Tandem Fabry-Perot Spectrometer

SQUEAN: Spectrometer for QUasar in EArly uNiverse

Presented at

The 2nd Survey Science Group Workshop, High1 Resort on

2012 Feb 14 by

Soojong Pak (Kyung Hee University)

Classification of Spectrome-ters

Types of Dispersing Elements

Mechanism Type Image

refraction Prism Spec.Slit(1D)diffraction,

interference Grating Spec.

reflection,interference

Fourier Transform Spec. Imaging

(2D)Fabry-Perot Spec.

Slit Sp. vs. Imaging Sp.

Imaging Spectrome-ter

W

L

SpatialSpectral

To p V ie w

S id e V iew

d

Slit Spectrometer

DATA Format

Spatial Direction

Spec

tral D

irect

ion

Spatial Direction

Spec

tral D

irect

ion

Spatial Direction

Spat

ial D

irec

tion

Spatial Direction

Imaging Spectrome-ter

Slit Spectrometer

Other Kinds of Imaging Spectrometer: Integral Field Unit

Other Kinds of Imaging Spectrometer:Multi-Object Spectrometer

What is Fabry-Perot Spectrometer?

FinesseRRF

1

Fabry-Perot Parameters

oo md cos2Path Difference

)cos2(sin)1(41

)1(),,,(2

2

2

d

RR

RTI

dI

Profile Instrument

d

m = 1 2 3 ….

Basic Etalon Equations• Conventions

– : Spectral Resolution– We assumed that the incident angle is zero, and the mirror space is in vacuum, – It is convenient to use wave numbers, .– : mirror distance for at order m– : Free Spectral Range in units of wave number– : Corresponding mirror distance for FSR at m– : Full Width at Half Maximum of the instrument profile in units of wavelength– : Corresponding mirror distance for

• Etalon Equations

Simulated Spectra

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.1000 0.1200 0.1400 0.1600 0.1800 0.20001/wavelength [1/um]

Relat

ive In

tensity

10 um 5 um

m=10m=9m=8 m=11 m=12 m=13m=7

FSR

Δ 𝜆𝐹𝑆𝑅=𝜆𝑚+1 −𝜆𝑚=1

2𝑑=𝜆𝑚=

1𝑚 𝜆

Simulated Spectra

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.1000 0.1200 0.1400 0.1600 0.1800 0.20001/wavelength [1/um]

Relat

ive In

tensity

10 um 5 um

Order Sorting Filter

Simulated Spectra

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.1000 0.1200 0.1400 0.1600 0.1800 0.20001/wavelength [1/um]

Relat

ive In

tensity

10 um 5 um

Order Sorting Method of Tandem Fabry-Perot

Telescope

Collimator Camera LensDetector

FP-A(m=20)

FP-B(m=250)

Disadvantage of FPSpatial Direction

Spec

tral D

irect

ion

Spatial Direction

Spec

tral D

irect

ion

Spatial Direction

Spat

ial D

irec

tion

Spatial Direction

Takes Long Time for Wide Spectral Band

Advantage of FPSpatial Direction

Spec

tral D

irect

ion

Spatial Direction

Spec

tral D

irect

ion

Spatial Direction

Spat

ial D

irec

tion

Spatial Direction

Takes Many Targets for Short Spectral Band

Suggested Fabry-Perot Spectrometer

Specifications

• Target Emission Lines at Optical Bands– [OII] 372.7nm– H 486.1nm– [O III] 495.9 500.7nm

– H 656.2 nm– [SII] 671.6 673.1 nm

• Spectral Resolutions– The spectral resolution R = Finesse X m,

where Finesses comes from the FP mirrors reflectivity and the order of interference, m, from the mirrors distance.

– If Finesse=40 and m=50-250, we can expect that R = 2000 – 10000• FOV (in case we use CQUEAN CCD)

– 13 um 1024 X 1024– Total FOV 5 X 5 arcmin with 0.27 arcsec/pixel

Sciences (1/2)

• Emission Lines of Star Forming Regions in the Galaxy (Soojong Pak)

• Emission Lines of Star Forming Regions in the nearby galaxies (Luis Ho suggested)

• Emission Lines of Merging AGNs (Julia Comerford suggested)– Ref. Comerford et al. 2012, ApJ, 753, 42, Kpc-Scale Spatial Offsets in Double-

Peaked Narrow-Line AGN. I– Ref. Liu et al. 2011, ApJ, 737, 101, AGN Pairs from the SDSS. I.

• Narrow Emission Line Survey of Galaxies at z=1.– H_beta 486nm, [OII] 372.7nm– Ref. Glazebrook et al. 2004, AJ, 128, 2652, Cosmic Star Formation History to

z=1 from Narrow Emission Line Selected Tunable Filter Survey

Sciences (2/2)

• Dark Matter in Globular Clusters (Karl Gebhardt)– 1000 Stellar velocities at the edges of the visible clusters in order to constrain the

dark matter distributions.– R=10000 for velocity accuracy of 1 km/s– m_R = 20 – 21 mag

• Chemical Composition Studies in Globular Cluster (Chris Sneden)– a search for (the rare) Li-rich giant stars.  The Li I resonance line is at

6708A– characterizing Na variations in clusters.  One could choose Na D lines,

but probably I would be happier with one of the 5680A doublet lines.– searching for Ba abundance variations.  Probably the 6496A or 6141A

lines are best.– finding out the level of metallicity variations as a function of evolution-

ary state.  One could use one of the Ca IR triplet lines, for example.

