Figure 3

The radii of the Q-PV ring under different TCs and focal lengths. (a) The relationship between TC (l = 0, 5, 10, 15, 20) and r. The dots were fitted by straight-line fit method. The slopes of fitting lines with TCs of 1,5 and 10 are k(0), k(5) and k(10), respectively. (b) The relationship between f and r when l equals to 5, r0 equals to 5 μm.