• Laser Solutions
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• v.18 no.4
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• pp.17-22
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• 2015

In this paper, ablation rate of $Al_2O_3$ ceramics by femtosecond laser fluence is derived with experimental method. The automatic three axis linear stage makes laser optics to move with high spatial resolution. With 10 times objective lens, minimal pattern width of $Al_2O_3$ is measured in the focal plane. Ablated surface area is shown as linear tendency increasing number of machining times with various laser power conditions. Machining times is most sensitive condition to control $Al_2O_3$ pattern width. Also, the linear increment of pattern width with laser power change is investigated. In high machining speed, the ablation volume rate is more linear with fluence because pulse overlap is minimized in this condition. Thermal effect to surrounding medium can be minimized and clean laser process without melting zone is possible in high machining speed. Ablation volume rate decelerates as increasing machining times and multiple machining times should be considered to achieve proper ablation width and depth.

• Korean Journal of Optics and Photonics
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• v.16 no.3
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• pp.235-238
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• 2005

A Multiple electron beam lithography system with arrayed microcolumns has been developed for high throughput applications. The small size of the microcolumn opens the possibility for arrayed operation on a scale commensurate. The arrayed microcolumns based on of Single Column Module (SCM) concept has been fabricated and successfully demonstrated. Low energy microcolumn lithography has been operated in the energy range from 250 eV to 300 eV for the generation of nano patterns. Probe beam current at the sample was measured about >1 nA at a total beam current of $0.5\;{\mu}A$ and a working distance of $\~1\;mm$. The magnitude of probe beam current is strong enough for the low energy lithography. The thin layers of PMMA resist have been employed. The results of nano-patterning by low energy microcolumn lithography will be discussed.

• Korean Journal of Optics and Photonics
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• v.12 no.2
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• pp.115-120
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• 2001

In the present study, we described in detail a precise correction method of the copper emission spectra obtained from a highpressure and high-temperature pulsed plasma-jet. The pulsed plasma-jet is initiated from an electro-thermal capillary discharge through a small orifice, and expanded rapidly into an atmosphere. In order to characterize the plasma, fundamental measurements such as the plasma excitation temperature or electron number density are essential. However those spectral lines which are directly related to the excitation temperature or electron number density may be distorted by the spectral response of the optical instruments used. Therefore, in this paper, we discuss some efforts to derive precise correction methods of the copper emission spectra obtained from the pulsed plasma-jet. a-jet.

• Korean Journal of Optics and Photonics
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• v.35 no.5
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• pp.218-227
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• 2024

The tabletop-scale terahertz (THz) light sources using femtosecond laser pulses are primarily based on spatiotemporal changes in electron charge. This review introduces a new scheme where the spin angular momentum of electrons contributes to THz wave generation. By focusing on laser-induced spin current generation in ferromagnets, we review the outstanding characteristics observed in nanometric ferromagnetic/nonmagnetic thin films, including high power, ultra-broadband, and polarization tunability. Additionally, research on various application technologies is introduced, including the development of devices combining semiconductors, large-area THz devices, and flexible THz devices, all based on nanoscale thin films. Through this, the principle of spintronic THz emission can be understood, contributing the advancement of various application studies utilizing electron spin as a next-generation THz optical device.

• Journal of Korean Ophthalmic Optics Society
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• v.17 no.2
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• pp.135-141
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• 2012

