• Medical Lasers
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• v.8 no.2
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• pp.97-100
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• 2019

Facial pores are a visible topographic feature of skin surfaces and are generally the enlarged openings of pilosebaceous follicles. Enlarged facial pores can be a significant cosmetic problem, particularly for women. Recently, gold nanoshell-mediated photothermal therapy (PTT) has been reported to be effective in treating recurrent acne. The treatment of enlarged facial pores with gold nanoshell-mediated PTT produced excellent results with no side effects. The two cases reported here demonstrate the possibility of gold nanoshell-mediated PTT as a safe and effective treatment for enlarged facial pores.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.3
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• pp.7-13
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• 2007

In the optical module for optical communications, the flip chip bonding is used fer the precise alignment of the optical fiber and optical device. In flip chip bonding, the optical device is aligned and welded while observing the alignment mark of substrate and chip by using flip chip bonder in order to bond the optical device at the exact position. In this research, optical passive alignment method of photodiode(PD) flip chip bonding is suggested for low cost optical subassembly. By using the visible He-Ne laser (633nm wavelength), photodiode is easily aligned with emitting spot on the optical fiber with the help of stereoscopic alignment system. We compensated wavelength dependent deviation about 4m to find out real alignment position of 1550nm input laser by ray tracing. The maximum optical coupling efficiency between the optical fiber and photodiode was about 23.3%.

• Restorative Dentistry and Endodontics
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• v.22 no.1
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• pp.267-277
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• 1997

The purpose of this study was to evaluate the shear bond strength of light-cured glass ionomer cements to dentin surface according to curing time induced by argon laser. In this study, 160 extracted human molars with sound crown were used. The dentin surface of these teeth were exposed with high speed diamond bur under water spray and polished with 120, 320, 400, 800, 1200 grits sand paper. 160 extracted human molars were randomly assigned into four groups (control, experimental 1, 2 & 3) with 40 teeth each. Control group used a visible light curing unit, XL 1000(3M Co., U.S.A) and experimental groups used argon laser($SPECTRUM^{TM}$). And then each group subdivided into two groups (A, B) according to filling materials. Subdivided A group used Fuji II LC(GC Co., Japan), B group used Vitremer(3M Co., U.S.A). The curing units and curing time of each group were as follows : Control group : visible light, 40 seconds Experimental group 1 Experimental group 2 Experimental group 3 : argon laser, 10 seconds : argon laser, 20 seconds : argon laser, 30 seconds The glass ionomer cements were bonded to dentin surface of each specimen. The specimens were stored in 100% relative humidity at 37"c for 7days. And then, the shear bond strength were measured by universal testing machine(Shimatzu Co. Japan) at crosshead speed of 5mm/min and 100kg in full scale and analyzed statistically. The following results were obtained : 1. Experimental group 2-A showed the highest shear bond strength with $9.87{\pm}1.24$ kgf and control group B showed the lowest shear bond strength with $4.08{\pm}0.78$ kgf(P<0.01). 2. The Fuji II LC showed higher shear bond strength with $9.49{\pm}1.24$ kgf than that of the Vitremer with $4.23{\pm}1.24$ kgf. There was significant difference between Fuji II LC and Vitremer(p<0.01). 3. There was no significant differences among experimental groups according to curing time induced by argon laser. 4. There was no significant differences between control group and experimental groups according to curing units.

• Current Optics and Photonics
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• v.2 no.1
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• pp.79-84
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• 2018

We present a novel and simple method to enable spatially selective $ZnAl_2O_4$ nanocrystal formation on the surface of $B_2O_3$-$Al_2O_3$-ZnO-CaO-$K_2O$ glass by employing localized laser heating. Optimized precipitation of glass-ceramics containing nanocrystals doped with $Eu^{3+}$ and $Yb^{3+}$ ions was performed by controlling $CO_2$ laser power and scan speed. Micro-x-ray diffraction and transmission electron microscopy revealed the mean size and morphology of nanocrystals, and energy dispersive x-ray spectroscopy showed the lateral distribution of elements in the imaged area. Laser power and scan speed controled annealing temperature for crystalization in the range of 1.4-1.8 W and 0.01-0.3 mm/s, and changed the size of nanocrystals and distribution of dopant ions. We also report more than 20 times enhanced downshift visible emission under ultraviolet excitation, and 3 times increased upconversion emission from $Eu^{3+}$ ions assisted by efficient sensitizer $Yb^{3+}$ ions in nanocrystals under 980 nm excitation. The confocal microscope revealed the depth profile of $Eu^{3+}$ ions by showing their emission intensity variation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.4A
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• pp.219-226
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• 2012

We investigated the performance of a visible light communication (VLC) transceiver applicable to both of illumination and wireless communication. we considered the visibility of VLC, the easy connection for wireless communication and high-speed transmission and implemented VLC transceiver based on edge-emitting laser diode and silicon photodiode. The proposed VLC transceiver is designated to operate in a full duplex mode at high speed of 120 Mbit/s. The shielding method that is employed as a means to reduce the light cross coupling effect inside the VLC transceiver is proposed and its performance is experimentally measured. We also applied optical antenna to have the larger angle of field of view (FOV) to novel structure of VLC transceiver and examined and analyzed their bit error rate performance, photometric result with respect to the transmission distance, the coverage range and the tilt degree as transmission link characteristic between two transceivers without optical antenna and with optical antenna.

