1 (-1 + (4*(-1 + Sqrt[1 + k^2/(c - I*k0)^2])*(c - I*k0)^2)/k^2 - (2*(-1 + Sqrt[1 + k^2/(2*c - I*k0)^2])*(2*c - I*k0)^2)/k^2 + Sqrt[Pi]*(I*Piecewise[{{0, k^2/k0^2 <= 1}}, (2*k0*Sqrt[k^2 - k0^2])/(k^2*Sqrt[Pi])] + Piecewise[{{(k^2 + 2*k0*(-k0 + Sqrt[-k^2 + k0^2]))/(k^2*Sqrt[Pi]), k^2/k0^2 < 1}, {(1 - (2*k0^2)/k^2)/Sqrt[Pi], k^2/k0^2 > 1}}, 0]))/(2*k0^2)
2 SeriesData[k, Infinity, {(2*c^2)/k0^2, (-3*(c^3 - I*c^2*k0))/k0^2, 0, (5*(3*c^5 - (7*I)*c^4*k0 - 6*c^3*k0^2 + (2*I)*c^2*k0^3))/(4*k0^2), 0, (-7*(9*c^7 - (31*I)*c^6*k0 - 45*c^5*k0^2 + (35*I)*c^4*k0^3 + 15*c^3*k0^4 - (3*I)*c^2*k0^5))/(8*k0^2), 0, (15*(85*c^9 - (381*I)*c^8*k0 - 756*c^7*k0^2 + (868*I)*c^6*k0^3 + 630*c^5*k0^4 - (294*I)*c^4*k0^5 - 84*c^3*k0^6 + (12*I)*c^2*k0^7))/(64*k0^2)}, 2, 11, 1]