Reducing or decreasing light scattering effects of suspended particles in water is one of the key technical issues of the direct spectroscopy chemical oxygen demand (COD) water quality detection. Therefore, based on the Mie scattering theory, the improved continued fractions combining with backward recursion algorithm is used to study ultraviolet (UV)-visible light scattering properties on the alga and sand suspended particles in water. The light scattering models of spherical particles in water is built. The changes of light scattering intensity and scattering angle are analyzed and calculated with particle size in the range of 1~200 μm and the incident wavelength in the range of 200~1000 nm. The simulation results show that when the particle size and the wavelength of incident light change, the scattered light intensity and angle are significantly changed with two types of suspended particles. It is helpful to improve resolution and degrade the effect of scattering of detection of water quality using UV-visible absorption spectroscopy.

Helmet display (HMD) is the core hardware of virtual display technology. It is a small display device mounted on the helmet to produce visual images for the user. The MHD system mainly consists of an image source, optical, and support system. Still, the traditional optical subsystem cannot achieve the functions of the ideal optical system, such as being light-weight, small in size, and having an extensive field angle. This paper established the proper initial model, and the optimal control conditions and surface upgrade strategy were determined. Herein, the design scheme of the free-form prism with good performance was obtained. We solve the feature of large volume and complicated structure of optical components of helmet display and describe the design idea of free-form prism in detail. In this paper, the system resolution we designed is 800 × 600, the Modulation transfer function (MTF) value of the prism is more significant than 0.1 at the spatial resolution of 30lp/mm, and the distortion is less than 5%. The exit pupil diameter of the system is 8mm, and the field angle is 26°×20°.