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Chapter 10: Optimization and Troubleshooting
Following installation, some applications may require special attention in order to obtain
optimal system performance. The system optimization and troubleshooting tips below
have been provided to help the end-user maximize experimental results and troubleshoot
potential problems.
Optical Optimization
The best way to increase the signal to noise ratio of a measurement is to increase signal
strength at the detector by increasing optical power at the source or by increasing the
integration time of the detector.
In cases where this is not possible, additional optical signal can usually be coupled into
the system by minimizing the losses in the optical coupling from the source to the sample
and/or from the sample to the spectrograph entrance slit. Checking the coupling optics for
correct alignment and focus will often increase the signal level.
Incorrect f/# matching may cause stray light inside the spectrometer and be collected by
the detector. Use correctly aligned and focused f/# matching optics to eliminate this
possibility. For more information on f/# matching and coupling optics, please refer to
The
Optics of Spectroscopy
, www.jobinyvon.com/usadivisions/oos/index.htm.
Stray light entering the spectrometer system through methods other than the entrance slit
may interfere with the measurement. Reduce the possibility of stray light by securing all
covers and closing all unused entrance or exit ports. When running any experiments, turn
off all unnecessary room lights, including computer monitors.
Spatial Optimization
Often the optical signal of interest that is imaged on to the array occupies only part of the
total array area. Sections of the array that are not illuminated will only add noise to the
measurement. Taking advantage of the Area selection capabilities of Synapse, select a
reduced portion of the CCD active area and reduce the dark signal and associated noise
from the unused area. Susceptibility to cosmic rays will be reduced proportionately as
well.
The best way to match the portion where the signal is located is to acquire a full-chip
image of the signal. With the image, the area can be easily defined to just include the
section of the CCD that is illuminated. If the actual signal is too weak to be seen in an
image, increase the integration time or try to approximate the signal using the exact same
collection optical setup, but substitute a brighter signal. Refer to your software manual
for instructions on defining the active area(s).