5. The next step: developing attosecond-scale pulses

As we have just seen, ultrashort pulse lasers are full of promise. We have entered the attosecond age (1 as = 10 ^–18 s). Wave trains are of greater spectral width than those used in femtochemistry, which only observes the movements of molecules and chemical reactions, in order to study the ultrafast movements of electrons in atoms. Currently, ultrashort pulse generation is limited to 3.8 fs by the use of broadband laser techniques such as Ti ³⁺ -doped sapphire. At λ = 800 nm, the broadband maximum of Ti ³⁺ , the wave oscillation lasts 2.5 fs, which means that the wave train corresponds to just over one period! We would then have to use lasers emitting at much shorter wavelengths in the ultraviolet, but these lasers do not have the optimization achieved by...