Purpose: Polymerization of HEMA(2-hydroxyethyl methacrylate) which can be used in the soft contact lens has been performed by using electron beam(EB) irradiation, and examined the best condition for the polymerization. Comparing the physical properties of the contact lenses to the one fabricated by thermal polymerization method, we check the use possibility of the EB irradiation to the fabrication of the soft contact lens. Methods: We investigated the degree of polymerization of the HEMA according to the composition of the monomer, the additive ratio and the dose of electron beam (0~120 kGy). The degree of polymerization was measured depending on the EB dose to research the best synthetic condition under the EB irradiation. The physical properties of the contact lens such as water content(%), oxygen transmissibility(Dk/t) and optical transmittance were analysed by using the FT-IR results with comparing the two different polymerization method (thermal and electron beam polymerization) with same additive ratio. Results: When the dose of electron beam was above 100 kGy, the degree of polymerization of HEMA was above 99% with regardless using cross-linker and initiator. The water content of the lens fabricated by EB method showed 10% higher than the one by the thermal method which was 40%. The lens fabricated by EB method also showed higher oxygen transmissibility(Dk/t) as same with the water content, and showed twice higher value in the lens fabricated by pure HEMA. According to the FT-IR results, hydrophilic property of the lens fabricated by EB method was increased due to increasing the intermolecular hydrogen bonding. It showed above 90% optical transmittance in the visible range of wavelength on the contact lenses fabricated by the both of two different polymerization method. Conclusions: The polymerization of HEMA without cross-linker and initiator was successful above 100 kGy of EB irradiation. Moreover the lens fabricated from the polymer synthesized by pure HEMA with 100 kGy of EB showed the highest water content and oxygen transmissibility. Therefore EB irradiation is another possible method to synthesize the polymer which can be used for the soft contact lens.

• Journal of the Korean Vacuum Society
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• v.14 no.4
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• pp.258-262
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• 2005

We report on the field emission properties from vertically aligned carbon nanotubes (CNTs) produced by a triode PECVD with a SiNx capping layer on metal catalyst. It is found that the CNTs density can be controlled by the capping layer thickness and decreases with increasing SiNx thickness. The CNT density of $\~$ 104/$cm^{2}$ exhibited highest electron emission characteristics, the threshold field of 1.2 V/$\mu$m and the current density of 0.17 mA/$cm^{2}$ at 3.6 V/$\mu$m. We have carried out investigation of electron emission stability under ambient gas of N2. The electron emission stability was improved with decreasing CNT density. Under $1\times$$10^{-5}$ Torr ambient pressure, the CNTs in 5 $\mu$m hole show electron emission current higher than $1\times$$10^{-4}$ A/cm2 and it's electron emission uniformity has $2\%$.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.7-8
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• 2010

The surface conductive layer (SCL) of chemical vapor deposition (CVD) diamonds has attracting much interest. However, neither photoemission electron microscopic (PEEM) nor micro-spectroscopic (PEEMS) information is available so far. Since SCL retains in an ultra-high vacuum (UHV) condition, PEEM or PEEMS study will give an insight of SCL, which is the subject of the present study. The sample was made on a Ib-type HTHP diamond (001) substrate by non-doping CVD growthin a DC-plasma deposition chamber. The SCL properties of the sample in air were; a few tens K/Sq. in sheet resistance, ${\sim}180\;cm^2/vs$ in Hall mobility, ${\sim}2{\times}10^{12}/cm^2$ in carrier concentration. The root-square-mean surface roughness (Rq) of the sample was ~0.2nm as checked by AFM. A $2{\times}1$ LEED pattern and a sheet resistance of several hundreds K/Sq. in UHV were checked in a UHV chamber with an in-situ resist-meter [1]. The sample was then installed in a commercial PEEM/S apparatus (Omicron FOCUS IS-PEEM) which was composed of electro-static-lens optics together with an electron energy-analyzer. The presence of SCL was regularly monitored by measuring resistance between two electrodes (colloidal graphite) pasted on the two ends of sample surface. Figure 1 shows two PEEM images of a same area of the sample; a) is excited with a Hg-lamp and b) with a Xe-lamp. The maximum photon energy of the Hg-lamp is ~4.9 eV which is smaller that the band gap energy ($E_G=5.5\;eV$) of diamond and the maximum photon energy of the Xe-lamp is ~6.2 eV which is larger than $E_G$. The image that appear with the Hg-lamp can be due to photo-excitation to unoccupied states of the hydrogen-terminated negative electron affinity (NEA) diamond surface [2]. Secondary electron energy distribution of the white background of Figs.1a) and b) indeed shows that the whole surface is NEA except a large black dot on the upper center. However, Figs.1a) and 1b) show several features that are qualitatively different from each other. Some of the differences are the followings: the two main dark lines A and B in Fig.1b) are not at all obvious and the white lines B and C in Fig.1b) appear to be dark lines in Fig.1a). A PEEMS analysis of secondary electron energy distribution showed that all of the features A-D have negative electron affinity with marginal differences among them. These differences can be attributed to differences in the details of energy band bending underneath the surface present in SCL [3].

