• Current Optics and Photonics
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• v.7 no.6
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• pp.714-720
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• 2023

Laser cleaning has the advantages of environmental protection, precision, and high efficiency, and has good prospects for application in removing oxide films on the surface of aluminum alloy. This paper discusses the cleaning threshold and cleaning mechanism of aluminum alloy surface oxide film. A nanosecond pulsed laser was used to remove a 5-㎛-thick oxide film from the surface of 7A04 aluminum alloy, and the target surface temperature and cleaning depth were simulated. The effects of different laser energy densities on the surface morphology of the aluminum alloy were analyzed, and the plasma motion process was recorded using a high-speed camera. The temperature measurement results of the experiment are close to the simulation results. The results show that the laser cleaning of aluminum alloy oxide film is mainly based on the vaporization mechanism and the shock wave generated by the explosion.

• Current Optics and Photonics
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• v.2 no.5
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• pp.448-452
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• 2018

A three-wavelength $Pr^{3+}:YLF$ laser at 604 nm, 607 nm and 640 nm simultaneously output by Fabry-Perot (F-P) etalon has been obtained. A 444 nm blue laser diode is used for pumping the $Pr^{3+}:YLF$ crystal, and a 0.1 mm F-P etalon is inserted in the resonator to select wavelength. The theoretical model of three-wavelength $Pr^{3+}:YLF$ laser is established, by adjusting the tilt angle of the etalon, the transmittances of the different wavelengths can be controlled, and the threshold values can be made to equalize by controlling the loss among different wavelengths. In the experiment, when the tilt angle of etalon is $9^{\circ}$ and the optimized length of resonator is 48 mm, the total output power of 25 mW at the three-wavelength is achieved at incident pump power of 7.5 W.

• Proceedings of the Korean Society of Laser Processing Conference
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• 1998.11a
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• pp.0-0
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• 1998

-Part I- As market needs become more various, the production of smaller quantities of a wider variety of products becomes increasingly important. In addition, in order to meet demands for more efficient production, long-term unmanned factory operation is prevailing at a remarkable pace. Within this context, laser machines are gaining increasing popularity for use in applications such as cutting and welding metallic and ceramic materials. FANUC supplies four models of $CO_2$ laser oscillators with laser power ranging from 1.5㎾ to 6㎾ on an OEM basis to machine tool builders. However, FANUC has been requested to produce laser oscillators that allow more compact and lower-cost laser machines to be built. To meet such demands, FANUC has developed six models of Slab type YAG laser oscillators with output power ranging from 150W to 2㎾. These oscillators are designed mainly fur cutting and welding sheet metals. The oscillator has an exceptionally superior laser beam quality compared to conventional YAG laser oscillators, thus providing significantly improved machining capability. In addition, the laser beam of the oscillator can be efficiently transmitted through quartz optical fibers, enabling laser machines to be simplified and made more compact. This paper introduces the features of FANUC’s developed Slab type YAG laser oscillators and their applications. - Part II - All-solid-state lasers employing laser diodes (LD) as a source of pumping solid-state laser feature high efficiency, compactness, and high reliability. Thus, they are expected to provide a new generation of processing tools in various fields, especially in automobile and aircraft industries where great hopes are being placed on laser welding technology for steel plates and aluminum materials for which a significant growth in demand is expected. Also, in power plants, it is hoped that reliability and safety will be improved by using the laser welding technology. As in the above, the advent of high-power all-solid-state lasers may not only bring a great technological innovation to existing industry, but also create new industry. This is the background for this project, which has set its sights on the development of high-power, all-solid-state lasers with an average output of over 10㎾, an oscillation efficiency of over 20%, and a laser head volume of below 0.05㎥. FANUC Ltd. is responsible for the research and development of slab type lasers, and TOSHIBA Corp. far rod type lasers. By pumping slab type Nd: YAG crystal and by using quasi-continuous wave (QCW) type LD stacks, FANUC has already obtained an average output power of 1.7㎾, an optical conversion efficiency of 42%, and an electro-optical conversion efficiency of 16%. These conversion efficiencies are the best results the world has ever seen in the field of high-power all-solid-state lasers. TOSHIBA Corp. has also obtained an output power of 1.2㎾, an optical conversion efficiency of 30％, and an electro-optical conversion efficiency of 12%, by pumping the rod type Nd: YAG crystal by continuous wave (CW) type LD stacks. The laser power achieved by TOSHIBA Corp. is also a new world record in the field of rod type all-solid-state lasers. This report provides details of the above results and some information on future development plans.

