An exhaust mixing device for mixing an exhaust produced by an engine with a reagent exhaust treatment fluid that is dosed into the exhaust from a dosing module. Electron beams emitted from electron emission elements of a multi electron beam generating unit receive the lens effect of a lens electrode. An insulating partition wall 13 is disposed between receiving blades 17, 17 in a standing manner, the sensor 16 is accommodated inside the partition wall, and arrangement is performed such that a portion of the sensor faces the through-hole. The optimization means adjusts a parameter and the parameter is an input to a filter. The threshold value is used to further determine an energy density of the elongate pulse laser beam for the phase change process.