Different Mesh lines and styles in the same plot

Question

After searching, I learned how to make "GridLines" in DensityPlot by Mesh/MeshFunctions.

Here I'd like to draw an addition Mesh line at Q=6^(0.25) via Mesh/MeshFunctions or other ways and highlight it with a different style.

Please have a look at my code below:

Manipulate[
 DensityPlot[EsEtSin, {defocus, -1, 4}, {Q, 0, 3},
  FrameLabel -> {"D", "Q"}, PlotPoints -> 30,

  Mesh -> {{Sqrt[(8 n + 3)/2]}}, MeshFunctions -> {#1 &}, 
  MeshStyle -> {Thick, Cyan}, 

  Epilog -> 
   Inset[Framed["Q=\!\(\*SuperscriptBox[\(6\), \(1/4\)]\)", 
     RoundingRadius -> 5, Background -> White], {0.5, 1.8}]],

 {{n, 0, "Pass Band No."}, 0, 3, 1, ControlType -> Setter},

 Initialization :> (q0 = .1; delta = .1;
   EsEt = E^(-(\[Pi]^2/2) (delta^2 Q^4 + 2 q0^2 (Q^3 - defocus Q)^2));
    EsEtSin = EsEt Sin[\[Pi] (1/2 Q^4 - defocus Q^2)])
 ]

Any help is highly appreciated.

Answer 1

I think this is a well-framed question that deserves a proper answer, so I'm putting eqwene sedai's comment on record.

DynamicModule[{defocus},
  Manipulate[
    DensityPlot[EsEtSin, {defocus, -1, 4}, {Q, 0, 3}, 
      FrameLabel -> {"D", "Q"},
      PlotPoints -> 30,
      Mesh -> {{Sqrt[(8 n + 3)/2]}, {6^.25}},
      MeshFunctions -> {#1 &, #2 &}, 
      MeshStyle -> {{Thick, Cyan}, {Thick, Red}},
      Epilog ->
        Inset[
          Framed["\!\(\*SuperscriptBox[\(6\), \(1/4\)]\)", 
            RoundingRadius -> 5, Background -> White], 
          {0., 1.75}]],
    {{n, 0, "Pass Band No."}, Range[0, 3]},
    Initialization :> (
      q0 = .1;
      delta = .1;
      EsEt = E^(-(π^2/2) (delta^2 Q^4 + 2 q0^2 (Q^3 - defocus Q)^2));
      EsEtSin = EsEt Sin[π (1/2 Q^4 - defocus Q^2)])]]