Full Record

New Search | Similar Records

Author
Title Advances in Holographic Optical Trapping
URL
Publication Date
University/Publisher University of Gothenburg / Göteborgs Universitet
Abstract Holographic optical trapping (HOT) is a technique for non-invasive dynamic anipulation of multiple microscopic objects, which has been used for many applications in the life sciences during the past decade. The technique uses holographic beam steering with a spatial light modulator (SLM) to direct light to the desired positions of optical traps. In many cases, the control of the optical intensity of the traps is impaired by imperfections in the SLM. This has limited the use of HOT for applications sensitive to variations in the trap intensities, such as optical force measurement (OFM). Also, the algorithms for optimization of holograms used in HOT are computationally demanding, and real-time manipulation with optimized holograms has not been possible. In this thesis, four different methods for improving the accuracy of holographic beam steering are presented, along with a novel application for the combination of HOT and position measurement. The control of trap intensities is improved by compensating for crosstalk between pixels, and for spatial variations of the phase response of the SLM; and by dumping a controlled amount of light to specified regions away from the traps. Variations in trap intensities occurring when updating the SLM with new holograms are suppressed by enforcing a stronger correlation between consecutive holograms. The methods consist of modifications of the algorithm used for hologram generation, or alternative methods for post-processing of generated holograms. Applications with high stability requirements, such as OFM with HOT, will benefit from the presented improvements. A method for reducing computation time for hologram optimization is also presented, allowing the accuracy improvements to be used also for time critical applications. Further, it is shown that position measurement of nanowires, held by multiple optical traps, can be used to probe the orientational structure and defects in liquid crystal materials.
Subjects/Keywords Optical tweezers; Holographic optical trapping; Optical force measurement; Spatial light modulators; Holographic beam steering; Liquid crystals
Language en
Country of Publication se
Record ID handle:2077/32606
Other Identifiers 978-91-628-8697-4
Repository goteborg
Date Retrieved
Date Indexed 2020-01-03

Sample Search Hits | Sample Images

…where a HOT system is used to characterize liquid crystal materials by an unconventional optical manipulation method. After an introduction to optical tweezers and holographic optical trapping in 1.3 Structure of this Thesis chapter 2, the algorithms…

…viii Contents 1 Introduction 1.1 Optical Trapping . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Holographic Optical Tweezers . . . . . . . . . . . . . . . . . . . 1.3 Structure of this Thesis…

…1 1 2 2 2 Optical Trapping 2.1 Optical Forces . . . . 2.2 Single Trap Setup . . 2.3 Multiple Trap Setups 2.4 Holography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5 7 8 9 3 Holographic Beam Steering 3.1 Scalar…

…11 11 12 12 13 14 15 16 18 18 18 20 21 21 22 . . . . 27 27 28 28 29 . . . . . . . . . . . . . . . . 4 Liquid Crystals 4.1 Nematic LC . . . . . . . . . 4.2 Chirality . . . . . . . . . . . 4.3 The LC cell . . . . . . . . . 4.4 Electro-Optical…

…5 Spatial Light Modulators 5.1 Liquid Crystal SLMs Used in this Work . . . . . . . 5.1.1 Electrical Addressing . . . . . . . . . . . . . 5.1.2 Increased SLM Fill Factor . . . . . . . . . . 5.1.3 Optical Addressing . . . . . . . . . . . . . . 5.2…

…53 53 8 Optical Trapping in LC Materials 8.1 Nanowires in LC . . . . . . . . . . . 8.2 Optical Trapping of Nanowires in LC 8.2.1 Local Pitch Measurements . . 8.2.2 Probing Defects in Cholesteric 57 57 57 58 58 . . . . . . LC…

…61 References 67 x 61 62 63 Chapter 1 Introduction 1.1 Optical Trapping history of optical trapping dates back to 1970, when Arthur Ashkin T he showed how micrometer sized latex spheres could be trapped in the region of highest intensity of…

…two counter propagating laser beams [1]. Ashkin and coworkers at Bell Laboratories investigated optical levitation and dual beam trapping of dielectric objects and atoms throughout the 1970:s and early 80:s, gaining relatively little…

.