The mechanical assembly of the G0 GMS laser light source box is complete. Here are some pictures.
http://www.npl.uiuc.edu/ftp/G0/detectors/pictures/gms/gms1.jpg
This shows the exterior of the container. Nitrogen gas and electrical
energy enter on the right hand side, photons come out of the connector
bank on the left hand side.
http://www.npl.uiuc.edu/ftp/G0/detectors/pictures/gms/gms2.jpg
Interior, viewed from the right hand end.
http://www.npl.uiuc.edu/ftp/G0/detectors/pictures/gms/gms3.jpg
Interior, directly above the optics. Light leaves the laser in
a fiber, and the fiber loops around and terminates in a Newport holder.
The light leaving the fiber is focused by two f=50mm lenses and then one
f=100mm lens. The expanded, parallel beam hits the front face of
the fiber cluster assembly (aluminum box).
http://www.npl.uiuc.edu/ftp/G0/detectors/pictures/gms/gms4.jpg
Interior, viewed from the left hand end. Here you see all the
optics again, and also the fibers coming out of the fiber cluster assembly
and their ends connected to the bulkhead.
http://www.npl.uiuc.edu/ftp/G0/detectors/pictures/gms/gms5.jpg
The end of one fiber cable.
Recall that the fiber clusters are arranged on the face of the cluster
assembly in this manner:
http://www.npl.uiuc.edu/exp/G0/docs/g0_tgm_July98/img005.GIF
The central cluster of seven fibers corresponds to the first row of
seven output connectors seen in
gms1.jpg.
The other 15 rows of 19 output connectors correspond to the other 15
clusters arranged in a circle.
The optics used in the system are very similar to the design earlier proposed (http://www.npl.uiuc.edu/exp/G0/docs/g0_tgm_July98/img003.GIF) except that there is one additional lens in use. There is still no masking system, but I have recently begun to give this item some attention.
Fiber Cluster Assembly Tests
Some tests of the fiber cluster system have been completed. We
have a test system remarkably similar to the schematic for the full detector
setup (http://www.npl.uiuc.edu/exp/G0/docs/g0_tgm_July98/img002.GIF)
except that we only use one phototube and lightguide, and the lightguide
is short and straight.
The signal from the phototube is observed in a storage scope and the
area of the signal (in nano-Volt-seconds) is measured.
The first test was done with the optics arranged "by eye" without too much attention paid to the intensity, uniformity or parallelism of the beam. The results may be seen in http://www.npl.uiuc.edu/exp/G0/docs/g0_tgm_Dec99/gms_test_1.ps. The blue entries in the boxes A1:S16 correspond to the outputs of the connectors seen in gms1.jpg. The red entries are the averages for all the fibers in each cluster. The green averages are for the entire set of fibers ("Overall") or for just the fibers in the circle, excluding the central cluster ("Circle"). The histogram on the bottom left is for the entire set of fibers -- note the bimodal distribution. The graph on the bottom right plots the average for each fiber cluster on the circle vs. the location of the cluster, in degrees. Evidently the beam is not directed straight at the fiber cluster array, since there is a sinusoidal dependence of the average light output. The sinusoidal dependence of the beam intensity produces the bimodal distribution of fiber light outputs.
The light emerging from the fibers in a particular cluster is very uniform! Just a few fibers (L2, H3,and P8) significantly deviate from the average in their respective clusters. Since the fibers are all essentially identical, just a few fibers need to be observed in order to center the laser beam on the fiber cluster array.
For the second test, all the optical components were optimized:
Stability Tests
Just two stability tests have seen done so far. A short term test (1000 seconds) showed a FWHM in the output of one fiber of 1.4%. A somewhat longer term test (25,000 seconds) showed a FWHM of 2.0%. Longer term tests, covering days, will be performed later.
Things To Do
