• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1505-1509
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• 2004

A novel technique for fine particle beam focusing under the atmospheric pressure is introduced using a radiation pressure assisted aerodynamic lens. To introduce the radiation pressure in the aerodynamic focusing system, a 25 mm plano-convex lens having 2.5 mm hole at its center is used as an orifice. The particle beam width is measured for various laser power, particle size, and flow velocity. In addition, the effect of the laser characteristics on the beam focusing is evaluated comparing an Ar-Ion continuous wave laser and a pulsed Nd-YAG laser. For the pure aerodynamic focusing system, the particle beam width was decreased as increasing particle size and Reynolds number. For the particle diameter of 0.5 ${\mu}m$, the particle beam was broken due to the secondary flow at Reynolds number of 694. Using the Ar-Ion CW laser, the particle beam width becomes smaller than that of the pure aerodynamic focusing system about 16 %, 11.4 % and 9.6 % for PSL particle size of 2.5 ${\mu}m$, 1.0 ${\mu}m$, and 0.5 ${\mu}m$ respectively at the Reynolds number of 320. Particle beam width was minimized around the laser power of 0.2 W. However, as increasing the laser power higher than 0.4 W, the particle beam width was increased a little and it approached almost a constant value which is still smaller than that of the pure aerodynamic focusing system. The radiation pressure effect on the particle beam width is intensified as Reynolds number decreases or particle size increases relatively. On the other hand, using 30 Hz pulsed Nd-YAG laser, the effect of the radiation pressure on the particle beam width was not distinct unlike Ar-Ion CW laser.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.1 s.232
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• pp.110-115
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• 2005

A novel technique for fine particle beam focusing under the atmospheric pressure is introduced using a radiation pressure assisted aerodynamic lens. To introduce the radiation pressure in the aerodynamic focusing system, a 25m plano-convex lens having 2.5mm hole at its center is used as an orifice. The particle beam width is measured for various laser power, particle size, and flow velocity. In addition, the effect of the laser characteristics on the beam focusing is evaluated comparing an optical tweezers type and pure gradient force type. For the pure aerodynamic focusing system, the particle beam width was decreased as increasing particle size and Reynolds number. Using the optical tweezers type, the particle beam width becomes smaller than that of the pure aerodynamic focusing system about $16\%,\;11.4\%\;and\;9.6\%$ for PSL particle size of $2.5{\mu}m,\;1.0{\mu}m,\;and\;0.5{\mu}m$, respectively. Particle beam width was minimized around the laser power of 0.2W. However, as increasing the laser power higher than 0.4W, the particle beam width was increased a little and it approached almost a constant value which is still smaller than that of the pure aerodynamic focusing system. For pure gradient force type, the reduction of the particle beam width was smaller than optical tweezers type but proportional to laser power. The radiation pressure effect on the particle beam width is intensified as Reynolds number decreases or particle size increases relatively.

• Journal of Welding and Joining
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• v.7 no.4
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• pp.12-21
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• 1989

Laser beam welding parameters have experimentally investigated, using a continuous wave 3kW $CO_2$ laser with the various travel speeds, beam mode and laser beam power in low carbon steels. An optimum position of focus and the effect of shielding gas on penetration depth with varying the flow range of 0.5 to 5.1m/min have been combined to investigate the effect of laser power and travel speed on penetration depth and bead width. It is found that the optimum position of focus in 3kW class laser is 0.5 to 1.5mm below the surface of the material. The flow rate of shielding gas affects the penetration depth and He is more effective than Ar. The penetration depth in laser welds of low carbon steels is between two and four times of the bead width. Laser beam welding of butt joints in 2mm thick carbon steel has been carried out to establish a weldability lobe. The lobe indicating acceptable welding conditions is introduced.

• International Journal of Precision Engineering and Manufacturing
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• v.8 no.4
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• pp.50-55
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• 2007

Stereolithography (SLA) is a technique using a laser beam to cure a photopolymer liquid resin with three-dimensional computer-aided design (CAD) data, The accuracy of the prototype, the build time, and the cured properties of the resins are controlled by the SLA process parameters such as the size of the laser beam, scan velocity, hatch spacing, and layer thickness, In particular, the size of the laser beam is the most important parameter in SLA, This study investigated the curing properties of photopolymers as a function of the laser beam size, The cure width and depth were measured either on a single cure line or at a single cure layer for various hatch spacings and laser beam sizes, The cure depth ranged from 0.23 to 0.34 mm and was directly proportional to the beam radius, whereas the cure width ranged from 0.42 to 1.07 mm and was inversely proportional to the beam radius, The resulting surface roughness ranged from 1.12 to $2.23{\mu}m$ for a ratio of hatch spacing to beam radius in the range 0.5-2.0 at a beam radius of 0.17 mm and a scan velocity of 125 mm/sec.

