The precursor nanoparticles of nickel hydroxide (Ni(OH)₂) and nickel oxide (NiO) were successfully converted into the latter by the reaction of nickel chloride with hydrazine at ambient temperature. (TGA) and (DSC) were adapted for annealing the precursor products at different annealing temperatures (210, 285, 350, 390, 425, and 450 °C). XRD, TEM, and UV-VIS absorption spectroscopy were used to characterize the products. Both the band edge and energy gap values decrease with increasing annealing temperatures. Hysteresis loops are visible in the M-H curves of annealed (350 °C and 390 °C) precursor NiO NPs, indicating the presence of ferromagnetic Ni domains. However, NiO nanoparticles annealed at higher temperatures (425 °C and 450 °C) had a straight M-H curve, indicating paramagnetic properties. NiO NPs were used to study photocatalysis in the degradation of the MB dye. As annealing temperatures increased, the catalyst caused the degradation of MB. The sample that was annealed at 450 °C, however, exhibits the maximum photocatalytic activity, reaching up to 72.4% after being exposed to visible light. In other words, it was discovered that as the catalyst’s annealing temperature rose, so did the rate of MB’s photocatalytic degradation.

In a wide spectral range of 400 to 1000 nm, the channeled spectra formed from the interference of polarized white light are used to extract the dispersion of phase birefringence $Δn(λ)$ of polyethylene and cellulose triacetate (CTA) polymer sheets. The $Δn(λ)$ of polyethylene and CTA sheets is fitted to Cauchy dispersion function with relative error of order $1.2×10−4$ and $4×10−4$, respectively. The dispersion of group birefringence $Δng(λ)$ of polyethylene and CTA is also calculated and fitted to Ghosh dispersion function with relative error of order $7×10−4$ and $5×10−4$, respectively. Furthermore, the phase and group retardations introduced by polyethylene and CTA sheets are also calculated. The amount of phase retardation confirms that polyethylene and CTA sheets can act as multiple order half and quarter wave plates working at many different wavelengths through the spectral range 400 to 1000 nm. For polyethylene and CTA sheets, a large difference between group and phase retardance is observed at a short wavelength ($λ≈400nm$), while such difference progressively diminished at a long wavelength ($λ≈1000nm$). Finally, a zero order polyethylene quarterwave plate working at 544 nm and dual wavelength CTA quarterwave plate working at 510 and 680 nm are experimentally realized.

We report the first, to our knowledge, systematic experimental realization and quantitative chromatic-sensitivity analysis of multiple-order wave plates fabricated from natural single-crystal barite in the near-infrared (NIR) spectral region. In the present work, wave plates of varying thicknesses were designed and demonstrated at key NIR wavelengths (985, 1062, 1310, and 1550 nm). The phase retardation was analyzed using a Cauchy dispersion-based model, and the spectral sensitivity was quantified through differentiation of the retardation expression with respect to wavelength. The results reveal that the chromatic sensitivity is dominated by the geometrical phase term and scales linearly with both the wave-plate order m and plate thickness t . Furthermore, the spectral sensitivity increases significantly at shorter wavelengths due to the (1/ λ ² ) dependence of the dominant term. Experimental Gaussian fits confirm the wavelength-dependent bandwidth narrowing at higher orders. These findings provide a comprehensive understanding of the chromatic behavior of multiple-order barite wave plates and establish design guidelines for near-infrared polarization control applications. The present work represents, to our knowledge, the first quantitative framework linking birefringence dispersion, wave-plate order, and chromatic sensitivity in natural barite crystals for near-infrared polarization applications.