AO wavefront sensing detector developments at ESO
High Energy, Optical, and Infrared Detectors for Astronomy IV
The detector is a critical component of any Adaptive Optics WaveFront Sensing (AO WFS) system. The required combination of fast frame rate, high quantum efficiency, low noise, large number and size of pixels, and low image lag can often only be met by specialized custom developments. ESO's very active WFS detector development program is described. Key test results are presented for newly developed detectors: a) the e2v L3Vision CCD220 (the fastest/lowest noise AO detector to date) to be
... date) to be deployed soon on 2nd Generation VLT instruments, and b) the MPI-HLL pnCCD with its superb high "red" response. The development of still more advanced laser/natural guide-star WFS detectors is critical for the feasibility of ESO's E-ELT. The paper outlines: a) the multi-phased development plan that will ensure detectors are available on-time for E-ELT first-light AO systems, b) results of design studies performed by industry during 2007 including a comparison of the most promising technologies, c) results from CMOS technology demonstrators that were built and tested over the past two years to assess and validate various technologies at the pixel level, their fulfillment of critical requirements (especially read noise and speed), and scalability to full-size. The next step will be towards Scaled-Down Demonstrators (SDD) to retire architecture and process risks. The SDD will be large enough to be used for E-ELT first-light AO WFS systems. For full operability, 30-50 full-scale devices will be needed. Examples of past custom developments at ESO are the e2v CCD50 and the MIT/LL CCID-35. ESO funded e2v Technologies (e2v) to develop the CCD50. The CCD50 is a 24 µm square 128x128 pixels split frame transfer back illuminated CCD. Low read noise of 5e-at 1000fps was achieved by reading out through 16 conventional output amplifiers, each at 1Mpixel/sec. The CCD50 has been successfully used on the ESO NACO and MAD instruments as well as at other international observatories.