1.3: Applications

• High time resolution: Ultrafast Spectroscopy, tracing of ultrafast physical processes in condensed matter (see Figure 1.3), chemical reactions, physical and biological processes, influence chemical reactions with femtosecond pulses: Femto-Chemistry (Noble Prize, 2000 to A. Zewail), high speed electric circuit testing and sampling of electrical signals, see Figure 1.4.

Figure 1.3: Pump-probe setup to extract time constants relevant for the carrier dynamics in semiconductors.

Figure 1.4: High speed A/D conversion with a high repetition rate picoor femtosecond laser.

• High spatial resolution: $c\tau_{\text{FWHM}}$; optical imaging, e.g. optical coherence tomography, see Figs. 1.5-1.8).

Figure 1.5: Setup for optical coherence tomography. Courtesy of James Fujimoto. Used with permission.

Figure 1.6: Cross section through the human eye. Courtesy of James Fujimoto. Used with permission.

Figure 1.7: Comparison of retinal images taken with a superluminescence diode (top) versus a broadband Ti:sapphire laser (below). Courtesy of James Fujimoto. Used with permission.

• Imagaing through strongly scattering media:

Figure 1.8: Imaging of the directly transmitted photons results in an un-blurred picture. Substitution for x-ray imaging; however, transmission is very low.

• High bandwidth: massive WDM optical communications, many channels from one source or massive TDM, high bit-rate stream of short pulses.
• High intensities: Large intensities at low average power $\Rightarrow$ Nonlinear frequency conversion, laser material processing, surgery, high intensity physics: x-ray generation, particle acceleration, ...