We present a holographic optical tweezers system capable of position clamping multiple particles. Moving an optical trap in response to the trapped object's motion is a powerful technique for optical control and force measurement. We have now realised this experimentally using a Boulder Nonlinear Systems Spatial Light Modulator (SLM) with a refresh rate of 203Hz. We obtain a reduction of 44% in the variance of the bead's position, corresponding to an increase in effective trap stiffness of 77%. This reduction relies on the generation of holograms at high speed. We present software capable of calculating holograms in under 1 ms using a graphics processor unit. and force in optical tweezers using high-speed video microscopy," Opt. Express 16, 14,56114,570 (2008). 13. P. J. Rodrigo, L. Gammelgaard, P. Bøggild, I. Perch-Nielsen, and J. Glückstad, "Actuation of microfabricated tools using multiple GPC-based counterpropagating-beam traps," Opt. Express 13, 6899-6904 (2005
High-resolution, liquid-crystal spatial light modulators (SLMs) are being used as dynamic phase screens 1,2 for testing optical systems and as optical wavefront compensators 3,4 to dynamically correct distortions. An SLM provides hundreds of waves of adjustable phase modulation across the aperture of the device. Some of this phase adjustment can be used to compensate for distortions internal to the SLM such as backplane curvature. Because of modulo-2π operation, the dynamic range of the device is not significantly decreased by adding phase compensation, as long as the phase shift over the aperture is only a few waves. In this paper, we will discuss the techniques being used to determine the correct phase compensation for SLMs and how the compensation is being applied through the SLM control software.
Visual and dynamical measurement of Rayleigh-Benard convection by using fiber-based digital holographic interferometry J. Appl. Phys. 112, 113113 (2012) Guide-star-based computational adaptive optics for broadband interferometric tomography Appl. Phys. Lett. 101, 221117 (2012) Limits of elemental contrast by low energy electron point source holography J. Appl. Phys. 110, 094305 (2011) Cantilever biosensor reader using a common-path, holographic optical interferometer Appl. Phys. Lett. 97, 221110 (2010) Extended depth of focus in a particle field measurement using a single-shot digital hologram Appl. Phys. Lett. 95, 201103 (2009) Additional information on Rev. Sci. Instrum. Holographic optical tweezers have found many applications including the construction of complex micron-scale 3D structures and the control of tools and probes for position, force, and viscosity measurement. We have developed a compact, stable, holographic optical tweezers instrument which can be easily transported and is compatible with a wide range of microscopy techniques, making it a valuable tool for collaborative research. The instrument measures approximately 30×30×35 cm and is designed around a custom inverted microscope, incorporating a fibre laser operating at 1070 nm. We designed the control software to be easily accessible for the non-specialist, and have further improved its ease of use with a multi-touch iPad interface. A high-speed camera allows multiple trapped objects to be tracked simultaneously. We demonstrate that the compact instrument is stable to 0.5 nm for a 10 s measurement time by plotting the Allan variance of the measured position of a trapped 2 μm silica bead. We also present a range of objects that have been successfully manipulated.
Improvements in silicon foundry processes have made possible high-resolution, light-efficient backplanes capable of driving electro-optic modulators with higher voltage signals. The higher voltage provides the excitation to achieve sub-millisecond response times with a wave of phase modulation when used with dual-frequency nematic liquid crystals. By combining dual-frequency phase modulators with high-voltage silicon backplanes, compact spatial light modulators become available for applications that need fast, high-throughput modulators such as optical signal processing, adaptive wavefront correction, optical signal routing or beamsteering, and active diffractive optics.
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