Dual fiber probe with 3D-printed micro-lens for Brillouin microscopy

Brillouin spectroscopy is a powerful technique for non-invasive micromechanical analysis of biological materials such as tissues and cells. Conventional bulk-optical Brillouin spectroscopy systems, however, face challenges in translation to endoscopic applications due to strong parasitic background signals using single optical fibers. To overcome this issue, dual fiber approaches have been proposed, but they suffer from poor overlap of excitation and collection beam paths. In this work, we present a dual fiber-integrated probe with a tip diameter below 300 μm. Using tailored freeform 3D-printed micro-optics, we achieve a precise overlap of the foci to map mechanical properties with a resolution below 10 μm in lateral and 45 μm in axial direction. We detail the probe's design, fabrication, and optical simulations and present experimental results demonstrating high-resolution Brillouin measurements from polymer and protein solution samples. Our findings indicate that this dual fiber probe could significantly advance fiber-integrated Brillouin spectroscopy, with promising applications in materials science and biomedical diagnostics.