Quantization of electromagnetic field

• I
Hello everybody,

It is known that electric field operator is shown as

$\hat{E}(r,t)=-i\sum_{k,\lambda}\sqrt{\frac{\hbar\omega_k}{2\epsilon V}}\left(a(t)^\dagger_{k,\lambda} e^{-ik.r} - a(t)_{k,\lambda} e^{ik.r} \right) \hat{e}_{k,\lambda}$

But if I need to represent an electrostatic field in a quantized form, how to proceed?

Thank you everybody.