[asac][almanews] ALMA Memos 445 Released

[Stacy Oliver]

ALMA MEMO #445

ALMA Line Length Correction System: Report on Tests in Japan

Larry D’Addario, Sarmad Al Banna, and Bill Shillue,
National Radio Astronomy Observatory (NRAO), Tucson, Arizona, USA;

Masato Ishiguro and Akitoshi Ueda,
National Astronomical Observatory of Japan (NAOJ), Mitaka, Tokyo, Japan;

and Ken-Ichi Nakagawa and Mitsuru Musha,
University of Electro-Communications (UEC), Chofu-shi, Tokyo, Japan

2003/02/03

A preliminary version of the ALMA line length correction system, which will stabilize the electrical length of the optical fibers
used to distributed the LO reference  signals from the center to each antenna, has been constructed in the form of a semi-portable
test instrument. The length stabilization technique is dependent on use of a frequency-stable master laser. Such a laser is not yet
available, but the University of Electro Communications (UEC) in Japan has a laser with very good long term stability. Therefore the
test instrument was brought to Japan and a series of measurements was made using the UEC laser with the goal of verifying the
accuracy of the length stabilization technique. The tests allowed us to set an upper limit on the delay variation in the stabilized
path of about 70 fsec over 1 hour. It is possible that the system meets the ALMA goal of about 6 fsec delay variation (1.26 µm fiber
length variation) over at least 100 sec, but establishing this was beyond the limits of these tests.

View a pdf version of ALMA Memo #445.
http://www.alma.nrao.edu/memos/html-memos/alma445/memo445.pdf

Download a postscript version of ALMA Memo #445.
http://www.alma.nrao.edu/memos/html-memos/alma445/memo445.ps

_______________________________________________
Almanews mailing list
Almanews at listmgr.cv.nrao.edu
http://listmgr.cv.nrao.edu/mailman/listinfo/almanews