Transcript FIRST Telescope Peer Review

Bridging the “THz Gap”
John C. Pearson
Jet Propulsion Laboratory, California Institute of Technology
Geoff Blake
California Institute of Technology
Susanna Widicus Weaver
Emory
David Plusquellic
NIST
FarIR Laboratory Workshop 2012
29-31 Oct 2012
What is the THz gap?
The THz gap – The spectral region above where
electronics becomes difficult due to the scale
required to minimize parasitic capacitance and
below where quantum mechanical devices become
small enough to be readily feasible
– Historically ~1-10 THz
The THz gap contains rotational transitions of very
light molecules, fine structure transitions of many
abundant atoms, many large amplitude vibrations,
and the lowest vibrational modes of large
molecules
Sources limit coherent receivers as well
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Bridges
Historical methods of bridging the THz gap
– Laser side band (low power, often no absolute frequency reference,
limited tuning range)
– Tunable Far Infrared Two lamb dip stabilized CO2 lasers mixed with
a microwave source in a Metal Insulator Metal diode (low power,
limited tuning range per pair of laser lines, complex system)
– Photo mixing Two lasers with THz difference, low power limited to
lower part of THz gap. If frequency comb is used as a reference
frequency can be very precise
– Electronic upconversion A.K.A. frequency multiplication currently
limited to 3 THz
– Fourier Transform spectroscopy (limited resolution, low source
brightness, diffraction spillover losses)
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Why do we need a bridge
~Half of Herschel time was devoted to photometery to
determine why stars form
– We now know that the dust is filamentary and that stars form
where filaments join.
– Photometry has thus far been unable to determine what causes
stars to form
 Magnetic fields? Polarization?
 Turbulence? Velocity resolved lines?
 Phase/composition of gas/dust?
 Interaction with the ISM?
– All except polarization requires spectroscopy
 Need strong lines and array receivers
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What is in the THz Gap 1/2
Galaxies:
Strongest Features to 6 THz are fine
structure lines
– CII, OI, NII, NIII, OIII
Strongest molecular lines
– CO, H2O, OH,
Lines that remain to be studied
– CH Ground state 2.01 THz
– HD 2.675 THz
– HeH+ 2.01 THz
– CH2 1.96/2.3 THz
– CH2+ (no lab data)
– FH+
– H2D+ ground state
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What is in the THz Gap 2/2
Above 6 THz
NeIII, NeV, SIII, OIV, SiII
H2 S(0) 28 microns
H2 S(1) 17 microns
Dust peaks near 100 microns
General black body shape
UIR (PAH?) bands peak at 6 microns
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What we can do now 1/2
J=41 aR
Methanol with a multiplier
Can easily find
Log(I(T))=-6.0 in the data
Possible to assign many transitions
vt=2 2810+/- to vt=0 2815+/-
vt=1 E1 K=12-11 Q-branch
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Fourier Transform Spectroscopy
8-1-7-2 v4 s-s l=1 to l=-1
9-4 v4 s l=1 – 8-3 2v2 S
80-73 GS A
29-31 Oct 2012
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FarIR Laboratory Workshop 2012
92 v4 l=-1 A-8-2 v4 l=-1 S
80-73 GS S
95 v4 l=1 S-84 2v2 S
11 2v2 S-100 v4 l=-1
81-2 v4 S l=-1-7
4 v4 l=1 A
85-75 v2 A-S
Long path ~190 Meter synchrotron source FTIR spectrum of NH3
Other Techniques
Geoff Blake – THz time domain Spectroscopy
Susanna Widicus Weaver – High Sensitivity THz Spectroscopy
David Plusquellic – Chirp Pulse THz Spectroscopy
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29-31 Oct 2012