spectrometer simulation

A. Ealet Berkeley, december 2002 1

Spectrometer simulation

Note in http://www.astrsp-mrs/snap/spectro/spectrosim.ps

● Why we need it now● What should be simulated● How to do it● Work plan● Conclusion

A.BonissentA.EaletC.MacaireE.PrietoA.Tilquin


● Previous stage, only laboratory tests and

simulation of slicer alone have been performed.

● This is sufficient to ensure that an instrument can be built with adequate performance.

● Now to study the real performances on the full instrument, we need a complete simulation

Past


● Needed in the present phase for

– Optimizing the design: balance cost and simplicity (reliability) for best possible physics

– compute realistic efficiency – evaluate tolerance– evaluate calibration procedure– produce realistic data to develop and test data

processing algorithms

● At term, it will be used in detailed MC studies for physic analysis

Why


Specifications

OK ?

Optical design

Optical simulation

No

Optomechanical simulation

Library of psf

yes

Optimisation process


● At the end of phase A, we need a Final design of the instrument with estimated (and justified) performances

● Simulation and data reduction software for evaluation should be ready well before

simulation spring 2003data reduction prototype spring 2004

Développement plan


● Full SNAP simulation

SN simulation

analysis

propagation

Data reduction

instrument

Detector pixel data

physic

Data cube

Lightcurvespectra

Lightcurvespectra

Cosmo models

Physic parameters


● Spectrometer simulation

telescope

optical sim

readout

pixellisation

slicer

spectrograph

fit Data cubei,j,adc

Parameterization constants

x,y,

x,ypsf1

x,y,psf2

x,y,psf3

i,j,Qij

i,j,Qij

Pixel parameterization


TF of amplitude from object plane to pupil plane then to imageApply geometry and phase (zernike) on pupilApply geometry on imageCompute intensity to evaluate efficiencyInterpolate position x,y at each step (need parametrisation)

Output is position on the detector for each point and wavelength with an associated PSF

Very long and CPU intensive

Method

Telescopext,yt,

Slicerxs,ys

Slitxf,yf

prismxl,yl

Detectorxd,yd

pei

Compute Psf and transmission at each x,y,

pupilxp,yp

TF

p peipei ppsf

TFTF TF TF


Psf shape and size depends on x,y,(small amount of) energy is lost by diffractionGeometry affects performance

psf

slice


0.9 m

1.7 m

Slice 0

Slice 2


Zernike Polynomia

from Zeemax are used to introduce aberrations

Depend of,x,y

They need to be extrapolate on each point of the image plan

Use Neural Network technique to do extrapolation

Zernike polynomial of slicer for = 1.7 m


psf

slice

Efficiency study

Gobal efficiencyTelescope+slicer+spectrograph


R=/pixel

Simulation checking: spectral resolution


➢ DESIGN OPTIMISATION➢ Test optic➢ Play with optic to study tolerance➢ Efficiency/nb of pixel ➢ Visible/IR efficiency vs spectral resolution/detector➢ optimise spatial resolution => detector noise optimisation➢ Reduce Nb of mirrors : better transmission but may need

more space, more complex optics

● TEST DATA– Slit effect : Position of SN in slice => translation of spectrum;– SN may cover several slices : need to add translated

spectra– Optical distorsions– Pixellization– Dithering– Detector and electronics : efficiency, noise, cosmics ...

Used for :


Distorsions on the detector

U s

patia

l dim

ensi

on

V spectral dimension

Detector pixelsdo not coincide with = Cte or x = Cte

20 pixel/slice


Full simulation of slicer unit OK

Full simulation of telescope and spectrometer OK

Interpolate for intermediate points using Neural Network technique. OK

library of PSF for a grid of x,y,; under work

From library of PSF+ geometry (x,y,-> detector indices) to be done

Pixellisation : integrate over pixels Add dark current, readout noise etc... Include galaxy

Dithering (spatial, spectral) If useful, we may use general purpose code developed by CRAL (SNIFS,

SN factory).

Current Status


● Detailed simulation of the spectrometer is needed in this phase to quantify performances

● CPU intensive : not appropriate for physics

simulation ● Parametric simulation under development, based on

the library of PSF should be appropriate for a full SNAP simulation (not for SNAPfast).

Conclusion


Spectrograph: Performances

telescope

Relay optics

Slicer

Optic straylight diffra.

Spectro

Mirrors prism dichroic

Detector

Vis / NIR

#elements

4 1 3 1 1 2 1 1 1 1

Efficiency/ 0.98 0.98 0.98 0.99 0.95 0.98 0.81 0.95 0.9

0.6

(0.8)

cumulative 0.92 0.90 0.85 0.84 0.80 0.77 0.62 0.59 0.53

0.35

(0.47)

Gain on mirror transmission, loose on diffraction/prism (complete simulation)Globally equivalent


Design issues

•Spectral resolution : optimization visible /IR( R(IR [1-1.4] m) < 100 but don’t need to join the 2 detectors )

•Polarization: specification needed – impact on spectrograph•Design

•Spatial resolution : 0.15”. Issue vs the radiation rate

•Wavelength range 1.7 m short for the Si line , 1.8 mm betterbut detector cut issue , issue on temperature

spectrometer simulation

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