Determination of the glass wall effect in optical measurement of temperature in liquid using Mach–Zehnder interferometer
For optical experiments in which the change of refractive index is monitored, the refractive index of glass would change due to the change of temperature along the walls, and, as a result, the measurements of temperature and concentration would be affected. Because of this, one may use another temperature measurement technique parallel with a Mach–Zehnder interferometer (MZI). For instance, thermocouples or thermometers can be implemented inside the walls to obtain the temperature at the walls and close to the liquid region. The main limitation of this technique is that it provides information at a specific location and not along the walls or inside the liquid zone. On the other hand, the measurement is performed at the location close to the liquid region and not inside the liquid. Thus, in this study, we suggest using the optical method with some modifications that clear up the mentioned limitations. Accordingly, the optical effect of glass in the laser interferometry experiment is first studied. Then, we suggest two experimental methods based on modifications in the experimental setup and the image processing technique of MZI to accurately determine the glass effect and remove this effect from the temperature and concentration measurements. Implementing any of these techniques results in accurate measurement of the temperature and concentration of the liquid in any rectangular cell. Finally, according to the results of this study, it can be claimed that a temperature profile can be obtained precisely using MZI, and the existence of other apparatus to measure the temperature is redundant for the MZI setup. This outcome offers a simpler and more precise measurement of either temperature or concentration profiles of any transparent liquid.