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Fibre Linked ECHelle Astronomical Spectrograph

07-09 May 2010Bebra - Spektroskopietagung 20101

Integration and alignment of FLECHAS

CAOS

CAOS group Astelco


Gerardo AvilaVadim BurwitzCarlos GuiraoJesús Rodriguez

Martin DietzelPeter Aniol

CAOS

Purposes of our presentation


Summary of our spectrographsFLECHAS specificationsOptical designIntegration and alignment of the instrumentSpectra acquisitionBrief data reduction

CAOS

Spectrographs:


Ponchado (reflecting grating) 1994Fiasco (reflecting grating) 1997Loros (prisms) 2001Leches (échelle) 2002Besos (prism) 2003Ingratos (Grism) 2004Tragos (transmission grating) 2005Baches (échelle) 2005Dados (reflecting grating) 2006Pucheros (échelle) in preparation with UCCFlechas (échelle) 2009Next: Flechas++ (échelle)

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Spectrographs:


PONCHADO INGRATOS

BESOS

DADOSTRAGOS LECHES

BACHES

FIASCO

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FLECHAS requirements


Medium resolving power (R: 7000-11000)Wavelength range: 395 nm – 750 nmMechanical stability (no flexures)Adapted to 1.2m telescope at F/10Off the shell optic and mechanic componentsNo moving partsSimple and robust mechanical designLow maintenance

CAOS

Features


What drives the design of the spectrograph? :Échelle size !!

Fibre link to the telescope Small fibre coreFibre works at low F/# to reduce focal ratio degradationMini and micro lenses to match telescope and spectrograph apertures

Full parabolic mirror working as off-axisTransmission grating as X-disperserPhoto-tele-objective to image the spectrum on CCDLarge “unexpensive” CCD size.

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Optical design


Full parabola as collimator

Output fibre end

CCD Tele-objective X-disperser Échelle

9º

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Optical design


To the question: why 9º between the collimator and objective beams?

This “grating” angle should be as small as possible in order to approach the Littrow configuration where the efficiency is the maximum. In the FLECHAS case, we found that 9º was the best compromise between the size of the camera objective and the optical table.

CAOS

Spectrograph


Parabola f 444 mm, ø 75 mm, Edmund OpticsCollimator beam F/18Pupil 25 mmÉchelle 79 li/mm 63º 25 50 9, ThorlabsX-disperser 200 li/mm 10º 58 58 10, NewportObjective f 200 F/2.8, CanonCCD Atik 11000 4008 2672 9 µm (24 35)

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Fibre link


Telescope1.2 m at F/10Plate scale: 58.2 µm/arcsecPinhole: 150 µm = 2.6 arcsec

Fibre 50 µm and 20 m long, Polymicro FBPInput lens GRIN f = 450 µm, L = 1 mm,

ø 0.5 mm, GrinTechConversion beam F/10 to F/3 in fibreOutput lens Doublet f = 5 mm, ø 3 mm, Linos“Slit” ø 308 µm at F/18

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Beam injection


s

f = 450um f '

φ

F/10 tel

F/3 fib Telescope pupil 45 umTelescope Image (Star 150 um)

F F '

50 um

We have use the principle to projectthe telescope pupil on the fibre input end

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Wavelength (nm)

20 m

FBP FVP

Fibre transmission (internal) in 20 m. FLECHAS uses the FBP type

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Fibre Head


motorized 45ºmirror forTh-Ar lamp

micro-lens in front of fibre

200 µm Ni pinhole in front of micro-lens

pinhole viewer

95ºsolenoid

fibre input explosion

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Output Beam


Fibre 50um

F/3F/18

308 um spot41 mm

f 5 mm

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This fibre link for a 30 cm Telescope


Best match F/10 telescopePlate scale 14.5 µm/arcsecSky aperture 10.3 arcsec ! (150 µm pinhole)

F/3 in fibre: good FRD100 µm pinhole => 6.9 arcsec, but the aperture into

the fibre falls to F/4.5. The FRD isat the limit of acceptance

Increasing resolution? The output spot is 308 µm.Need of an image slicer!

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Steps to integration and alignment


Setup of the 9º angle between collimator and ÉchelleSetup of the fibre-parabola optical axisAlignment of parabola with respect to the optical axisInstallation of auto-collimator mirrorFinding the parabola focusAlignment of the output fibre endAlignment of the ÉchelleAlignment of the objective and cameraAlignment of the cross-disperserInstallation of the enclosureExample of spectra and calibration data reduction

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Set up of the optical table


300 mm

600 mm lower cover

posts

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Definition of the 9º angle between collimator and Échelle


the other side of theruler set 9º

one side of ruler parallel to breadboard

9º

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Alignment of parabola by auto-collimation


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Definition of the parabola optical axis with a laser


axis 55mm above breadboard

adjust height of parabola with a paper

mask and a hole in center

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Alignment of parabola


adjust center of parabola in “x-y” untillaser beam returns.

tilt parabola in y untillaser beam returns

…then clamp parabola to base

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Installation of auto-collimator mirror


set a flat mirror with a hole,

in front of parabola

with the help of anothersmall flat mirror

tilt thebig flat mirror

until laser returns

flat mirror faces nowparabola in auto-collimation

laser can nowbe removed

set a test fibre ~ in focusof parabola: 444mm

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Finding the parabola focus


inject laser in fibre. The outputis projected to the parabola

The collimated beam is projectedto the flat mirror, backto parabola, then

back to fibre. Focus is locatedwhere input and output coincide.

