We study ultrafast phenomena in materials and devices using a femtosecond laser source. The materials we are currently investigating include semiconductors, nanostructures, and organic materials. By probing transient processes over femtosecond, picosecond and nanosecond time scales, we gain further insight into the fundamental nature of such material systems.

The front-end of the ultrafast laser source consists of a Kerr-lens mode-locked Ti:sapphire oscillator producing 30 fs-wide pulses at a wavelength of 800 nm. These pulses can be used directly in pump-probe experiments, but for the most part they are used to seed a 1 kHz multipass Ti:sapphire amplifier system which generates ultra-short pulses with energies of about 0.7 mJ per pulse.[ Laser source photo][ amplifier system photo]. An optical parametric amplifier ( OPA) and difference frequency generator (DFG) provide short pulses in the wavelength range from 0.5 to 18 microns. A terahertz pulse source (see next paragraph) is also powered by the Ti:sapphire amplifier system. (A schematic of the laser source is shown below.)

OUR LAB IS NOW LOCATED IN THE BRAND NEW CCIS PHASE I BUILDING (Centennial Centre for Interdisciplinary Sciences). [ Take a look!] (Photo taken in August 2006 while we were still setting things up.) More recent photo: [ Lab photo from Spring 2007]

One of the main experimental techniques used in the lab is time-resolved terahertz pulse spectroscopy. Terahertz (THz) pulses are sub-picosecond, single-cycle, electromagnetic transients with a broad frequency spectrum centered in the terahertz (far-infrared) region and extending from about 0.1 to 3 THz. The amplitude and phase of the electric field in this freely propagating terahertz pulse can be detected coherently. Taking the Fourier transform of the time-domain waveform provides information on the complex far-infrared optical properties of materials over a broad range of frequencies. This technique, therefore, provides both spectroscopic information in the far-infrared as well as sub-picosecond time resolution of transient processes in materials. The lab is also equipped with a low-temperature optical cryostat for transmission and reflection studies down to 2 K. (A schematic of the THz pulse setup is shown below.)

We are also measuring the third-order nonlinear optical properties of organic materials using time-resolved optical Kerr effect (OKE) techniques. This technique allows us to study fundamental structure/property relationships in organic molecules, but it can also be used to study nonlinear optical effects in other material systems (i.e. chalcogenides). The work on organics is being done in collaboration with Dr. Rik Tykwinski in the Department of Chemistry at the University of Alberta (Tykwinski group).

The new Ultrafast Nanotools Laboratory (CFI NIF) is currently under development in CCIS Phase I, and will house a brand new ultrafast laser source, UHV-STM, and near-field scanning optical microscope (NSOM).

• Ultrafast spectroscopy of materials and devices.
• Photophysics and transient photoconductivity in organic molecular crystals and thin films measured by time-resolved terahertz pulse spectroscopy (TRTS - a non-contact technique). These studies address fundamental issues regarding the nature of photoexcitations and carrier transport in organic semiconductors over sub-picosecond to nanosecond time scales.
• Ultrafast carrier dynamics in semiconductor nanostructures measured by time-resolved terahertz pulse spectroscopy (TRTS). This technique allows us to investigate mobile carrier dynamics and capture times with sub-picosecond time resolution and over a temperature range from 5 K to 300 K. We are currently studying carrier dynamics in semiconductor nanowires and quantum dots. (Supported by CIPI) We are also studying the nature of terahertz conductivity in nanomaterials such as silicon nanocrystal thin films.
• Nonlinear optical properties of organic materials using ultrafast Kerr gate techniques (DOKE: differential optical Kerr effect). Exploring structure-property relationships provides insight into the nature of nonlinear optical processes in organic materials. Understanding these properties may lead to the use of organic materials in ultrafast all-optical switching applications or enhanced two-photon absorption materials.
• Time-resolved studies of the photoresponse of fast photodetectors (i.e. novel detector structues, MSM photodiodes, organic photodetectors).
• Terahertz time-domain spectroscopy (THz-TDS) of nanomaterials.
• Terahertz imaging, extreme terahertz sources and applications.

