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Yoo, Hongki,Song, Incheon,Kim, Taehoon,Gweon, Dae-Gab IOP Pub 2007 Measurement science & technology Vol.18 No.8
<P>We present a simple method to improve the lateral resolution of stimulated emission depletion microscopy. In stimulated emission depletion microscopy, a saturated zero-centred spot is usually used to achieve a high lateral resolution. Using a half-coated phase plate, a zero-centred spot was made with a narrow and steep gap at the centre. Numerical and experimental results show that by simply inserting a central obstacle as a pupil filter, it is possible to reduce the central gap of the zero-centred spot. Thus we can get a higher lateral resolution, although this sacrifices light efficiency.</P>
Hongki Yoo,Seungwoo Lee,Dongkyun Kang,Taejoong Kim,Daegab Gweon,Sukwon Lee,Kwangsoo Kim 한국정밀공학회 2006 International Journal of Precision Engineering and Vol.7 No.4
Confocal scanning microscopy is a measurement technique used to observe micrometer and sub-micrometer features due to its high resolution, nondestructive properties, and 3D surface profiling capabilities. The design, implementation, and performance test of a confocal scanning microscopy system are presented in this paper. A short-wavelength laser (405 ㎚) and an objective lens with a high numerical aperture (0.95) were used to achieve the desired high resolution, while the x-and y-axis scans were implemented using an acousto-optic deflector and galvanomirror, respectively. An objective lens with a piezo-actuator was used to scan the z-axis. A spatial resolution of less than 138 ㎚ was achieved, along with successful 3D surface reconstructions.
Kim, Hongki,Lee, Yoon Ho,Lyu, Taecheon,Yoo, Jong Heun,Park, Taiho,Oh, Joon Hak The Royal Society of Chemistry 2018 Journal of materials chemistry. A, Materials for e Vol.6 No.37
<P>The poor oxidative stability of tin-based perovskites has been an obstacle to their widespread implementation in high-performance solar cells. Herein, quasi-two-dimensional (quasi-2D) tin-based perovskite solar cells are fabricated with significantly improved performance and stability, by introducing an additional formamidinium thiocyanate (FASCN) additive into quasi-2D tin-based perovskites. The incorporation of the FASCN additive greatly prevents quasi-2D tin-based perovskites from oxidation during film formation, through strong chemical interactions with the tin component (Sn<SUP>2+</SUP>). Moreover, it results in a coarser perovskite grain and a higher degree of crystallinity in the out-of-plane direction, leading to enhanced optoelectronic performance of quasi-2D tin-based perovskites. The best-performing tin-based perovskite solar cell shows an efficiency of 8.17% under reverse scan with a steady-state efficiency of 7.84% at a maximum power point (MPP), while retaining over 90% of its initial efficiency after 1000 hours in a glovebox filled with nitrogen. These results demonstrate a versatile, yet simple methodology that can be applied to other lead-free perovskites suffering from poor oxidative stability.</P>
Fiber-optic raster scanning two-photon endomicroscope using a tubular piezoelectric actuator.
Do, Dukho,Yoo, Hongki,Gweon, Dae-Gab SPIE--the International Society for Optical Engine 2014 Journal of biomedical optics Vol.19 No.6
<P>A nonresonant, fiber-optic raster scanning endomicroscope was developed using a quarter-tubular piezoelectric (PZT) actuator. A fiber lever mechanism was utilized to enhance the small actuation range of the tubular PZT actuator and to increase its field-of-view. Finite element method simulation of the endoscopic probe was conducted for various conditions to maximize its scanning range. After fabricating the probe using a double clad fiber, we obtained two-photon fluorescence images using raster beam scanning of the fiber. The outer diameter of the probe was 3.5 mm and its rigid distal length was 30 mm including a high numerical aperture gradient index lens. These features are sufficient for input into the instrumental channel of a commercial colonoscope or gastroscope to obtain high resolution images in vivo.</P>
Kang DongKyun,Yoo HongKi,Lee SeungWoo,Gweon Dae-Gab Optical Society of Korea 2005 Current Optics and Photonics Vol.9 No.1
In light microscopy, spatial resolution is limited by diffraction effect. Confocal microscopy has improved resolutions in both lateral and axial directions, but these are still limited by diffraction effect. Confocal self-interference microscopy (CSIM) uses interference between two perpendicularly polarized beams to enhance lateral resolution. In previous research, we proposed a calcite plate with its optic-axis perpendicular to the propagation angle and one of the boundary surfaces of the plate. This type of plate is not widely used to our knowledge. In this paper, we change the calcite plate to more common one, which is commercially available. This calcite plate has its optic axis in the plane of incidence. We analyze the characteristics of this calcite plate and numerically compare the performances of CSIM in previous research and CSIM with the commercial calcite plate. Numerical results show improved performance when using the commercial calcite plate
Lee SeungWoo,Kang DongKyun,Yoo HongKi,Kim TaeJoong,Gweon Dae-Gab,Lee Suk-Won,Kim Kwang-Soo Optical Society of Korea 2005 Current Optics and Photonics Vol.9 No.1
We describe the design and the implementation of video-rate reflection confocal scanning microscopy (CSM) using an acousto-optical deflector (AOD) for the fast horizontal scan and a galvanometer mirror (GM) for the slow vertical scan. Design parameters of the optical system are determined for optimal resolution and contrast. The OSLO simulations show that the performances of CSM are not changed with deflection angle and the wavefront errors of the system are less than 0.012λ. To evaluate the performances of designed CSM, we do a series of tests, measuring lateral and axial resolution, real time image acquisition. Due to a higher axial resolution compared with conventional microscopy, CSM can detect the surface of sub-micrometer features. We detect 138㎚ line shape pattern with a video-rate (30 frm/sec). And 10㎚ axial resolution is archived. The lateral resolution of the topographic images will be further enhanced by differential confocal microscopy (DCM) method and computational algorithms.
Spectroscopic optical coherence tomography: A review of concepts and biomedical applications
Nam, Hyeong Soo,Yoo, Hongki Informa UK (TaylorFrancis) 2018 Applied spectroscopy reviews Vol.53 No.2
<P>Optical coherence tomography (OCT) is a 3-dimensional high-resolution imaging modality based on an interferometry and is widely used in a large variety of medical fields. Spectroscopic OCT (S-OCT) is a signal-processing method that uses the raw interferograms generated by OCT to investigate depth-resolved spectroscopic profiles of a sample. The spectroscopic information provided by S-OCT can be used to enhance the contrast of OCT images and overcome the limitations of gray-scale OCT images that describe only morphology. In this review, we present the concepts behind S-OCT as well as acquisition methods and description of obtainable spectroscopic properties. Furthermore, this review covers the biomedical applications of the spectroscopic information that can be obtained with S-OCT, including measurements of hemoglobin concentrations, blood oxygen saturation levels, atherosclerotic plaque detection, evaluation of burn injuries, contrast enhancement using exogenous contrast agents, and detection of precancerous lesions.</P>