In this paper, we propose an effective method for extracting the important parameters like radius of curvature, conic constant, and deformation coefficients indwelling unknown aspheric surfaces. These parameters can be inversely found from measured data by using the method that is based on aspheric equations and conic surfaces. To demonstrate the precision of the method, it is compared with a higher-order polynomial curve fit, employing two different examples. In a theoretical case, each largest fitting error (or shape error) resulted from the two methods appears a significant difference in precision. Lastly, we apply the proposed method to a real example and show the results.
In this study, the evaluation method for the responsivity and noise characteristics of a commercial infrared thermal imaging camera and a custom-made sensor module was presented. Signal transfer functions (SiTFs) and noise equivalent temperature differences (NETDs) of the two sensor modules were obtained by using a differential mode blackbody that is able to control the temperature difference ΔT between an infrared target and its background. And we verified the suitability of our evaluation method through the comparison between the found NETD and the specification of the camera. In addition, the difference of 0.01 K of the two noise equivalent temperature differences calculated from with and without nonuniformity correction suggests that the nonuniformity correction is essential process for the evaluation of the infrared thermal imaging cameras. Finally, in case of the custom-made sensor module, only temporal NETD was found because of its higher nonuniformity characteristics.
We have developed a direct laser lithography system for fabrication of precision diffractive optical elements such as
Fresnel zone plates and computer-generated holograms. The developed lithography system has possible working area up
to 360 mm and minimum linewidth of 0.5 μm. To assure the performance of the lithography system, the performance
evaluation was carried out on the moving stages, the writing head module, and the light source, respectively. In this
paper, we report the performance evaluation including the standard uncertainties of each part, the combined standard
uncertainty, and finally the expanded uncertainty to give a particular level of confidence.
The auto-focusing is one of the important parts in the automated vision inspection or measurement using optical
microscopes. Moreover, laser micromachining or laser lithography requires a high speed and precision auto-focusing. In
this paper, we propose and realize an auto-focusing system using two cylindrical lenses, which is the enhanced version of
the previous astigmatism method. It shows very good performances, especially very high speed and the largest
defocusing range in comparison with the previous astigmatic methods. The performance of our auto-focusing system was
evaluated by tracing the linear stage whose position was monitored by a commercial laser interferometer.
We propose a new method based on direct laser writing to fabricate reference chromium patterns on a silicon wafer. Our
method is able to fabricate a maximum 360-mm-diameter pattern with 651-nm position uncertainty. The minimum
pattern size is about 0.8 μm (line width value) and the maximum available height of the pattern is slightly over 400 nm.
We present experimental results on the output power stabilization of an Ar<sup>+</sup> laser for a direct circular laser writing system (CLWS). Instability of the laser output power in the CLWS causes resolution fluctuations of being fabricated diffractive optical elements or computer-generated holograms. For the purpose of reducing the power fluctuations, we have constituted a feedback loop with an acousto-optic modulator, a photodetector, and a servo controller. Here very important things are proper conception of the servo controller and selection of a proper photodetector depending on what kinds of lasers to be controlled. In this system, we have achieved the stability of ± 0.20 % for 12 minutes and the relative intensity noise level of 2.1 x 10<sup>-7</sup> Hz<sup>-1/2</sup> at 100 Hz. In addition, we applied our system to a 2 mW internal mirror He-Ne laser. As a consequence, we achieved the output power stability of ± 0.12 % for 25 minutes.
KRISS Space Optics Research Center has tested large aspheric surfaces by using interferometry and a series of computer-generated hologram (CGH). In this case it is necessary to fabricate various CGHs in the laboratory level. To address this purpose we are developing and improving a simple and precise laser writing system which uses a cylindrical or circular coordinate. In our system 300 mm diameter CGH can be fabricated with 0.8 μm spatial resolution in radial direction. The writing source Ar+ laser is stabilized by intensity feedback, and gives us approximately 800 mW after the stabilization process at 457.9 nm wavelength. The stabilized beam power is controlled again to make 256 different intensity levels. We also used an auto-focusing technique with astigmatic lenses for the purpose of focusing the writing beam on the material surface.