Canary Experiments

OPTICON workpackages 1, 6, 7 and 10 have come together in a campaign of instrument and concept development at the Observatorio de los Muchachos, La Palma, Spain.

As part of workpackage 10: “AO networking” and workpackage 1: “Calibration and Test Tools for Adaptive-Optics E-ELT Instruments”, an advanced Adaptive Optics (AO) test facility, “CANARY”, has been offered to the community to test new AO algorithms and AO corrected instrumentation.

This includes a novel integral field unit (IFU) utilising photonic microlens, fibre and reformatting technology developed as part of workpackage 6: “Astrophotonics” to feed a spectrograph containing a multiplexed volume phase holographic (VPH) grating from workpackage 7: “Innovative Photosensitive Materials for Diffractive and Reflective Optical Elements”. In combination these novel technologies provide a compact and light efficient high-resolution IFU aimed at exoplanet characterisation, and named MCIFU.

This large experiment also featured the on-sky testing of two concepts from workpackage 10: “AO networking”, working together for the first time. Novel AO control schemes to specifically correct for local turbulence in the telescope dome and high-speed turbulent layers high in the Earth’s atmosphere require real-time input from on-site turbulence monitoring instrumentation for calibration. This was achieved by feeding advanced control algorithms with concurrent vertical turbulence profiles measured by the Stereo-SCIDAR instrument.

Other experiments supported by workpackage 10 included the first on-sky test of two new types of wavefront sensor. The pupil-modulated point-diffraction interferometer (m-PDI) is a new type of wavefront sensor for the calibration of astronomical instruments and for high-contrast adaptive optics. The larger family of point-diffraction interferometers (PDI) has shown promise in applications such as calibration of non-common path aberrations (NCPAs) and co-phasing of segmented mirrors. By using a diffraction grating placed on a pupil, the m-PDI modulates the input electric field to achieve an extended dynamic range well beyond the ±π/2 of other standard PDIs. Other advantages, besides the high accuracy which characterises this type of interferometer, include a chromatic bandwidth of about 200 nm (up to ~400 nm), a highly stable and compact near common-path configuration and little noise propagation from scintillation. The purpose of testing this instrument on the CANARY bench was to show that it was able to do accomplish two things: 1) to measure slowly changing aberrations between its path and that of other WFSs (SH, Mach-Zehnder), with multiple narrow and broadband internal sources, and 2) to sense fast AO residuals from CANARY's SCAO loop, providing a first verification for future XAO work. Preliminary results show that the m-PDI was successful at the first task, staying within its dynamic range even with broadband light. With respect to the measurement of on-sky residuals, more analysis is yet to be done to assess the overall performance of our instrument.

The Canary bench in July 2019