Optical trapping and directional high-speed rotation by radiation pressure are demonstrated for anisotropic micro-objects fabricated by reactive ion-beam etching. These micro-objects, which have shape dissymmetry (not bilateral symmetry but rotational symmetry) in the horizontal cross section, rotate about the laser beam axis in the designed direction in a liquid medium (e.g., water or alcohol). The rotation speed is almost proportional to the input laser power.
The feasibility of room-temperature (RT) bonding of vertical-cavity surface-emitting laser (VCSEL) chips on silicon (Si) substrates with Au microbumps was demonstrated by Au–Au surface-activated bonding. The diameter at the top, the height, and the pitch of Au microbumps measured approximately 5, 2, and 10 µm, respectively. Following activation of the Au surfaces with argon radio-frequency plasma, Au–Au bonding was carried out using contact at RT in ambient air. The measured results of light–current–voltage (L–I–V) characteristics indicated no significant degradation of the VCSEL chips after bonding.
Fluorinated polyimide micro-objects (6–7.5 μm cross-sectional radius) fabricated using reactive ion etching have been both optically trapped and simultaneously rotated in both high and low relative–refractive index surrounding media. Symmetrical micro-objects with a low relative–refractive index were optically trapped by exerting optical radiation pressure through their center openings by using a strongly focused trapping laser beam. Micro-objects were both trapped and rotated by the radiation pressure when the horizontal cross sections of these objects showed dissymmetry (that is, not bilateral but rotational symmetry). In the case of micro-objects with a high relative–refractive index, the pressure is exerted on the outer walls. For objects with a low relative–refractive index, the pressure is exerted on the inner walls. The rotation speed versus optical power (typically, 0.4–0.7 rpm/mW) and the axial position of the laser focal point were investigated for high relative–refractive index micro-objects. The optically induced torque generated by a TEM01* (doughnut)-mode laser beam was found to be greater than that generated by a TEM00-mode laser beam.
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