• Journal of Welding and Joining
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• v.15 no.6
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• pp.85-95
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• 1997

This study is to investigate the optimum conditions of Nd:YAG laser beam welding for Zircaloy-4 end cap closure by optical fiber transmission. Laser welding parameters which affect the penetration depth and bead width were experimentally examined using the various beam radius by the beam quality analyzer, joint geometries of end cap and the laser parameters which mean pulse width, repetition rate and pulse energy. Also, an optimum welding speed and the effect of assistant gas with varying the flow rate of He were investigated. We found that the laser average power for the end cap welding will be 230W and rotation speed must not exceed 8 RPM, the best position of focus using optical fiber with 600.mu.m will be 2 to 3mm below the surface of the material.

• Journal of the Optical Society of Korea
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• v.17 no.6
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• pp.486-490
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• 2013

A portable infrared laser transmitter delivering a highly uniform detectable beam was demonstrated. It incorporates a flexible beam shaper, comprising a perforated diffuser sheet in conjunction with a pinhole. The beam shaper plays the prominent role of flexibly tailoring the incoming light via both scattering and diffraction, in order to equalize the effective beam width over a long distance. The intensity profile of a generated beam was practically observed, demonstrating that a substantially uniform beam of 70-cm width was achieved for a given threshold detection level, with an average deviation of 6% over a range of 600 m.

• Laser Solutions
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• v.1 no.1
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• pp.24-29
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• 1998

A new wide laser beam optical system for the laser materials processing has been developed with a polygonal mirror. It consists of polygonal mirror and cooling part that prevents the surface of rotating polygonal mirror from damage by heat. The polygonal minors have been designed and made as 24 and 30 facets in pyramid type. This system provides a uniform linear laser heat source with the surface scanning width from 15 to 50mm according to the scanning height To examine the wide laser beam, He-Ne laser is used. Also, Acryl is used to confirm the laser beam pattern by bum-pattern print To analyze the energy distribution of the wide laser ben empirical values and theoretical values are compared and discussed. To improve the efficiency of the wide laser beam optical system, methods are suggested by the optical theories. For larger area processing like turbine blade, drawing blade, cold roller and guide plate, optimal overlapping locations have been calculated and analyzed by geometric and optical theories.

• Laser Solutions
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• v.16 no.4
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• pp.12-16
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• 2013

For mass production of electronic devices, the processing of the printing roll is one of the most important key technologies for printed electronics technology. A roll of printing process, the gravure printing that is used to print the electronic device is most often used. The indirect laser processing has been used in order to produce printing roll for gravure printing. It consists of the following processing that is coating of photo polymer or black lacquer on the surface of printing roll, pattering using a laser beam and etching process. In this study, we have carried out study on the coating and etching for $25{\mu}m$ line width on the printing roll. To do this goals, a $4{\mu}m$ coating thickness and 20% average coating thickness of the coating homogeneity of variance is performed. The factors to determine the thickness and homogeneity are a viscosity of coating solution, the liquid injection, the number of injection, feed rate, rotational speed, and the like. After the laser patterning, a line width of $25{\mu}m$ or less was confirmed to be processed through etching and the chromium plating process.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.1089-1092
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• 2001

In the stereolithography process, build parameters are laser power, scan velocity, scan width, bean diameter, layer thickness and so on. These values are determined according to product accuracy and build time. Build time can be reduced by improving of scan velocity, laser power, layer thickness, hatching space and so on. But variation of these parameters influence part accuracy, surface roughness, strength. This paper observed cure properties in various beam diameter. In order to examine these, relationships of scan velocity and cure depth, scan velocity and cure width according to various beam diameter in one scan line are measured. And cure thickness is measured according to beam diameter and scan velocity in scan surface of one layer. For reduction of build time, beam diameter and scan velocity is proposed in stereolithography process.

• Korean Journal of Optics and Photonics
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• v.10 no.6
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• pp.512-517
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• 1999

Quenched dye laser (QDL), which operates with relaxation oscillation mode, is one of the most powerful source for ultra-short pulse light. In this paper, the output characteristics of QDL is theoretically analyzed by a computer simulation. The QDL is assumed that the laser dye is Rhodamine 6G which has the oscillation wavelength of 590 nrn and that the active length is 5 mm and that the pumping source is XeCllaser which has oscillation wavelength of 308 nm. It is revealed ilim the pulse width of short cavity dye laser reduced less than 1/100 than pumping pulse duration and has the linear relationship with spatial width of pumping beam approximately. In addition, it is revealed that the short cavity dye laser is a powerful candidate of pulse width variable light source, which is adjusted by spatial size of pumping beam_ beam_