이경세 교수

A cellular-level study of the pathophysiology is crucial for understanding the mechanisms behind human diseases. Recent advances in quantitative phase imaging (QPI) techniques show promises for the cellular-level understanding of the pathophysiology of diseases. To provide important insight on how the QPI techniques potentially improve the study of cell pathophysiology, here we present the principles of QPI and highlight some of the recent applications of QPI ranging from cell homeostasis to inf

We present a time-multiplexing structured illumination control technique for optical diffraction tomography (ODT). Instead of tilting the angle of illumination, time-multiplexed sinusoidal illumination is exploited using a digital micromirror device (DMD). The present method effectively eliminates unwanted diffracted beams from binary DMD patterns, which deteriorates the image quality of the ODT in the previous binary Lee hologram method. We experimentally show the feasibility and advantage of t

The word 'holography' means a drawing that contains all of the information for light-both amplitude and wavefront. However, because of the insufficient bandwidth of current electronics, the direct measurement of the wavefront of light has not yet been achieved. Though reference-field-assisted interferometric methods have been utilized in numerous applications, introducing a reference field raises several fundamental and practical issues. Here we demonstrate a reference-free holographic image sen

A simple and cost-effective method is presented for quantitative phase imaging. A common-path lateral phase shifting interferometer is realized through attaching a compact filter set to the output port of an existing microscope. The working principles, design criteria, and limitations are also derived and explained. In order to demonstrate the capability and applicability of the method, the optical phase images of a microsphere and individual human red blood cells are measured with high stabilit

Non-resonant lasers exhibit the potential for stable and consistent narrowband light sources. Furthermore, non-resonant lasers do not require well-defined optics, and thus has considerably diversified the available types of laser gain materials including powders, films, and turbid ceramics. Despite these intrinsic advantages, the practical applications of non-resonant lasers have been limited so far, mainly because of their low power efficiency and omnidirectional emission. To overcome these lim

We present synthetic Fourier transform light scattering, a method for measuring extended angle-resolved light scattering (ARLS) from individual microscopic samples. By measuring the light fields scattered from the sample plane and numerically synthesizing them in Fourier space, the angle range of the ARLS patterns is extended up to twice the numerical aperture of the imaging system with unprecedented sensitivity and precision. Extended ARLS patterns of individual microscopic polystyrene beads, h

Rewinding the arrow of time via phase conjugation is an intriguing phenomenon made possible by the wave property of light. Here, we demonstrate the realization of a one-wave optical phase conjugation mirror using a spatial light modulator. An adaptable single-mode filter is created, and a phase-conjugate beam is then prepared by reverse propagation through this filter. Our method is simple, alignment free, and fast while allowing high power throughput in the time-reversed wave, which has not bee

Abstract It has been recently demonstrated that wavefront information can be directly measured using the speckle‐correlation scattering method. The realization of speckle‐correlation scattering requires the use of a diffusive layer; however, it poses technical challenges in characterizing the transmission matrix of the diffusive layer or precisely fabricating an engineered random metasurface. Herein, liquid crystal geometric phase diffusers are exploited for single‐shot reference‐free holographi

Speckle patterns have been utilized in various sensing applications, due to their excellent sensitivity to the states of light, yet the physical interpretation of that very feasibility has remained unclear. How much optical information could be encoded as intensity speckle, and retrieved from it? This work shows that speckle determines the ``coherency matrix'', which contains information about the amplitude, phase, polarization, and coherence properties of incident light, as functions of positio

Owing to its unique penetrating power and high-resolution capability, X-ray imaging has been an irreplaceable tool since its discovery. Despite the significance, the resolution of X-ray imaging has largely been limited by the technical difficulties on X-ray lens making. Various lensless imaging methods have been proposed, but are yet relying on multiple measurements or additional constraints on measurements or samples. Here we present coherent speckle-correlation imaging (CSI) using a designed X

A novel optical holographic technique is presented to simultaneously measure both the real and imaginary components of the complex refractive index (CRI) of a protein solution over a wide visible wavelength range. Quantitative phase imaging was employed to precisely measure the optical field transmitted from a protein solution, from which the CRIs of the protein solution were retrieved using the Fourier light scattering technique. Using this method, we characterized the CRIs of the two dominant

Given the low absorption contrast of X-rays, phase shift has been playing an important role as an alternative source of contrast in X-ray nanoimaging. Numerous phase-measuring techniques have been proposed, most of which, however, are based on significant assumptions or sample translations. In this study, we propose the application of Kramers–Kronig (KK) relations in the spatial domain as a solution to allow the X-ray quantitative phase image to be directly calculated from the measured intensity

High-power fiber lasers are powerful tools used in science, industry, and defense. A major roadblock for further power scaling of single-frequency fiber laser amplifiers is stimulated Brillouin scattering. Efforts have been made to mitigate this nonlinear process, but these were mostly limited to single-mode or few-mode fiber amplifiers, which have good beam quality. Here, we explored a highly multimode fiber amplifier in which stimulated Brillouin scattering was greatly suppressed due to a redu

We show that an intensity speckle can be directly interpreted as the properties of incident light - amplitude, phase, polarization, and coherency over spatial positions. Revisiting the speckle-correlation scattering matrix (SSM) method [Lee and Park, Nat. Comm. 7, 13359 (2016)], we successfully extract the intact information of incident light from an intensity speckle snapshot as the form of coherency matrix. The idea is verified experimentally by introducing the peculiar states of light that ex

In coherent imaging systems, parasitic fringes and concentric patterns could commonly be found due to the unwanted multiple reflections [1]. One fundamental solution for the coherent noise is to use a temporally incoherent light source. However, maintaining the full-field interference fringe contrast using temporally incoherent light is not straightforward for interferometric imaging techniques such as quantitative phase imaging (QPI). Fortunately, several brilliant incoherent QPI techniques hav