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Laser ablation to form precision optics

in Powerkiting - Unna 20.02.2019 07:25
von xzbbvfvbh • 110 Beiträge

Precise shaping of optical components using conventional polishing methods, resulting in low wavefront distortion is an extremely difficult task, especially for optical components greater than 50 cm or less than 1 cm. Wavefront measurements are difficult, whether large or small. It is much more convenient if the optical components can be manufactured and measured at the same time. It is also convenient for medium-sized optics, but there are several options for handling procurement high efficiency UV and IR grade optical mirrors. Jitsuno and his colleagues at the Institute of Laser Engineering at Osaka University have developed a technique for simultaneous shaping and phase measurement with minimal wavefront distortion. This technique, called laser ablation, uses a 193 nm ArF excimer laser to shape the optics and a phase shift interferometer to detect aberrations in the field. Researchers have tried to shape glass and quartz in this way, but the debris makes the surface rough and unacceptable. But for plastics, the ablated material reacts with O2 in the atmosphere, and the amount of debris is negligible. Combining the uniform ablation properties of the plastic with the plano/spherical/aspherical/cylindrical/paraboloid/off-axis optical mirrors properties of the glass, a 50 μm thick UV-dried resin is applied to the glass substrate. The experimenter used an excimer laser to create a flat and spherical surface on a 5 cm diameter glass-plastic hybrid substrate. The luminous flux used is 45 mJ/cm2 to minimize surface roughness. Laser ablation shaping can re-form the microlens of the laser diode after installation to compensate for the position error plane. The wavefront distortion starting point is 3.0 λ, and after laser ablation, it drops to 0.17 λ on 90% of the surface. The spherical starting point is 2.5 λ, and an aspherical component with a wavefront of less than 0.2 λ is generated by shaping. The laser operates at 17 Hz and the process takes 4 hours. A good performance standard polisher takes 6 hours to achieve the same level of glass matrix. The precision and surface roughness that laser ablation can achieve make it widely used in general-purpose optics. It can also be used for the back-shaping of refractive optics. It may be especially suitable for micro-lens or single-mode fiber of laser diodes because It can also reshape the surface after assembly to compensate for positional errors. After the researchers published their results, they have been experimenting in this field. Because of the wavefront error in the laser diode, the Shack-Hartman sensor was used, which is more sensitive to surface ripples in polymethacrylate. Recently, they successfully smoothed the surface with ablation using a new customizable large size optical prism. Single mode fibers have proven to be easier, but the surface roughness is still unsatisfactory.

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