To ease the focusing processreduce the parabola with a

paper mask with two windows.

the projected laser beam will be

only reflected in these windows

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Finding the parabola focus


laser beam is collimated byparabola

the beam is reflected in flat mirror

and un-do its way back

parabola focus is located when

both returned images coincide in space with the output fibre

test fibre is now in parabola focus

we can also remove flat mirror

CAOS

Alignment of the output fibre end


set a microscope with reticule infront of test fibre

Locate output fibre position.

center and focus in reticule theimage of the output fibre

do not touch or move the fibre!!

adjust position and focus with the microscope only!!

remove test fibre. Do not touch microscope anymore!!

set final output fibre in front ofthe microscope.

Slide fibre output in its supportuntil image focuses in rotation center (white screen).

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Alignment of the output fibre end


the fibre support permits rotation In two axis...

to center a laser beam projectedby output fibre (F/#=18.5)

to be centered off-axis in left window of parabola

now clamp the fibre to thebread-board

CAOS

Alignment of the Échelle


install the echelle support nextto fibre output.

Be careful not vignettingfibre output!!

center collimated laser beamin the inclined echelle surface

use echelle to mark the secondaxis parallel to bread-board

rotate echelle until laser beam isprojected against a paper screen

adjust rotation until projectionis parallel to bread-board

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Alignment of the objective and camera


fix a paper mask to the capof the objective

center laser projection on the objective

slide back until camera is left outside enclosure

Be careful not vignetting the collimated beam from parabola!

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Alignment of the cross-disperser


set x-disperser between echelleand objective

slide it untilbeam projectsin center of objective

Slide x-disperser just beforevignetting collimated beam from parabola

remove paper masksfrom parabola and

objective

tight clamps from all components!

alignment is now completed!

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Centring, rotation and focus of the spectrum


A

AB

B

C

C

BC Focus

Focus

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Installation of the enclosure


enclosure is reinforced insidewith neoprene stripes to prevent/reduce light pollution

cuts in enclosure are also covered with neoprene.

with a cut forCCDcamera

and a cut forthe fibre

enclosure is mountedapart

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Handles to take it away !


enclosure is nowcompleted!! attach handles

remove posts with rubber feet

Ready!

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Wavelength calibration


With MIDAS (also available in Windows with Cygwin)Based in “SET CONTEXT/ECHELLE”Requires:

Spectrum of a halogen lamp for order identificationSpectrum of a thorium-argon lamp for line identificationAn Atlas of a Thorium-Argon spectrum 400-900nm

Provides:Semi-automatic calibration: Two pair of lines are identified by hand, 1300 lines automaticallyResolving Power (R=λ/Δλ) calculated in 1000 lines Order by order calibration andit merges all orders in one continued spectrum

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Orientation


RED

REDBLUE

BLUE

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Spectrum repetition


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Identifying orientation


RED

BLUE

BLUE?RED?

RED

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Identifying orientation


BLUE RED

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Calibration data:


Spectrum of an halogen lamp:

Spectrum of a thorium-argon lamp:

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Order identification


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Th-Ar. how many lines?


~2000!

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First, manual line identification:


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Then, automatic line identification:


~1300 lines identified!

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Tolerance in the identification


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Resolving Power (R=λ/Δλ)


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Spectrum of the Sun order by order


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Merged spectrum of the Sun


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Detailed spectrum of the Sun


Natrium doublet

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Optical efficiency


Fibre link 60 %Parabola 90 %Échelle 50 % (including vignetting)X-disperser 78 %Canon objective 90 %

Total 19 %

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Optical efficiency


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Canon 200mm F/2.8 EF

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Optical efficiency


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X-disperser Newport

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Improvements


Image slicer to increase resolution (x1.8)CCD camera with higher QE (QSI?)Mechanical improvements

Échelle support with tiltFibre support with height adjustmentSmaller and light tightness enclosure

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Image slicer


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Image slicer

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Alignment verification after transport


The alignment tool set a set a paper maskto parabola with

a tiny hole in center

inject a laser through inclinedtool holes

when aligned, the reflected laser should always hit the same reference point.

when aligned, the laser should hit the parabola in its center

CAOS

Alignment verification after transport


fix a flat mirror in its support.It has been previously alignedfor auto-collimation

Inject laser In fibre.

beam returns byauto-collimation

alignment is correctif beam returns in same output

CAOS

Mechanical parts


echelle

CAOS


Thank you for your patience and attention !

CAOS web page:

spectroscopy.wordpress.com

ASTELCO web page:

http://www.astelco.com/

integration and alignment of flechas - wordpress.cominstall the echelle support next. to fibre...

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