Surface plasmon-polaritons (SPPs) is a collective oscillation of light and electrons that propagate at the boundary between metal and dielectric. The lifetime of such excitations can vary from few femtoseconds till picoseconds in the optical range of spectrum. Since the development of femtosecond lasers became possible to study and to use this ultrafast processes in devices and applications. 

Fig.1 Time-resolved intensity correlation functions measurement setup. Ti:Sa — titanium-sapphire femtosecond laser. Pulse duration — 150 fs, tunable wavelength from 690 nm to 1020 nm, repetition rate of 80MHz, integral power of 1.5-3 V. Step of scanning delay line is 13 fs. BBO — nonlinear crystal. PMT — photomultiplier tube.

Various shaping options (Fig.2), namely, broadening, compression, delaying, advancing, and splitting of the pulses are revealed by spectral tuning of the pulse carrier wavelength in the vicinity of surface plasmon resonances, since such pulse modification strongly depends on the interplay between parameters of the fs-pulse and SPP resonance, for example, laser pulse duration should be comparable with the SPP relaxation time. 

Fig.2. Measured correlation functions and reconstructed pulses reflected from the 1D plasmonic crystal for carrier wavelength λ₀ in the range from 722 nm to 780 nm.

Fig. 3. Schematics of the ultrafast polarization conversion with plasmonic crystals.

Ultrafast Magnetooptical Kerr Effect in Magnetoplasmonic Crystals

On the other hand, since the MOKE enhancements is induced by SPP, that have a limited femtosecond lifetime, then the time-dependent transverse magnetooptical Kerr effect (TMOKE) can be experimentally observed within femtosecond laser pulses. Non-trivial evolution of TMOKE is demonstrated  by means of correlation function spectroscopy within 200 fs-pulses and 45 fs-pulses reflected from 1D nickel and iron-based magnetoplasmonic crystals [8,9]. Exciting SPPs with magnetic field-dependent dispersion of ferromagnetic metals allows to control the shape of the reflected pulse (Fig.4). 

Fig. 4. Illustration of the ultrafast time-dependent TMOKE. The incident pulse shown in red is transformed into an SPP wave with the dispersion law depending on the magnetization of the sample. The influence of SPPs is stronger at later time moments. As a consequence, the reflected pulse contains different profile for different sample magnetization directions giving rise to intra-pulse time-dependent TMOKE.