Profile Measurement by Using a Femtosecond Laser Chromatic Confocal Probe

2020 ◽  
Author(s):  
Ryo Sato ◽  
Yuki Shimizu ◽  
Hiraku Matsukuma ◽  
Wei Gao
Keyword(s):  
Thermal Stability ◽  
Femtosecond Laser ◽  
Surface Profile ◽  
Sample Surface ◽  
Measurement Range ◽  
Laser Source ◽  
Profile Measurement ◽  
Experimental Setup ◽  
Chromatic Confocal Probe ◽  
Surface Profile Measurement

Abstract Confocal probes are widely employed in many industrial fields due to the depth-sectioning effect. The author’s group has also proposed a chromatic confocal probe employing a mode-locked femtosecond laser source which can realize an axial resolution of 30 nm and a measurement range of 40 μm Efforts have also been made to improve the thermal stability of the developed femtosecond laser chromatic confocal probe so that the probe can be applied for long-term displacement measurement or surface profile measurement. Meanwhile, surface profile measurement has not been carried out by using the developed femtosecond laser chromatic confocal probe. For the verification of the performance of developed probe in profile measurement, in this paper, an experimental setup is built and a basic experiment is carried out. By using the probe with further improved thermal stability, the measurement of a sample surface profile is carried out. In this paper, the development of the experimental setup with the femtosecond laser chromatic confocal probe, as well as the results of the surface profile measurements, is presented.

scholarly journals Investigation and Improvement of Thermal Stability of a Chromatic Confocal Probe with a Mode-Locked Femtosecond Laser Source

2019 ◽  
Vol 9 (19) ◽  
pp. 4084 ◽  
Author(s):  
Ryo Sato ◽  
Yuki Shimizu ◽  
Chong Chen ◽  
Hiraku Matsukuma ◽  
Wei Gao
Keyword(s):  
Thermal Stability ◽  
Thermal Expansion ◽  
Femtosecond Laser ◽  
Thermal Instability ◽  
Theoretical Calculations ◽  
Surface Profile ◽  
Laser Source ◽  
Profile Measurement ◽  
Chromatic Confocal Probe ◽  
Thermal Stability Of

An intentional investigation on the thermal stability of a mode-locked femtosecond laser chromatic confocal probe, which is a critical issue for the probe to be applied for long-term displacement measurement or surface profile measurement requiring long-time scanning, is carried out. At first, the thermal instability of the first prototype measurement setup is evaluated in experiments where the existence of a considerably large thermal instability is confirmed. Then the possible reasons for the thermal instability of the measurement setup are analyzed quantitatively, such as the thermal instability of the refractive index of the confocal lens and the thermal expansion of mechanical jigs employed in the probe. It is verified that most of the thermal instability of the measurement setup is caused by the thermal expansion of mechanical jigs in the probe. For the improvement of the thermal stability of the probe, it is necessary to employ a low thermal expansion material for the mechanical jigs in the measurement setup and to shorten the optical path length of the laser beam. Based on the analysis result, a second prototype probe is newly designed and constructed. The improved thermal stability of the second prototype probe is verified through theoretical calculations and experiments.

Development of an Optical Angle Sensor With a Mode-Locked Femtosecond Laser Source for Surface Profile Measurement

2020 ◽  
Author(s):  
Yuki Shimizu ◽  
Shota Takazono ◽  
Yuri Kanda ◽  
Hiraku Matsukuma ◽  
Wei Gao ◽  
...  
Keyword(s):  
Femtosecond Laser ◽  
Surface Profile ◽  
Single Mode ◽  
Single Mode Fiber ◽  
Laser Source ◽  
Profile Measurement ◽  
Angle Sensor ◽  
Optical Setup ◽  
Optical Modes ◽  
Optical Angle Sensor

Abstract Angle sensors based on the laser autocollimation are often employed to evaluate surface profiles of a target of interest. The authors have developed a femtosecond laser angle sensor, in which a spectrometer or an optical spectrum analyzer with a single-mode fiber is employed as the photodetector for simultaneous capturing of the multiple optical modes. In this paper, the concept of the femtosecond laser angle sensor is applied to evaluate the surface profile of a target of interest. An optical setup is designed in such a way that each mode in the spectrum of the mode-locked femtosecond is utilized as the laser beam to measure the local slope of a measurement target at each different point to evaluate the surface profile. Some basic experiments are carried out by using the developed optical setup with a mode-locked femtosecond laser source to evaluate basic performances of the developed optical setup as an optical angle sensor.

scholarly journals Measurement Range Expansion of Chromatic Confocal Probe with Supercontinuum Light Source

2021 ◽  
Vol 15 (4) ◽  
pp. 529-536
Author(s):  
Hiraku Matsukuma ◽  
◽  
Ryo Sato ◽  
Yuki Shimizu ◽  
Wei Gao
Keyword(s):  
Light Source ◽  
Range Expansion ◽  
Wide Spectrum ◽  
Surface Profile ◽  
Measurement Range ◽  
Detection Sensitivity ◽  
Laser Source ◽  
Supercontinuum Light Source ◽  
Chromatic Confocal Probe ◽  
Measurable Range

Confocal probes have been widely adopted in various industries owing to their depth-sectioning effects. A dual-detector differential chromatic confocal probe using a mode-locked femtosecond laser source is proposed herein, and the measurement range expansion of the probe using a supercontinuum light source is discussed. Supercontinuum light has an extremely wide spectrum. A simulation based on wave optics is performed to evaluate the detection sensitivity and measurable range by considering the chromatic aberration of the lens materials. Additionally, an experimental setup is constructed using a supercontinuum light source, and its feasibility is validated. A measurable range of 200 μm is adopted in the experiment, and three-dimensional surface profile measurements are performed. However, the developed confocal probe has not been used for surface topography measurements. Experiments are conducted to verify the performance of the developed probe.