• D. G. Cooke, F. A. Hegmann, Yu. I. Mazur, Zh. M. Wang, W. Black, H. Wen, G. J. Salamo, T. D. Mishima, G. D. Lian, and M. B. Johnson, “Ultrafast carrier capture dynamics in InGaAs/GaAs quantum wires”, J. Appl. Phys. 103, 023710 (2008).[ PDF]
• F. Blanchard, L. Razzari, H.-C. Bandulet, G. Sharma, R. Morandotti, J.-C. Kieffer, T. Ozaki, M. Reid, H. F. Tiedje, H. K. Haugen, and F. A. Hegmann, “Generation of 1.5 micro-Joule single-cycle terahertz pulses by optical rectification from a large aperture ZnTe crystal”, Optics Express 20, 13212 (2007).[ PDF]
• M. Walther, D. G. Cooke, C. Sherstan, M. Hajar, M. R. Freeman, and F. A. Hegmann, “Terahertz conductivity of thin gold films at the metal-insulator percolation transition”, Phys. Rev. B 76, 125408 (2007).[ PDF]
• D. G. Cooke, A. N. MacDonald, A. Hryciw, A. Meldrum, J. Wang, Q. Li, and F. A. Hegmann, “Ultrafast terahertz conductivity of photoexcited nanocrystalline silicon”, J. Mater. Sci.: Mater. Electron. DOI 10.1007/s10854-007-9248-y, (2007).[ PDF]
• O. Ostroverkhova, D. G. Cooke, F. A. Hegmann, R. R. Tykwinski, S. R. Parkin, and J. E. Anthony, "Anisotropy of transient photoconductivity in functionalized pentacene single crystals", Appl. Phys. Lett. 89, 192113 (2006).[ PDF]
• A. D. Slepkov, F. A. Hegmann, R. R. Tykwinski, K. Kamada, K. Ohta, J. A. Marsden, E. L. Spitler, J. J. Miller, and M. M. Haley, "Two-photon absorption in two-dimensional conjugated quadrupolar chromophores", Opt. Lett. 31, 3315 (2006).[ PDF]
• D. G. Cooke, F. A. Hegmann, E. C. Young, and T. Tiedje, "Electron mobility in dilute GaAs bismide and nitride alloys measured by time-resolved terahertz spectroscopy", Appl. Phys. Lett. 89, 122103 (2006).[ PDF]
• D. G. Cooke, A. N. MacDonald, A. Hryciw, J. Wang, Q. Li, A. Meldrum, and F. A. Hegmann, "Transient terahertz conductivity in photoexcited silicon nanocrystal films", Phys. Rev. B 73, 193311 (2006).[ PDF]
• O. Ostroverkhova, D. G. Cooke, F. A. Hegmann, J. E. Anthony, V. Podzorov, M. E. Gershenson, O. D. Jurchescu, and T. T. M. Palstra, "Ultrafast carrier dynamics in pentacene, functionalized pentacene, tetracene, and rubrene single crystals", Appl. Phys. Lett. 88, 162101 (2006).[ PDF]
• M. Walther, M. R. Freeman, and F. A. Hegmann, "Metal-wire terahertz time-domain spectroscopy", Appl. Phys. Lett. 87, 261107 (2005).[ PDF]
• M. Walther, G. S. Chambers, Z. Liu, M. R. Freeman, and F. A. Hegmann, "Emission and detection of terahertz pulses from a metal-tip antenna", J. Opt. Soc. Am. B 22, 2357 (2005).[ PDF]
• O. Ostroverkhova, S. Shcherbyna, D. G. Cooke, R. F. Egerton, F. A. Hegmann, R. R. Tykwinski, S. R. Parkin, and J. E. Anthony, "Optical and transient photoconductive properties of pentacene and functionalized pentacene thin films: Dependence on film morphology", J. Appl. Phys. 98, 033701 (2005).[ PDF]
• O. Ostroverkhova, D. G. Cooke, S. Shcherbyna, R. F. Egerton, F. A. Hegmann, R. R. Tykwinski, and J. E. Anthony, "Bandlike transport in pentacene and functionalized pentacene thin films revealed by transient photoconductivity measurements", Phys. Rev. B 71, 035204 (2005).[ PDF]
• D. G. Cooke, F. A. Hegmann, Yu. I. Mazur, W. Q. Ma, X. Wang, Z. M. Wang, G. J. Salamo, M. Xiao, T. D. Mishima, and M. B. Johnson, "Anisotropic photoconductivity of InGaAs quantum dot chains measured by terahertz pulse spectroscopy", Appl. Phys. Lett. 85, 3839 (2004).[ PDF]
• Aaron D. Slepkov, Frank A. Hegmann, Sara Eisler, Erin Elliott, and Rik R. Tykwinski, "The surprising nonlinear optical properties of conjugated polyyne oligomers", J. Chem. Phys. (Communications) 120, 6807 (2004).[ PDF]
• F. A. Hegmann, "Ultrafast carrier dynamics in conjugated polymers and organic molecular crystals", Physics in Canada 59, 127 (2003). (Special issue on Polymer Physics, March/April 2003).[ PDF]
• K. P. H. Lui and F. A. Hegmann, "Fluence and temperature dependent studies of carrier dynamics in radiation-damaged silicon-on-sapphire and amorphous silicon", J. Appl. Phys. 93, 9012 (2003).[ PDF]
• F. A. Hegmann, R. R. Tykwinski, K. P. H. Lui, J. E. Bullock, and J. E. Anthony, "Picosecond transient photoconductivity in functionalized pentacene molecular crystals probed by terahertz pulse spectroscopy", Phys. Rev. Lett. 89, 227403 (2002).[ PDF]
• Aaron D. Slepkov, Frank A. Hegmann, Yuming Zhao, Rik R. Tykwinski, and Kenji Kamada, "Ultrafast optical Kerr effect measurements of third-order nonlinearities in cross-conjugated iso-polydiacetylene oligomers", J. Chem. Phys. 116, 3834 (2002).[ PDF]
• K. P. H. Lui and F. A. Hegmann, "Ultrafast carrier relaxation in radiation-damaged silicon-on-sapphire studied by optical-pump-terahertz-probe experiments", Appl. Phys. Lett. 78, 3478 (2001).[ PDF]

