Micron-level measurement light spot is an important quota for confocal laser with non-contact surveying micro-target in fusion.The spot size was needed to be micron level to realize precision 1 μm theoretical analysis.According to the Guass distribution of laser theory

the optical system of GJ—Ⅳ confocal probe was studied

not only from the stucture

but also the parameter in order to achieve micron-size focusing spot.Error analysis of the measurement was followed.The experiment showed that when the measuring spot size was 10 μm

working distance was 20 mm

measuring precision is 0.04 %.It was fully demonstrated that the designed optical system satisfied the need of the micro-target measurement.In many aspects

such as measuring scale

measuring light spot size

measuring precision

etc.It can promote the progress of laser-based nuclear fusion

which had great practical value.