A speckle noise suppression method in digital holography is proposed by the angular diversity with a phase-only spatial light modulator (SLM). The minimal angular difference of illumination beams is quantitatively analyzed to ensure the noncorrelation of any two speckle patterns, and then the phase-only SLM is employed to generate a series of tilted illumination beams. Comparing with the typical methods, the tilted illumination beams are controlled dynamically and accurately, which makes it possible to record a large number of holograms. Finally, using an image-plane digital holographic system, 117 holograms are recorded respectively, and the synthesized reconstructed images are obtained with the greatly suppressed speckle noise which is in good agreement with the theoretical results. The experimental results demonstrate the effectiveness, repeatability, and practicability of the proposed approach.

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Heavy metal pollution of agricultural and urban soils limits economic progress in the rapidly developing society. Terahertz technology is applied to detect heavy metal pollutants under existence of multiple pathways of their dissemination. In this study, terahertz time-domain spectroscopy (THz-TDS) is employed as an advanced probing technique in combination with traditional detecting methods to measure the adsorption ability of trivalent chromium ions on bentonite. The concentration of chromium ions and the weight of bentonite are known to influence on the adsorption capacity of the latter. It is tested here by both qualitative and quantitative measurements of two mentioned parameters. The adsorption process of chromium ions by bentonite is monitored using THz-TDS. The adsorptions signal from samples at 0.5 THz gradually increases with the increase of bentonite weight or chromium ion concentration. It would appear to indicate that terahertz could be used for quantitative detection of metal ions. Secondly, the ratios of results obtained by inductively coupled plasma mass spectrometry (ICP-MS) and the THz-TDS ones are stabilized at 0.105  ±  0.014 as the bentonite weight or chromium ion concentration increase. Such finding confirms that terahertz technology can be used for the quantitative detection of metal ions. Using the relationship between the ICP-MS test results and the THz-TDS ones, the amplitude value of bentonite is obtained to be 13.925 at the concentration of chromium ions of 0.05 mol/L, the mass of bentonite sample involved in adsorption of 1.5 g, and the detection frequency in THz-TDS measurements of 0.5 THz. The adsorption coefficient of bentonite is calculated to be 1.44%. Increase of the chromium ion concentration to 0.2 mol/L, and the mass of bentonite involved in adsorption to 3 g leads to the increase of the amplitude corresponding to adsorbed chromium ions to about 19.463, and the adsorption coefficient to about 2.1%. Obtained results demonstrate that terahertz technology is promising to meet the ever-increasing requirements in mineral analyses for rapid detection of chemical contaminants and measurement of the adsorption efficiencies of materials.