Joong-Sung Lee

Fourier-transform terahertz near-field imaging of one-dimensional slit arrays: mapping of electric-field-, magnetic-field-, and Poynting vectors

We present 2D measurements of the full THz electric field behind a sample consisting of multiple slits in a metal foil. Our measurements, which have a sub-wavelength spatial, and a sub-period temporal resolution, reveal electric field lines, electric field vortices and saddle points. From our measurements we are able to reconstruct the magnetic field and, finally, the position and time-dependent Poynting vector which shows the flow of energy behind the sample. Our results show that it is possible to study the flow of light near sub-wavelength plasmonic structures such as slit-arrays and, by implication, other metamaterial samples.

Invisible plasmonic meta-materials through impedance matching to vacuum

We report on perfect transmission in two-dimensional plasmonic matamaterials in the terahertz frequency range, in which zeroth order transmittance becomes essentially unity near specific resonance frequencies. Perfect transmission may occur when the plasmonic metamaterials are perfectly impedance matched to vacuum, which is equivalent to designing an effective dielectric constant around epsilonr = -2. When the effective dielectric constant of the metamaterial is tuned towards epsilonr and the hole coverage is larger than 0.2, strong evanescent field builds up in the near field, making perfect transmission possible.

Dielectric constant engineering with polymethylmethacrylate-graphite metastate composites in the terahertz region

A method for manufacturing terahertz absorber is presented. Varying fractions of graphite powder are mixed with the host poly methylmethacrylate powder and compress molded. The shielding efficiency, together with real and imaginary parts of the dielectric constant, is unambiguously determined by terahertz time domain spectroscopy in the continuous frequency range of 0.1–1.6THz. While the composites are absorptive in most of the frequency range with relatively small reflection, it turns metallic at a high enough graphite fraction of 35.7%: there exists a zero crossing of the real part of dielectric function er(ω) to negative values below 0.22THz. Our method provides an easy-to-control way of manufacturing terahertz absorbers with a wide range of shielding efficiency and low reflectance.

Phonon-induced dynamic resonance energy transfer

In a network of interacting quantum systems, achieving fast coherent energy transfer is a challenging task. While quantum systems are susceptible to a wide range of environmental factors, in many physical settings their interactions with quantized vibrations, or phonons, of a supporting structure are the most prevalent. This leads to noise and decoherence in the network, ultimately impacting the energy-transfer process. In this work, we introduce a novel type of coherent energy-transfer mechanism for quantum systems, where phonon interactions are able to actually enhance the energy transfer. Here, a shared phonon interacts with the systems and dynamically adjusts their resonances, providing remarkable directionality combined with quantum speed-up. We call this mechanism phonon-induced dynamic resonance energy transfer and show that it enables long-range coherent energy transport even in highly disordered systems.

Quantum noise reduction in intensity-sensitive surface-plasmon-resonance sensors

We investigate the use of twin-mode quantum states of light with symmetric statistical features in their photon number for improving intensity-sensitive surface plasmon resonance (SPR) sensors. For this purpose, one of the modes is sent into a prism setup where the Kretschmann configuration is employed as a sensing platform and the analyte to be measured influences the SPR excitation conditions. This influence modifies the output state of light that is subsequently analyzed by an intensity-difference measurement scheme. We show that quantum noise reduction is achieved not only as a result of the sub-Poissonian statistical nature of a single mode, but also as a result of the non-classical correlation of the photon number between the two modes. When combined with the high sensitivity of the SPR sensor, we show that the use of twin-mode quantum states of light notably enhances the estimation precision of the refractive index of an analyte. With this we are able to identify a clear strategy to further boost the performance of SPR sensors, which are already a mature technology in biochemical and medical sensing applications.

Comment on ‘Energy transfer, entanglement and decoherence in a molecular dimer interacting with a phonon bath’

We show that the influence of the shared phonon bath considered in Hossein-Nejad and Scholes (2010 New J. Phys. 12 065045) on the exciton transfer in a two-molecule system can be reproduced by that of an independent bath model.

Terahertz transmission through rectangular apertures: Far- and near-field studies

We report that the terahertz transparency occurs at the fundamental shape resonance of the rectangular holes regardless of the areal coverage. The funneling of energy at the fundamental resonance is also confirmed at the near-field.

Terahertz field mapping of poynting vectors through a one-dimensional grating

We experimentally study Poynting vector flows when terahertz waves transmit through a multiple slit arrays. Our methods provide a new way of visualizing energy flows and determining different diffraction orders in the near-field.

Terahertz inverse-Fourier transform image synthesis

Starting from terahertz time-domain spectroscopy, we obtain electric field vector images at each frequency component. We then synthesize images for diffraction from a single slit for an arbitrary incident waveform by inverse Fourier-transformation.

Transmission Resonances by Combined Effects of Fabry-Perot and Surface Plasmons in the THz Region of Metallic Gratings

To study transmission resonances in periodic metal arrays of slits, we used the THz time domain spectroscopy system wih high power THz sources. The resonance peaks of zero-order transmission spectra are attributed to the combined effects of Fabry -Perot and surface plasmon resonances. Fabry-Perot effect enhances the transmission when two resonances cross but does not alter the surface plasmon peak positions. These results are in agreement with theoretical calculations.