Oct 30, 2003 PFIS - Student Wkshop 1

The Prime Focus Imaging Spectrograph – Old

Challenges and New OnesK. Nordsieck, Principal Investigator

Jeff Percival, Eric Burgh, Michael SmithUniv of Wisconsin

Ted Williams, Chuck JosephRutgers University

Darragh O'Donoghue + SAAO• Old Challenges

– What kind of scientific observations?– Big telescope Big instrument optics– Making good use of your observing time

• New Ones– The SALT prime focus– New optics: holography

Oct 30, 2003 PFIS - Student Wkshop 2

Making a Powerful Astronomical Instrument

• Efficiency– Minimize loss in optics

– Extract maximum data

Spectroscopy: composition, motion

Polarimetry: structure, magnetic field

– Observe many objects simultaneously

• Resolution– Spread out colors more

Spectrograph

Spectro-polarimeter

Imager

Imaging

Imaging

High-Speed

High-Speed

Oct 30, 2003 PFIS - Student Wkshop 3

Perseus Cluster of Galaxies

Perseus A in Hydrogen Light

Imaging Spectroscopy

Filters

Fabry-Perot etalons(selects wavelength) M

any

wavele

ngths

Oct 30, 2003 PFIS - Student Wkshop 4

Hubble Deep Field

(South)

Up to 100 Spectra

Slitmasks(selects objects)

Filters

VPH Grating(Splits colors)

Multi-Object Grating Spectroscopy

Oct 30, 2003 PFIS - Student Wkshop 5

Optics Design Challenges

• For highest efficiency: use lenses instead of mirrors

• Need many lenses to correct color aberration CAD

• Wavelength range: require crystals to work into UV

• Lenses need to be very large (up to 25 cm)

• Assembled into large holders with coupling fluid

Sodium Chloride (salt)

Sodium

Chloride (salt)

Fused Quartz

Fused QuartzFused Quartz

Fused Silica

Fused S

ilica

Fused S

ilica

Fused S

ilica

Fused S

ilica

Fused S

ilica

Calcium

Fluoride

Calcium

Fluoride

Calcium

Fluoride

Calcium Fluoride

Calcium Fluoride

Calcium Fluoride

Calcium Fluoride

300 nm UV Blue Green Yellow Red Infrared

400

500

600

700

800

900

WavelengthPFIS range

Col

lim

ator

Camera

Tel

esco

pe F

ocus

Grating

CCD detector

Oct 30, 2003 PFIS - Student Wkshop 6

Collimator

Fused Quartz CaF2 Fused Quartz

Fused Quartz CaF2CaF2

CaF2Fused Silica

(NaCl)

Oct 30, 2003 PFIS - Student Wkshop 7

Camera

CaF2Fused SilicaCaF2

CaF2

Fused SilicaNaCl

(Fused Silica)

(Fused Silica)

(Fused Silica)

Oct 30, 2003 PFIS - Student Wkshop 8

Multi-object Spectroscopy with custom masks

• Laser-cut slit masks

• Unique mask cut for each individual observation

• Slit mask magazine will hold 30 multi-object slit masks

• Reload once/ week

Giant Elliptical Galaxy NGC1399

at focus of telescope:

Mask with slits cut in it to let through selected nebulae in galaxy

Oct 30, 2003 PFIS - Student Wkshop 9

New Challenges: on SALT

Prime FocusTracker

Prime FocusSpectrograph

Motion of tracker and illumination of primary mirror as an object sets

The instrument must be:

Oct 30, 2003 PFIS - Student Wkshop 10

Small and Lightweight

DEIMOS on Keck 3x4m, 9000 kg

PFIS on SALT 1.5x2m, 500 kg

Open space frame welded from hollow square tubes of invar (low- expansion stainless steel)

Oct 30, 2003 PFIS - Student Wkshop 11

StiffCAD 3D model of PFIS structure

FEA ("Finite Element Analysis") showing how it bends under gravity

Plus model of how tracker moves and PFIS optics shows how image moves during exposure

Parallel to Dispersion

0

10

20

-80 -60 -40 -20 0 20

Declination (deg)

mic

ron

s/ t

rack Spec

Perpendicular to Dispersion

0

10

20

-80 -60 -40 -20 0 20

Declination (deg)

mic

ron

s/ t

rack

Spec

Oct 30, 2003 PFIS - Student Wkshop 12

Remote control

Filter Jukebox

Grating Jukebox

Shutter

Slitmask Jukebox

Waveplate Rotator

Etalon Insertors

Camera Articulation

Oct 30, 2003 PFIS - Student Wkshop 13

Compact

New technology:

• Grating "grooves" formed by hologram

• Interference pattern from two laser beams on gelatin film

• Efficient, large, inexpensive custom gratings

Oct 30, 2003 PFIS - Student Wkshop 14

Astronomical Instrumentation is a exciting business. A big demand for:

Astronomers

Physicists

Optical Engineers

Mechanical Engineers

Software Engineers

...........