Concept for three-dimensional optical addressing by ultralow one-photon absorption method.

With respect to experimental condition, we have investigated the point spread function of a high numerical aperture objective lens, taking into account the absorption effect of the studied material. By using a material possessing an ultralow one-photon absorption (LOPA) coefficient at the excitation wavelength, the light beam can penetrate deeply inside the material and be tightly focused into a subwavelength spot, almost the same as in the absence of material. Combining tight focusing and ultralow absorption conditions, we show that LOPA-based microscopy is thus capable of three-dimensional imaging and fabrication with long penetration depth up to 300 μm. As compared to the commonly used two-photon absorption microscope, the LOPA method allows simplification of the experimental setup and also minimization of the photodamaging or bleaching effect of materials.