Canada-France-Hawaii Telescope Canada-France-Hawaii Telescope
6 Future of Adaptive Optics at CFHT Recently, the company EG&G, who fabricated the APDs for the WFS, put on the market a new model of APDs with QE approximately 2 times superior to the older model. This means a gain of almost one magnitude on reference sources. At this stage we are also investigating the optical fiber coupling of between the micro-lens array and the APDs; trying to minimize losses.
An idea has been suggested to us, to optimize the use of photons for visible observation. Right now the only choice are to split the light between the WFS and science path in the ratios 85/10, 10/85 and 50/50. We are investigating designs of beamsplitter which would transmit the V, R, I broad bands to the science path, and reflect the rest of the visible to the wavefront sensor. This would be equivalent to sending some 90% of the light in the science path and approximately 80% to the WFS.
Given the choices made at the time of fabrication, the AO bonnette can be easily upgraded. The real-time computer can handle easily the computation for a 19 electrodes system. Therefore, it would be possible to increase the number of electrodes, in order to increase the order of correction. This will insure a better AO correction and strehl ratio for short wavelength observations (0.4 to 0.7 micron). Such modification would imply the fabrication of another bimorph mirror, wavefront lenslet array and the addition of power supply sources for the supplementary electrodes and APDs for the supplementary apertures.
The second aspect of improvement would be the implementation of laser guide star facility to increase sky coverage. This possibility has been mentioned at the AOB Workshop in Quebec (1994) and received with enthousiasmus by the community of users. However, it is not known whether funds are available for this or whether it will be authorized or not by the Institute for Astronomy, manager of the Mauna Kea site.
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