Hybrid endomicroscopic objective with monolithic multi-material achromatic triplet fabricated using two-photon lithography

We report a hybrid miniaturized achromatic objective for nonlinear endomicroscopy that combines two-photon polymerization (2PP)-fabricated polymer optics with a commercial glass lens. The objective achieves 0.6 numerical aperture with dual-wavelength correction at 775 and 860 nm and a 200 µm field of view, all within a 3 mm housing compatible with a hypodermic tube. Fabrication leverages sequential multi-step two-photon polymerization (2PP) to produce a monolithic multi-material triplet with submicron precision. The triplet incorporates two photoresists with different dispersion properties printed in successive steps with post-processing and marker-based realignment between steps, yielding a single monolithic optic that eliminates adhesives while correcting chromatic aberrations. Imaging tests with USAF resolution targets, biological samples, and two-photon fluorescence microscopy of pollen grains demonstrate near-diffraction-limited performance across the design wavelength range. The approach offers a practical method for compact optical systems in biomedical applications.