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

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

THz: seeing the unseen Fluorescent marker pen: lid on bolo Cameron Lee 2009 University of Wollongong Australia pyro

THz: seeing the unseen Bubble wrap: one bubble with water pyro Cameron Lee 2009 University of Wollongong Australia pyro

THz: seeing the unseen invisible invisible Eye sees through water Eye does not see through lid University of Wollongong Australia pyro

700 nm 428 THz 400 nm 749 THz

University of Wollongong Australia

Overview of THz @ UOW; 1 of 4 Blackbody radiation 20x10 -12 Blackbody 15 1000 K 1500 K 2000 K 4 10 3 2 5 1 0 0.0 0.2 0.4 0.6 0.8 1.0 x10 15 0 10x10 12 0 2 4 6 8 Frequency (Hz) University of Wollongong Australia

Overview of THz @ UOW; 2 of 4 Far-infrared (THz) laser 120 THz Laser Lasant CH 3 OH 100 CH 2 F 2 80 60 40 20 S. Hargreaves and R. A. Lewis 0 10x10 12 0 2 4 6 8 Journal of Materials Science: Materials in Frequency (Hz) Electronics 18 , S299 (2007) University of Wollongong Australia

Overview of THz @ UOW; 3 of 4 Two-colour photomixing Graphic: Toptica University of Wollongong Australia

Overview of THz @ UOW; 4 of 4 Graphic: R. Mendis University of Wollongong Australia

Ultrashort pulses induce polarization E THz E pump P Graphic: A. Lewis University of Wollongong Australia

THz generation by ultrashort pulses methods mechanisms geometry Photoconductivity (PC) polarization pump-beam power Transient Current (TC) magnetic field temperature Optical Rectification (OR) bias control University of Wollongong Australia

Evidence for Transient Currents 400 In-plane magnetic field InP rotates radiating dipole 300 Saturation Photodiode signal (µV) with excitation fluence 400 - carrier screening 200 300 200 100 100 0 0.00 0.05 0.10 0.15 0.20 0.25 Excitation fluence (µJ/cm 2 ) S. Hargreaves, R. A. Lewis S. Hargreaves, R. A. Lewis 0 Applied Physics Letters Applied Physics Letters 0 60 120 180 240 300 360 93 , 242101 (2008) 93 , 242101 (2008) Magnetic field angle (degrees) University of Wollongong Australia

Optical Rectification - geometry Graphic: A. Lewis University of Wollongong Australia

Optical Rectification - geometry Graphic: A. Lewis University of Wollongong Australia

Optical Rectification - geometry Graphic: A. Lewis University of Wollongong Australia

Optical Rectification - geometry Graphic: A. Lewis University of Wollongong Australia

Optical Rectification - geometry University of Wollongong Australia pyro

Optical Rectification - geometry University of Wollongong Australia pyro

GaAs - Optical Rectification University of Wollongong Australia pyro

GaAs - Optical Rectification University of Wollongong Australia pyro

GaBiAs GaBi x As 1 -x M. Henini et al. Applied Physics Letters 94 , 251909 (2007) University of Wollongong Australia

GaBiAs Not transient currents K. Radhanpura, S. Hargreaves, R. A. Lewis, M. Henini Applied Physics Letters 94 , 251115 (2009) 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) University of Wollongong Australia

GaBiAs (a) (b) (a) Bulk (b) Surface (c) Sum of bulk and surface Optical Rectification (c) K. Radhanpura, S. Hargreaves, R. A. Lewis, M. Henini Applied Physics Letters 94 , 251115 (2009) 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 University of Wollongong Australia