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- Engström, David, 1976, et al.
(författare)
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Calibration of spatial light modulators suffering from spatially varying phase response
- 2013
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 21:13, s. 16086-16103
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Tidskriftsartikel (refereegranskat)abstract
- We present a method for converting the desired phase values of a hologram to the correct pixel addressing values of a spatial light modulator (SLM), taking into account detailed spatial variations in the phase response of the SLM. In addition to thickness variations in the liquid crystal layerof the SLM, we also show that these variations in phase response can be caused by a non-uniform electric drive scheme in the SLM or by local heating caused by the incident laser beam. We demonstrate that the use of a global look-up table (LUT), even in combination with a spatially varyingscale factor, generally does not yield sufficiently accurate conversion forapplications requiring highly controllable output fields, such as holographicoptical trapping (HOT). We therefore propose a method where the pixeladdressing values are given by a three-dimensional polynomial, with twoof the variables being the (x;y)-positions of the pixels, and the third theirdesired phase values. The coefficients of the polynomial are determined bymeasuring the phase response in 8×8 sub-sections of the SLM surface; thedegree of the polynomial is optimized so that the polynomial expressionnearly replicates the measurement in the measurement points, while stillshowing a good interpolation behavior in between. The polynomial evaluationincreases the total computation time for hologram generation by onlya few percent. Compared to conventional phase conversion methods, for an SLM with varying phase response, we found that the proposed methodincreases the control of the trap intensities in HOT, and efficiently preventsthe appearance of strong unwanted 0th order diffraction that commonlyoccurs in SLM systems.
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| 2. |
- Engström, David, 1976, et al.
(författare)
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Grid-free 3D multiple spot generation with an efficient single-plane FFT-based algorithm
- 2009
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Ingår i: Optics Express. - 1094-4087. ; 17:12, s. 9989-10000
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Tidskriftsartikel (refereegranskat)abstract
- Algorithms based on the fast Fourier transform (FFT) for the design of spot-generating computer generated holograms (CGHs) typically only make use of a few sample positions in the propagated field. We have developed a new design method that much better utilizes the information-carrying capacity of the sampled propagated field. In this way design tasks which are difficult to accomplish with conventional FFT-based design methods, such as spot positioning at non-sample positions and/or spot positioning in 3D, are solved as easily as any standard design task using a conventional method. The new design method is based on a projection optimization, similar to that in the commonly used Gerchberg-Saxton algorithm, and the vastly improved design freedom comes at virtually no extra computational cost compared to the conventional design. Several different design tasks were demonstrated experimentally with a liquid crystal spatial light modulator, showing highly accurate creation of the desired field distributions.
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| 3. |
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| 4. |
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| 5. |
- Engström, David, 1976, et al.
(författare)
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Steering accuracy of a spatial light modulator-based single beam steerer: guidelines and limitations
- 2008
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Ingår i: SPIE Proceedings. - : SPIE. - 0277-786X .- 1996-756X. - 9780819472588
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Konferensbidrag (refereegranskat)abstract
- The positioning accuracy when a phase-only one dimensional spatial light modulator (SLM) is used for beam steering is limited by the number of pixels and their quantized phase modulation. Optimizing the setting of the SLM pixels individually can lead to the inaccuracy being a significant fraction of the diffraction limited spot size. This anomalous behaviour was simulated numerically, and experiments showed the same phenomena with very good agreement. However, by including an extra degree of freedom in the optimization of the SLM setting, we show that the accuracy can be improved by a factor proportional to the number of pixels in the SLM.
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| 6. |
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| 7. |
- Persson, Martin, 1979, et al.
(författare)
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Minimizing intensity fluctuations in dynamic holographic optical tweezers by restricted phase change
- 2010
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Ingår i: Optics Express. - 1094-4087. ; 18:11, s. 11250-11263
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Tidskriftsartikel (refereegranskat)abstract
- We present a method for reducing intensity fluctuations that typically occur when a spatial light modulator is updated between consecutive computer generated holograms. The method is applicable to most iterative hologram generating algorithms and minimizes the average phase difference between consecutive holograms. Applications with high stability requirements, such as optical force measurement with holographic optical tweezers, should benefit from this improvement. (C) 2010 Optical Society of America
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