Experimental Study on Broadband Coherent Anti-Stokes Spectroscopy
HOU Guo-hui, CHEN Bing-ling, LUO Teng, LIU Jie, LIN Zi-yang, CHEN Dan-ni*, QU Jun-le*
Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
Abstract：Our imaging system is based on a super-continuum source, which can provide all the samples’ active Raman vibration mode in a range from 0～4 000 cm-1 at the same time. The coming probe pulse interacts with the sample, forming the broadband coherent anti-Stokes Raman scattering (CARS) signal. Then, the image can be reconstructed according to the different chemical bonds, and the distribution of different chemical bonds in the sample can be obtained. In this paper, 110-nm pure polystyrene beads formed a certain thickness of thin films, which can endure high power, by tuning the detection pulse and super-continuum pulse overlay time, measuring the time distribution of the CARS signal and then using exponential decay curve fitting through a chemical bond signal intensity at 1 000 cm-1. This is called the dephasing time. Additionally, it was compared with the CARS dephasing time reported in the literature, and it was determined that it belonged to two-colour or three-colour CARS. To inspect the system application in biological imaging, we carried out the in vivo tissue biology application experiment through recorded data reconstructed in the CARS image at 2 940 cm-1 and the distribution of CH chemical bonds in tissues, and then directly used wavelet transform for image denoising. The denoised image had a clearer outline, and the results showed that the resonant part of the CARS signal contrast was strong and directly using the wavelet transform denoising method can obtain a better image effect. However, the signal-to-noise ratio of the resonant signal was poor, so the use of this approach was not appropriate, and other methods needed to be used to obtain a good signal contrast with the image. Then, according to the interest chemical bond with a good signal contrast to reconstruct image, after the wavelet transform for image denoising, the image will not only become clear and smooth, but have a good vision effect.
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