Aberration correction in holographic optical tweezers

Abstract

Abstract:Holographic or diffractive optical components are widely implemented using spatial light modulators within optical tweezers to form multiple, and/or modified traps. We show that by further modifying the hologram design to account for residual aberrations, the fidelity of the focused beams can be significantly improved, quantified by a spot sharpness metric. However, the impact this improvement has on the quality of the optical trap depends upon the particle size. For particle diameters on the order of 1 µm, aberration correction can improve the trap performance metric, which is the ratio of the mean square displacement of a corrected trap to an uncorrected trap, in excess of 25%, but for larger particles the trap performance is not unduly affected by the aberrations typically encountered in commercial spatial light modulators.

Design strategies for optimizing holographic optical tweezers set-ups

“…Figure 10b (left and right) corresponds to the images captured at the two foci when a pair of optical traps is generated. The effect, which also takes place at normal incidence, reveals the lack of flatness of the device surface and seems to be a widespread problem [35]. Figure 11.…”

“…Figure 12b shows the captured images of the two traps at the mid-point of the two foci (left) and the spots after correction (right). A more quantitative approach to characterizing and correcting SLM aberrations can be found in [35]. A final possibility for determining phase correction would be to use a Shack-Hartmann wave-front sensor, as this allows accurate and automated measurements of the wave aberration.…”

Spatial fluorescence cross‐correlation spectroscopy by means of a spatial light modulator

“…The exact values were dependent upon the location of the laser beam on the LCOS micro display and upon the flatness of its surface, which is mechanically deformable. Then, we investigated the possibility of correcting the distorted wavefront by addressing spherical and astigmatism corrections to the SLM [21]. However, the efficiency of this method was found to be quite limited because the amplitude of the phase modulation of our LCOS device is λ/2, while the total wave-front distortion overcomes this value (see Fig.…”

Holographic aberration correction: optimising the stiffness of an optical trap deep in the sample

“…Optimising the stiffness of the optical trap is crucial for a range of applications such as trapping nanoparticles, reducing laser damage in biological samples and minimising the required power for creating complex optical landscapes [3]. Research investigating aberration correction based on a spatial light modulator (SLM) includes correcting for system intrinsic aberrations like astigmatism [4][5][6] and optimising beam quality for focusing through turbid media [7,8].…”