Specifications

Chapter 3 First Light 33
Interface tab page (Setup Hardware): High Speed PCI
Cleans and Skips tab page (Setup Hardware): Default
Experiment Setup Main tab page
• Exposure Time: 10 ms
• Accumulations & Number of Images: 1
Experiment Setup Timing tab page
• Timing Mode: Free Run
• Shutter Control: Normal
• Safe Mode vs. Full Speed: Safe (Asynchronous)
Focusing
The detector mounting hardware provides two degrees of freedom, focus and rotation. In
this context, focus means to physically move the detector back and forth through the
focal plane of the spectrograph. The approach taken is to slowly move the detector in and
out of focus and adjust for optimum while watching a live display on the monitor,
followed by rotating the detector and again adjusting for optimum. The following
procedure, which describes the focusing operation with an Acton 300I spectrograph, can
be easily adapted to other spectrographs.
1. Mount a light source such as a mercury pen-ray type in front of the entrance slit of
the spectrograph. Any light source with line output can be used. Standard fluorescent
overhead lamps have good calibration lines as well. If there are no “line” sources
available, it is possible to use a broad band source such as tungsten for the
alignment. If this is the case, use a wavelength setting of 0.0 nm for alignment
purposes.
2. With the spectrograph properly connected to the controller, turn the power on, wait
for the spectrograph to initialize. Then set it to 435.8 nm if using a mercury lamp or
to 0.0 nm if using a broadband source.
Hint: Overhead fluorescent lights produce a mercury spectrum. Use a white card
tilted at 45 degrees in front of the entrance slit to reflect overhead light into the
spectrograph. Select 435.833 as the spectral line.
3. Set the slit to 25 µm. If necessary, readjust the Exposure Time to maintain optimum
(near full-scale) signal intensity.
4. Slowly move the detector in and out of focus. You should see the spectral line go
from broad to narrow and back to broad. Leave the detector set for the narrowest
achievable line.
Note that the way focusing is accomplished depends on the spectrograph, as follows.
• Long focal-length spectrographs such as the Acton 300i: The
mounting adapter includes a tube that slides inside another tube to move the
detector in or out as required to achieve optimum focus.