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Wollongong to Ann Arbor Presentation scheduled start time: Ann Arbor - - PowerPoint PPT Presentation

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Wollongong to Ann Arbor Presentation scheduled start time: Ann Arbor 11 am EDT, Thursday, July 15, 2010 Wollongong 1 am EST, Friday, July 16, 2010 University of Wollongong Australia The nature of terahertz emission from GaAsBi Roger

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SLIDE 1

Australia University of Wollongong

Wollongong to Ann Arbor

Presentation scheduled start time: Ann Arbor 11 am EDT, Thursday, July 15, 2010 Wollongong 1 am EST, Friday, July 16, 2010

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SLIDE 2

The nature of terahertz emission from GaAsBi

Roger Lewis

Institute for Superconducting and Electronic Materials, University of Wollongong, Australia

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SLIDE 3

University of Wollongong Australia

THz: seeing the unseen

pyro bolo

Fluorescent marker pen: lid on

Cameron Lee 2009

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SLIDE 4

University of Wollongong Australia

pyro pyro

Bubble wrap: one bubble with water

THz: seeing the unseen

Cameron Lee 2009

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SLIDE 5

University of Wollongong Australia

THz: seeing the unseen

pyro

Eye does not see through lid Eye sees through water invisible invisible

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SLIDE 6

700 nm 428 THz 400 nm 749 THz

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SLIDE 7

University of Wollongong Australia

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SLIDE 8

University of Wollongong Australia

Overview of THz @ UOW; 1 of 4

Blackbody radiation

20x10-12 15 10 5 10x1012 8 6 4 2 Frequency (Hz) Blackbody 1000 K 1500 K 2000 K 4 3 2 1 1.0 0.8 0.6 0.4 0.2 0.0 x1015

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SLIDE 9

University of Wollongong Australia

Overview of THz @ UOW; 2 of 4

Far-infrared (THz) laser

120 100 80 60 40 20 10x1012 8 6 4 2 Frequency (Hz)

Lasant CH3OH CH2F2

THz Laser

  • S. Hargreaves and R. A. Lewis

Journal of Materials Science: Materials in Electronics 18, S299 (2007)

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SLIDE 10

University of Wollongong Australia

Overview of THz @ UOW; 3 of 4

Two-colour photomixing

Graphic: Toptica

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SLIDE 11

University of Wollongong Australia

Overview of THz @ UOW; 4 of 4

Graphic: R. Mendis

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SLIDE 12

University of Wollongong Australia

Graphic: A. Lewis

Epump ETHz P

Ultrashort pulses induce polarization

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University of Wollongong Australia

THz generation by ultrashort pulses mechanisms

Optical Rectification (OR) Transient Current (TC) geometry polarization pump-beam power magnetic field temperature bias control

methods

Photoconductivity (PC)

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SLIDE 14

University of Wollongong Australia

Evidence for Transient Currents

400 300 200 100 Photodiode signal (µV) 360 300 240 180 120 60 Magnetic field angle (degrees)

400 300 200 100 0.25 0.20 0.15 0.10 0.05 0.00 Excitation fluence (µJ/cm2)

InP In-plane magnetic field rotates radiating dipole Saturation with excitation fluence

  • carrier screening
  • S. Hargreaves, R. A. Lewis

Applied Physics Letters 93, 242101 (2008)

  • S. Hargreaves, R. A. Lewis

Applied Physics Letters 93, 242101 (2008)

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SLIDE 15

University of Wollongong Australia

Optical Rectification - geometry

Graphic: A. Lewis

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SLIDE 16

University of Wollongong Australia

Optical Rectification - geometry

Graphic: A. Lewis

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SLIDE 17

University of Wollongong Australia

Optical Rectification - geometry

Graphic: A. Lewis

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SLIDE 18

University of Wollongong Australia

Optical Rectification - geometry

Graphic: A. Lewis

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SLIDE 19

University of Wollongong Australia

pyro

Optical Rectification - geometry

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SLIDE 20

University of Wollongong Australia

pyro

Optical Rectification - geometry

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SLIDE 21

University of Wollongong Australia

pyro

GaAs - Optical Rectification

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SLIDE 22

University of Wollongong Australia

pyro

GaAs - Optical Rectification

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SLIDE 23

University of Wollongong Australia

GaBiAs

  • M. Henini et al.

Applied Physics Letters 94, 251909 (2007)

GaBixAs1-x

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University of Wollongong Australia

GaBiAs

Not transient currents

  • K. Radhanpura, S. Hargreaves,
  • R. A. Lewis, M. Henini

Applied Physics Letters 94, 251115 (2009)

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SLIDE 25

University of Wollongong Australia

GaBiAs

Azimuthal angle dependence

  • epilayer

quite different to substrate

  • K. Radhanpura, S. Hargreaves,
  • R. A. Lewis, M. Henini

Applied Physics Letters 94, 251115 (2009)

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SLIDE 26

University of Wollongong Australia

GaBiAs

  • K. Radhanpura, S. Hargreaves,
  • R. A. Lewis, M. Henini

Applied Physics Letters 94, 251115 (2009)

(a) Bulk (b) Surface (c) Sum of bulk and surface Optical Rectification (a) (b) (c)

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SLIDE 27

University of Wollongong Australia

Conclusion

Optical rectification produces THz radiation

THz field emitted is in general polarized and depends in detail on

  • angle of incidence of pump beam
  • polarization of pump beam
  • index hkl of crystal face
  • azimuthal angle of sample relative to pump beam

In GaBiAs the THz radiated depends strongly on

  • crystal face hkl
  • bulk optical rectification term
  • surface field-induced optical rectification term

So THz emission acts as a sensitive surface probe