Spatial Three-Mirror Off-Axis Freeform Optical System without Any Symmetry

Off-axis reflective microscope objective with a centimeter scale field of view and micron resolution

Microscope objectives with wide field-of-view (FOV) and high resolution are urgently needed for the frontier research in life sciences. However, traditional transmission microscope objectives typically have a narrow FOV and severe chromatic aberration. A new off-axis reflective microscope objective with a centimeter scale FOV and micron resolution is proposed in this paper. This objective, with its simple structure, can operate over a wide wavelength range. A design method for a wide FOV optical system is presented, which can eliminate the obstruction of the rays and control the intermediate image plane. Using this method, we design a novel off-axis four-mirror microscope objective with a FOV of 10 mm × 1.5 mm and a numerical aperture of 0.33.

Multi-field cosine condition in the design of wide-field freeform microscope objectives

To break through the limitations of the classical sine condition, a multi-field cosine condition (MCC) is proposed in this paper. Building on this condition, a design method for wide field-of-view (FOV) freeform aplanatic systems is also proposed. This design method ensures that the optical system meets the MCC by correcting the mapping relationships of rays that originate from different apertures on both the object and image sides of the optical system. Using this method, we have successfully designed a chromatic-aberration-free and unobstructed freeform off-axis reflective microscope objective that is characterized by a wide FOV, an extensive spectral working range, and an extended working distance. The objective, which comprises only three freeform mirrors, has a numerical aperture (NA) of 0.4, magnification of 20×, an FOV of 2 mm × 2 mm, and an extended working distance of up to 60 mm. The objective demonstrates imaging quality close to the diffraction limit across the visible band to the short-wave infrared band (0.4-3 µm). When compared with a transmission-type wide-field microscope objective with identical NA and magnification properties, the reflective microscope objective nearly triples the FOV.

Steep freeform measurement method based on a normal transverse differential confocal

A normal transverse laser differential confocal freeform measurement (NTDCFM) method was proposed to address the high-precision measurement difficulty of steep freeform surfaces with large variations in inclination, scattering, and reflectance. Using D-shaped diaphragm technology, the freeform surface under test (FSUT) axial variation transformed into a spot transverse movement on the detection focal plane. Meanwhile, a 2D position sensitive detector (PSD) was used to obtain the normal vector of the sampling points so that the measuring sensor's optical axis could track the FSUT normal direction. The focus tracking method extended the sensor measurement range. Theoretical analysis and experimental results showed that the axial resolution of the NTDCFM was better than 0.5 nm, the direction resolution of the normal vector was 0.1°, the maximum surface inclination could be measured up to 90°, the sensor range was 5 mm, and the measurement repeatability of the FSUT was better than 9 nm. It provides an effective new anti-inclination, anti-scattering, and anti-reflectivity method for accurately measuring steep freeform surfaces.