Fig. 1. Light spot energy flow distribution measurement device on collector tube surface of LFR system

Fig. 2. Schematic of basic measurement principle

Fig. 3. Diagram of experimental device

Fig. 4. Surface of Lambertian target

Fig. 5. Calibration test chart

Fig. 6. Transmissivity test chart of attenuation sheet

Fig. 7. Spot image

Fig. 8. Gray image of spot image

Fig. 9. Histogram of gray distribution of focus spot image

Fig. 10. Split graph with a threshold of 20

Fig. 11. Energy flow density distribution map of focus spot

Fig. 12. Projection distribution map of energy flow density of spot on target surface

Fig. 13. Energy flow density distribution map of focus spot along x-direction