| The research on the structure and function of neuronal networks is extremely important for understanding brain's information processing and integration mechanism. Two-photon microscopy (TPM) has the potential to become an important tool for neuronal networks'research, due to its advantages of high spatial resolution, deep penetration, and low photodamage. In order to detect the fast functional signal of neuronal networks at millisecond scale, the temporal resolution of TPM needs to be increased. In recent years, acousto-optic deflector (AOD) has become a popular beam scanner in developing fast scanning TPM, because the acousto-optic scanning does not involve mechanical inertia and can provide versatile scanning modes, such as fast raster scanning and random-access point scanning. Compared with the conventional galvanometer scanner, the scanning range of AOD is smaller, which leads to a small field of view (FOV) of TPM and therefore limits its applications in large neuronal networks. In order to obtain a two-photon microscope with large FOV, the frequency bandwidth will be widened to enlarge the system's scanning range in this thesis. Therefore, this study focuses on the development of wide-band AOD for TPM, and mainly includes three parts:the establishment of the thermal analysis method for AOD, the design and realization of wide-band AOD, and the construction of large FOV TPM based on wide-band AOD.(1) The thermal sources of AOD is analyzed which includes acoustic absorption and transducer heating. The methods of calculating heating power of both thermal sources are studied. Based on the finite element analysis (FEA) software, a numerical analyzing model for the thermal effects analysis is built. The spatial temperature distributions in the crystal and the temperature changes over time are acquired. The simulation results are validated by experimental results. Using this model, the device with more complicated structure can be simulated conveniently. The AOD's thermal performance in different heat dissipation schemes can be evaluated, which would be helpful in guiding the thermal design of high-power AOD.(2) Wide-band AOD is custom designed by means of improving the device's technical parameters. The new AOD works at 840 nm wavelength which is suitable for TPM. The experimental test results indicate that the 3- dB bandwidth of the new device reaches 60 MHz, and the diffraction efficiency is between 40% and 80%. The scan range increases to 74 mrad from the previous 47 mrad. All the operating frequencies are designed to be lower than 100 MHz to decrease the acoustic absorption. Unlike the commercial products, the bandwidth design in this study does not obey the one-octave principle, which has been proved to be feasible in the practice.(3) A TPM system based on the two-dimensional wide-band AODs is built. The research consists of the dispersion compensation, the systematic optical path, the hardware control, and software control. The imaging performances of the system are measured. The spatial resolution across the whole FOV is 0.58-2.12μm laterally and 2.17-3.07μm axially. The total scan range of the system reaches 93 mrad (5.3°), which can basically meet the requirement of 5-6°for most objectives. The FOV is 418μm under 40 X objective, which is more than twice as much as that based on conventional AODs. The AOD-based large FOV two-photon microscope could provide a new platfonn for researches on the structure and function of neural circuits.
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