THz Generation and Nanoscale Chemical Imaging with Quantum Cascade Lasers
Aug 14, 2012
from 11:00 AM to 01:00 PM
|Where||ENGR. IV Bldg., Maxell Rm. 57-124|
|Contact Name||Prof. Ben Williams|
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University of Texas at Austin
In this talk, I will present the results of two of our research projects. I will start with a simple technique for nanoscale mid-infrared spectroscopy that we have developed recently. Subwavelength resolution is achieved by detecting optical absorption through measuring local photothermal expansion with an atomic force microscope (AFM). Spatial resolution is principally determined by the dimension of a high-intensity ‘hot spot’ at the end of a metalized AFM and is below 50 nm. Tunable quantum cascade lasers are used as light sources. To detect minute sample expansions, we moved the repetition rate of the laser pulses in resonance with the AFM cantilever bending frequency and benefited from the resultant resonant enhancement. We were able to take mid-IR images and vibrational spectra of polymer films as thin as 10 nm with l/170 spatial resolution.
In the second part of the talk, I will present the results of our project aimed to develop room-temperature broadly-tunable semiconductor sources based intra-cavity difference-frequency generation (DFG) in dual-wavelength mid-infrared quantum cascade lasers (QCLs) designed to have giant optical nonlinearities. “Cherenkov” phase-matching scheme is used to effectively extract THz radiation along the whole length of the laser waveguide. Our devices provide directional terahertz emission over 1.2-4.5 THz range with over 0.2 mW/W2 mid-infrared-to-terahertz conversion efficiency at room temperature.
Mikhail Belkin received BS degrees in Physics and Mathematics from Moscow Institute of Physics and Technology in 1998 and PhD in Physics in from the University of California at Berkeley in 2004. During his PhD work in the group of Prof. Yuen-Ron Shen, Dr. Belkin has developed a novel method of spectroscopy of chiral media based on sum-frequency generation. He then switched fields from spectroscopy to optoelectronics and joined Prof. Federico Capasso group in the School of Engineering and Applied Sciences at Harvard University where he held a position of a postdoctoral fellow (2004-2006) and a research associate (2006-2008). In Fall 2008, he joined the faculty of the Electrical and Computer Engineering Department of the University of Texas at Austin as an Assistant Professor.
His current research interests include the development of terahertz and mid-infrared quantum cascade lasers, giant optical nonlinearities in semiconductor nanostructures, sub-wavelength resolution microscopy and chem/bio sensing in mid-infrared and terahertz range, and optical metamaterials.
Dr. Belkin’s awards include DARPA Young Faculty Award (2012), NSF CAREER Award (2012), and AFOSR Young Investigator Program Award (2009). He is a local chapter chair of the IEEE Photonics Society and a senior member of the IEEE.