A differential method was used to investigate the focal ratio degradation (FRD) exhibited by, and throughput of, a selection of current-generation optical fibres. These fibres were tested to establish which would be best suited to feed the High Resolution Spectrograph being built for the Southern African Large Telescope (SALT), as well as for future instruments on WIYN and SALT. The double re-imaging system of Bershady et al. (2004) was substantially modified to improve image quality and measurement efficiency, and to permit a direct FRD-measurement in the far-field. The re-imaging method compares the beam profile produced by light which passes through a fibre to that which does not. Broad and intermediate band-pass filters were used between 400-800 nm to test for wavelength dependence in the observed FRD over a wide range in beam-speeds. Our results continue to be at odds with a mico-bend model for FRD. We conclude that the new Polymicro FBP fibre is the most suitable product for broadband applications.
[1]
Lawrence W. Ramsey,et al.
Focal ratio degradation in optical fibers of astronomical interest
,
1988
.
[2]
Ian R. Parry,et al.
A method for determining the focal ratio degradation of optical fibres for astronomy
,
1994
.
[3]
Matthew A. Bershady,et al.
SparsePak: A Formatted Fiber Field Unit for The WIYN Telescope Bench Spectrograph. II. On-Sky Performance
,
2005
.
[4]
Jeremy R. Allington-Smith,et al.
Fibre systems for future astronomy : anomalous wavelength-temperature effects
,
2007
.
[5]
M. Bershady,et al.
SparsePak: A Formatted Fiber Field Unit for the WIYN Telescope Bench Spectrograph. I. Design, Construction, and Calibration
,
2004,
astro-ph/0403456.