This figure was created using Wolfram language 12.0.0 for Microsoft Windows (64-bit) (April 6, 2019). The source code follows (formatted as a .wl package file).
(* ::Package:: *)
(* ::Title:: *)
(*Spiral phase plate*)
(* ::Input:: *)
(*spp=Module[{num=20,aux,aux2,i=0,step=0.01,offset=0.2,circ,faces,base,segments,verts,end},*)
(*circ=CirclePoints[num];*)
(*AppendTo[circ,First[circ]];*)
(*aux={##,0}&@@@circ;*)
(*base=Polygon[aux];*)
(*aux2={##,offset+step i++}&@@@circ;*)
(*verts={0,0,#}&/@aux2[[;;,-1]];*)
(*end={aux2[[1]],verts[[1]],verts[[-1]],aux2[[-1]]};*)
(**)
(*aux=Partition[aux,2,1];*)
(*aux2=Partition[aux2,2,1];*)
(*verts=Partition[verts,2,1];*)
(**)
(*faces=Join[#1,#2[[{-1,1}]]]&@@@Transpose[{aux,aux2}];*)
(*segments=Join[#1[[{-1,1}]],#2]&@@@Transpose[{verts,aux2}];*)
(**)
(*{Polyhedron/@faces,base,Polyhedron/@segments,Polyhedron[end]}*)
(*];*)
(* ::Input:: *)
(*spp=Graphics3D[{(*EdgeForm[],*)Specularity[10],Opacity[.7,Setting@ColorSetter[RGBColor[0.7686274509803922, 0.8196078431372549, 0.9568627450980393]]],Lighting->{{"Ambient",LightGray},{"Directional",White,{-1,-1,15}},{"Directional",White,{1,1,15}}},spp},Boxed->False,Lighting->"Neutral",ViewPoint->{0.68,2.28,2.41},ViewVertical->{0.353,0.22,0.91},ImageSize->2000];*)
(* ::Input:: *)
(*SetDirectory[NotebookDirectory[]]*)
(* ::Input:: *)
(*Export["spp.svg",sppaux]*)
(*Export["spp.png",sppaux,ImageResolution->200]*)