Measurement and modeling of the focusing of 15 femtosecond optical pulses with a high-numerical-aperture objective

Pulse broadening of ultrashort optical pulses, as short as 15 femtoseconds, due to the propagation through high- numerical-aperture microscope objectives can be pre- compensated to ensure temporal pulse integrity at the focal point. The predictions from dispersive ray-tracing calculations show excellent agreement with the experimental results from two-photon absorption autocorrelation for the Zeiss CP-Achromat 100X/1,25 oil microscope objective. From this, general predictions can be inferred for dispersion in most types of microscope objectives. Key element to the work is a carefully designed dispersion pre- compensation configuration, which minimizes pulse broadening due to residual third order dispersion. The capability to focus these ultrashort pulses with control of the pulse definition at the focal point is important for two-photon absorption and time-resolved microscopy.