Optical detrapping in KTN deflectors by light in the near-infrared imaging window

Electro-optical deflectors (EODs) offer unparalleled scanning speed for laser-scanning microscopy and other applications, but suffer from limited deflection range. EODs based on potassium tantalate niobate (KTN) crystals feature some of the highest numbers of resolvable spots. These deflectors rely on internal electric fields generated by trapped electrons to enable beam scanning. However, visible light induces rapid optical detrapping of trapped charges, and thus, KTN-based deflectors are typically continuously recharged with a bias voltage that effectively limits the range of the deflector. Recent work has proposed the use of KTN-based EODs for biological imaging with infrared excitation light, but quantitative data on near-infrared optical detrapping is lacking. Here, we present quantitative measurements of optical detrapping in KTN deflectors across the NIR-I and NIR-IIa biological imaging windows (700–1300 nm), a range that is particularly important for deep tissue imaging and nonlinear microscopy. Using a two-beam polarization interferometer, we measured trapped charge density as a function of photon fluence. We observed that the optical detrapping rate decreases dramatically with increasing wavelength. The charge density decay curves exhibit multi-exponential behavior that cannot be explained by a single-trap model without recapture, indicating the presence of multiple trap species or substantial recapture. These measurements provide critical quantitative guidance for selecting operating wavelengths and charge-scan duty cycles for KTN-based EODs in near-infrared imaging applications.