Ocean Optics S2000 - Manual (Page 102)

Appendix B: Adjusting the Focus for Collimating
Lenses
In order to obtain accurate data, the light entering and exiting a sample by means of a fiber/collimating lens
assembly must be well collimated. The following is a description of how to adjust the focus of light so that
accurate data is collected by the spectrometer. (All collimating lenses are already adjusted at the time of
manufacture such that light emerging from a 200
µ
m fiber/collimating lens assembly is collimated.)
Adjust the focus of the collimating lens on your light source.
1. Connect the fiber that you are going to use as the illumination fiber in your setup to the light source. Ensure
the connection is tight. The female SMA connector of the fiber must be screwed all the way into the male
connector of the lamp.
2. Turn on the lamp and inspect the light beam emitted from the other end of the fiber by pointing the fiber at a
light-colored object such as a white piece of paper. The distance is not too critical but should be at least
3 inches from the surface. Loosen the set screw on the fiber barrel of the light source with an Allen wrench.
3. After the set screw has been loosened, slide the inner barrel of the collimating lens on the light source until
you see an even intensity across the beam spot. The spot of light should be uniform; there should be no
fluctuations in intensity and color. There should not be any dimmer rings of light surrounding the center spot.
4. Once the inner barrel is positioned so that a well-focused, uniform spot of light is obtained, tighten the set
screw with the Allen wrench. Do not put down the fiber and then tighten the set screw. Try to continue to hold
the fiber 3 inches from the surface while you tighten so that if the inner barrel of the collimating lens slips and
distorts the spot of light, you will be able to readjust the focus. Now the collimating lens on the light source is
focused for the fiber.
Adjust the focus of the next collimating lens in your setup.
5. For this part of the procedure, the illumination fiber is still connected to the lamp and its collimating lens and
the lamp is still on. Now take the second collimating lens in your setup (removed from the illumination side of
a cuvette holder, for example) and screw it onto the other end of the illumination fiber. Make sure the fiber and
the second collimating lens are completely connected. Point this end of the fiber at least 2 meters away from a
wall. If the beam spot on the wall is too faint, you may need to dim the room lights.
6. Loosen the set screw that holds the barrel of this second collimating lens in place and slide the barrel until the
spot of light focused on the wall has crisp edges. You are looking for the sharpest and cleanest image possible.
Tighten the set screw. Do not put the fiber down and then tighten the set screw. Try to continue to hold the
fiber with the spot of light focused on the wall while you tighten the set screw so that if the inner barrel of the
collimating lens slips and distorts the image while tightening, you will be able to readjust the focus. Now that
the second collimating lens has been refocused, remove it from the end of the fiber and install it back into your
setup (back into a cuvette holder, for example).
Continue to adjust the focus of the other collimating lenses in your setup.
7. You have completed adjusting the focus of the collimating lenses in the illumination part of your setup.
Continue to adjust the focus of the other collimating lenses in your setup. If the read fiber is the same diameter
size as the illumination fiber, repeat step 6 with each collimating lens in your setup. If the read fiber is a
different diameter size than that of the illumination fiber, you need to remove the illumination fiber from the
light source, connect the read fiber to the light source, and repeat step 6 for every collimating lens on the read
part of your setup.
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