The upcoming SCALES instrument for W.M. Keck Observatory will enable coronagraphic imaging and low-/mid-resolution IFS observations over 2-5 micron wavelengths, using two separate HgCdTe Teledyne Imaging H2RG detectors. These detectors are wired for slow-mode readout at a pixel clock rate of ~100kHz, but when operated with a Teledyne Imaging SIDECAR ASIC followed by an AstroBlank/Markury Scientific MACIE controller card, the system can be operated at faster clock rates up to 30MHz, a mode referred to as hybrid fast-slow readout. We perform room-temperature laboratory tests of detector readout to demonstrate feasibility of hybrid readout using a MUX in place of the H2RG, before proceeding into room-temperature and cold tests with the H2RG detector. We test and optimize full-frame data acquisition with pixel clock rates from 5-30 MHz. We discuss the next steps in detector system testing and verification.
The Wide Field Phasing Testbed for the Giant Magellan Telescope1 is comprised of six pairs of off-axis parabolas, an Offner relay and several additional fold mirrors. To align this optical system we used a Leica laser tracker and a 4D interferometer. The laser tracker was used to accurately position each fold mirror on the optical bench by measuring the position of a spherically mounted retroreflector with the laser tracker, first directly and then in reflection off the mirror to be aligned. The mirror was adjusted until the reflected image was in the correct location. Key to this operation was custom software that read in the Zemax prescription file specifying the location of each optic; interfaced with the laser tracker to measure the location of fiducial SMRs on the optical bench; performed transformations between coordinate systems attached to the laser tracker, the optical bench, the Zemax model, and the individual optics; and finally displayed the real-time position errors in a large font so that the optic could be easily adjusted to the correct location. The OAPs were also positioned using the laser tracker in conjunction with the interferometer. An SMR was placed at the desired focal position of the OAP using the laser tracker. This same SMR served as the return sphere for the interferometer which was used to adjust out tilt and astigmatism errors. With this system we were able to align the full optical system efficiently and in a deterministic way.
The Wide Field Phasing Testbed will be used to test phasing and active optics systems planned for the doubly segmented Giant Magellan Telescope. The testbed consists of a set of optical relays in which are located segmented and deformable mirrors that represent the GMT M1 and M2 mirrors. The testbed output beam has the GMT’s f/8.16 focal ratio and has a back focal distance large enough to allow using a full-scale prototype of one unit of the Acquisition Guiding and Wavefront Sensing System. The testbed will reproduce the telescope field dependent aberrations that result from misalignment of M1 and M2. Over its 20mm diameter field of view, the testbed will generate aberrations corresponding to the 20′ field of the GMT. A rotating turbulence screen and zero-deviation prisms in the testbed will generate seeing limited images that correspond to typical atmospheric seeing and dispersion conditions expected at the GMT. The software for the testbed is designed to allow connection of the testbed wavefront sensing analysis components to simulations of the testbed optical system, as well as to conform to the planned software interfaces of the GMT’s telescope control system.
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