The generation of second-harmonic radiation in a nonlinear dielectric by an arbitrary broad-band optical signal is analyzed and application of the theory is made to harmonic generation by a short pulse. The spectrum and time dependence of the harmonic radiation is calculated in terms of the corresponding quantities for the fundamental pulse. Several types of pulses, including a frequency-swept pulse, are treated. Experimental results on the second-harmonic spectrum are presented and compared with the theory, as are previously reported results on the time dependence. Copyright © 1969, by The Institute of Electrical and Electronics Engineers, Inc.