Invited Speakers :Dr Christophe Buisset

Dr Christophe Buisset 

Activity status and future plans for the Optical Laboratory of the National Astronomical Research Institute of Thailand

Christophe Buisset1, Apirat Prasit, Marie-Angelie Alagao1, Weerapot Wanajaroen1, Piyamas Choochalerm1, Saran Poshyachinda1, Boonrucksar Soonthornthum1, Apichat Leckngam1, Griangsak Thummasorn1, Thierry Lepine 2,3, Yves Rabbia4

1National Astronomical Research Institute of Thailand, Siripanich Building, 191 Huay Kaew Road, Muang District, Chiangmai, Thailand 50200;
2Institut d’Optique Graduate School, 18 rue Benoît Lauras 42000 Saint-Etienne, France
3Université de Lyon, CNRS, Laboratoire Hubert Curien (UMR 5516), 18 Rue Benoît Lauras F-42000, Saint-Etienne
4Université Côte d'Azur, OCA, CNRS, Lagrange, Boulevard de l’Observatoire B.P. 4229 F-06304 NICE Cedex 43 

Technical scope:
Optics in Astronomy

The National Astronomical Research Institute of Thailand has developed since June 2014 an optical laboratory that comprises all the activities and facilities related to the research and development of new instruments in the following areas: telescope design, high dynamic & resolution imaging systems and spectrographs. The current activities comprise: i) the development of a focal reducer for the 2.4 m Thai National Telescope, ii) the development of the Evanescent Wave Coronagraph dedicated to the high contrast observations of star close environments and iii) the development of low resolution spectrographs for the TNT and for the 0.7 m telescopes of NARIT regional observatories. 

The focal reducer is specified to image a 15’ circle field of view on the 4K camera with a pixel scale equal to 0.42’’/pixel. The spatial resolution will be better than 1.2’’ over the full visible spectral domain [400 nm, 800 nm]. This system comprises 1 doublet placed on a robotic rail and placed on the center section of the TNT and 1 triplet placed in front of the camera. The optical and mechanical design activities as well as the manufacturing of most of the mechanical parts have been fully performed at NARIT. In this paper, we describe the design and the performance of this instrument and we present the development status. In particular, we present the results of the manufacturing activity and we present the plans for the future integration and assembly tests.

 The Evanescent Wave Coronagraph (EvWaCo) testbed aims at developing a new kind of coronagraph that involves the frustration of the total internal reflection to produce the coronagraphic effect. This, in order to perform observation of star close environment in the near-infrared and visible bands. The main advantage with respect to other coronagraphs is that: i) this instrument is partially chromatic and ii) the start light can be collected for example to install a wavefront sensor to compensate the wavefront error high frequency variations. This instrument provides a contrast equal to few 10^-6 at a distance comprised between 10 and 20 Airy radii. This, in polychromatic and unpolarised light at the wavelengths equal to 780 nm and 880 nm respectively. In this paper, we present our most recent results and we describe the design and the specifications of the future setup upgrade planned for 2018. This upgrade will include a turbulence simulator and a deformable mirror to demonstrate the capability of EvWaCo to obtain high contrast values while observing through the atmosphere. The low resolution spectrograph currently in development at NARIT has been designed to provide a spectral resolution close to 1000 over the spectral band [400 nm, 800 nm]. This, over a linear field of view of width equal to 3’ arcminutes at the focal plane of the Thai National Telescope. We also consider the possibility to perform slit less mode observations over a circular field of view of diameter equal to 3’. The design concept was provided by Pof. John Meaburn and comprises a 25 mm long chrome slit, a collimator, a grism and a focusing optics. The grism has been manufactured at Kaiser Optical Systems, Inc and comprises 630 lines/mm for a size equal to 65 mm x 65 mm. The focusing optics is a commercial NIKON lens of focal f = 50 mm and aperture number f/1.2. The instrument also includes an integrating sphere to calibrate the instrument spectral response over the specified field of view. NARIT has integrated and aligned a first version of the setup to measure the setup image quality and to verify that the setup is free of critical ghost images. In this paper, we present the status of the development of this instrument and the performance we have obtained.
Keywords: Astronomical instrumentation, Telescope, Coronagraph, Spectrograph, Optical Design

         Dr Christophe Buisset received the degree of optical engineering from the Institut d’Optique Graduate School (Orsay and Saint-Etienne, France) in 2004 and his PhD in Science of the Universe in 2007 from the Université Nice Sophia Antipolis (Nice, France). Between 2007 and 2013, we worked as an engineer on the development of space optical instruments at the company Thales Alenia Space (Cannes, France). In particular, between 2009 and 2013 he was the optical architect of the cryogenic camera and of the Fourier Transform Spectrograph of the future satellite Meteosat Third Generation InfraRed Sounder (MTG IRS).
            Since 2013 he has been working as a researcher at the National Astronomical Research Institute of Thailand (NARIT). His work has been dedicated to the development of the NARIT Optical laboratory by initiating and leading some projects in telescope design, coronagraphy and spectroscopy. In particular, he has been working at the improvement of the TNT optical performance and on the development of a new kind of focal reducer for large telescopes. Since 2016, he has been leading the development of a new kind of achromatic coronagraph that involves the evanescent waves to cancel out the light from a star to observe the stellar close environment.