Holographic optical tweezers aberration correction using adaptive optics without a wavefront sensor

摘要

Holographic or diffractive optical components, such as a spatial light modulator (SLM), can be used in optical tweezers for the creation of multiple and modified optical traps. In addition to this, SLMs can also be used to correct for aberrations within the optical train resulting in an improved trapping performance. Typically an electrically addressed SLM may deviate from flatness by up to 4λ, dominated by astigmatism due to the overall curvature of the SLM surface. This astigmatism may be corrected by adding the appropriate hologram to the SLM display resulting in a dramatic improvement in the fidelity of the focussed spot. The impact that this correction has on the performance of the optical trap is most noticeable for small particles. For the SLM used in this study, the improvement in trap performance for a 0.8 μm diameter particles can be in excess of 25%. However, for 5 μm diameter particles our results show an improvement of less than 0.5%. This dependence upon particle size is most probably associated with the relative size of the PSF and the trapped particle. Once the PSF is significantly smaller than the particle diameter, further reduction brings little improvement in trap performance.