| Since Dennis Gabor proposed holography in 1948,the development of laser and optocoupler devices has greatly promoted the rapid progress of digital holography.Digital holography uses charge-coupled devices to record holograms and use computer for numerical preocessing to achieve reconstruction of digital holograms.Digital holographic microscopy has been rapidly developed in recent years due to its flexibility in numerical reconstruction and its features of non-contact,high resolution,and realtime imaging.Microfluidic chip structured with micro-sized channels is a new kind of micro experiment platform for biochemical tests,also called as a microchip lab,in which some tests and experiments in biology,chemistry and bio-medicine can be implemented base on the microfluid effect in microchannels.In the past decade,despite the rapid development of microfluidic chip technology,the existing imaging detection methods can no longer meet the needs of real-time non-contact detection of microfluidic chips.Especially,for the enclosed microfluidic channels,there has been a lack of effective imaging methods.In addition,the current research on microfluidics is also limited by imaging methods,especially for the study on the microfluidic effect in transparent or near-transparent solutions.Unfortunately,the existing imaging means such as optical microscopy,electron microscopy and atomic force microscopy are not suitable for imaging microfluidic channels and microfluidics therein,so new microscopic imaging technology should be introduced.In this thesis,digital holographic imaging method for quantitative detection of microfluidic chip is investigated to achieve high-resolution 3D microscopic imaging for microchannels and micromaterials in a microfluidic chip.Main studies include: realtime dual-wavelength digital holographic imaging,spato-temporal digital holographic imaging with area scanning,and the measurement and characterization methods for imaging thin film by digital holography.The main research work and its results are summarized as follows:In the first part,real-time digital holographic imaging methods for microchannels and microfluidic solutions are studied.Firstly,a co-path digital holography imaging system based on polarization-multiplexing is builded.By using a pair of orthogonal polarization beams to transmit in the same optical interference path and to record hologram separately on a CCD sensor area in off-axis digital holographic system,simultaneous crosstalk-free recording of two holograms respective to two different wavelengthes is achieved.Secondly,based on the characteristics of Fourier spectrum distribution of off-axis digital holograms,off-axis spectrum automatic filtering algorithm and dual-wavelength spectrum correlation filtering algorithm are presented,and by using the algorithms,the first-order spectral information for single-and dual-wavelength digital holograms can be extracted accurately.In particular,the dualwavelength correlation spectrum filtering algorithm can quickly implement the filtering of two Fourier spectrums for dual-wavelength holograms,according to the position relationship of two holograms’ Fourier spectrums in the common-path setup;thirdly,the digital holographic measurement method of refractive index for liquid solution carried in microchannels is given,and then the refractive indexes of 10% sodium fluorescein solution and 5% polyamide solution each injected in Y-type microfluidic chip are obtained from their reconstructed phases,respectively.In the second part,based on the microfluidic motion characteristics in microfluidic channels,the improvement of imaging resolution with spatio-temporal scanning digital holography is studied.The process of synthesizing spatio-temporal holograms is described,and its effect of improvement on imaging resolution is analyzed.In addition,the imaging reconstruction method based on area scanning digital holograms and motion decomposition is presented,and the reconstruction procedures are discussed in detail.In the experiment,the area scanning digital holographic recording is performed with a USFA resolution target in motion.The results demonstrate that the presented area-scanning and synthesizing spatio-temporal holograms can effectively achive the improvement of image resolution along the scanning direction.Moreover,the speckle noise suppression for reconstruction imaging of spatio-temporal digital holograms is discussed.The enhancemen of the imaging fidelity by recording area-scanning holograms and constructing multiple phase-shift holograms is proposed,and the experiment results show that imaging resolution and signal-to-noise ratio of reconstructed images of a USFA resolution target are improved.Finally,in the spatiotemporal scanning digital holographic experiment,the high-throughput counting experiment of red blood cells flowing through the microfluidic chip pipeline is performed,and a three-dimensional counting algorithm for holographic particle image velocity tracing is proposed.In the third part,the method of using digital holographic imaging to characterize microfluidic effect of thin-film surface is investigated.The film thickness measured by digital holographic imaging is described.Furthermore,a single-wavelength digital holographic imaging system is used to measure the change in thickness of the central region of a bubble film,when it is close to rupture,and further the changes of film thickness with time and its radius during its drainage period are obtained.By establishing the space-time distribution map of the film drainage process,the digital holographic imaging and characterization of the microfluid effect during a thin-film drainage period by is realized,and the backflow phenomenon of the liquid flow on the film surface is shown clearly.According to the characteristics of particle tracking on the thin film,a digital holographic particle tracing algorithm based on image correlation recognition is given.Then,particle trajectory with fluid flowing on the surface of bubble film during the film growth process is achieved,by recording digital hologram of bubble film during its growth period and tracing the particles on the surface of bubble film.In summary,this thesis describes a digital holographic imaging method for quantitative detection of microfluidic chips,and implements digital holographic imaging measurement and characterization for microfluidic channel,micro structure,and microfluidic effects in microfluidics.The research work in this thesis provides an effective imaging means for some related fields. |
