Dr Oleg Mitrofanov

Biography

• Terahertz spectroscopy and near-field imaging
• Devices for THz applications
• Charge trapping phenomena in materials with point defects
• Light-matter interactions
• Contact details:
• Office: Dept of EEE

Research Interests

Current research is focused on the development of optical and THz technologies and application of advanced characterization methods, such as THz near-field imaging and spectroscopy. Studies are directed toward understanding the physics of materials and systems with strong light-matter interactions and development of new devices.

Recent Publications

• B. Bowden, J. A. Harrington, and O. Mitrofanov, Silver/polystyrene-coated hollow glass waveguides for the transmission of terahertz radiation, Opt. Lett. 32, 2945-2947 (2007). [PDF link]

This work describes low-loss waveguides for THz radiation (1-3 THz). Cylindrical hollow metallic waveguides with a thin dielectric coating can be designed to support the HE11 mode. These waveguides showed good mode quality with the total loss below 1 dB/m at 2.5 THz. Low-loss THz waveguides open possibilities for new applications in communications and sensing.

• O. Mitrofanov, D.V. Lang, C. Kloc, M.J. Wikberg, T. Siegrist, W.-Y.  So, M.A. Sergent, and A.P. Ramirez, Oxygen-Related Bandgap State in Single Crystal Rubrene, Phys. Rev. Lett. 97, 166601 (2006). [PDF link]

To understand the impact of molecular structure on electronic properties of organic solids we investigate crystalline rubrene, which exhibits the highest hole mobility among organics. Using photoluminescence spectroscopy with single- and two-photon excitation and charge transport analysis we found that large variations of the carrier density in rubrene is caused by an oxygen-related impurity, which acts as an acceptor state.

• O. Mitrofanov, S. Schmult, M. J. Manfra, T. Siegrist, N. G. Weimann, A. M. Sergent, and R. J. Molnar, High-reflectivity ultraviolet AlGaN/AlGaN distributed Bragg reflectors, Appl. Phys. Lett. 88, 171101 (2006). [PDF link]

Fabrication of high-reflectivity distributed Bragg reflectors for GaN optical devices, such as GaN VCSELs and microcavities, has long been a challenging task due to the in-plane strain caused by a large lattice constant mismatch between GaN and AlN. This work describes AlGaN/GaN DBR structures, where the tensile and compressive strains are compensated in each multilayer period. This approach relaxes constraints on the DBR design. It allowed fabrication of high-reflectivity (>99%) wide stop-band DBRs.

• O. Mitrofanov, Terahertz near-field electro-optic probe based on a microresonator,  Appl. Phys. Lett. 88, 091118 (2006). [PDF link]

High-resolution imaging with THz waves requires near-field methods to overcome the diffraction limit. This work describes a miniature electro-optic probe for THz near-field microscopy. A microresonator structure enhances the sensitivity of the probe allowing THz imaging and local spectroscopy with spatial resolution of several micrometers.

Biography

• Senior Lecturer, Electronic and Electrical Engineering, UCL, 2007-present
• Member of Technical Staff, Bell Laboratories, Murray Hill, NJ, 2001-2007
• Research Student, Bell Laboratories, Murray Hill, NJ, 1998-2001
• Ph. D. Applied Physics, NJIT and Rutgers University, 2001
• M.S. Materials Science, NJIT, 1998
• B.S. Physics, Moscow State University, 1997

Research

Figure 1. High-resolution THz imaging using an integrated near-field probe with a 10μm aperture. Images show E-field ‘snapshots’ near a micro-strip dipole antenna illuminated by a THz pulse (λavg = 600μm). The near-field approach allows imaging and spectroscopic studies on a scale much smaller than the wavelength of THz radiation.

Figure 2. Optical probe for detection of E-field. Using femtosecond optical pulses E-fields with frequencies of several THz can be detected. An electro-optic crystal (GaAs) mounted on a tip of a fibre changes the polarization state of light in the presence of THz field. Electro-optic effect is enhanced when an optical resonator (inset) is placed instead of the bulk crystal. This miniature probe allows local THz spectroscopy and mapping of E-field with spatial resolution of several micrometers.