Diffractive hyperchromatic objective for chromatic confocal microscopy.

The limited focal shift of conventional achromatic objectives constrains the maximum imaging depth of chromatic confocal microscopes. To address this, we designed a hyperchromatic confocal microscope using diffractive optical elements, which was fabricated by single-point diamond turning (SPDT). This design takes advantage of the small Abbe number of diffractive optical elements to introduce a significant longitudinal chromatic shift. The resulting chromatic confocal microscope achieved a maximum imaging depth of 750 µm and a lateral resolution of 0.78 µm across a wavelength range of 600-810 nm. The system's imaging capabilities were demonstrated by capturing detailed images of biological samples, including cucumber seed cavities, pig kidney, and human forearm skin. These results confirmed the microscope's effectiveness in visualizing key cellular structures, underscoring its potential for high-resolution biological imaging.