Imaging with an Ultrashort Pulsed Beam

Abstract

Ultrashort pulsed laser illumination has become more and more important in modern optical microscopy. Time-resolved optical microscopy and nonlinear optical microscopy are two examples of using ultrashort pulsed laser beams in optical microscopy, which are playing a crucial role in biological studies. Due to the effect of material dispersion of a lens, diffraction patterns by a lens or an aperture, which are the topics of this chapter, may be changed in particular when the pulse width is in the range of sub-picoseconds or shorter. The method for generating ultrashort pulsed beams, called mode-locking, is first briefly described in Section 5.1. Temporal and spectral behaviours of an ultrashort pulsed beam are discussed in Section 5.2. Diffraction of an ultrashort pulsed beam by a circular aperture, an opaque disk, and a serrated aperture are given in Section 5.3. In Section 5.4, the transmittance of a lens under ultrashort pulsed beam illumination is derived. With this expression, the light distribution in a focal region of a lens is discussed in Section 5.5. Finally, the coherent transfer function and the optical transfer function for a lens are presented in Section 5.6.