The interaction between an intense laser beam and the corona of an irradiated spherical target causes the generation of second harmonic (2ω0) emission at the optical density (n c ) and 3/2 harmonic emission (3ω0/2) at the quarter critical density (n c /4). Potentially, a number of mechanisms can be responsible for the generation of these harmonics, but for laser fusion, resonant absorption at n c and the two plasmon and stimulated Raman instabilities at n c /4 are of particular concern because of their capability of producing fast electrons.