Yongjin Shin

Pit and rim formation during laser marking of acrylonitrile butadiene styrene plastic

Pit and rim formation on the acrylonitrile butadiene styrene (ABS) plastic surface was evaluated after it was irradiated by CO2 and Nd:yttrium-aluminum-garnet (YAG) laser beams. Our results show that the thermal effect floor was well observed at the outer wall of the pit with CO2 laser irradiation while it was not the case with Nd:YAG laser irradiation. The volume and depth of the pit formation increase proportionally with laser irradiation energy while there are significant differences in the slope, width, and full width at half maximum of the pit formation with two different types of laser irradiations. This result shows that CO2 laser irradiation leads to a better cooling contraction effect while Nd:YAG laser irradiation induces a better recoil pressure effect during the interaction between ABS plastic and laser beam irradiation. The shape of the laser marking could vary significantly depending on the traveling path of molten plastic during injection molding of ABS plastic. Therefore, the selection of ...

Determination of optimal view angles for quantitative facial image analysis

In quantitative evaluation of facial skin chromophore content using color imaging, several factors such as view angle and facial curvature affect the accuracy of measured values. To determine the influence of view angle and facial curvature on the accuracy of quantitative image analysis, we acquire cross-polarized diffuse reflectance color images of a white-patched mannequin head model and human subjects while varying the angular position of the head with respect to the image acquisition system. With the mannequin head model, the coefficient of variance (CV) is determined to specify an optimal view angle resulting in a relatively uniform light distribution on the region of interest (ROI). Our results indicate that view angle and facial curvature influence the accuracy of the recorded color information and quantitative image analysis. Moreover, there exists an optimal view angle that minimizes the artifacts in color determination resulting from facial curvature. In a specific ROI, the CV is less in smaller regions than in larger regions, and in relatively flat regions. In clinical application, our results suggest that view angle affects the quantitative assessment of port wine stain (PWS) skin erythema, emphasizing the importance of using the optimal view angle to minimize artifacts caused by nonuniform light distribution on the ROI. From these results, we propose that optimal view angles can be identified using the mannequin head model to image specific regions of interest on the face of human subjects.

Analysis of laser engraving image inside crystal and PMMA

Recently techniques for two dimensional (2D) or three dimensional (3D) image engraving inside crystal have been developed utilizing its transparency and high refractive index. However, due to the low tolerance against shock, heaviness and high cost of crystal, poymethyl methacryslate (PMMA) can be an attractive alternative for the laser engraving because PMMA has comparable transparency and refractive index to crystal while it is much easier to process. In this paper, we present the preliminary evaluation of PMMA as laser engraving material, potentially replacing crystal. For the comparative evaluation of crystal and PMMA, we used a 3D Laser Engraving System with a Q-switched 2nd harmonic Nd:YAG laser. Pulse energy and repetition rate of Nd:YAG laser were 26.9 mJ and 50 ~ 60 Hz, respectively to produce dot engravings inside crystal and PMMA. Also, the pulse duration time was less than 10 ns. We observed the size and shape of engraved points inside both material and resulting image formation depending on the distance between points (100 ~ 150 μm) as a function of laser power output. For the surface image comparison, an optical microscopy was used, and the cross sectional views of individual points were scanned every 10 μm using an optical coherence tomography (OCT) system. Our results demonstrate that laser engraving inside PMMA created better defined image formation from pure melting process rather than from cracking process inside crystal. We also present optimal 3D laser engraving conditions for PMMA as an alternative material to improve upon crystals disadvantages.

Optical coherence tomography in material deformation by using short pulse laser irradiation

We demonstrate the feasibility of OCT imaging for the investigation of samples, which are processed by the short pulse laser. The use of short pulse lasers in various material processing have provided the advantages such as a high peak power and a small heat affected zone over conventional methods based on mechanical treatment. However, due to the improper application of the lasers, the unwanted surface or structural deformation of materials and the thermal damages around an irradiation spot can be caused. Thus, the real-time monitoring/evaluation of laser processing performance in-situ is needed to prevent the excessive deformation of the material and to determine optimal processing conditions. As a standard method to investigation of the material processing by using the lasers, the scanning electron microscopy (SEM) or the transmission electron microscopy (TEM) observation of a physically cleaved surface is used although sample damages are given during the cleaving and polishing process. In this paper, we utilized the OCT advantages such as high resolution and non-invasive investigation to evaluate the laser processing performance. OCT images for the deformation monitoring of the ABS plastic present correlation with images obtained from conventional investigation methods. OCT images of the maxillary bone clearly show the difference in the pit formation of the biological sample at different irradiation conditions. We prove the potential of OCT for the evaluation of laser-processed various samples. Integrating OCT system into a laser processing system, we can visualize the effect of laser-based treatments in clinical and industrial fields.

