Advanced Astronomy for Heliophysics Plus (ADAHELI+) is a project concept for a small solar and space weather mission with a budget compatible with an European Space Agency (ESA) S-class mission, including launch, and a fast development cycle. ADAHELI+ was submitted to the European Space Agency by a European-wide consortium of solar physics research institutes in response to the “Call for a small mission opportunity for a launch in 2017,” of March 9, 2012. The ADAHELI+ project builds on the heritage of the former ADAHELI mission, which had successfully completed its phase-A study under the Italian Space Agency 2007 Small Mission Programme, thus proving the soundness and feasibility of its innovative low-budget design. ADAHELI+ is a solar space mission with two main instruments: ISODY+: an imager, based on Fabry–Pérot interferometers, whose design is optimized to the acquisition of highest cadence, long-duration, multiline spectropolarimetric images in the visible/near-infrared region of the solar spectrum. XSPO: an x-ray polarimeter for solar flares in x-rays with energies in the 15 to 35 keV range. ADAHELI+ is capable of performing observations that cannot be addressed by other currently planned solar space missions, due to their limited telemetry, or by ground-based facilities, due to the problematic effect of the terrestrial atmosphere.
In this paper we present the laboratory characterization and performance evaluation of the First Light Adaptive
Optics (FLAO) the Natural Guide Star adaptive optics system for the Large Binocular Telescope (LBT). The
system uses an adaptive secondary mirror with 672 actuators and a pyramid wavefront sensor with adjustable
sampling of the telescope pupil from 30×30 down to 4×4 subapertures. The system was fully assembled in the
Arcetri Observatory laboratories, passing the acceptance test in December 2009. The performance measured
during the test were closed to goal specifications for all star magnitudes. In particular FLAO obtained 83%
Strehl Ratio (SR) in the bright end (8.5 magnitudes star in R band) using H band filter and correcting 495
modes with 30×30 subapertures sampling. In the faint end (16.4 magnitude) a 5.0% SR correcting 36 modes
with 7×7 subapertures was measured. The seeing conditions for these tests were 0.8" (r0 = 0.14m @ 550 nm)
and an average wind speed of 15m/s. The results at other seeing conditions up to 1.5" are also presented. The
system has been shipped to the LBT site, and the commissioning is taking place since March to December 2010.
A few on sky results are presented.
Telescopes of 8 meter class, like Large Binocular Telescope (LBT), are based on the concept of Deformable
Secondary Mirror (DSM); in order to calculate the best DSM shape that correct the measured aberrations we need to
calibrate the AO system, so we need a correlation between the DSM and the wave front sensor (WFS), i.e. we need
the Interaction Matrix (IM). Usually we obtain the IM in laboratory or at the telescope using as source a reference
fiber that illuminates both the deformable mirror and wave front sensor. But in case of LBT and all large telescopes,
this technique can be very difficult or sometimes impossible, and calibration may be required to be performed on
sky. So we need new calibration techniques, and we investigate about sinusoidal modulation one for LBT case. In
the Arcetri solar tower (inside Arcetri Observatory) we recreated a set up environment similar to the telescope, and
thanks to that we can test the calibration system in the same condition of the LBT. In preparation for the test some
simulations of this sinusoidal modulation technique were needed, in order to choose the best parameters that
increased SNR and reduced integration time. The paper will detail the simulation results of the calibration LBT
system made with this new technique, and these results will be used to drive our tests in the tower.
The paper is describing the present status of the LBT first light AO system. The system design started in January 2002 and is now approaching the final test in the Arcetri solar tower. Two key features of this single conjugate AO system are the use of an adaptive secondary mirror having 672 actuators and a pyramid wavefront sensor with a maximum sampling of 30x30 subapertures. The paper is reporting about the adaptive secondary mechanical electrical and optical integration, and the wavefront sensor unit integration and acceptance test. Finally some lab test of the AO system done using an adaptive secondary prototype with 45 actuators, the so called P45 are described. The aim of these test was to get an estimate of the system limiting magnitude and to demonstrate the feasibility of a new technique able to measure AO system interaction matrix in a shortest time and with higher SNR with respect to the classical interaction matrix measurement. We are planning to use such a technique to calibrate the AO system in Arcetri and later at the LBT telescope.
In the technological development for the ELTs, one of the key activities is the phasing and alignment of the primary mirror segments. To achieve the phasing accuracy of a small fraction of the wavelength, an optical sensor is required. In 2005 has been demonstrated that the Pyramid Wavefront Sensor can be employed in closed loop to correct simultaneously piston, tip and tilt errors of segmented mirror. The Pyramid Phasing Sensor (PYPS) is based on the sensing of phase step on the segment edges; this kind of phasing sensors have the common limitation of the signal ambiguity induced by the phase periodicity of πδ/λ on the mirror surface step δ, when the wavelength λ is used for the sensing. In this paper we briefly describe three different techniques that allow to solve the phase ambiguity with PYPS. As first we present experimental results on the two wavelengths closed loop procedure proposed by Esposito in 2001; in the laboratory test the multi-wavelength procedure allowed to exceed the sensor capture range of ±λ/2 and simultaneously retrieve the differential piston of the 32 mirror segments starting from random positions in a 3.2 λ wavefront range, the maximum allowed by the mirror stroke. Then we propose two new techniques based respectively on the segment and wavelength sweep. The Segment Sweep Technique (SST) has been successfully applied during the experimental tests of PYPS at the William Herschel Telescope, when 13 segments of the NAOMI DM has been phased starting from a random position in a 15λ range. The Wavelength Sweep Technique (WST) has been subject of preliminary tests in the Arcetri laboratories in order to prove the concept. Each technique has different capture range, accuracy and operation time, so that each can solve different tasks required to an optical phasing sensor in the ELT application. More in detail the WST and SST could be used combined for the first mirror phasing when the calibration required for the closed loop operations are not yet available. Then the closed loop capture range can be extended from ±λ/2 to ±10λ with the multi-wavelength closed loop technique.