time is the exposure time for each pixel in the array. Each of the pixels is “read” in turn and
the time between readings controls the amount of charge in each CCD sensor. The charge decreases with
every photon that hits the sensor, so if there are not many photons around it takes a long time to reduce
the charge. Too many photons will discharge the sensor completely in a short time.
If the time is too long, the sensors will “saturate” and the spectrum line will go off scale. This does not
harm the sensor, but the data you collect will have no value.
For very dim sources a longer integration time is needed, but the penalty is more noise for less signal. The
default integration time is 100 ms.
The integration time is set in the Integration Time filed in the status bar at the bottom of the screen.
Intensity
Intensity is the default mode.
The y-axis reads Intensity, which is a count of how many photons have hit each pixel in the array during
one integration time. It is a relative measurement.
Intensity mode is ideal for most physics-based applications using just the fiber optic input.
Store Dark Spectrum
Before we can move on to any mathematical comparisons between sample spectra we have to tell the
spectrometer where zero is. To do this, block any light entering the fiber and click the Store dark
spectrum icon.
You will not see any change, but the Overture software now has a zero or “dark” reading stored for every
wavelength.
Reference spectrum
Next we have to tell the spectrometer about the source we are comparing to. This is the reference source.
Typically this would be a cuvette containing a colorless solvent, but no dissolved sample.
Set up your reference sample so that the highest point on the intensity y-axis is about 85% of full scale.
Click the store reference spectrum icon. You will see no change, but your reference spectrum is now
stored.
Be careful. If you change anything about your reference source now, you must store a new reference. You
can click the icon to update the reference as many times as you like. If you change the integration time
you will need to store a new reference reading.
Once you have stored dark and reference spectra, the Transmission and Absorbance modes are enabled.