C. Arcidiacono (carmelo@arcetri.astro.it) is with the Department of Astronomy and Space Science, University of Florence, Largo Enrico Fermi 5, I-50125 Florence, Italy.
E. Diolaiti and M. Tordi are with the Department of Astronomy, University of Padova, Vicolo dell’Osservatorio 3, I-35132 Padua, Italy.
R. Ragazzoni, J. Farinato, and E. Vernet are with the Istituto Nazionale di Astrofisica, Astrophysical Observatory of Arcetri, Largo Enrico Fermi, 5, I-50125 Florence, Italy.
E. Marchetti is with the European Southern Observatory, Karl-Schwarzschild-Strasse, 2, D-85748 Garching bei Munchen, Germany.
The Layer-Oriented Simulation Tool (LOST) is a numerical simulation code developed for analysis of the performance of multiconjugate adaptive optics modules following a layer-oriented approach. The LOST code computes the atmospheric layers in terms of phase screens and then propagates the phase delays introduced in the natural guide stars’ wave fronts by using geometrical optics approximations. These wave fronts are combined in an optical or numerical way, including the effects of wave-front sensors on measurements in terms of phase noise. The LOST code is described, and two applications to layer-oriented modules are briefly presented. We have focus on the Multiconjugate adaptive optics demonstrator to be mounted upon the Very Large Telescope and on the Near-IR-Visible Adaptive Interferometer for Astronomy (NIRVANA) interferometric system to be installed on the combined focus of the Large Binocular Telescope.
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Computed for the parameters in Ref. 31. The SR is compared in columns 6 and 7 to that given in Ref. 31, and the two are approximately the same. The error values are the standard deviations of the instantaneous SR contribution to the long-exposure SR computed during the simulation.
Ref. 31.
Table 2
Comparison of LOST MAD Simulations and the Simulation Described in Ref. 14a
The same eight-star asterism over a 2-arc-sec FoV is assumed in both cases, as is an identical atmospheric model characterized by an overall r0 = 0.83 m at the K band and the Kolmogorov power spectrum.
For each layer an outer scale of 20 m is assumed. r0 was computed for the K band.
Table 4
Common Simulation Parameters Considered for the MADa
D (m)
FoV (arc min)
λscience (μm)
λWFS (μm)
ΔλWFS (μm)
MR,sky
Exposure Time (s)
Overall Quantum Efficiency
Delay Time (ms)
8
2
2.2
0.55
0.4
20.0
1.0
0.2
2.5
The pixel size of the phase screens is always 0.07 m/pixel, with a diameter of 112 pixels. The overall quantum efficiency, 0.2, gives a flux of 5.36 × 1011 photons/s at λ = 0.55 μm wavelength (Δλ = 0.4 μm bandwidth) and for a star of magnitude V = 0.
Table 5
Common Simulation Parameters Used in the MAD Simulations
DM
Altitude (km)
Gain
WFS Sampling
Integration Time (ms)
RON (rms)
Dark
Zernike Modes
1
0
0.6
8 × 8
5.0
4.5 e-/pixels/frame
500 e-/pixels/s
59
2
8.5
0.6
7 × 7
10.0
3.5 e-/pixels/frame
500 e-/pixels/s
36–43
Table 6
LINC-NIRVANA Common Simulation Parameters of Both Channelsa
D (m)
FoV
λscience (μm)
λWFS (μm)
ΔλWFS (μm)
MR,sky
Exposure Time (s)
Overall Quantum Efficiency
Delay Time
8.2
2′ and 6′
1.2 and 2.2
0.75
0.5
20.0
1.0
0.3
2× integration time
In the interferometric mode we consider the same parameters for both arms. In this case instead of the measured (mirror) modes of the DMs we use the Zernike polynomials, assuming that DMs are able to reproduce every Zernike polynomial.
Table 7
AO System Parameters Used in the NIRVANA Simulationsa
DM
Altitude (km)
Gains
Integration Time (ms)
RON (rms)
Dark
Zernike Modes
1
0.1
0.55
8.0
3.5 e-/pixels/frame
500 e-/pixels/s
609
2
6
0.45
6.0
3.5 e-/pixels/frame
500 e-/pixels/s
324
The binning factors used are 2 × 2 for the ground layer DM and 4 × 4 for the high DM.41,42 In both cases the WFS sampling is 12 × 12.
