Study On Temporal Dispersion And Optimazation Of Spatial Arrangement In Optical Time-stretch Imaging

Optical time-stretch imaging(OTSI)with temporal resolution of picosecond and spatial resolution of micrometer is a new type of ultrafast imaging technology developed in recent years.As a crucial diagnostic and detection tool,it has shown enormous value of scientific and application on ultrafast and non-repeated transient phenomena in the fields of microscopic particle detection,chemical dynamics research and biological cell imaging.The working principle of OTSI is mainly divided into two aspects.One is the frequency to time mapping based on the theory of dispersion Fourier transform,which converts the pulse with spatial information in frequency-domain into time-domain.The second is the spatial to frequency mapping based on spectral encoding principle,which encodes the spatial information of the sample onto the spectra of the pulse in frequency-domain by utilizing scanning beam in spatial field.However,the spectrum of optical time-stretch imaging is generally limited to 1550 nm wavelength band due to the inherent limitations of traditional temporal dispersive media,which affects the promotion of its application fields.And the study on the improvement of coupling efficiency in fiber also have shortcomings.This dissertation aims at the issues and research deficiencies mentioned above in the current OTSI system.The exploratory researches on temporal dispersion and the optimization of spatial arrangement in the system have carried out by combining with three type of newly time-domain dispersion configuration and spectral encoding in space using 4-f system.The above is based on the relationship between angular dispersion and time dispersion,material dispersion,and 4-f system.The main contents and innovations are as follows:In terms of temporal dispersion,firstly,the theoretical model of the temporal dispersion of the grating pair structure is studied.The dispersion of-10.2 ps/nm/m is obtained at 0.8 μm wavelength region,and the time-stretch imaging scheme based on the grating pair structure is proposed.The theoretical temporal resolution and spatial resolution of the system can reach 14.3 ps and 16 μm,respectively.Secondly,the temporal dispersion of the prism pair structure and the principle of pulse stretching are studied.The dispersion of-0.5 ps/nm/m can be obtained at 2.0μm wavelength region.A ultrafast time-stretch imaging scheme based on the prism pair is proposed,which can theoretically achieve the maximum time resolution of 11.5 ps and the dispersion loss of less than 1 d B.Thirdly,a time-stretch imaging scheme based on transparent media is proposed,and the temporal dispersion structure of transparent media is designed.The theoretical dispersion of 15 ps/nm/m can be obtained in the wavelength band of 0.62μm,and the imaging system has a temporal resolution of 0.6 ps and a spatial resolution of 28 μm.As a key part of the optical time-stretch imaging,spectral encoding in space plays a decisive role in the transmission efficiency of optical field of the whole system.The coupling system structure is optimized in this subject.By combining the 4-f system and spectral encoding,the spectrally encoded imaging has been designed based on the 4-f configuration with symmetric arrangement,which improved the coupling efficiency of free space light to optical fiber from less than 20% to 70%.A high-efficiency spectrally encoded imaging experiment using 4-f system was implemented on the self-made sample and natural objects,simultaneously.This thesis studies the temporal dispersion of three novel arrangements,and expands the applicable spectral range of the OTSI system to visible and near-infrared bands.The optical loss,cost and complexity of the system can be effectively reduced at the same time.The spectrally encoded system based on 4-f configuration can greatly improve the coupling efficiency and the energy utilization.The innovative research of this project provides significant theoretical guidance and practical application value for further expanding the application of optical time-stretch imaging and improving the performance of the system.