• Journal of the korean academy of Pediatric Dentistry
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• v.27 no.1
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• pp.161-168
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• 2000

The purpose of this study was to develop a practical caries activity test using laser fluorescence. The subjects of study were 30 children of $7\sim10$ years old. Fluorescence from initial carious lesion of teeth illuminated by an argon laser(488nm) was observed through barrier alter. For evaluation of accuracy and propriety of this method fer caries activity test, teeth with initial caries lesion on buccal or labial surface of children was examined with visual inspection and laser fluorescence. Visual examination for the dDfFtT and the $Cariescreen^{(R)}$ test were also done. The results from the present study can be summarized as follows: 1. Laser fluorescence test could differentiate initial caries lesions more easily than visiual inspection. 3. There was highest correlation(= 0.73) between laser fluorescent test and $Cariescreen^{(R)}$ test and. And also apparent correlation(= 0.66) exists between laser fluorescent test and caries experience measured by dDfFtT.

• Laser Solutions
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• v.3 no.1
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• pp.29-37
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• 2000

For a development purpose of thick metal / metal Graded-Boundary Materials(GBM), a basic research on the fabrication of Ni-Cr/steel GBM was carried out by a laser beam and its mechanical properties and thermal characteristics were investigated. In order to produce a compositionally graded boundary region between substrate steel and added Ni-Cr alloy, a series of surface alloying treatments was performed with a high power CO$_2$ laser beam. Ni-Cr sheet was placed on a low carbon steel plate(0.18%C), and then a CO$_2$ laser beam was irradiated on the surface to produce a homogeneous alloyed layer. On this first surface-alloyed layer, another Ni-Cr sheet was placed and then the CO$_2$ laser beam was irradiated again to produce second surface-alloyed layer. Sequential repetitions of laser surface alloying treatment 4 times resulted in a graded-boundary region with the thickness of about 1.4mm. Simultaneous concentration profiles of different kinds of alloying elements(Ni and Cr) showed from 42%Ni, 45%Cr and 13%Fe on surface region to 0%Ni, 0%Cr and 99%Fe in substrate region. Also a thermal conductivity gradient resulted in graded-region and its value changed from 0.03㎈/cm s$\^{C}$ in surface region to 0.1㎈/cm s$\^{C}$ in substrate region. Microstructural observation showed that any visible root porosities and solidification shrinkage cracks were not formed in graded region between alloyed layer and substrate region during rapid cooling.

• Laser Solutions
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• v.14 no.2
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• pp.17-23
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• 2011

Active thin films are ubiquitous in the manufacture of all forms of flat panel display (FPD). One of the most widely employed thin films is indium tin oxide (ITO) and metal films used electrically conductive materials in display industries. ITO is widely used for fabrication of LCD, OLED device, and many kinds of optical applications because of transparency in visible range and its high conductivity and metal films are also widely employed as electrodes in various electric and display industries. It is important that removing specific area of layer, such as ITO or metal film on substrate, to fabricate and repair electrode in display industries. In this work, we demonstrate efficient selective ablation process to ITO and aluminum film on glass using a femtosecond laser (${\lambda}p=1025nm$) respectively. The femtosecond laser with wavelength of 1025nm, pulse duration of 400fs, and the repetition rate of 100kHz was used for selectively removing ITO and Al on glass in the air. We can successfully remove the ITO and Al films with various pulse energies using a femtosecond laser.

• The korean journal of orthodontics
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• v.16 no.2
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• pp.43-51
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• 1986

The highly accurate laser holographic interferemotry method was used to determine in what way low-magnitude forces during maxillary expansion are transmitted to the entire maxillary complex and its surrounding structures. The experiments were carried out on a dryed human skull which had a perfectly preserved, normally aligned maxillary dental arch and intact alveolar process. The skull was fixed within a constructed metal frame which ensured maximal stability of the object. The optical equipment and the object were mounted on antivibration table. Interferograms were taken on the lateral and frontal sides of the maxillary complex, using the 10mW He-Ne laser and the double-exposure method. Analysis of the fringe pattern on the recorded object surface was performed by graphically determining the deformation curves related to the bony surface in selected horizontal and vertical planes. On the basis of this study, the following conclusions can be drawn: 1. The density of the interference fringes was gradually increased with the degree of expansion force. 2. Mechanical reactions on the maxillary complex, circummaxillary sutures, and surrounding bones were clearly visible, even with the lowest loading degree. 3. The amount of bone displacement was greater in application of the force after $90^{\circ}$ turn than in initial application of the same force. 4. The direction of interference fringes on the bony surface was similar at all loading degrees.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.5 s.182
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• pp.190-196
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• 2006

Transparent materials are widely used in the fields of optic parts and bio industry. We have experiment to find out the characteristics of the micromachining inside transparent materials using femtosecond laser pulses. With its non-linear effects by very high peak intensity, filament (plasma channel) was formed by the cause of the self-focusing and the self-defocusing. Physical damage could be found when the intensity is high enough to give rise to the thermal stress or evaporation. At the vicinity of the power which makes the visible damage or modification, the structural modification occurs with the slow scanning speed. According to the polarization direction to the scanning direction, the filament quality is quite different. There is a good quality when the polarization direction is parallel to the scanning direction. For fine filament, we could suggest the conditions of the high numerical aperture lens, the short shift of focusing point, the low scanning speed and the low power below 20 mW. As the examples of optics parts, we fabricated the fresnel zone plate with the $225{\mu}m$ diameter and Y-bend optical wave guide with the $5{\mu}m$ width.