• Journal of Korean Ophthalmic Optics Society
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• v.10 no.4
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• pp.283-292
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• 2005

This study investigated the effects of naringin, and chitosan in rabbits' corneas. Naringin, a glycone of naringenin, is a widely distributed bioflavonoid in the grapefruit and citrus peel, and it has already been reported as an antioxidant, antimicrobial, and anticancer agent. It has been used as a food preservatives and cosmetics. One of the natural preservatives, chitosan has also used in food preservatives, health drinks, and teas. Chitosan is distributed in the epithelium of crustacea, insects, and fungi. Naringin and chitosan have no harmful effects of cytotoxicity in the human body and they are recognized as an antibacterial for various forms of bacteria. The purpose of this study is to search for the ideal percentage of natural products to substitute the chemical preservatives occuring within the cornea and conjunctiva cytotoxicity and inflammations as wearing on soft contact lens. The present study compared the morphology of corneal epithelium and endothelium observed by light microscopy (LM) and transmission electron microscopy (TEM). In vivo methods, We investigated the effects of natural preservatives on soft contact lens. We inserted 3-4 drops of the naringin and chitosan, directly on rabbits' corneas 4 times per a day during one week. After enucleation of cornea, morphorgical damages of the epithelium and endothelium were observed by LM and TEM. In view of ultrastructure, chitosan caused siginficant damage on the epithelium and endothelium of cornea. The damage of cells was higher in chitosan treated cornea than 0.01, 0.1, and 1% of naringin. The 1% of naringin also expressed cell damage seriously. The results suggest that the most important thing is to use the reasonable percentage of preservatives for contact lens solutions.

• Journal of Korean Ophthalmic Optics Society
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• v.15 no.1
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• pp.55-60
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• 2010

Purpose: We investigated the changes of plastic lens after etching of coating films by comparing uncoated lens. Methods: CR-39, middle index and high index lenses of 0 (zero) diopter were etched at $80^{\circ}C$ and room temperature using a coating remover, and then changes of refractive power, transmittance and surface morphology were investigated. Results: There were no differences in refractive power and transmittance between uncoated and etched lenses. The etching rate was similar in both CR-39 and middle index lens, but in the case of high index lens, it was slower and less steady than the others. From the SEM observation of lens surface, etching damage was found out on the surface of etched lens. It was shown the least damage in middle index lens but the most damage in high index lens. Conclusions: If the etching of coating films is demanded on condition that the surface of ophthalmic lenses are not damaged, a using of most adequate coating remover based on lens material should be considered, and a caution for proper etching conditions is required.

• Journal of Korean Ophthalmic Optics Society
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• v.5 no.2
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• pp.167-173
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• 2000

Four glasses of $B_2O_3-Bi_2O_3-PbO-SiO_2$ (BBPS) system were prepared by melting the appropriate amounts of reagent grade oxides of $B_2O_3$, $Bi_2O_3$, PbO, and $SiO_2$ in an open crucible. The differential thermal analysis showed crystallization temperature decreased with increasing $Bi_2O_3$ or PbO content in the sample. The structures of glasses system were studied using scanning electron microscopy and Fourier transform-Infra red (FT-IR) spectroscopy. The UV cut-off and refractive index were found to be sensitive to the $Pb^{+2}$ and $Bi^{+3}$ content in the glasses. The behavior of the IR spectra of the glasses in the BP series was consistent with a role of $Bi_2O_3$ as a network former. In the BP series of glasses, the result of IR spectrum indicated that PbO behaved as a network former.