Remote focusing optical tweezers for 3D imaging

We present a remote focusing optical tweezer utilizing a 4f symmetrical optical system to compensate the high-order aberration during annular light refocusing. The position of the optical trap can be adjusted beyond the range of one hundred micrometers in the axial direction by means of tuning the position of the mirror placed in the focal region of the illumination objective lens. This optical tweezer can be combined with a sectioning microscope to realize three-dimensional (3D) imaging, e.g., a confocal microscope using a single water immersion objective lens. All optical elements are placed in one side of the sample, which is very useful for application in fields such as radiation biology, where radiation or magnetism disturbance must be introduced on the other side of the sample. In the experiment, a 10 µm diameter silicon dioxide microsphere and pollen cells immersed in the water are translated along the axis using the optical tweezer and, meanwhile, the sectioning images are obtained using the confocal microscope.