Trapping Performance Measurement And Optimization Of Holographic Optical Tweezers

Holographic optical tweezers(HOTs)use the tightly focused laser beam to simultaneously capture multiple particles dynamically in 3D space.With the advantages of low photon-damage,high manipulation accuracy and non-mechanical contact,HOTs have been widely used in the study of micromechanics in the fields of biology and physics.In particularly,quantitative measurement of small forces and displacement with(HOTs)is finding increase findings.By loading computer generated hologram(CGH)in the system,a variety of complex light fields can be modulated to manipulate the particles in 3D space.CGHs are the key issue in achieving high-quality capture of HOTs.Although HOTs can generate a variety of optical fields to achieve complex manipulation of multiple particles,the most widespread and significant part is still the point light trap.Nowadays,a lot of hologram optimization algorithms have been widely reported,including direct and iterative algorithms,point light trap and continuous light field calculation methods.These algorithms have significant differences in efficiency,uniformity and calculation time of reproduced light fields,which will affect the performance of manipulation.However,the holographic optical trapping performance relying on the algorithms has not been studied systematically yet.Moreover,the calculation time of the high quality light field algorithm is very long,which affects the efficiency of the experiment seriously and makes it difficult to apply HOTs to real-time capture.In this thesis,we compared the light fields' intensity distribution,optical traps' stiffness,system's overall efficiency and calculation time of six hologram algorithms.And proposed a new CGH algorithm,which can significantly improve the calculation speed and reproduced light fields' resolution of large poing traps array.The research in this thesis covers the following aspects1.Theoretical analysis and systematic comparisons of the capture characteristics of HOTs based on six different CGH algorithms(GSW,GAA,GS,SR,S and RM algorithms)were given.We introduced the principles of the six algorithm and calibrated the performance of different particle sizes,different array sizes,random lattices,and dynamic manipulation.According to our results,a fact-based choice for how to choose a suitable computational hologram generation algorithm for different application scenarios has been provided.For the case of no requirement of calculation time,GSW performs best.When there is a need to generate holograms in real-time,SR algorithm is more suitable,but at the same time there will have problems of poor efficiency and uniformity of the optical trap.2.A further optimization HOTs system was built.We introduced the working principle of HOTs system in detail and provided the selection basis of key components.Moreover,the correction method for system aberrations,the pre-experiment preparations such as system calibration,sample preparation,etc.,the image processing method of the captured results and the calibration method of the optical trap stiffness were been described in detail.It provides a comprehensive and detailed operation guide for the capture experiment of HOTs.3.A new CGH algorithm which can generate large array optical traps in high manipulation accuracy and speed was proposed.We first optimized the speed of GSW algorithm,including phase truncation and GPU acceleration.The calculation time has been improved by more than 10 times.But due to the hardware limitations,large array light traps cannot be generated with GPU acceleration.Then,we proposed a new FFTGS algorithm based on Fast Fourier Transform.Zero padding was used to increase the position accuracy by 4 times and the phase truncation and GPU acceleration module was used to optimize the calculation speed by 10 times.