Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.adass.org/adass/proceedings/adass00/reprints/P2-32.pdf Дата изменения: Wed May 30 01:31:07 2001 Дата индексирования: Tue Oct 2 11:22:41 2012 Кодировка: Поисковые слова: adaptive optics

Astronomical Data Analysis Software and Systems X ASP Conference Series, Vol. 238, 2001 F. R. Harnden Jr., F. A. Primini, and H. E. Payne, eds.

CAOS Simulation Package 3.0: an IDL-based To ol for Adaptive Optics Systems Design and Simulations
Marcel Carbillet, Luca Fini, Bruno Femenґa, Armando Riccardi, Simone i Esposito Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy ґ Elise Viard, Francoise Delplancke, Norbert Hubin ё European Southern Observatory, Karl-Schwarzschild Strasse 2, 85748 Garching-bei-Munchen, Germany Ё Abstract. The IDL-based simulation software Code for Adaptive Optics Systems (CAOS) was originally developed to simulate the behavior of generic adaptive optics systems. The modular structure of the software allows the simulation of a great variety of different systems and is particularly suited for the adoption of graphical techniques for the programming of applications. It is actually composed of a global user interface (the CAOS Application Builder ­ presented in Fini et al. 2001), and a set of specific modules: the CAOS Simulation Package. We present in this paper the last version (3.0) of the CAOS Simulation Package, together with an example of an application to the Large Binocular Telescope interferometer adaptive optics system.

1.

Introduction

In the framework of the "Laser Guide Star for 8-m Class Telescopes" Training and Mobility of Researchers network funded by the European Union, an IDL-based software package has been developed to simulate generic adaptive optics (AO) systems. The structure of the software is modular. Each elementary physical process such as turbulence in atmospheric layers, propagation of light from source to observing telescope and through the turbulent layers, the wavefront sensor, is modeled in a specific module. The resulting software, called Code for Adaptive Optics Systems (CAOS), is composed of a global graphical user interface (GUI), the CAOS Application Builder (Fini et al. 2001), and a set of specific modules--the CAOS Simulation Package. A list of modules and brief descriptions are presented in Section 2. An example of an application to the Large Binocular Telescope (LBT) interferometer AO system is presented in Section 3. References to more information about CAOS are given in Section 4.

249 c Copyright 2001 Astronomical Society of the Pacific. All rights reserved.


250 2.

Carbillet et al. The Modules of CAOS Simulation Package 3.0

Table 1 shows a complete list, together with a very brief description, of the modules of CAOS Simulation Package 3.0. Table 1. Module wavefront generation modules ATM - ATMosphere building SRC - SouRCe definition GPR - Geometrical PRopagation LGS-specific modules LAS - LASer generation NLS - Na-Layer Spot building wavefront correction modules TTM - Tip-Tilt Mirror DMI - Deformable MIrror wf sensing and reconstruction TCE - Tip-tilt CEntroiding SHS - Shack-Hartmann Sensor CEN - CENtroiding calculus TFL - Time FiLtering REC - REConstruction module calibration-oriented modules CFB - Calibration FiBer CSQ - Command SeQuencer MCA - Make CAlibration data other scientific modules IBC - Interf. Beam Combiner IMG - IMager module STF - STructure Function WFA - WaveFront Adding BSP - Beam SPlitter utility modules PSG - Phase Screen Generation DIS - data DISplay utility SAV - data SAVing utility RST - data ReSTore utility Descriptive list of the modules. Purpose to simulate the turbulent atmosphere to define the observed source to propagate the light to define the pro jected laser beacon to simulate the 3D sodium lgs the tip-tilt correcting mirror the deformable correcting mirror to reconstruct the tip-tilt to simulate the Shack-Hartmann sensor spots formation to compute the SH centroids to emulate commands time-filtering to reconstruct the wavefront to define a calibration fiber to generate calibration commands to elaborate calibration data to to to to to to to to to simulate co-phasing of two beams simulate image formation compute the structure function linearly combine two wavefronts emulate a beam-splitter device generate turbulent phase screens display any kind of input data save cubes of data (XDR format) restore XDR cubes of data

