Precision Tuning and Improved Stability of a Universal Birefringent Filter
Abstract
Basic modifications of the Sacramento Peak Observatory Universal Birefringent Filter system and resultant major improvements in its performance are described. Spectral tuning is accomplished by rotating the nine birefringent elements that comprise the filter. For this, stepper motors are used under computer control, where one step is equivalent to a precision of 0.0025 Å (at 7000 A) for the narrowest bandpass element. The element angles are accurately set for an arbitrary wavelength by an algorithm derived from known tune solutions. Absolute wavelength calibration is provided by a He-Ne laser source, while an integrated monochromator can be used for the same purpose, though less accurately, throughout the 4100 A to 7000 A spectral range of the filter. The filter is maintained in a thermally stable environment controlled to a precision of 0.05° C; any incremental temperature change in the filter itself can be detected and its effects compensated by means of a laser calibration. In operation, the filter can typically be tuned to a selected wavelength in less than is with a precision of 1 mÅ.
- Publication:
-
Los Alamos Conference on Optics 1983
- Pub Date:
- 1983
- DOI:
- 10.1117/12.934744
- Bibcode:
- 1983SPIE..380...77S
- Keywords:
-
- VELOCITY FIELDS;
- OBSERVATIONS;
- INSTRUMENTATION