Dual differential confocal method for surface profile measurement with a large sensing measurement range

2020 ◽  
Vol 59 (3) ◽  
pp. 614
Author(s):  
Rongjun Shao ◽  
Weiqian Zhao ◽  
Lirong Qiu ◽  
Yun Wang ◽  
Ruirui Zhang ◽  
...  
Keyword(s):  
Surface Profile ◽  
Measurement Range ◽  
Profile Measurement ◽  
Surface Profile Measurement

An Electrostatic Force Probe for Surface Profile Measurement in Noncontact Condition

2013 ◽  
Vol 7 (6) ◽  
pp. 714-719 ◽  
Author(s):  
So Ito ◽  
◽  
Zhigang Jia ◽  
Shigeaki Goto ◽  
Keiichiro Hosobuchi ◽  
...  
Keyword(s):  
Electrostatic Force ◽  
Surface Profile ◽  
Sample Surface ◽  
Contact Condition ◽  
Scanning Probe ◽  
Profile Measurement ◽  
Electrostatic Probe ◽  
Probe Microscope ◽  
Basic Characteristics ◽  
Surface Profile Measurement

A scanning probe microscope with an electrostatic force probe has been introduced for the dimensional measurement of the surface profile measurement. Since the intensity of the electrostatic force is strongly depended on the distance between a probe and the sample surface, the electrostatic force probe can be used for the measurement of the surface profile in non contact condition. In order to detect the electrostatic force between the probe tip and the sample surface, a method of the frequency modulation AFM has been employed. When the bias voltage is applied between the probe and the surface, the resonance frequency of the probe oscillation is shifted owing to the electrostatic force. In this paper, the basic characteristics of the electrostatic probe are investigated, experimentally. And then, the absolute distance between the probe tip and the sample surface is calculated by using the differences of the frequency shift of the probe. Finally, the measurement of surface profile is demonstrated in non-contact condition by utilizing the developed electrostatic force probe.

scholarly journals An Off-Axis Differential Method for Improvement of a Femtosecond Laser Differential Chromatic Confocal Probe

2020 ◽  
Vol 10 (20) ◽  
pp. 7235
Author(s):  
Chong Chen ◽  
Yuki Shimizu ◽  
Ryo Sato ◽  
Hiraku Matsukuma ◽  
Wei Gao
Keyword(s):  
Femtosecond Laser ◽  
Focal Plane ◽  
Signal To Noise Ratio ◽  
Single Mode ◽  
Measurement Range ◽  
Single Mode Fiber ◽  
Differential Method ◽  
Laser Source ◽  
Dual Detector ◽  
Chromatic Confocal Probe

This paper presents an off-axis differential method for the improvement of a femtosecond laser differential chromatic confocal probe having a dual-detector configuration. In the proposed off-axis differential method employing a pair of single-mode fiber detectors, a major modification is made to the conventional differential setup in such a way that the fiber detector in the reference detector is located at the focal plane of a collecting lens but with a certain amount of off-axis detector shift, while the fiber detector in the measurement detector is located on the rear focal plane without the off-axis detector shift; this setup is different from the conventional one where the difference between the two confocal detectors is provided by giving a defocus to one of the fiber detectors. The newly proposed off-axis differential method enables the differential chromatic confocal setup to obtain the normalized chromatic confocal output with a better signal-to-noise ratio and approaches a Z-directional measurement range of approximately 46 μm, as well as a measurement resolution of 20 nm, while simplifying the optical alignments in the differential chromatic confocal setup, as well as the signal processing through eliminating the complicated arithmetic operations in the determination of the peak wavelength. Numerical calculations based on a theoretical equation and experiments are carried out to verify the feasibility of the proposed off-axis differential method for the differential chromatic confocal probe with a mode-locked femtosecond laser source.

scholarly journals A Method for Expansion of Z-Directional Measurement Range in a Mode-Locked Femtosecond Laser Chromatic Confocal Probe

2019 ◽  
Vol 9 (3) ◽  
pp. 454 ◽  
Author(s):  
Chong Chen ◽  
Ryo Sato ◽  
Yuki Shimizu ◽  
Taku Nakamura ◽  
Hiraku Matsukuma ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
Femtosecond Laser ◽  
Intensity Ratio ◽  
Theoretical Calculations ◽  
Expansion Method ◽  
Measurement Range ◽  
Laser Source ◽  
Peak Wavelength ◽  
Dual Detector ◽  
Chromatic Confocal Probe

A method is proposed to expand the Z-directional measurement range of a fiber-based dual-detector chromatic confocal probe with a mode-locked femtosecond laser source. In the dual-detector chromatic confocal probe, the Z-directional displacement of a measurement target is derived from the peak wavelength in the normalized intensity ratio from the two light intensities obtained by the two identical fiber detectors. In this paper, a new method utilizing the main-lobe and side-lobes of axial responses acquired from both the normalized intensity ratio Ia and the invert normalized intensity ratio In, which is the inverse of Ia, is proposed to obtain the seamless relationship between the peak wavelength and the Z-directional displacement of a measurement target. Theoretical calculations and experimental investigation are carried out to demonstrate the feasibility of the proposed measurement range expansion method.

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