Optical coherence tomography in pulmonary imaging: feasibility study

We suggest that Optical coherence tomography (OCT) is a potential imaging modality capable of assisting diagnosis in pulmonary medicines. OCT can provide extremely high resolution imaging and be performed with flexible fiber-optic bronchoscopy with small diameter endoscopic probes. In this study, animal models of trachea, and lung surface were to investigate utility of OCT in pulmonary. Normal, malignant, and infectious disease animal model samples measured by OCT were compared to standard histologic H&E light microscopic imaging of the same sites.

Investigation of pit formation in multilayer optical storage disks using optical coherence tomography

We propose anovel application of optical coherence tomography (OCT) to monitor pit formation in laser irradiated optical storage materials. A multilayer optical storage recordable compact disk, is composed of multiple layers, each of different structure. Disks were irradiated with a Q-Switched Nd:YAG laser with an energy of 373 mJ. Post-irradiated disks were evaluated by OCT and those images were compared with optical microscopy. Our results indicate that OCT is a useful instrument to investigate pit formation in mulitlayer optical storage disks and might also provide information to optimize optical memory technology.

Application of Optical Coherence Tomography for Functional Film Imaging

We propose the application of high-resolution Optical Coherence Tomography (OCT) in nonbiomedical and biomedical elds. OCT imaging is performed in the biomedical eld for anterior chamber and a tooth, and in the non-biomedical eld for an air-gap imaging, multilayer-thin-lm imaging, and laser-spot-mark monitoring. Our results suggest that OCT is a potential method, with a few microns resolution, for non-destructive investigations in material science and biological research.

The application of optical coherence tomography for monitoring of the laser marking performance

We have demonstrated the utility of optical coherence tomography (OCT) as a nondestructive diagnostic tool to evaluate the laser marking performance. The pit formed at different laser marking conditions was imaged by using conventional scanning electron microscope and OCT. OCT images verified feasibility and potential for monitoring of laser processing.

Spot marking of the multilayer thin films by Nd:YAG laser

We separated the multilayer structure of CD-R(compact disk-recordable) and investigated optimal spot marking conditions and physical and chemical transitions in response to various laser beam energh levels. Spot marking(80 spot size) was produced on the surface of each layer using a Q-switched Nd:YAG laser between 27 mJ and 373mJ. By investigating resulting pit formation with Optical Microscopy(OM) and Optical Coherence Tomography(OCT), we analyzed the formation process of spot marking in the multilayer structure of different chemical composition. The localized heating of the substrate in the multilayer thin film caused the short temporal thermal expansion, and absorbed optical energy between reflective and dye interfaces melted dye and increased the volume. During the cooling phase, formation of pit and surrounding rim can be explained by three distinct processes; effect of surface tension, evaporation by spontaneous temperature increase due to laser energy, and mass flow from the recoil pressure. Our results shows that the spot marking formation process in the multilayer thin film is closely related to the layers` physical, chemical, and optical properties, such as surface tension, melt viscosity, layer thickness, and chemical composition.

Effects of curvature and view angle on quantitative imaging of erythema and melanin content in facial port wine stain skin

In cutaneous vascular laser surgery, hemoglobin and melanin are important skin chromophores that influence treatment of port wine stain (PWS) birthmarks. A potential problem in quantitative chromorphore evaluaton is the error in image analysis associated with a number of factors, including nonuniform illumination and skin curvature. In this study, we used a mannequin head model to investigate how the accuracy of image analysis is influenced by view angle and facial curvature. Our results indicate that view angle and facial curvature affect the accuracy of the recorded color information. From this analysis, we propose that optimal view angles can be determined on an individual patient basis to analyze features on different regions of the face.