Full Holonomic control of colloidal particles is achieved by combining mostly rotational magnetic manipulation with translational manipulation by holographic optical tweezers (HOT) in a single integrated setup shown in the Figure. This allows us to define arbitrary positions and orientations of individual and multiple particles of interest. The HOT is built using a fiber laser operating at 1064 nm with output powers of up to 10 W. The trapping beam passes through a polarizer (P), two lenses (L1, L2) forming a telescope used to re-size the beam diameter to slightly overfill the active area of a computer controlled, dynamically addressable LC-based Spatial Light Modulator (SLM), which generates a dynamic phase mask that creates and controls optical traps at a refresh rate of up to 20 Hz. The trapping beam is directed to the back aperture of a 100× NA=1.42 oil immersion objective via two lenses (L3, L4), linearly polarized by a half wave plate and polarizer and fed into the microscope by reflection from a dichroic mirror. Imaging is done through a combination of conventional polarizing microscopy and nonlinear optical imaging that can operate in both reflection and transmission modes, with reflection mode being the primary configuration when implementing full three-axis holonomic manipulation.
Integrated holonomic magnetic and holographic optical manipulation system. (a) Electromagnetic iron or air core solenoids arranged in an orthogonal Cartesian frame mounted on an inverted microscope. The solenoids are driven by amplified power supplies via computer controlled DAQ. The holographic optical trap (HOT) is comprised of a fiber laser at 1024 nm up to 10 W. Trapping optics: polarizer (P), lenses (L1, L2, L3, L4), computer controlled, dynamically addressable liquid crystal based Spatial Light Modulator (SLM), a 100× NA=1.42 oil immersion objective (OBJ), half wave plate (HWP), polarizer/rotator (PR) and a dichroic mirror (DM). The trapping beam is focused on the sample slide. This system is integrated with a powerful optical microscope that is capable of fluorescent confocal, three photon, and polarizing microscopy. (b) The magnetic and optical colloid handle can be translated along the x, y or z axis using the HOT, and rotated in yaw, pitch and roll using magnetic fields. This allows for full holonomic control.