[1] Denk W, Strickler J H, Webb W W. Two-photon laser scanning fluorescence microscopy[J]. Science, 1990, 248(4951): 73-76.
[2] Zipfel W R, Williams R M, Webb W W. Nonlinear magic: multiphoton microscopy in the biosciences[J]. Nature Biotechnology, 2003, 21(11): 1369-1377.
[3] Masters B R, So P T, Gratton E. Multiphoton excitation fluorescence microscopy and spectroscopy of in vivo human skin[J]. Biophysical Journal, 1997, 72(6): 2405-2412.
[4] Li H, Xia X Y, Chen T A, et al. Applications of two-photon excitation fluorescence lifetime imaging in tumor diagnosis[J]. Chinese Journal of Lasers, 2018, 45(2): 0207010.
[5] Wang J, Lin F. Progress of two-photon laser scanning fluorescence microendoscope based on optical fiber[J]. Laser & Optoelectronics Progress, 2010, 47(8): 081701.
[6] Zhao Y, Nakamura H, Gordon R J. Development of a versatile two-photon endoscope for biological imaging[J]. Biomedical Optics Express, 2010, 1(4): 1159-1172.
[7] Knittel J, Schnieder L, Buess G, et al. Endoscope-compatible confocal microscope using a gradient index-lens system[J]. Optics Communications, 2001, 188(5/6): 267-273.
[8] Wu Y C, Li X D. Combined influences of chromatic aberration and scattering in depth-resolved two-photon fluorescence endospectroscopy[J]. Biomedical Optics Express, 2010, 1(4): 1234-1243.
[9] Do D, Yoo H, Gweon D G. Fiber-optic raster scanning two-photon endomicroscope using a tubular piezoelectric actuator[J]. Journal of Biomedical Optics, 2014, 19(6): 066010.
[10] Li Z, Yang Z, Fu L. Scanning properties of a resonant fiber-optic piezoelectric scanner[J]. Review of Scientific Instruments, 2011, 82(12): 123707.
[11] Cui Q, Chen Z Y, Zhang Z H, et al. Recent advances in multicolor two-photon imaging technique[J]. Laser & Optoelectronics Progress, 2017, 54(6): 060002.
[12] Zong W J, Wu R L, Li M L, et al. Fast high-resolution miniature two-photon microscopy for brain imaging in freely behaving mice[J]. Nature Methods, 2017, 14(7): 713-719.
[13] Kingslake R. Lens design fundamentals[M]. Salt Lake City: Academic Press, 1978.
[14] Yan J, Zheng Y, Zheng X L, et al. Real-time optical diagnosis of gastric cancer with serosal invasion using multiphoton imaging[J]. Scientific Reports, 2016, 6: 31004.
[15] Zinter J P, Levene M J. Maximizing fluorescence collection efficiency in multiphoton microscopy[J]. Optics Express, 2011, 19(16): 15348-15362.