Ultrafast Optical Imaging and Microspectroscopy
Ultrafast microscopy combines the capabilities of femtosecond pump probe spectroscopy with the ability to image and monitor individual objects, down to the single particle and single molecule level. This combination of temporal, spatial and spectral resolution is necessary when studying charge and energy transfer processes in heterogeneous and nanostructured materials, which are increasingly common in the fields of photovoltaics and photocatalysis. Acquisition of images evolving on the femtosecond timescale, similarly to the acquisition of femtosecond photoluminescence and absorption spectra, must rely on optical gating techniques as there are no electronic devices capable of operating in this time domain. In this chapter we describe two all-optical realizations of femtosecond microscopy which are most general and straightforward to implement: wide-field Kerr-gated fluorescence microscopy (KGFM) and scanning pump probe transient absorption microscopy (PPTAM).