• Laser Solutions
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• v.7 no.1
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• pp.29-36
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• 2004

The dynamics of laser-induced plasma/shock wave and the interaction with a surface in the laser shock cleaning process are analyzed by optical diagnostics. Shock wave is generated by a Q-switched Nd:YAG laser in air or with N$_2$, Ar, and He injection into the focal spot. The shock speed is measured by monitoring the photoacoustic probe-beam deflection signal under different conditions. In addition, nanosecond time-resolved images of shock wave propagation and interaction with the substrate are obtained by the laser-flash shadowgraphy. The results reveal the effect of various operation parameters of the laser shock cleaning process on shock wave intensity, energy-conversion efficiency, and flow characteristics. Discussions are made on the cleaning mechanisms based on the experimental observations.

• Laser Solutions
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• v.5 no.2
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• pp.31-38
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• 2002

This paper describes the process of nanoparticle synthesis by laser ablation of consolidated microparticles. We have generated nanoparticles by high-power pulsed laser ablation of Al, Cu and Ag microparticles using a Q-switched Nd:YAG laser (wavelength 355 nm, FWHM 5 ㎱, fluence 0.8∼2.0 J/㎠). Microparticles of mean diameter 18∼80 ㎛ are ablated in the ambient air The generated nanoparticles are collected on a glass substrate and the size distribution and morphology are examined using a scanning electron microscope and a transmission electron microscope. The effect of laser fluence and collector position on the distribution of particle size is investigated. The dynamics of ablation plume and shock wave is analyzed by monitoring the photoacoustic probe-beam deflection signal. Nanosecond time-resolved images of the ablation process are also obtained by laser flash shadowgraphy. Based on the experimental results, discussions are made on the dynamics of ablation plume.

• Korean Journal of Optics and Photonics
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• v.4 no.4
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• pp.428-433
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• 1993

The second harmonic of Q-switched Nd:YAG laser beam with gaussian mode is cut off by pinhole of a certain radius and its central portion passed through pinhole is focused by converging lens. It is confirmed that the shape of this beam in focal region is central symmetric but non-gaussian. Change of transmittance due to self-focusing is investigated by scanning (z-scan) $CS_2$ of 1 mm thickness in the focal region. It is found that the observed results can be consistently explained by Fresnel theory within 1.5% accuracy and efficiency of self-focusing depends on spatial shape of incident beam.

• Medical Lasers
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• v.10 no.4
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• pp.242-245
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• 2021

Acne vulgaris is a common inflammatory skin disease of the pilose-baceous unit. It appears as lesions consisting of comedones, papules, pustules, and nodules of varying shapes and severity. In general, the first-line treatment for acne vulgaris includes topical and oral medication. Recently, various physical modalities have also been investigated. The use of laser therapy is steadily increasing because of its fewer side effects, short procedure time, and rapid results. In particular, laser therapy assisted with carbon suspension application is effective for acne vulgaris but may sometimes result in discomfort due to odor and dust formation during the procedure. Herein, we report that acne vulgaris and enlarged facial pores can be safely and effectively treated with laser therapy assisted with diamond particle suspension and gold microparticle application, which can address the discomfort caused by the carbon suspension application.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.12
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• pp.894-898
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• 2013

Zinc oxide(ZnO) was sputtered on various glass and flexible substrates such as polyethylene terephthalate(PET) and polycarbonate(PC). A Q-switched $Nd:YVO_4$ laser with a wavelength of 1,064 nm was used for the direct etching of ZnO films. It was possible to obtain laser etched line patterns on the ZnO films on PC substrate at some specific laser beam conditions. In the flexible substrates, more thermal energy of laser beam is expected to be spreaded for the etching process.

• Korean Journal of Optics and Photonics
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• v.11 no.4
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• pp.294-298
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• 2000

The output characteristics of intracavity frequency doubling of laser-diode end-pumped Nd:S-VAP laser were investigated. Nd:S-VAP is suitable for a microchip laser medium, which has a low threshold property because of a very high value of the stimulated emission cross-section and lifetime product. The threshold energy measured was 81 J.ll. The second harmonic output energy measured was $126\mu\textrm{J}$at a pump energy of $2\mu\textrm{J}$. We described for intracavity frequency doubling by using theoretical calculations. Q-switched second harmonic energy measured was $15\mu\textrm{J}$per pulse with a pulse-width of 26 ns. at a pump energy of 2 mJ and an $M^2$ of 1.47 represented a good beam quality. ality.

• Korean Journal of Optics and Photonics
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• v.16 no.2
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• pp.146-151
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• 2005

We fabricated pyrromethene 597(PM597) solid-state dyes which were dissolved in PMMA(poly- methylmethacrylate) and characterized the lasing characteristics. The laser was end-pumped by a frequency doubled Q-switched Nd : YAG laser. We obtained the slope efficiency of $76\%$ at lasing wavelength of 585 nm. We demonstrated the laser lifetime to be more than 100,000 shots with output energy of 250 mJ and repetition rate of 4 Hz by adding singlet oxygen quencher DABCO(1,4-diazabicyclo [2,2,2]octane) to the solid-state dye.

• Laser Solutions
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• v.7 no.2
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• pp.11-18
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• 2004

We propose a novel 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 aQ-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 multilayer optical storage disks and might also provide information to optimize optical memory technology.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.4
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• pp.283-292
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• 2009

Laser-based ultrasonic sensing requires the probe with fixed fecal length, but this requirement is not essential in laser-based ultrasonic generation. Based on this fact, we designed a pulsed laser-based ultrasonic wave propagation imaging (UWPI) system with a tilting mirror system for rapid scanning of target, and an in-line band-pass filtering capable of ultrasoaic mode selection. 1D-temporal averaging, 2D-spatial averaging, and 3D-data structure building algorithms were developed far clearer results allowing fur higher damage detectability. The imaging results on a flat stainless steel plate were presented in movie and snapshot formats which showed the propagation of ultrasound visible as a concentric wavefield emerging from the location of an ultrasonic sensor. A hole in the plate with a diameter of 1 mm was indicated by the scattering wavefields. The results showed that this robust UWPI system is independent of focal length and reference data requirements.

• Journal of Photoscience
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• v.5 no.1
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• pp.33-37
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• 1998

One macroscopic effect in the free-running Er:YAG laser is an accumulation of microscopic effects. Understanding of the exogenous water induced mechanical effect on the dental hard tissue by the Qswitched Er:YAG laser has an important impact on the further understanding of the free-running Er:YAG laser ablation on the dental hard tissue. The Q-switched Er:YAG laser (1-$\mu$s-long pulse width) was used in the recoil pressure measurement with an aid of water-jet system and a pressure transducer. The amplitude of the recoil pressure depends on the tooth surface conditions (dry and wet) and the volume of the water upon it. Wet surfaces yielded higher recoil pressure than that of dry, surface, and as the volume of the exogenous water drop increased, the amplitude of the recoil pressure increased also.