The liquid refractive index is one of the important optical parameters reflecting the properties of solution. A simple scheme based on shading effect for measuring liquid refractive index is presented. When a light beam passes through the liquid, the total reflection occurs at the interface with the air to produce a shading effect, forming a circular shading pattern, and its radius is related to the refractive index of the liquid. Based on this principle, a liquid refractive index measurement system based on smartphone is built. A rectangle colorimetric dish with tested liquid is illuminated by He-Ne laser. A white stickable label paper is attached to one side of colorimetric dish. Then the circular shading pattern displayed on label paper can be recorded by smartphone. A smartphone data processing program was developed to calculate the liquid refractive index from the image taken by smartphone. System calibration and smartphone shooting parameters are discussed in detail. The refractive index measurement experiments of sucrose solution and sodium chloride solution with different concentrations demonstrate the feasibility and effectiveness of the proposed method.
We present a simple and effective method for dual-wavelength phase imaging in Lensless Reflection Digital Holographic Microscopy (LRDHM). A filter is inserted between beam splitter and mirror in LRDHM. By adjusting the filter and mirror, the propagation directions of two reference beams of different wavelengths can be separated, and thus two off axis holograms with different fringe directions are simultaneously captured by a monochrome camera. Our scheme is available for real-time dual-wavelength phase imaging but requires minimum optical element and system modification for LRDHM. A series of simulations on wavefront interference analysis for using a filter is discussed in detail. We demonstrate the validity of proposed method with a step target.
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