Infrared Sensors and TelescopesInfrared Sensors and Telescopes

Astrophysical Studies from Radio− to Gamma−Ray Energies.

Almudena Arcones Segovia22.11.2002

What is Infrared?

1−5µm near IR5−30µm mid IR30−200µm far IR>350µm submm

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SPECTRAL REGION

WAVELENGTH RANGE (microns)

TEMPERATURE RANGE

(degrees Kelvin) WHAT WE SEE

Near−Infrared (0.7−1) to 5 740 to (3,000−

5,200)

Cooler red stars Red giants

Dust is transparent

Mid−Infrared 5 to (25−40) (92.5−140) to 740

Planets, comets and asteroids

Dust warmed by starlight

Protoplanetary disks

Far−Infrared (25−40) to (200−350)

(10.6−18.5) to (92.5−140)

Emission from cold dust

Central regions of galaxies

Very cold molecular clouds

Why is IR important?

� There is dust which hides a lot of things (star−forming regions, remmants of dead stars, galactic center).

� Active galaxies which emit in X−ray but because of the dust they emit in IR.

� The visible light from distant galaxies is shifted till IR.

Visible , near−infrared (2MASS), and mid−infrared (ISO) view of the Horsehead Nebula.

[OIII] 5007A

radio galaxy MRC0406−244

Atmospheric windows

Atmospheric emissions

� OH vibration−rotation bands� O2 IR atmospheric bands� The near−IR nightglow continuum

Background

Early IR astronomy.� 1800 William Herschel discovered IR.� 1856 astronomers used thermocouples to

detect radiation from Moon.� 1948 Moon�s surface is covered with fine

powder.� Early 1900�s IR from Jupiter and Saturn and

from bright stars.� 1960�s new and sensitive IR detectors.

New technology.� 1950�s astronomers started to use lead−

sulphide (PbS) detectors to study IR in the 1 to 4 micron range.

� 1961 development of the germanium bolometer, hundred of times more sensitive than previus detectors and capable of detecting all IR wavelengths.

� 1980�s development of IR array detectors.

Detectors.

There are two classes of detectors used in IR:

� Photon detector

� Thermal detector

The thermal detectors: bolometers.Brass Wires25 m diameter

Ge:Ga Thermistor1mm x 1mm x 1mm

Sapphire Substrate3mm x 3mm x 0.25mm

Indium Solder

120 nm BiAbsorving Film

µ

Stycast 2850FTEpoxy

Photon detectorIntrinsic

Materials:

− Germanium Ge− Lead sulphide PbS− Indium antimonide InSb− Mercury Cadmium Telluride

HgCdTe

applied electric field

conduction band

valence band

E =hc/λg cophotoexcitation

electron

hole

Photon detector Extrinsic

applied electric field

conduction band

valence band

photoexcitation

electron

hole

photoexcitationaceptor level

donor levelEi

Ei

Photon detector. Extrinsic

129:Sb28.8:Sb

119.6:B28.2:B

115:Ga27.6:P

37.6:Zn23.1:As

30.2:Cu18.1:Al

20.7:Cd17.6:Bi

13.8:Hg17.1:Ga

8.27:AuGermanium (Ge)8.0:InSilicon (Si)

λc (µm):ImpurityBase λc (µm):ImpurityBase

IR arrays− basics principles

� Store the electrical charge at the site generation (pixel).

� Transfer the charge on each pixel to a single outlets (multiplaxing task).

� Enable the carges to be moved as a voltage which can then be converted or digitalized into a number for storage in a computer.

Hybrid detector.

� Si is not more sensible to photons λ>1.1µm.

Detector properties:

� Dark current (diffusion, thermal generation−recombination of charge and leak current) and cooling.

� Noise sources

� Quantum efficiency

Quantum efficiency:

<2%mid−IRPtSi

60%near−IRHgCdTe

80%near−IRInSb

QEUse in:Array

Ground based IR observatories.

� They can detect near−IR� Best location is on a high, dry montain� Astronomers can study wavelength centred at 1.25,

1.65, 2.2, 3.5, 4.75, 10.5, 19.5 and 35 µm� IR telescopes are designed to limit the amount of the

thermal emission fom the telescope and the atmosphere that reach the detectors

� Astronomers make measure both the emision from our atmosphere and from the object they are observing

Ground based IR observatories.

