1 / 9

What is 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. What is the THz gap?.

zulema
Download Presentation

What is the THz gap?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. John C. PearsonJet Propulsion Laboratory, California Institute of TechnologyGeoff BlakeCalifornia Institute of TechnologySusanna Widicus WeaverEmoryDavid PlusquellicNIST

  2. 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

  3. 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)

  4. 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

  5. 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

  6. 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

  7. What we can do now 1/2 Methanol with a multiplier Can easily find Log(I(T))=-6.0 in the data Possible to assign many transitions J=41 aR vt=2 2810+/- to vt=0 2815+/- vt=1 E1 K=12-11 Q-branch

  8. Fourier Transform Spectroscopy • Long path ~190 Meter synchrotron source FTIR spectrum of NH3 8-1-7-2 v4 s-s l=1 to l=-1 95 v4 l=1 S-84 2v2 S 111 2v2 S-100 v4 l=-1 9-4 v4 s l=1 – 8-3 2v2 S 92 v4 l=-1 A-8-2 v4 l=-1 S 8-2 v4 S l=-1-74 v4 l=1 A 85-75 v2 A-S 80-73 GS S 80-73 GS A

  9. Other Techniques • Geoff Blake – THz time domain Spectroscopy • Susanna Widicus Weaver – High Sensitivity THz Spectroscopy • David Plusquellic – Chirp Pulse THz Spectroscopy

More Related