Three-dimensional focusing through scattering media using conjugate adaptive optics with remote focusing (CAORF).

The small correction volume for conventional wavefront shaping methods limits their application in biological imaging through scattering media. We demonstrate large volume wavefront shaping through a scattering layer with a single correction by conjugate adaptive optics and remote focusing (CAORF). The remote focusing module can maintain the conjugation between the adaptive optical (AO) element and the scattering layer during three-dimensional scanning. This new configuration provides a wider correction volume by better utilization of the memory effect in a fast three-dimensional laser scanning microscope. Our results show that the proposed system can provide 10 times wider axial field of view compared with a conventional conjugate AO system when 16,384 segments are used on a spatial light modulator. We also demonstrate three-dimensional fluorescence imaging, multi-spot patterning through a scattering layer and two-photon imaging through mouse skull tissue.

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.

Submicrometer 3D structures fabrication enabled by one-photon absorption direct laser writing.

We demonstrate a new 3D fabrication method to achieve the same results as those obtained by the two-photon excitation technique, by using a simple one-photon elaboration method in a very low absorption regime. Desirable 2D and 3D submicrometric structures, such as spiral, chiral, and woodpile architectures, with feature size as small as 190 nm have been fabricated, by using just a few milliwatts of a continuous-wave laser at 532 nm and a commercial SU8 photoresist. Different aspects of the direct laser writing based on ultralow one-photon absorption (LOPA) technique are investigated and compared with the TPA technique, showing several advantages, such as simplicity and low cost.