• Current Optics and Photonics
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• v.7 no.6
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• pp.738-744
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• 2023

Graphene-based saturable absorbers (SAs) are widely used as laser mode-lockers at various laser oscillators. In particular, transmission-type graphene-SAs with ultrabroad spectral coverage are typically manufactured on transparent substrates with low nonlinearity to minimize the effects on the oscillators. Here, we developed two types of transmitting graphene SAs based on CaF₂ and ZnSe. Using the graphene-SA based on CaF₂, a passively mode-locked mid-infrared Cr:ZnS laser delivers relatively long 540 fs pulses with a maximum output power of up to 760 mW. In the negative net cavity dispersion regime, the pulse width was not reduced further by inhomogeneous group delay dispersion (GDD) compensation. In the same laser cavity, we replaced only the graphene-SA based on CaF₂ with the SA based on ZnSe. Due to the additional self-phase modulation effect induced by the ZnSe substrate with high nonlinearity, the stably mode-locked Cr:ZnS laser produced Fourier transform-limited ~130 fs near 2,340 nm. In the stable single-pulse operation regime, average output powers up to 635 mW at 234 MHz repetition rates were achieved. To our knowledge, this is the first attempt to achieve shorter pulse widths from a polycrystalline Cr:ZnS laser by utilizing the graphene deposited on the substrate with high nonlinearity.

• Journal of the Korea Computer Industry Society
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• v.2 no.4
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• pp.565-572
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• 2001

At the most recent years, laser medical instruments, laser applications and laser nuclear fusion need strong visible light and ultraviolet rays. Nonlinear optical devices, such as harmonic generators and parametric oscillators, provide a means of extending the frequency range of available laser sources. Frequency conversion is a useful technique for extending the utility of high-power lasers. It utilizes the nonlinear optical response of an optical medium in intense radiation fields to generate new frequencies. These progresses have been used to generate high-power radiation in all spectral regions, from the ultraviolet to the far infrared. Optical parametric oscillators and amplifiers generate two waves of lower frequency They are capable of generating a range of wavelengths from a single frequency source, in some cases spanning the entire visible and near infrared regions. Consequently, in order to obtain the green light, the pulsed Nd:YAG laser using multiple-mesh PFN(Pulsed Forming Network) method with Nonlinear optical device was adopted. We compared the current pulseshapes with the laser output energy, and conversion efficiency.

• Laser Solutions
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• v.13 no.1
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• pp.11-15
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• 2010

Indium tin oxide (ITO) provides high electrical conductivity and transparency in the visible and near IR (infrared) wavelengths. Thus, it is widely used as a transparent electrode for the fabrication of liquid crystal displays (LCDs) and organic light emitting diode displays (OLRDs), photovoltaic devices, and other optical applications. Lasers have been used for removing coating on polymer substrate for flexible display and electronic industry. In selective removal of ITO layer, laser wavelength, pulse energy, scan speed, and the repetition rate of pulses determine conditions, which are efficient for removal of ITO coating without affecting properties of the polymer substrate. ITO coating removal with a laser is more environmentally friendly than other conventional etching methods. In this paper, pattering of ITO film from polymer substrates is described. The Yb:KGW femtosecond laser processing system with a pulse duration of 250fs, a wavelength of 1030nm and a repetition rate of 100kHz was used for removing ITO coating in air. We can remove the ITO coating using a scanner system with various pulse energies and scan speeds. We observed that the amount of debris is minimal through an optical and a confocal microscope, and femtosecond laser pulses with 1030nm wavelength are effective to remove ITO coating without the polymer substrate ablation.

• Medical Lasers
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• v.10 no.3
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• pp.146-152
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• 2021

Background and Objectives Although lasers have been widely applied in tissue treatment, the light penetration depth in tissues is limited by the tissue turbidity and affected by its absorption and scattering characteristics. This study investigated the effect of using an optical clearing agent (OCA) on tissue to improve the therapeutic effect of 1064 nm wavelength laser light by reducing the heat generated on the skin surface and increasing the penetration depth. Materials and Methods A diode laser (λ = 1064 nm) was applied to a porcine specimen with and without OCA to investigate the penetration depth of the laser light and temperature distribution. A numerical simulation using the finite element method was performed to investigate the temperature distribution of the specimen compared to ex-vivo experiments using a thermocouple and double-integrating sphere to measure the temperature profile and optical properties of the tissue, respectively. Results Simulation results showed a decrease in tissue surface temperature with increased penetration depth when the OCA was applied. Furthermore, both absorption and scattering coefficients decreased with the application of OCA. In ex-vivo experiments, temperatures decreased for the tissue surface and the fat layer with the OCA, but not for the muscle layer. Conclusion The use of an OCA may be helpful for reducing surface heat generation and enhance the light penetration depth in various near-infrared laser treatments.

• Korean Journal of Optics and Photonics
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• v.27 no.3
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• pp.95-100
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• 2016

High-power quasi-continuous-wave (qcw) operation in Yb-doped double-clad fiber lasers with near-diffraction-limited quality of the output beam is reported. Based on numerical simulation, we built a simple, all-fiberized Yb fiber laser, and a fiber-based master-oscillator power amplifier (MOPA). Both laser systems have successfully produced qcw output with average power greater than 150 W at 1080 nm and 10 ms pulse duration at 10 Hz repetition rate, corresponding to a peak power greater than 1.5 kW for 205 W of pump power at 976 nm. Laser performance, including beam quality and slope efficiency, was characterized in both configurations. Prospects for power scaling and applications are discussed.