• Current Optics and Photonics
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• v.5 no.6
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• pp.721-729
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• 2021

We demonstrate a Pr³⁺:YLF 639.7-nm laser with single-frequency output based on the Q-switched pre-lase technology, pumped by a fiber-coupled GaN blue laser diode. The pre-lase technology is realized by the step-type loss of the acousto-optical Q-switched device. The conclusions of the theoretical research are verified experimentally. The mode-suppression ratio was 44 dB at the single-frequency laser output. Detection by interferometer verified the realization of the stable single-frequency laser. In addition, the emission spectrum had a linewidth of 139.9 MHz, measured by Fabry-Perot interferometer. The single-frequency laser's single-peak power was over 19.7 W with 98.8-ns pulse duration, obtained under an absorption power of 1.74 W.

• Current Optics and Photonics
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• v.4 no.4
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• pp.273-276
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• 2020

We report on the relationship between output current for quadrant photodetector (QPD) and bias voltage in silicon-based p-i-n (positive-intrinsic-negative) QPD examined using millisecond pulse laser (ms pulse laser) irradiation. The mechanism governing the relationship was further studied experimentally. The output current curves were obtained by carrying out QPD under different bias voltages (0-40 V) irradiated by ms pulse laser. Compared to other photodetectors, the relaxation was created in the output current for QPD which is never present in other photodetectors, such as PIN and avalanche photodetector (APD), and the maximum value of relaxation was from 6.8 to 38.0 ㎂, the amplitude of relaxation increases with bias value. The mechanism behind this relaxation phenomenon can be ascribed to the bias voltage induced Joule heating effect. With bias voltage increasing, the temperature in a QPD device will increase accordingly, which makes carriers in a QPD move more dramatically, and thus leads to the formation of such relaxation.

• Journal of the Optical Society of Korea
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• v.20 no.5
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• pp.541-546
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• 2016

In this paper, by using the Rayleigh-Sommer field theory and the cross-spectral density function, the analytical expression for the intensity distribution of a double half-Gaussian hollow beam in a turbulent atmosphere is obtained. The influence of the initial spot size of this beam on its propagation properties in a turbulent atmosphere is simulated, and the intensity distributions for such beams with different spot sizes are obtained. The results show that the initial spot size has an important influence on the propagation properties in the near field, while this influence in the far field is very weak.

• Korean Journal of Optics and Photonics
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• v.26 no.2
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• pp.98-102
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• 2015

The radiative quantum efficiency of a solid-state laser was measured by photoacoustic spectroscopy with a PZT as the detector. The radiative quantum efficiency was about 58.3 % for a laser-diode pumped Nd:S-VAP laser under lasing conditions. The measurement of radiative quantum efficiency was presented as an effective method for the optimization of a laser resonator.

• Proceedings of the Optical Society of Korea Conference
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• 1989.02a
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• pp.1-4
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• 1989

The Alexandrite (Cr:BeAl2O4) laser is one of the promising tunable (vibronic) solid state laser developed recently in the near infrared region (700~800nm) of the spectrum. The thermal lensing effect of rod may effect stable mode osicillation of the solid state laser. A design procedure of the Alexandrite laser resonator considering rod thermal lensing effect and misaligment sensitivity of the resonator will be presented.

• Journal of the Optical Society of Korea
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• v.15 no.1
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• pp.56-60
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• 2011

We demonstrate passive mode-locking of a Cr:forsterite laser with a single-walled carbon nanotube saturable absorber mirror (SWCNT-SAM). Without compensation of intra-cavity dispersion, the self-mode-locked laser generates 11.7 ps pulses at a repetition rate of 86 MHz. The dispersion-compensated laser yields ultrashort pulses as short as 80 fs near $1.25\;{\mu}m$ at 78 MHz with average output powers up to 295 mW, representing the highest power ever reported for mode-locked solid-state lasers based on saturable absorption of SWCNTs in this spectral region.

• 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.