2011-02-08 2011 IR Workshop

McDonald Observatory

Otto Struve 2.1m tele-scope

CQUEAN at 2.1m telescope

2011-02-08 2011 IR Workshop

Control PC

Guide CCD field rotator

Guide CCD

Science CCD

Motor for guide CCD field rotator

Filter Wheel

Science CCD Camera (Andor iKon-M 934 BR-

DD)

2011-02-08 2011 IR Workshop

CCD E2V Deep Depletion Chip

Pixels 1024 x 1024, 13μm

Readout Speed

2.5 MHz (0.4 sec)1 MHz (1 sec)50 kHz (20 sec)

QE Better than 25% at 1 μm

Fringe NoneRD Noise

(Measured) 8.1 electrons/pixel

Possible Designs of Tandem Fabry-Perot

FP-A(m=20)

FP-B(m=250)

Serial Configuration of 2 etalons

Integrated Configuration of 3 mirrors

Etalon Specifications for Tandem Fabry-Perot

• Basic Specifications– We use two etalons for high spectral resolution (ET-H) and low spectral resolution

(ET-L). – The ET-L will sort the overlapped orders of ET-H. – We also need broad band filters for the overlapped orders of ET-L. – The mirror sets and housing of ET-H and ET-L are identical. The only difference is

the mirror distances.

• Etalon Specs

Etalon Finesse [nm] m R d [nm]

ET-H 15 650 250 3750 81,250 2.60 325 0.17 21.7

ET-L 15 650 20 300 6,500 32.5 325 2.17 21.7

ET-H 40 650 250 10000 81,250 2.60 325 0.065 8.1

ET-L 40 650 20 800 6,500 32.5 325 0.813 8.1

Fore-Optics Design

• We need collimator units and camera units • before and after the Fabry-Perot.

Telescope

Collimator Camera LensDetector

FP-A(m=150)

FP-B(m=10)

Fore-Optics Design with Traditional Lens System

Example from CQUEAN Focal Reducer

Fore-Optics Design with Off-Axis Mirrors

• We can apply the off-axis mirror design of Dr. Seunghyuk Chang.

The mirrors of a confocal system do not need to have a common axis for a perfect image at the system focus

Eccentric section of an on-axis parent system

Re-imaging Optics for KASINICS(cf. Offner System)

Schwartzschild-Chang Type Telescope

- from "Inverse Cassegrain" -

on-axis(Schwartzschild Type)

off-axis (Schwartzschild-Chang Type)D=50mm, F/D=2 et al. 2011

(Kim, Pak, Chang et al. 2010)

paraboloid

ellipsoid

Off-Axis Design for SQUEAN (by Chang)

Off-Axis Design for SQUEAN (by Chang)

Spot Diagrams

13um

(x,y)

Project Roadmap and Required Re-sources

Work Definition GS Labor[year]

Cost [M KRW] Comments

Etalon Development 3 60Fore-Optics (Off-Axis Mirrors or Lens) 2 30

Telescope Interface and Structure 0.5 10Instrument Operation Software 0.5Data Reduction Software 1 Karl GebhardtTelescope Installation and Commis-sioning 0.5 30

TOTAL 7.5 130

Cost includes HW and Travel.

Appendix

Fabry-Perot Etalon Vendors

• Bristol Instruments– They make the replacement FP mirrors for OLD Burleigh RC series.– The basic price for one set of mirrors starts from $8,000.– The man in the company recommends www.lightmachinery.com for custom-

made etalons.

• LightMachinery.com

Etalon

• LightMachinery.com– They make customized Etalon mirrors.– Piezo Tunable Etalons with clear aperture of 4 mm.– Ian Miller, Director of R&D, gives very kind detailed technical supports.

PZT Tunable Etalon Housing

• ThorLabs.com – Scanning Fabry-Perot Interferometer: SA210-5B

• 535-820 nm, 10 GHz FSR• $2,533• This is for laser, but we can use this for scanning test.

– PZT Drives & Actuator: PE4• Micrometer Travel Range = 4mm with 1 um resolution• PZT Travel Range = 15 um with 10 nm resolution• 3 X $479.60 / unit

– Open-Loop PZT Controllers: MDT693A• 3 Channel • $1,580

– Piezoelectric Actuators• Open Loop Piezo Actuator, 17um/150V: AE0505D16F, $153• Full Bridge Strain Gauge Piezo Actuators, AE0505D16F: PZS001, $175• Strain Gauge Amplification Circuit, AMP002, $161

• www.PhysikInstrumente.com

Coefficient of Thermal Expansion

• Fused Silica – CTE = 0.55 ppm/K

• Invar– CTE = 0-2 ppm/K

• Piezo Material– CTE = 6E-3/K

http://www.piceramic.com/datasheet/Piezo_Material_Datasheet_Cofefficients_Temperature_Measurements.pdf