• Journal of the korean academy of Pediatric Dentistry
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• v.47 no.4
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• pp.446-453
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• 2020

The purpose of this study was to evaluate the effect of Indocyanine Green (ICG) and near-infrared (NIR) diode laser on Streptococcus mutans biofilms depending on ICG concentrations. S. mutans biofilms were formed on a Hydroxyapatite disk, and 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 mg/mL ICG solutions dissolved in sterile distilled water and a NIR diode laser having a power of 300 mW and a wavelength of 808 nm were applied to the biofilms. The temperature changes of the biofilm surface according to the concentrations of the ICG solution were measured using a 1-channel thermocouple thermometer. Compared to the control group, in the groups with only the 3.0, 4.0, 5.0 mg/mL ICG solution application, and in the groups with the 1.0, 2.0, 3.0, 4.0, 5.0 mg/mL ICG solution application and light irradiation, a statistically significant decrease in the bacterial counts were observed. The temperature increase according to the concentration of the ICG solutions was 9.53℃, 10.43℃, 11.40℃, 12.10℃, 12.67℃, and 13.63℃ in ICG solutions of 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 mg/mL respectively. This study presents the potential for clinical application of ICG and NIR diode lasers as a new method for preventing dental caries.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.209-210
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• 2006

We have successfully termed brown colored patterns inside of a transparent borosilicate glass generally known as BK7, laying the focus of near infrared Ti: sapphire femtosecond laser beam in the bulk BK7 glass. It is important to keep the laser power well below the damage threshold of BK7 in forming the color center. Thanks to the low laser power, there was no laser induced mechanical damage such as cracks or threads in the color formed area. From the absorbance spectrum and its gaussian fitting, we found the band gap of BK7, 4.21eV, and three absorption edges.

• Applied Chemistry for Engineering
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• v.32 no.3
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• pp.299-304
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• 2021

This study focuses on the preparation of acetaminophen (AP) imprinted functional biomaterials for a transdermal drug delivery using mung bean starch (MBS), polyvinyl alcohol (PVA), sodium benzoate (S) as a crosslinking agent, glycerol (GL) as a plasticizer, and melanin (MEL) as a photothermal agent. The prepared AP imprinted biomaterials were characterized using FE-SEM and their physical properties were evaluated. The photothermal effect and AP release property for functional biomaterials were examined with the irradiation of near infrared (NIR) laser (1.5 W/cm²). When the NIR laser was irradiated on functional biomaterials with/without the addition of MEL, the temperature of MEL added biomaterial increased from 25 ℃ to 41 ℃, whereas the biomaterial without MEL increased from 25 ℃ to 28 ℃. Results indicate that there is the photothermal effect of prepared biomaterial with the addition of MEL. Based on the results, AP release properties were evaluated using standard buffer solutions and artificial skin. It was found that AP release rates of MEL added AP loaded biomaterials were 1.2 times faster than those of MEL non-added AP loaded biomaterials when irradiating with NIR laser. We envision that the developed functional biomaterials can be utilized for an acute pain-killing treatment.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.2
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• pp.99-103
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• 2015

One-dimensional photonic crystals (1D PCs) were fabricated by RF sputtering technique on p-Si (100), and fused quartz substrates. The 1D PCs structures consisted of $TeO_x$ (x=1.42), and $SiO_2$ with the difference refractive index. In order to estimate the effect on a defect level within 1D PCs structures, samples were prepared with both normal, and defect mode. The structural and optical properties were confirmed by Scanning electron microscope (SEM), and Ultraviolet visible near-infrared spectrophotometer (UV-VIS-NIR) respectively. In the case of a 1D PC normal mode without defect layer, it had a photonic band gap (PBG) in the near infrared (NIR) region. In the case of a 1D PC defect mode with defect layer, it had a sharp transmission band owing to a defect level, and moved towards the longer wavelength after exposing He-Cd laser with a wavelength of 325 nm.

• Journal of Biomedical Engineering Research
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• v.36 no.5
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• pp.191-197
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• 2015

Laser acupuncture is defined as the stimulation of traditional acupuncture points with low-intensity, nonthermal laser irradiation. Possible advantages in using laser acupuncture are the noninvasive, painless and low risks of infection treatment. The purpose of this study is to assess the effect of laser acupuncture on the quality and waveform of arterial pulses. Ten acupuncture points were stimulated repeatedly three times in 30 individuals by laser with emission in the near infrared spectral region (808 nm) using an out power and power density of 45 mW and $143W/cm^2$. The analysis of pulse quality and waveform was performed based on the measurement of arterial pressure of the left and right wrist, using a 3-dimensional blood pressure pulse analyzer. Excess-like pulse quality of subjects before laser acupuncture changed significantly to balanced pulse quality after 10, 20, and 30 minutes of laser acupuncture; coefficient of deficient or excess, $C_{DE}$, decreased significantly from 0.68 before acupuncture to 0.61, 0.55, and 0.55 after 10, 20, 30 minutes of laser acupuncture ($$p{\leq_-}0.006$$), respectively. Other pulse qualities, floating or sinking, slow or rapid, choppy or slippery did not change significantly by laser acupuncture (p > 0.05). Pulse waveform analysis showed that amplitude of main peak (systolic function or aortic compliance, $h_1$) of left and right artery pulse waves decreased significantly after 10, 20, and 30 minutes of laser acupuncture (p < 0.05). Other parameters, duration of one cardiac cycle (T), duration of rapid systolic ejection ($T_1$), duration of the systolic phase ($T_4$), and duration of the diastolic phase ($T_5$) of left and right artery pulses did not change significantly after laser acupuncture (p > 0.05).