Pii: S0000-0000(00)00000-0

P0005 Particular care must be used when characterizing the excitation beam in nonlinear optical experiments compared to linear measurements. By definition, nonlinear optical phenomena depend on the electric field to high order. The higher the order, the more sensitive the observed behavior depends on the input. Extracting a representative nonlinear coefficient from an experiment, for example, becomes progressively more difficult as the order of the optical nonlinearity increases. In other words: the errors associated with optical beam characterization get magnified by the order of the nonlinearity under study. P0010 There is an extensive nomenclature for characterizing the light (almost always laser light) interacting with the nonlinear optical medium. Different descriptions may be used depending on whether the excitation light is pulsed, continuous, or a continuous train of pulses. When a laser beam is constant or continuous, it is often described by its ‘cw power’. ‘Cw’ stands for ‘continuous wave’, an acronym taken from the nomenclature of electronics. The cw power of a laser is determined by placing a power meter in the path of a beam. Reptitively pulsed lasers can be characterized in the same way, provided the response time of the power meter is slower than the pulse separation period. This will almost certainly be the case with a continuously pumped mode-locked laser such as a dye laser, fiber laser, or Ti:sapphire laser, which produce pulses at repetition frequencies of tens of megahertz. Cw power may also be suitable for describing pulsed flashlamp lasers, gas discharge lasers, or any laser that is excited in a periodic fashion.