The optical properties of a biological tissue depend on its biochemical composition and its cellular and subcellular structure. In the visible and near-infrared range, the absorption properties are related to the concentration of chromophores, such as oxyhemoglobin and deoxyhemoglobin, fat and water [32]. Such chromophores vary significantly with tissue metabolism [33]. The scattering properties are related to the size distribution of cells and organelles, which are parameters used to differentiate normal from abnormal tissues in standard histopathology [34]. Therefore optical measurements have a strong potential for the development of noninvasive *in vivo* medical diagnostic tools, often called "optical biopsy". Such techniques should significantly improve the efficiency of biopsies or help in determining the tumor margins in a surgical field. According to our experimental data, the absorption coefficients, the reduced scattering coefficients, the optical penetration depths, the diffusion coefficients, the diffuse reflectance and the shifts of diffuse reflectance for normal stomach mucosa/submucosa tissues in the cardiac orifice at 635, 730, 808, 890 and 980 nm were determined in vitro. In our study, it is interesting to note the optical properties measured and their differences for the tissue samples at five different laser wavelengths. We believe the optical properties should help to pathological diagnosis and medical treatment for malignant or premalignant gastrointestinal mucosa with ease by using optical methods.

Figure 2 and Figure 3 show the absorption coefficients and the reduced scattering coefficients of tissue samples at five different laser wavelengths, respectively. From Figure 2 and Figure 3, it can be seen that the absorption coefficients for tissue samples increase with the increase of laser wavelengths, except for the absorption coefficient at 730 nm, and the reduced scattering coefficients for tissue samples decrease with the increase of laser wavelengths. There were significant differences in the absorption coefficients at five different laser wavelengths (*P* < 0.01). The maximum and the minimum absorption coefficients are 0.265 mm^{-1} at 980 nm and 0.0332 mm^{-1} at 730 nm, respectively. The maximum and the minimum differences of the absorption coefficients are 698% between 730 and 980 nm and 1.61% between 635 and 808 nm, respectively. There also were significant differences in the reduced scattering coefficients at five different laser wavelengths (*P* < 0.01). The maximum and the minimum reduced scattering coefficients are 1.19 mm^{-1} at 635 nm and 0.521 mm^{-1} at 980 nm, respectively. The maximum and the minimum differences of the reduced scattering coefficients are 128% between 635 and 980 nm and 1.15% between 890 and 980 nm, respectively.

Figure 4 shows that the optical penetration depths for tissue samples vary with the increase of laser wavelengths. There were significant differences in the optical penetration depths at five different laser wavelengths (*P* < 0.01). The maximum and the minimum optical penetration depths are 3.57 mm at 808 nm and 1.43 mm at 980 nm, respectively. The maximum and the minimum differences of the optical penetration depths are 150% between 808 and 980 nm and 5.36% between 730 and 890 nm, respectively. From Figure 5, it can be seen that the diffusion coefficients for tissue samples vary with the increase of laser wavelengths. There also were significant differences in the diffusion coefficients at five different laser wavelengths (*P* < 0.01). The maximum and the minimum diffusion coefficients are 0.608 mm^{-1} at 890 nm and 0.278 mm^{-1} at 635 nm, respectively. The maximum and the minimum differences of the diffusion coefficients are 119% between 635 and 890 nm and 12.0% between 890 and 980 nm, respectively. Figure 6 shows that the diffuse reflectance for tissue samples decrease with the increase of laser wavelengths. There were significant differences in the diffuse reflectance at five different laser wavelengths (*P* < 0.01). The maximum and the minimum diffuse reflectance are 0.456 at 635 nm and 0.0732 at 980 nm, respectively. The maximum and the minimum differences of the diffuse reflectance are 523% between 635 and 980 nm and 7.29% between 635 and 730 nm, respectively. From Figure 7, it can be seen that the shift Δx of diffuse reflectance for tissue samples vary with the increase of laser wavelengths. There also were significant differences in the shift Δx of diffuse reflectance at five different laser wavelengths (*P* < 0.01). The maximum and the minimum shift Δx of diffuse reflectance are 1.11 mm at 890 nm and 0.507 mm at 635 nm, respectively. The maximum and the minimum differences of the shift Δx of diffuse reflectance are 119% between 635 and 890 nm and 11.7% between 890 and 980 nm, respectively.

There are significant differences in the optical properties of the tissue samples between different wavelengths of laser (*P* < 0.01). Bashkatov, et al.[35] and Holmer et al.[36] have reported the optical properties of gastric tissue by different optical measurement methods, our data that the wavelength dependence of the absorption coefficient, the reduced scattering coefficient and the optical penetration depth of human stomach wall mucosa are very similar to compare the data of Bashkatov, et al. and Holmer et al. with our data in the spectral range from 600 to 1000 nm.