Femtosecond-pulse-front shaping with lenses

Abstract

Many applications of fs light pulses involve interactions with single lenses. Information on the pulse and phase front transformation are desirable in particular for imaging purposes and for on-axis focusing to achieve ultimately large intensities. The unavoidable interplay of chromatic and spherical aberration determines the space-time characteristics of the intensity distribution in the focal region of a single lens. Conditions are derived under which spherical aberration dominates. Here a temporally unbroadened, in-focus pulse occurs while the spatial distribution is that expected from an annular lens aperture and cw light. If chromatic aberration is the major aberration the in-focus pulses are considerably broadened. Both effects could clearly be measured in a modified Michelson setup using 100 fs pulses. In an intermediate parameter range both chromatic and spherical aberration contribute to the pulse broadening and to the spatial intensity pattern. From Fresnel diffraction we expect a small pulse to pass through a given on-axis point which can either precede or follow the in-focus pulse. Another weak intensity peak is produced by the pulse traveling on-axis. By measuring its separation from the main pulse, for example in the marginal focal plane one can estimate the aberration parameters.