( Group Photo (from 2004))

• Lyubov Titova
• Fuhai Su

• Jianbo Gao ..............(Ph.D. program, Physics.)
• Zhenyou Wang .........(Ph.D. program, Physics.)
• Tyler Cocker ...........(Ph.D. program, Physics.)
• Dan Lehnherr ..........(Ph.D. program, Chemistry.) (Co-supervised; Supervisor: Dr. Rik Tykwinski, Department of Chemistry)
• Ayesheshim Ayesheshim (M.Sc. program, Physics.)

• Rahma Al Harthy (M.Sc. Student)
• Dr. David Cooke (Ph.D. student)(Currently a postdoctoral researcher in the Department of Communications, Optics, and Materials, Nanophotonics Area, Technical University of Denmark) (David Cooke's web page)
• Dr. Aaron Slepkov (Ph.D. student)(Currently a postdoctoral researcher in the Department of Physics at Cornell University)
• Andrzej Tomalik (M.Sc. student)(Imaging Dynamics, Calgary, AB)
• Dr. Markus Walther (Postdoc)(Currently on faculty in the Department of Molecular and Optical Physics, University of Freiburg, Germany) (Markus Walther's web page)
• Dr. Oksana Ostroverkhova (Postdoc)(Currently an Assistant Professor in the Department of Physics, Oregon State University)
• Dr. Kris Lui

• Devin Baillie
• Alex Janzen
• Graham Hunter
• Eric Epp
• Ian Bushfield
• Sumudu Fernando
• Mohamed Hajar
• Craig Sherstan
• Geoff Chambers
• David Kastelan
• Aaron Levin
• Isaac Fan
• Brad Schultz
• Nathan Woodruff
• Brendan McClure
• Lloyd Barker
• Trevor Chan
• Joseph Ngai
• Iva Cheung
• Jeff Stollery
• Ryan Thompson
• Jason Zawalek
• Tim Brown
• Elizabeth von Hauff
• Eric Pasay
• Radislow Szturo
• Will Green