VTT has developed Fabry-Pérot Interferometers (FPI) for visible and infrared wavelengths since 90’s. Here we present
two new platforms for mid-infrared gas spectroscopy having a large optical aperture to provide high optical throughput
but still enabling miniaturized instrument size. First platform is a tunable filter that replaces a traditional filter wheel,
which operates between wavelengths of 4-5 um. Second platform is for correlation spectroscopy where the
interferometer provides a comb-like transmission pattern mimicking absorption of diatomic molecules at the wavelength
range of 4.7-4.8 um. The Bragg mirrors have 2-4 thin layers of polysilicon and silicon oxide.
Seeing measurements are crucial for the optimum design of (multi-conjugate) adaptive optics systems operating at solar
telescopes. For the design study of the 4-meter European Solar Telescope, to be located in the Canary Islands, several
instruments have been constructed and operated, at the Observatorio del Roque de los Muchachos (La Palma) and at the
Observatorio del Teide (Tenerife), to measure the properties of the ground layer and medium-high altitude turbulence.
Several units of short (42.34 cm) and two long (323.06 cm) scintillometer bars are, or are to be, installed at both
observatories. In addition to them, two wide-field wavefront sensors will be attached to the optical beams of the Swedish
tower, on La Palma, and of the German VTT, on Tenerife, simultaneously used with the normal operation of the
telescopes. These wavefront sensors are of Shack-Hartmann type with ~1 arcminute field of view. In this contribution,
the instruments setup and their performance are described.
Solar observations are performed over an extended field of view and the isoplanatic patch over which conventional
adaptive optics (AO) provides diffraction limited resolution is a severe limitation. The development of multi-conjugate
adaptive optics (MCAO) for the next generation large aperture solar telescopes is thus a top priority. The Sun is an ideal
object for the development of MCAO since solar structure provides multiple "guide stars" in any desired configuration.
At the Dunn Solar Telescope (DST) we implemented a dedicated MCAO bench with the goal of developing wellcharacterized,
operational MCAO. The MCAO system uses two deformable mirrors conjugated to the telescope
entrance pupil and a layer in the upper atmosphere, respectively. The high altitude deformable mirror can be placed at
conjugates ranging from 2km to 10km altitude. We have successfully and stably locked the MCAO system on solar
granulation and demonstrated the MCAO system's ability to significantly extend the corrected field of view. We present
results derived from analysis of imagery taken simultaneously with conventional AO and MCAO. We also present first
results from solar Ground Layer AO (GLAO) experiments.
Solar telescopes equipped with wide field of view Hartmann-Shack wavefront sensors (WFWFS) can be used
to measure the vertical distribution of optical turbulence strength at daytime.1 The method is based on the
computation of the angular covariance of local image displacements within the subapertures of the WFWFS,
similar to the SLODAR method which is used at nighttime telescopes.2 In this paper the basic principles of
the method are summarized, and practical limitations are shown. Moreover, the influence of compensating
ground-layer turbulence with a single conjugated adaptive optics system (SCAO) on the angular covariance
functions is modeled.