Effects of a laser beam profile to measure an aspheric mirror on a high-speed nanoprofiler using normal vector tracing method

Matsumura, Hirotoshi; Tonaru, Daisuke; Kitayama, Takao; Usuki, Koji; Kojima, Takao; Uchikoshi, Junichi; Higashi, Y.; Endo, K.

doi:10.1016/j.cap.2012.04.022

Cited by 6 publications

(1 citation statement)

References 3 publications

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“…The surface shape is obtained from the normal vectors and their coordinates using a reconstruction algorithm. The machine consists of an optical system with two goniometers and one linear motion stage and a specimen system with two goniometers [ 9 , 10 ].…”

Section: Reviewmentioning

confidence: 99%

Profile measurement of concave spherical mirror and a flat mirror using a high-speed nanoprofiler

et al. 2013

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Ultraprecise aspheric mirrors that offer nanofocusing and high coherence are indispensable for developing third-generation synchrotron radiation and X-ray free-electron laser sources. In industry, the extreme ultraviolet (wavelength: 13.5 nm) lithography used for high-accuracy aspheric mirrors is a promising technology for fabricating semiconductor devices. In addition, ultraprecise mirrors with a radius of curvature of less than 10 mm are needed in many digital video instruments. We developed a new type of nanoprofiler that traces the normal vector of a mirror's surface. The principle of our measuring method is that the normal vector at each point on the surface is determined by making the incident light beam on the mirror surface and the reflected beam at that point coincide, using two sets of two pairs of goniometers and one linear stage. From the acquired normal vectors and their coordinates, the three-dimensional shape is calculated by a reconstruction algorithm. The characteristics of the measuring method are as follows: the profiler uses the straightness of laser light without using a reference surface. Surfaces of any shape can be measured, and there is no limit on the aperture size. We calibrated this nanoprofiler by considering the system error resulting from the assembly error and encoder scale error, and evaluated the performance at the nanometer scale. We suppressed the effect of random errors by maintaining the temperature in a constant-temperature room within ±0.01°C. We measured a concave spherical mirror with a radius of curvature of 400 mm and a flat mirror and compared the results with those obtained using a Fizeau interferometer. The profiles of the mirrors were consistent within the range of system errors.

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Section: Reviewmentioning

confidence: 99%

Profile measurement of concave spherical mirror and a flat mirror using a high-speed nanoprofiler

et al. 2013

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High-accuracy three-dimensional aspheric mirror measurement with nanoprofiler based on normal vector tracing method

Kudo

Kitayama

Tokuta

et al. 2017

Optics and Lasers in Engineering

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On-machine self-calibration of rotary encoders in the normal vector tracing method

Miyawaki

Watanabe

Endo

2022

Review of Scientific Instruments

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We developed a nano-profiler to determine the shape from slope distribution data for highly accurate free-form surface shape measurement; for example, high-precision optical systems are required in the x-ray and semiconductor fields. An accuracy of ±0.2 µrad is required to achieve a shape measurement accuracy of 30 nm. The angle of the rotary stage is controlled by the rotary encoder, and the calibration curve of the rotary encoder is guaranteed by the national standard machine. However, the error associated with assembling the rotary encoder to the device is not included in the national standard machine's calibration data. Therefore, we propose a method that combines self-calibration with six encoder heads and calibration with a national standard machine. Using this method reduces the extent of calibration by the national standard machine and minimizes the influence of the assembly error. Furthermore, to verify whether the calibration in the proposed method is appropriate, a new encoder for evaluation was installed and evaluated. The results revealed that the influence of the assembly error was reduced to the minimum, and the difference in the calibration between the encoder for evaluation and the national standard machine was 0.027 µrad.

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Effects of a laser beam profile to measure an aspheric mirror on a high-speed nanoprofiler using normal vector tracing method

Cited by 6 publications

References 3 publications

Profile measurement of concave spherical mirror and a flat mirror using a high-speed nanoprofiler

Profile measurement of concave spherical mirror and a flat mirror using a high-speed nanoprofiler

High-accuracy three-dimensional aspheric mirror measurement with nanoprofiler based on normal vector tracing method

On-machine self-calibration of rotary encoders in the normal vector tracing method

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