A device for cleaning an artificial \u201cinfill turf\u201d field includes a rotating brush assembly and a basket for receiving waste and infill material. A polythiol oligomer exhibiting a greater refractive index than that of the polythiol compound having a functionality of two or greater used as the starting material is produced at a low cost, and a process for producing a practically useful polythiourethane resin exhibiting a stable great refractive index and a great Abbe number is provided. The biasing current generator is further constructed to create a thermal signal indicating an operating temperature.