Future development

Simulations show that reducing the chamber height increases the force due to LIDEP without loosing any of the resolution. In this way, it should be possible to produce a stier trap with the same input light and voltage. To do this, it will be necessary to create a ow chamber for LIDEP as the present method of trapping the colloid between two plates would suer from evaporation. If the chamber is reduced to a height similar to the size of the particle the upper surface will also have an eect on the drag coecient of the particle making it harder to move. This may give an optimum height for the chamber for a given particle size.

Figure 4.33: Scratches in the photoconductive layer cause electric eld gra- dients larger than those created by the light induced electrode. This causes the particles to be attracted to the faults rather than the light.

sary to know the size of the electrical trap created by a given optical spot, as we have shown here, but the minimum optical power necessary to produce this trap. For this reason future work should include reducing the optical power and remeasuring the LIDEP trap size. With these two pieces of information it would be possible to calculate the optimum amount to demagnify the im- age from a data projector onto the photoconductive surface so that the least number of pixels are used to create each LIDEP trap.

Another limitation of LIDEP is the need for a faultless photoconductive layer. Any scratches or imperfections in this layer create larger electric eld gradients than those created by the light induced electrode (see gure 4.33). This causes the particles to be attracted to the faults rather than the light. One way to make more uniform substrates may be to use sputtering rather than vapor deposition to produce the lm of a-Si:H. It may also be possible to use a photo-conducting polymer such as polyvinyl carbazole (PVK) to produce a more uniform photoconductive layer.

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[5] Value taken from Wikipedia www.wikipedia.org

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Conclusions

5.1

Microgears

We have demonstrated the design, fabrication and testing of form birefringent microgears. The form birefringence allows the transfer of Spin Angular Mo- mentum (SAM) from a circularly polarised beam to the microgears causing them to rotate. The rst microgears were made from silicon however it was found that they were not attracted to areas of high intensity as the scattering forces were stronger than the optical gradient force. Using the lower refrac- tive index of SU-8 allowed the microgears to be optically trapped leading to a successful demonstration of optically actuated rotation. The magnitude of the birefringence was measured as ∆nef f = 0.015±0.001 which was similar

to the simulated value of ∆nef f = 0.018±0.001. The microgears rotated at a