1. R.A. Millikan, Time, Matter and Values, The University of North Carolina Press, 1932.
2. G. Porter, Proc. Roy. Soc. London, A, 200(1950)284.
3. R.G.W. Norrish and G. Porter, Nature, 164(1949)658.
4. G. Poder, Nature, 215(1967)502.
5. N. Bloenbergen, Nonlinear Optics, W.A. Bengamin Inc., New York, 1956.