Yonsei University · Engineering
Professor Jae W. Hahn's research lab specializes in advanced photonic and plasmonic materials for stealth technology, sensing, and nanofabrication. The lab focuses on designing multispectral and multiband electromagnetic absorbers, plasmonic resonators, and metasurfaces for infrared stealth and camouflage applications. It also develops cutting-edge optical sensing systems, such as cavity ringdown spectroscopy with novel laser coupling techniques, and explores the fundamental limits of plasmonic lithography for nanoscale patterning. The integration of materials science, nanophotonics, and biomedical applications—particularly in pharmacokinetics under extracorporeal membrane oxygenation—demonstrates the lab’s interdisciplinary approach.
Figures are computed from collected data and may differ slightly.
Abstract Optical stealth technology is being developed to cope with high‐sensitivity infrared image detectors and various guided detectors. Infrared stealth technology has remarkable performance; however, future advancements in multi‐band stealth technology covering the entire optical frequency range, from visible to wide infrared, are key challenges regarding unmanned surveillance systems. Thus, a metal–semiconductor–metal (MSM) metasurface with Fabry–Pérot (F–P) and multiple plasmonic resonant
For the efficient operation of a cavity ringdown spectroscopy (CRDS) system utilized with a continuous-wave (cw) laser, we numerically analyze the coupling efficiency of a cw laser to a ringdown cavity in terms of changes in the scanning rate, the laser linewidth, and the mirror reflectivity. We also demonstrate a new simple design for a CRDS system that can produce a CRDS signal with only a piezoelectric transducer (PZT), without the acousto-optic modulator that is usually adopted to switch off
The impact of ECMO on PK varies among drugs in adult patients, and there is no consistent correlation between the effects observed in adult and infant studies. This review suggested that doses of imipenem, oseltamivir, rifampicin and voriconazole should be adjusted and therapeutic drug monitoring is needed when ECMO is used in adult patients. In the future, large PK trials in adults on ECMO are needed to provide optimal dosing guidelines. A PK/PD modelling approach will be useful for determining
Abstract The multispectral electromagnetic (EM) absorber based on the frequency selective surface (FSS) has been applied with interest in the field of stealth technology due to its ability to avoid detectors or guided weapons at multiple wavelengths simultaneously. The multispectral absorption performance is generally accomplished by stacking different types of FSS absorbers in multiple layers. Herein, a thin and flexible multispectral single‐layer FSS (MSLF) absorber is presented using a micro‐
Selective emitters comprising plasmonic resonators have been exploited for cooling devices or infrared stealth technology. While selective emitters have been designed using odd-order resonances, even-order resonances also emit anisotropic thermal radiation signals. Thermal radiation by even-order resonances in selective emitters can be experimentally detected by thermal imaging cameras, and such thermal emissions often degrade the observability of infrared detectors, rendering them inapplicable
A theoretical model is introduced to evaluate the ultimate resolution of plasmonic lithography using a ridge aperture. The calculated and experimental results of the line array pattern depth are compared for various half pitches. The theoretical analysis predicts that the resolution of plasmonic lithography strongly depends on the ridge gap, achieving values under 1x nm with a ridge gap smaller than 10 nm. A micrometer-scale circular contact probe is fabricated for high speed patterning with hig
Abstract Engineering reflective or thermal signatures is essential in stealth technology for enhancing survivability. For military weapons, infrared (IR) image fusion with reflective and thermal signatures or a laser guidance system has been adopted for detecting enemies. However, the control of reflective and thermal signatures over the entire mid‐IR (MIR) range requires a complex structure. Herein, integrated IR signature (IIRS) management with a multispectral selective absorber (MSA) against
We applied nonlinear interferometry of coherent anti-Stokes Raman spectroscopy (CARS) to measure the nonresonant third-order susceptibilities of various gases. Using argon as an internal calibration standard, we determined the effective nonresonant susceptibilities of acetylene, carbon dioxide, methane, nitrogen, oxygen, propane, carbon monoxide, Freon, and hydrogen from the amplitudes of the interference fringes of the CARS signals generated in the two gas cells. The electronic susceptibility w
To evaluate the uncertainty of concentration measurement using cavity ringdown spectroscopy, we analytically derived expressions for uncertainty for parameters, such as temperature, laser frequency, and ringdown time deviation, from the model equation. The uncertainties that are due to systematic errors in a practical cavity ringdown system were assessed through an experimental study of the PQ(35) transition in an A band of molecular oxygen. We found that, except for the line strength that is re
The reference wavelength method is used for a two-color pyrometer and, with the reference wavelength method, an analytical formula of the ratio temperature for the two-color pyrometer is derived. For one channel of the two-color pyrometer, with a triangular spectral response of 0.1-micro m FWHM and 2.0-micro m peak wavelength, the effective wavelength and the correction factors with several reference wavelengths are determined. By fitting the curves of the effective wavelength and the correction
Current research on multispectral stealth material technology focuses on practical functionalities such as optical transparency, flexibility, and lightweight. Herein, an optically transparent and single‐layer frequency‐selective surface (OTSF) absorber for dual‐band millimeter‐wave (MMW) absorption and low‐infrared (IR) emissivity is proposed. By adopting indium tin oxide and polyethylene terephthalate, the proposed OTSF absorber exhibits good optical transparency (76% transmittance in the 400–8
A Fabry-Perot wavemeter for analyzing a pulsed laser operating in a single longitudinal mode with an injection-seeding technique has been constructed with an array detector. This wavemeter permits the real-time measurement of both the wavelength and the spectral effectiveness of the laser pulse produced at 10 Hz. The performance of the wavemeter is checked with a frequency-stabilized He-Ne laser and a double Nd:YAG laser that operates in the single longitudinal mode. The precision of the wavemet
A new interpolation equation for the calibration of infrared pyrometers was derived by using the reference wavelength method. The errors associated with the new interpolation equation were calculated by comparing the temperature scale based on the interpolation equations with that determined by the fundamental method based on Planck's radiation law. To assess the usefulness of the new interpolation equation, the errors were compared with those associated with the interpolation equation previousl
Open papers in the app to read, cite, and organize with AI.
