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 determined by thermal diffusion length, which is smaller than 50 nm in typical chem/bio samples excited with nanosecond laser pulses. 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. Plasmonic tip enhancement of light intensity is used to further improve spatial resolution and sensitivity of the technique. We were able to take mid-IR images and vibrational spectra of polymer films as thin as 10 nm with l/170 spatial resolution. The extension of this method to THz spectral range and possible improvements to achieve monolayer sensitivity will also be discussed.
In the second part of the talk, I will present the results of our project aimed to develop broadly-tunable monolithic bandpass filters based on unique properties of long-range surface plasmon-polaritons. A small change of the refractive index of the cladding material in these filters may be translated into a large bandpass wavelength shift. We present experimental results with proof-of-principle devices operating at telecom wavelengths in which 0.004 change of the refractive index of the cladding material is translated into 210 nm bandpass tuning.
Mikhail Belkin received his B.S. degree in Physics and Mathematics from Moscow Institute of Physics and Technology in 1998 and Ph.D. in Physics from the University of California at Berkeley in 2004. From 2004 to 2008 he worked in Federico Capasso's group in the School of Engineering and Applied Sciences at Harvard University, first as a postdoctoral fellow and later as a research associate. He joined the faculty of the University of Texas at Austin in the fall of 2008.
Mikhail Belkin's current research interests include the development of novel quantum cascade lasers, giant optical nonlinearities in semiconductor nanostructures, mid-infrared and THz photonic and plasmonic systems for chemical sensing, and metamaterials in mid-infrared. Several of the recent publications he co-authored have received considerable media coverage, in particular his work on THz semiconductor laser sources based on intra-cavity difference-frequency generation (see MIT Technology Review, Laser Focus World, Science Daily, and others), a millimeter-sized mid-infrared spectrometer for chem/bio sensing (see MIT Technology Review, Photonics Spectra, Science Daily, and others), and THz quantum cascade lasers with record operating temperatures (see Optics.ORG).
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