Table 8
Long-Exposure Data of the Cases Taken into Account for NIRVANAa
Case
Max SR
Average SR
rms SR
Peak to Valley
Single channel
0.21
0.13
0.03
0.30
Interferometric
0.13
0.12
0.002
0.004
A differential piston error with standard deviation σpiston = λ/4 is considered for the interferometric case. The results listed here refer to the 2-arc-min FoV for the single-channel case and to the central 20 arc sec × 20 arc sec for the interferometric case. In both cases Magnitude R integrated on a 2-arc-min FoV was 14.18.
Tables (8)
Table 1
SR for Two Kinds of Noise: Photon Noise and RON, and Photon Noise Onlya
Computed for the parameters in Ref. 31. The SR is compared in columns 6 and 7 to that given in Ref. 31, and the two are approximately the same. The error values are the standard deviations of the instantaneous SR contribution to the long-exposure SR computed during the simulation.
Ref. 31.
Table 2
Comparison of LOST MAD Simulations and the Simulation Described in Ref. 14a
The same eight-star asterism over a 2-arc-sec FoV is assumed in both cases, as is an identical atmospheric model characterized by an overall r0 = 0.83 m at the K band and the Kolmogorov power spectrum.
For each layer an outer scale of 20 m is assumed. r0 was computed for the K band.
Table 4
Common Simulation Parameters Considered for the MADa
D (m)
FoV (arc min)
λscience (μm)
λWFS (μm)
ΔλWFS (μm)
MR,sky
Exposure Time (s)
Overall Quantum Efficiency
Delay Time (ms)
8
2
2.2
0.55
0.4
20.0
1.0
0.2
2.5
The pixel size of the phase screens is always 0.07 m/pixel, with a diameter of 112 pixels. The overall quantum efficiency, 0.2, gives a flux of 5.36 × 1011 photons/s at λ = 0.55 μm wavelength (Δλ = 0.4 μm bandwidth) and for a star of magnitude V = 0.
Table 5
Common Simulation Parameters Used in the MAD Simulations
DM
Altitude (km)
Gain
WFS Sampling
Integration Time (ms)
RON (rms)
Dark
Zernike Modes
1
0
0.6
8 × 8
5.0
4.5 e-/pixels/frame
500 e-/pixels/s
59
2
8.5
0.6
7 × 7
10.0
3.5 e-/pixels/frame
500 e-/pixels/s
36–43
Table 6
LINC-NIRVANA Common Simulation Parameters of Both Channelsa
D (m)
FoV
λscience (μm)
λWFS (μm)
ΔλWFS (μm)
MR,sky
Exposure Time (s)
Overall Quantum Efficiency
Delay Time
8.2
2′ and 6′
1.2 and 2.2
0.75
0.5
20.0
1.0
0.3
2× integration time
In the interferometric mode we consider the same parameters for both arms. In this case instead of the measured (mirror) modes of the DMs we use the Zernike polynomials, assuming that DMs are able to reproduce every Zernike polynomial.
Table 7
AO System Parameters Used in the NIRVANA Simulationsa
DM
Altitude (km)
Gains
Integration Time (ms)
RON (rms)
Dark
Zernike Modes
1
0.1
0.55
8.0
3.5 e-/pixels/frame
500 e-/pixels/s
609
2
6
0.45
6.0
3.5 e-/pixels/frame
500 e-/pixels/s
324
The binning factors used are 2 × 2 for the ground layer DM and 4 × 4 for the high DM.41,42 In both cases the WFS sampling is 12 × 12.
Table 8
Long-Exposure Data of the Cases Taken into Account for NIRVANAa
Case
Max SR
Average SR
rms SR
Peak to Valley
Single channel
0.21
0.13
0.03
0.30
Interferometric
0.13
0.12
0.002
0.004
A differential piston error with standard deviation σpiston = λ/4 is considered for the interferometric case. The results listed here refer to the 2-arc-min FoV for the single-channel case and to the central 20 arc sec × 20 arc sec for the interferometric case. In both cases Magnitude R integrated on a 2-arc-min FoV was 14.18.