• Laser Solutions
• /
• v.9 no.3
• /
• pp.7-13
• /
• 2006

Auto focusing system to find optimized focal position of laser beam used for material process has been investigated by using fiber confocal method. Wavelength of laser diode (LD) and diameter of single-mode fiber are 780nm and $5.3{\mu}m$, respectively. Intensity distributions of beam reflected from the surface of mirror and silicon bare wafer have been observed in a gaussian form. Experimental results show that focal position obtained by LD is shifted from one observed from surface scribed by laser about $80{\mu}m$. It is due to the difference of wavelength and each divergence of between LD and laser used for material process. It is confirmed that auto focusing control system through position calibration has operated steadily.

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

• Proceedings of the Korean Society of Laser Processing Conference
• /
• 2006.11a
• /
• pp.41-45
• /
• 2006

Auto focusing system to find optimized focal position of laser beam used for material process has been investigated by using fiber confocal method. Wavelength of laser diode (LD) and diameter of single-mode fiber we 780nm and $5.3{\mu}m$, respectively. Intensity distributions of beam reflected from the surface of mirror and silicon bare wafer have been observed in a gaussian form. Experimental results show that focal position obtained by LD is shifted from one observed from surface scribed by laser about $80{\mu}m$. It is due to the difference of wavelength and each divergence of between LD and laser used for material process. It is confirmed that auto focusing control system through position calibration has operated steadily.

• Laser Solutions
• /
• v.12 no.1
• /
• pp.19-24
• /
• 2009

Because of its fast and precise welding performance, laser welding is becoming a new excellent welding method. However, the precise focusing and robust seam tracking are required to apply laser welding to the practical fields. In order to laser weld a type of T joint like a circular pipe on a square pipe, which could be met in the three dimensional structure such as an aluminum space frame, a visual sensor system was developed for automation of focusing and seam tracking. The developed sensor system consists of a digital CCD camera, a structured laser, and a vision processor. It is moved and positioned by a 2-axis motorized stage, which is attached to a 6 axis robot manipulator with a laser welding head. After stripe-type structured laser illuminates a target surface, images are captured through the digital CCD camera. From the image, seam error and defocusing error are calculated using image processing algorithms which includes efficient techniques handling continuously changed image patterns. These errors are corrected by the stage off-line during welding or teaching. Laser welding of a circular pipe on a square pipe was successful with the vision tracking system by reducing the path positioning and de focusing errors due to the robot teaching or a geometrical variation of specimens and jig holding.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2004.03a
• /
• pp.325-326
• /
• 2004

Experiment of laser propulsion in free flight has never been conducted. At Institute of Fluid Science (IFS), Tohoku University, propulsive impulse generation by focusing on a rest projectile was demonstrated. Based on the ideas obtained from this experiment, experiment of laser propulsion of a projectile in flight by focusing $CO_2$ laser beam is being prepared for. The objective velocity increment in experiment is about 50 m/s.

• Laser Solutions
• /
• v.11 no.2
• /
• pp.33-38
• /
• 2008

Laser micromachining has increasingly been adopted in various advanced industries where the high-precision machining of large-area, high-density and multi-layered components is in a strong demand. To effectively meet the requirements, the laser micromachining process must be carefully monitored. In order to facilitate the development of a new laser micromachining process and/or a new system, we have fabricated a UV laser micromachining platform that is equipped with optical modules for monitoring the process online. They include a laser power stabilizing module, a module for laser-induced breakdown spectroscopy, and an auto-focusing module.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.8 no.2
• /
• pp.100-107
• /
• 1999

End milling experiments are conducted to investigate characteristics of laser beam signals due to tool fracture. The laser beam signals are obtained with adapt focusing of tool. Tool states are identified wit h scanning electron microscopy and optical microscopy. It is demonstrated that the laser beam signals provide reliable informations about the cutting processes and tool states. Moreover, tool fracture can be detected successfully using coefficient of variation.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.1 s.232
• /
• pp.110-115
• /
• 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 the Korean Society of Manufacturing Process Engineers
• /
• v.19 no.6
• /
• pp.96-101
• /
• 2020

In this paper, we present the results of our research to perform 3D laser scanning functions by adding a focusing lens to a conventional 2D laser scanner. For the optical design, the ray-tracing technique was used along with a total of four lenses as the variable incident focusing lens, the collimating lens, and the F-Theta lens. As design variables, the curvature of the incident focusing lens (Lens #1) was assumed to be us, l mm and sumed mm, and the incident angles were set at 0cidenus, l. In addition, the distance between the focusing lens and the collimating lens was set to vary from 5 mm to 15 mm. When the incident focal length was varied from 5 mm to 15 mm, the exit focal length was calculated to vary from 67.5 mm to 56.8 mm for the lens with R = 100 mm and from 108.5 mm to 99.0 mm for the lens with R = 150 mm. When the incident angle was 0°, the focal aberration was only slightly observable at 10㎛ in both the x- and y-direction. At 7.5° was the focal aberration of approximately 20~50㎛ was measured at 20㎛. To investigate the chromatic aberration of the designed optical device, the distortion of the focus was observed when the 550 nm beam was simulated on lens designed for a 980 nm wavelength.

• Journal of the Korean Society for Precision Engineering
• /
• v.26 no.6
• /
• pp.50-58
• /
• 2009

Micro laser fabrication techniques can potentially be used for the manufacture of microstructures on the thin flat surfaces with large diameter that are frequently used in semiconductor industries. However, the large size of wafers can cause the degraded machining accuracy of the surface because it can be tilted or distorted by geometric errors of machines or the holding fixtures, etc. To overcome these errors the off-line focusing error compensation method is proposed. By using confocal autofocus system, the focusing error profile of machined surface is measured along the pre-determined path and can be compensated at the next machining process by making the corrected motion trajectories. The experimental results for silicon wafers and invar flat surfaces show that the proposed method can compensate the focusing error within the level of below $6.9{\mu}m$ that is the depth of focus required for the laser micromachining process.