Dae-Sic Lee

High average-power ultrafast CPA Yb:KYW laser system with dual-slab amplifier

A diode-pumped, ultrafast Yb:KYW laser system utilizing chirped-pulse amplification in a dual-slab regenerative amplifier with spectral shaping of seeding pulse from a master oscillator has been developed. A train of compressed pulses with pulse length of 181 fs, repetition rate up to 200 kHz, and average power exceeding 8 W after compression and pulse picker was achieved.

Automated image analysis in multispectral system for cervical cancer diagnostic

Uterine cervical cancer is the second most common cancer in women worldwide. The accuracy of colposcopy is highly dependent on the physicians individual skills. In expert hands, colposcopy has been reported to have a high sensitivity (96%) and a low specificity (48%) when differentiating abnormal tissues. This leads to a significant interest to activities aimed at the new diagnostic systems and new automatic methods of coloposcopic images analysis development. The presented paper is devoted to developing method based on analyses fluorescents images obtained with different excitation wavelength. The sets of images were obtained in clinic by multispectral colposcope LuxCol. The images for one patient includes: images obtained with white light illumination and with polarized white light; fluorescence image obtained by excitation at wavelength of 360nm, 390nm, 430nm and 390nm with 635 nm laser. Our approach involves images acquisition, image processing, features extraction, selection of the most informative features and the most informative image types, classification and pathology map creation. The result of proposed method is the pathology map — the image of cervix shattered on the areas with the definite diagnosis such as norm, CNI (chronic nonspecific inflammation), CIN(cervical intraepithelial neoplasia). The obtained result on the border CNI/CIN sensitivity is 0.85, the specificity is 0.78. Proposed algorithms gives possibility to obtain correct differential pathology map with probability 0.8. Obtained results and classification task characteristics shown possibility of practical application pathology map based on fluorescents images.

Chaotic stimulated Brillouin scattering near the threshold in a fiber with feedback.

We investigate a nonlinear dynamical behavior of the stimulated Brillouin scattering (SBS) near the threshold in the presence of feedback. When a cw Nd:YAG laser is injected into a single mode optical fiber, the SBS signal exhibits intermittently appearing irregular self-pulsations near the threshold. By examining the time series of the SBS signals, we verify that spontaneous Brillouin scattering having a stochastic property is dramatically suppressed due to the feedback. We explain the chaotic phenomenon of SBS in the presence of feedback in comparison with that in the absence of feedback.

Multispectral autofluorescence imaging for detection of cervical lesions: A preclinical study

The aim of this study was to develop a novel optical imaging system for detecting protoporphyrin IX (PpIX) autofluorescence, to prove that PpIX autofluorescence is as useful as 5‐aminolevulinic acid (5‐ALA)‐induced fluorescence for detecting and localizing cervical cancer, and to monitor the change in PpIX autofluorescence or induced PpIX fluorescence before, during, and after photodynamic therapy (PDT).

Directly diode-pumped femtosecond laser based on an Yb:KYW crystal

Ultrashort pulse laser systems are widely used in many areas such as microprocessing of various materials, the generation of terahertz radiation, nonlinear optics, medical tomography, chemistry, and biology due to the high peak power and large spectral width. For a practical usage of the femtosecond lasers, they must be fairly compact and stable. These conditions are most fully met when laser media are used that allow direct pumping with the radiation from semiconductor injection lasers, which are more compact, reliable, and inexpensive than pumping with solid-state lasers. Since Ytterbium-doped crystals have a broad luminescence band for generating femtosecond pulses less than 500 fs wide, they are attractive as materials for lasers with direct diode pumping. Moreover, the position of the central luminescence wavelength of Yb:KGW and Yb:KYW crystals makes them promising priming sources of femtosecond pulses for amplifiers that operate at wavelengths close to 1 μm (Yb:KGW, Yb-glass, Nd-glass, Yb:YAG, etc.) We developed a femtosecond generator based on the Yb:KYW crystal with direct pumping by the radiation of a laser diode with fiber output of the pump radiation. The use of such pumping, as well as of chirped mirrors to compensate intracavity dispersion, made it possible to generate a continuous sequence of optical pulses 90 fs wide at a frequency of 87.8 MHz with a mean radiation power of more than 1 W. The product of the pulse width by the spectral width is close to the theoretical limit, and this indicates that there is no frequency modulation.

A novel imaging platform for non-invasive screening of abnormal glucose tolerance

Optical measurement of skin auto-fluorescence (SAF), most likely emanating from accumulated advanced glycation end-products (AGEs), has been proposed for the noninvasive diagnosis of glucose intolerance in clinical settings. Here, we developed a novel imaging system with transmission geometry for SAF measurement and compared its diagnostic performance in a Korean population.

Generalized phase synchronization in unidirectionally coupled LD pumped Nd:YAG lasers

We experimentally investigate phase synchronization between two detuned response chaotic laser systems coupled to a slightly different drive oscillator. Our result is that phase synchronization can occur between response laser systems when they are electronically driven by correlated (but not identical) inputs from the drive oscillator. We call this phenomenon generalized phase synchronization and clarify its characteristics using temporal behaviors and phase portraits.