In general, k lenses with different materials can achieve at most ( k + 1 ) color correction ( k ≥ 2 ). A superachromat containing three lenses is designed to achieve five-color correction in the 600–1600 nm waveband, where the maximum chromatic focal shift is controlled within 1/100,000 of the focal length, achieving an almost unprecedented result. Conditions for lens power combination of three thin lenses in contact are first derived based on the Buchdahl dispersion equation; then a metric is introduced to verify the five-color correction, and a correction method is proposed to improve the refractive index fitting accuracy of the Buchdahl model from ∼ 10 − 3 to ∼ 10 − 7 . By traversing 197 ecofriendly glass materials in the CDGM glass library iteratively, 113 initial structures are obtained in only 61.75 s, from which the structure with the minimum chromatic focal shift is selected to be optimized with Opticstudio. By setting up required operands, the final structure being within the diffraction limit in a field of view of ± 0.05 ∘ is obtained within only 6 s, where the maximum longitudinal chromatic aberration is close to the maximum chromatic focal shift. We provide a complete theoretical basis and important guidance for designing broadband superachromats with ( k + 2 ) color correction using only k lenses and the smallest chromatic focal shift, and based on the theories, we have developed a broadband interferometer.

The measurement of aspheric surfaces is very difficult and challenging. An optical system with a single coated lens is proposed for measuring large-aperture aspheric convex/concave surfaces. In this system, the first surface of the compensator is used as an auto-collimation surface, which can realize high-precision null compensation. Based on the third-order aberration theory, the initial design parameters of the system are obtained by analytical calculation, and the parameters are then optimized numerically. An oblate spheroid with an equivalent aperture of 426 mm is taken as an example, and the measuring accuracy of the proposed method can achieve 0.0063 λ rms.

Digital holographic microscopy is an important measurement method for micro-nano structures. However, when the structured features are of high-slopes, the interference fringes can become too dense to be recognized. Due to the Nyquist’s sampling limit, reliable wavefront restoration and phase unwrapping are not feasible. To address this problem, the interference fringes are proposed to be sparsified by tilting the reference wavefronts. A data fusion strategy including region extraction and tilt correction is developed for reconstructing the full-area surface topographies. Experimental results of high-slope elements demonstrate the validity and reliability of the proposed method.

Potassium dihydrogen phosphate (KDP) crystals are widely used in high-power laser systems and inertial confinement fusion applications. However, machining KDP crystals using ultra-precision fly-cutting technology poses challenges due to the combined elastic, plastic, and brittle deformation mechanisms, making it difficult to analyze the material removal process. This investigation aims to observe and analyze the elastoplastic behavior of KDP crystals in the ductile region, which has received limited attention in previous studies. Nanoindentation experiments were conducted to analyze the elasto-plastic transition in KDP crystals, employing an approach instead of the traditional Oliver–Pharr method. Additionally, a cutting experimental method was developed to observe the reverse behavior during manufacturing by introducing a process with a 0 nm depth of cut. The results reveal significant rebound deformation and anelastic behavior, providing a comprehensive understanding of the deformation mechanism in KDP crystals at the nano- and micro-scale cutting levels. This knowledge contributes to modifying the diamond turning process and optimizing the fabrication procedure of KDP crystals.

Infrared deflectometry is an efficient and accurate measuring method for curved surfaces fabricated via grinding or finish milling. The emitting properties and geometrical configurations of the infrared light source is a core component governing the measurement performance. In this paper, an infrared slit light source is designed based on the cavity structure of a polyimide heating film. This design ensures good stability and uniformity of the light source whilst effectively reducing background noise. Additionally, the light source can be applied as a calibration board for calibrating infrared cameras. The light source is aligned using a theodolite and cubic prism to control the positional deviations during scanning. Experimental results demonstrate that the proposed slit light source and calibration method can achieve a measurement accuracy of 1 µm RMS, which can meet the needs of rapid measurement in grinding. This approach provides a reliable, cost-effective, and efficient tool for surface quality assessments in optical workshops and has a broad application potential.