Unprotect[Power];
Power[0 | 0., 0 | 0.] = 1;
Protect[Power];
zR = 4965;
\[Lambda] = 632.8*10^(-6);
w = 1;
k = 2*Pi/\[Lambda];
a = 1;
b = z;
c = 0;
d = 1;
Intensity[r_, n_, z_] := (I*w^2)/(2*\[Lambda]*b)*Exp[-I*k*z]*
Exp[(-I*k*r^2)/(2*((a + b/(I*k*w^2/2))/(c + d/(I*k*w^2/2))))]*(\!\(
\*UnderoverscriptBox[\(\[Sum]\), \(m = 0\), \(n\)]\(
\*UnderoverscriptBox[\(\[Sum]\), \(s = 0\), \(100\)]\((\(-1\))\)^
m*2^\((\(-n\))\)*
Binomial[n, m]*\((\((n - 2*m)\)^\((s)\)/\(s!\))\)*
Gamma[1 +
s/2]*\((\(b/\((I*k*w^2/2)\)\)/\((a +
b/\((I*k*w^2/2)\))\))\)^\((1 + s/2)\)*
Hypergeometric1F1[\(-s\)/2,
1, \((\(-I\)*k*r^2)\)/\((2*
b*\((a + b/\((I*k*w^2/2)\))\))\)]\)\));
Plot[Abs[Intensity[0, 3, z]]/0.23589, {z, 0, 10 zR},
PlotPoints -> 100, AspectRatio -> 1/3, PlotRange -> All,
Axes -> {False, False}, Frame -> True,
FrameLabel -> {"z/mm", "I/Imax"}, PlotLabel -> "单层介质; r=0; n=3",
LabelStyle -> Directive[Bold, 15],
PlotStyle -> Directive[Black, Thickness[0.008]]]
DensityPlot[
Abs[Intensity[r, 3, z]]/0.23589, {z, 0, 10 zR}, {r, -10, 10},
PlotRange -> All, PlotPoints -> 100, AspectRatio -> 1/3,
Frame -> True, FrameLabel -> {"z/mm", "r/mm"},
PlotLabel -> "单层介质; I/Imax; n=3", LabelStyle -> {Bold, 15},
ColorFunction -> GrayLevel]
Plot[Abs[Intensity[0, 6, z]]/29.7558, {z, 0, 10 zR},
PlotPoints -> 100, AspectRatio -> 1/3, PlotRange -> All,
Axes -> {False, False}, Frame -> True,
FrameLabel -> {"z/mm", "I/Imax"}, PlotLabel -> "单层介质; r=0; n=6",
LabelStyle -> Directive[Bold, 15],
PlotStyle -> Directive[Black, Thickness[0.008]]]
DensityPlot[
Abs[Intensity[r, 6, z]]/29.7558, {z, 0, 10 zR}, {r, -10, 10},
PlotRange -> All, PlotPoints -> 100, AspectRatio -> 1/3,
Frame -> True, FrameLabel -> {"z/mm", "r/mm"},
PlotLabel -> "单层介质; I/Imax; n=6", LabelStyle -> {Bold, 15},
ColorFunction -> GrayLevel]
Plot[Abs[Intensity[0, 9, z]]/292312, {z, 0, 10 zR}, PlotPoints -> 100,
AspectRatio -> 1/3, PlotRange -> All, Axes -> {False, False},
Frame -> True, FrameLabel -> {"z/mm", "I/Imax"},
PlotLabel -> "单层介质; r=0; n=9", LabelStyle -> Directive[Bold, 15],
PlotStyle -> Directive[Black, Thickness[0.008]]]
DensityPlot[
Abs[Intensity[r, 9, z]]/292312, {z, 0, 10 zR}, {r, -10, 10},
PlotRange -> All, PlotPoints -> 100, AspectRatio -> 1/3,
Frame -> True, FrameLabel -> {"z/mm", "r/mm"},
PlotLabel -> "单层介质; I/Imax; n=9", LabelStyle -> {Bold, 15},
ColorFunction -> GrayLevel]

应该是跪在DensityPlot上了。（求和涉及特殊函数，二维矢量图形太难画。）此类问题通用改法是 ArrayPlot 配 Table：
ArrayPlot[
Table[Abs[Intensity[r, 3, z]]/0.23589, {z, 0, 10 zR, 10 zR/25}, {r, -10, 10,
10 zR/25}],
PlotRange -> All, AspectRatio -> 1/3,
Frame -> True, FrameLabel -> {"z/mm", "r/mm"},
PlotLabel -> "单层介质; I/Imax; n=3", LabelStyle -> {Bold, 15},
ColorFunction -> GrayLevel] // Quiet // AbsoluteTiming
几个Plot 可以考虑加上 MaxRecursion -> 0 ，不过不加应该也不至于太慢：