� In the mid−1960�s the first IR survey of the sky was made at the Mount Wilson Observatory (PbS detector, 2.2µm, 75% of the sky, 20 000IR sources)

� Partial Ir survey of the southern sky was made in 1948 at the Mount John Observatory in New Zeland

� The largest group of IR telescopes can be found in top of Mauna Kea on the island of Hawaii (1967)

Caltech 2.2 Micron Infared Telescope

Source: Space History

Source: Space History

Mauna Kea

IR astronomy takes off.

� IR detectors have been placed on balloons, rockets and airplanes => longer IR wavelength

� First IR all sky map resulted from a series of rocket flights by the Air Force Cambridge Research Laboratory (HiStar). λ=4, 10, 20 µm and 2363 sources

� 1963, germanium bolometer was attached to a balloon to make IR observations of Mars

IR astronomy takes off.

� 1966, the Goddard Institute of Space sciences used balloons to survey the sky at 100µm

� IR telescopes onboard aircraft such as the Kuiper Airborne Observatory

Far−Infared Spectrometer

Kuiper Airborne Observatory

IR astronomy from Earth�s orbit.

� By 1977, an international collaboration was formed by Netherlands, United States and Great Britain to develop IRAS (the IR Astronomical Satellite)� IRAS was succesfully launched on 25 January

1983� During 10 months scanned more than 96% off sky

four times (12, 25, 60, 100 µm, 350000sources)

� 1989 COBE: far−IR and microwaves

IR astronomy from Earth�s orbit.

� The European Space Agency launched the Infrared Space Observatory (ISO) in November 1995� ISO observed at wavelengths between 2.5 and

240 µm� It took data for about 2.5 year, until its supply of

liquid helium ran out� Contained instrument which measured details of

both shorter and longer wavelength region of IR spectrum, an IR camera which had two IR array and a photometer

IRAS In Orbit − Artist Rendition

Other projects

2MASS − The 2 Micron All Sky Survey (April 1997, March 1998 − 3.5 years) � Description: Highly uniform digital imaging

survey of the entire sky using two ground based telescopes: at Mt. Hopkins, AZ for viewing the northern sky and at Cerro Tololo, Chile for viewing the southern sky.

� Wavelengths: J H and Ks bands centered at 1.25, 1.65 and 2.17 microns.

Other projects

NICMOS − Near Infrared Camera and Multi−Object Spectrometer � Start−Duration: Attached to the Hubble Space

Telescope in February 1997 � Description: An infrared array consisting of 3

cameras and 3 spectrometers. � Goals: Provide spectra and high resolution images

in the near infrared of regions in space. � Wavelengths: 0.8 − 2.5 microns

Other projects

Keck Interferometer � Start−Duration: Began operation in 2000 � Description: The Keck Interferometer

Project will combine the twin Keck Telescopes with four smaller telescopes to form an interferometer which will have the same resolution as a single 85 meter telescope.

� Wavelengths: 1.6 − 10 microns

Other projectsSOFIA − The Stratospheric Observatory For Infrared Astronomy S

� tart−Duration: Scheduled to begin operations in 2004

� Description: SOFIA, a joint project between NASA and the German Space Agency, will be optical/infrared/sub−millimeter telescope mounted in a Boeing 747. Designed as a replacement for the very successful Kuiper Airborne Observatory, SOFIA will be the largest airborne telescope in the world.

� Wavelengths: The entire IR range

Other projectsThe Herschel Space Observatory

� Start−Duration: Launch planned in 2007 − > 3 years � Description: The Herschel Space Observatory is a

proposed European Space Agency infrared−submillimeter mission.

� Goals: The Herschel Space Observatory will perform spectroscopy and photometry over a wide range of infrared wavelengths. It will be used to study galaxy formation, interstellar matter, star formation and the atmospheres of comets and planets. The current plan is to merge Herschel with ESA’s PLANCK, mission.

� Wavelengths: 80 − 670 microns

Other projectsPLANCK

� Start−Duration: Launch planned in 2007 � Description: PLANCK is a proposed

European Space Agency (ESA) far infrared−submillimeter mission.

� Goals: PLANCK will image the anisotropies of the Cosmic Background Radiation over the entire sky with exceptional resolution and sensitivity.

� Wavelengths: 350−10,000 microns

THE END