Measurement error resulting from the defocus and quadratic caustic of a line-detecting microscope in line scale measurement was investigated. The relationship between the lateral shift and defocus was clarified and a procedure for measuring the lateral shift without changing the tilt of the line scale under measurement was proposed. An experiment was performed on line scale measurement to demonstrate the proposed measurement procedure using a line scale calibration system. The calibration system used in this experiment was a one-dimensional, laser-interferometric length measurement system for line scales developed by Nikon. The calibration system features a reduced Abbe's error, laser interferometer paths installed in vacuum and real-time calibration of the wavelength of the Zeeman laser, which is used for length measurement, using a 633 nm iodine-stabilized He–Ne laser. The line scale used for the experiment was 300 mm in length, and made of glass ceramics. The experimental result of the lateral shift stemming from the defocus and quadratic caustic of the optics of the line-detecting microscope was approximately 4 nm for a defocus range of ±10 µm. The possibility of reducing this type of error was also discussed.

It has been shown in previous literature that nearly diffraction limited focusing is possible by a doublet metalens up to almost 30 deg. This result indicates that metalenses can work well, even at oblique incidence. Although various meta-atoms have been proposed, as far as we know, there is no report that compares what kind of meta-atom is robust against oblique incidence. Here, we first numerically calculated the incident angle dependence of the three types of meta-atoms. The results show that the waveguide-type structure is the most robust to oblique incidence. Next, we performed rigorous electromagnetic simulations for the cylindrical doublet metalenses to compare the micropost type and waveguide type. These results indicate that a waveguide-type metasurface further improves the off-axis performance of the doublet lens previously introduced.

Determining the dynamics of electrons and ions emitted from a target material during laser ablation is crucial for desirable control of laser processing. However, these dynamics are still challenging to understand because of a lack of ubiquitous spectroscopic tools to observe tangled-up dynamics appearing at ultrafast timescales. Here by harnessing highly sensitive single-shot terahertz time-domain spectroscopy using an echelon mirror, we investigate pulse-to-pulse temporal profile of terahertz radiation generated from the material surface. We clearly found that the carrier–envelope phase and the electric field amplitude of the terahertz waveform systematically vary between the pre- and post-ablation depending on the laser fluence and irradiated pulse numbers. Our results provide a stepping-stone towards perception of Coulomb explosion occurring throughout the laser ablation process, which is indispensable for future laser processing applications.

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