Using the CAOS Application Builder, a simulation can be built by connecting together the required occurrences of the desired modules, represented by the boxes of Figure 1. The only constraints are those imposed by input/output types. Each module comes with an individual GUI in order to set its own physical and numerical parameters, during the design step or independently at a


CAOS: Tool for Adaptive Optics Design and Simulation

251

Figure 1. The CAOS worksheet corresponding to the LBT interferometer (left), together with the contour plots of two of the obtained PSFs: r-band, 1 off-axis, parallactic angle of 0 (up), and 120 (down). later time. The whole structure of a simulation can be saved as a "pro ject" that can be restored for later modifications and/or parameters upgrading. The IDL code, corresponding to the designed simulation, is written down during the saving of a pro ject, and it can be modified "by hand" in order to be completed with additional tasks not supported by the CAOS package. 3. An Example of an Application to the LBT Interferometer

Let's assume that we would like to simulate high-angular-resolution observations in the red and near-infrared wavelength bands1 , with the LBT interferometer2 and with AO correction. Figure 1 (left) shows the whole pro ject designed for such a purpose, with a natural guide star (NGS) of 10th magnitude for the AO sensing, either on-axis or 1 off-axis with respect to the astronomical ob ject. The turbulent atmosphere is modeled with two layers: a ground layer evolving along the baseline and weighted with 30% of the total turbulent energy, and an upper layer (at 10 km altitude) evolving orthogonally to the baseline and weighted with 70% of the total turbulent energy. For both layers the wind speed is 5 m/s. The total Fried parameter r0 is 20 cm (at 500 nm), and the wavefront outer-scale L0 is 40 m. Each pupil of the LBT interferometer has its
1 2

namely r (700±110 nm), j (1250±150 nm), h (1650±=175 nm), and k (2200±200 nm) 2в8.25 m with a 14.4 m baseline


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Carbillet et al.

own AO system made of a tip-tilt (TT) correction loop, and a high-orders (HO) correction loop. The HO loop is made of: a 34в34 Shack-Hartmann lenslet array with 8в8 pixels/sub-aperture and 0.15 /pixel for the sensing, a modal rejection of the Zernike modes over number 231 (20th radial order) during the wavefront reconstruction, and a 35в35 actuators deformable mirror (that corresponds to a pro jected inter-actuator distance of 23.5 cm on the primary mirror) for the correction. The TT loop contains a quad-cell detector (with 0.25 /cell). Both sensings are performed in r, the light from the NGS being split 95% for the HO loop and 5% for the TT loop, assuming an overall efficiency of 60% and a read-out noise of 3 e- rms. The time-filtering acts in each loop as a pure integrator, and the differential piston is supposed to be perfectly corrected. The scientific CCD ­ on which the point-spread function (PSF) corresponding to the astronomical ob ject is formed ­ make 128в128 pixels images3 . The total temporal history of each simulation run ­ one per value (0 , 60 , and 120 )ofthe parallactic angle ­ is 2.075 s (corresponding to 415 iterations of 5 ms each), but the resulting interferometric PSFs (one per band (four) and per off-axis (two) considered) are integrated over the last 2 s for sake of AO stability. For each of the simulation run, a different realization of the turbulent atmosphere was considered (since each parallactic angle corresponds to a different period of the observing run). Figure 1 (right) shows two of the 3в4в2 obtained PSFs, while Table 2 synthesizes the quality of all the 24 AO-corrected interferometric PSFs obtained in terms of Strehl ratio. Table 2. 0 0 60 120 Strehl ratios obtained for each of the interferometric PSF. r .606 .581 .557 j .851 .836 .816 h .907 .897 .878 k .946 .939 .921 1 0 60 120 r .554 .522 .504 j .827 .809 .791 h .893 .881 .864 k .938 .929 .912





4.

More Information...

For more information and references on the CAOS Simulation Package and the CAOS Application Builder, see http://www.arcetri.astro.it/caos. See also Correia et al. (2001) for a description of the CAOS-compatible simulation package AIRY (Astronomical Image Restoration in interferometrY). References Fini, L., Carbillet, M., Riccardi, A. 2001, this volume, 253 Correia, S., Carbillet, M., Fini, L., et al. 2001, this volume, 404

3

with 2.1 mas/pixel in r, 3.8 mas/pixel in j, 5.0 mas/pixel in h, and 6.7 mas/pixel in k