09:30 〜 09:45
▲ [19a-H116-3] Spatiotemporal link in optical frequency comb for sub-micron axial resolution imaging of a meter-order depth object
キーワード：Mode-locked lasers,Three-dimensional image acquisition,Interferometric imaging
Imaging at the radio frequency (RF) region is nowadays very useful because of a great potential for large volume metrology. Recently the appearance of a commercial frequency comb laser has allowed us to realize the imaging system using the long wavelength. The RFs generated by the beat signals of the harmonic frequency orders in the optical domain of the optical frequency comb laser can be observed and employed to measure meter-order depth object with accuracy of 4 μm at the root mean square error based on a single pixel camera. However, the accuracy was insufficient for general purposes in industrial mechanical parts measurement that is always required sub-micrometer accuracy. Additionally, the number of sampling points of 10 × 10 was also not high enough. Additionally, the optical frequency comb laser can be also used as an ultra-broad band one to achieve the profile of an object with much more precise and higher dynamic range by several interferometric methods. The optical interferometer has high lateral resolution and nanometer-ordered axial accuracy, but the disadvantage is short measurement range.
In this presentation, by combining the advantages of both of two interferometers using a spatiotemporal matching method, the object with meter-order depth can be measured with micro-scale lateral resolution and nanometer-scale axial accuracy. The proposed system was carried out in two steps. In the first step, the profile of the object with low spatial resolution was fast measured by the frequency comb interferometer by means of a single pixel camera. In the second step, the measurement was implemented by the optical interferometer using Michelson setup. Employing the profile obtained in the previous step, the reference mirror was moved to an appropriate position so that the very accurate and high lateral and axial resolution object’s profile can be partly observed by using low-coherence interference chromatic phase shifting technique. The profile of the object obtained by the optical interferometer was considered as an linear regression of the one reconstructed by frequency comb interferometer, therefore the profile of the object observed by optical interferometer was moved to the appropriated position based on the one obtained by frequency comb interferometer, the standard deviation (SD) was calculated by two profiles, the best matching position between frequency comb and optical interferometers was determined by the minimum SD value. The combination of two interferometers by matching the relative phases allowed measuring the meter-order depth object profile with and sub-micron resolution.
In this presentation, by combining the advantages of both of two interferometers using a spatiotemporal matching method, the object with meter-order depth can be measured with micro-scale lateral resolution and nanometer-scale axial accuracy. The proposed system was carried out in two steps. In the first step, the profile of the object with low spatial resolution was fast measured by the frequency comb interferometer by means of a single pixel camera. In the second step, the measurement was implemented by the optical interferometer using Michelson setup. Employing the profile obtained in the previous step, the reference mirror was moved to an appropriate position so that the very accurate and high lateral and axial resolution object’s profile can be partly observed by using low-coherence interference chromatic phase shifting technique. The profile of the object obtained by the optical interferometer was considered as an linear regression of the one reconstructed by frequency comb interferometer, therefore the profile of the object observed by optical interferometer was moved to the appropriated position based on the one obtained by frequency comb interferometer, the standard deviation (SD) was calculated by two profiles, the best matching position between frequency comb and optical interferometers was determined by the minimum SD value. The combination of two interferometers by matching the relative phases allowed measuring the meter-order depth object profile with and sub-micron resolution.