Equalized and
Diffraction-limited Field Spectrograph Experiment

Global diagram of the project (Click on each element for more information)

All large telescopes are equipped, or they will, with Adaptive Optics (AO) or Multi-Conjugate Adaptive Optics (MCAO) systems with Laser Guide Stars (LGS). These systems will be also essential for the new generation of large and Extremely Large Telescopes (30 - 100 m, ELT). In order to obtain the best from such facilities, it is required to have appropriate information about the structure of the atmosphere, about the turbulence and wind, as well as about the sodium layer. Statistical characterization of the atmosphere behaviour (seasonal, monthly, etc) is crucial for suitable designs, specially of MCAO systems. Besides, information on real time about those useful parameters to be used to adapt the operation of these systems will be of capital importance.

From the achievements obtained under the project with reference AYA2003-07728, we propose to extract and to analyze, on real time, the relevant information about the turbulence and mesospheric sodium to provide it to the AO/MCAO systems. Specifically, it will be applied to the development of a prototype made up by an AO system and an Equalized Integral Field Spectrograph (EIFS). It means, we plan to approach the development of a prototype to be used as a test-bed platform for future major projects for ELT's.

The tasks of wave-front sensing and correction will be included in an AO system that will provide a corrected beam to a equalized integral field spectrograph (EIFS). Both parts will be designed like a complete instrument, although with the characteristics of prototype. That is to say, we propose to undertake a system that provides astrophysical results but being a platform of testing for future competitive instruments in large telescopes. The AO system will be adapted at every moment to the detected characteristics of turbulence and sodium layer. The instrument will be used in TCS and OGS telescopes, using a matrix of 8x8 elements. Part of the team is developing a system based on the use of FPGAs (Rodríguez-Ramos et al 2005). The implementation and versatility of these devices makes them very suitable for AO systems. They allow a fast and easy adaptation of the control loop of the AO system. Presently, we can correct the wave-front before the sensor finishes the reading of the image. It means that we achieve a bandwidth of the control loop greater than 1 kHz, performances non-obtained, at the moment, by no system.

Some years ago, we developed a new technique of 3-D spectroscopy for objects of large dynamic range (Arribas, Mediavilla, Fuensalida 1998). The alternative to this framework would be to use a coronagraph in front of a current integral field spectrograph. Although the application, at that moment was successful, the greatest potential would be attained in the case of diffraction limited, that is to say, assembled with an AO system. The field covered by the fibre mallet will not be greater than 2 arc sec and with an spectral range 0.7 – 1 microns.

Global Diagram
Some characteristic parameters

EDiFiSE is currently planning for first complete test in late 2009 at the 1mOGS telescope at the Teide Observatory (Tenerife, Spain). After that, we will move to the GHRIL platform of the 4.2mWHT at the Roque the los Muchachos Observatory on La Palma (Spain).






The projects of telescopes of new generation (large and extremely large, ELT) are justified, to a great extent, if the spatial resolution imposed by the atmospheric turbulence improves substantially, including the last goal, which is to reach the limit of diffraction of the telescope. On a par of this, it is necessary to develop instruments that take advantage of these achievements in optimal form, that is to say, developments whose techniques and concepts allow a greater efficiency of the astronomical observation. In this frame, we understand that it is fundamental to know, with the greater possible statistical coverage, the structure of the atmosphere in all the aspects that influence in the yield of the AO/MCAO systems, not only the vertical distribution of the turbulence, but also the speed of the turbulence layers, or the spatial and temporal distribution of the abundance of sodium in the mesopause.  It is important, therefore, to improve the techniques and procedures of measure of these factors related to the spatial-temporal structure of the atmosphere, not only to facilitate its characterization, but also to include them in the process of observation with AO/MCAO systems, optimizing thus its efficiency.

On the other hand, it is required to advance in the identification (establishment) of strategies and concepts that allow extending the schemes of present AO/MCAO systems to the ELT. Aspects like the wave-front sensing of large fields or with elongated LGS, due to the detection outside axis, are still without solving.  Also, new proposals of astronomical instruments should be explored (it is indispensable), whose designs are connected and matched with the performances of AO/MCAO systems, so that they allow greater efficiency in the astronomical observation.

Integral Field Unit Spectrograph