We discuss the refractive-index measurement of biological tissues by total internal reflection. The methodology of the measurement is illuminated comprehensively, and an experimental setup, combined with a data processing program, is developed correspondingly. Refractive indices of typical tissue samples are measured by use of the developed methodology. The agreement of our measurements with the reported results shows the validity of our scheme, which has the potential for being a simple, quick, and low-cost practical means for determining the refractive index of a turbid medium. Moreover, an empirical formula for evaluating the refractive index of Intralipid suspensions with different concentrations is also presented according to experimental measurements.
To apply reflection ellipsometry to determine the real and imaginary parts of the refractive index of biological tissues simultaneously, we combine reflection ellipsometry with total internal reflection to warrant minimal influences by the strong scattering and absorption of biological tissues. A K9 glass prism with refractive index 1.51468 at wavelength 632.8 nm and a Glan prism polarizer with an angular sampling interval of 0.1 degrees were used in our experimental setup. Using the setup, the complex refractive indices of some typical mammalian tissues were measured under the wavelength of 632.8 nm. The results show that the indices of porcine muscle, liver, pancreas, and dermis tissues were 1.3713+0.062i, 1.3791+0.0087i, 1.3517+0.0113i, and 1.3818+0.0049i, respectively.
A slightly-off-axis interferometry based Hilbert phase microscopy (HPM) method is developed to quantitatively obtain the phase distribution. Owing to its single-shot nature and details detection ability, HPM can be used to investigate rapid phenomena that take place in transparent structures such as biological cells. Moreover, the slightly-off-axis interferometry owns higher effective bandwidth and more sensitivity than traditional off-axis interferometry. The proposed method takes advantages of the above techniques to obtain the phase image of the red blood cells and compared with the traditional off-axis interferometry and phase retrieval algorithm based on the FFT. The experimental results show that the proposed method owns fine spatial details and real-time imaging ability. We are sure that the proposed method provides a breakthrough for real-time observing and quantitative analyzing of cells in vivo.
Pulsed laser ablation in liquid (PLAL) is gradually becoming an attractive approach for nanomaterial fabrication because it is a chemically simple and clean method with high product purity. We studied the laser interaction with bulk target and particle products in detail, including mechanism process, target morphology and nanoparticle products. We captured three oscillations of one bubble after laser ablates the bulk target and calculated the variation of pressure and temperature inside the bubble. The results show that the first bubble oscillation has greatest impact on the nanomaterial synthesis, and the most powerful stages for the material synthesis during all the bubble oscillations are the beginning of each expansions and the end of each shrinks. Nanomaterial releases from the bubble at the end of each oscillations. In addition, based on the analysis of ablation cavity on the target, it is found that the cavity depth increases with the number of laser pulses, and then the depth tends to be under saturation status, which means it is difficult to obtain great improvement of the nanomaterial productivity just by prolonging the laser irradiation time. More importantly, the strong interaction between laser and particle products is presented clearly by time-resolved shadowgraphy, which can contributed to the modification of nanoparticle products.
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