Nonlinear optical excitation of plasmons in graphene: intensity and polarisation dependences
Recently, we demonstrated an all-optical coupling scheme for plasmons, which takes advantage of the intrinsic nonlinear optical response of graphene. Difference frequency mixing using free-space, visible light pulses generates surface plasmons in a planar graphene sample, where the phase matching condition can define both the wavevector and energy of surface waves and intraband transitions. Here we present intensity and polarisation dependences of this effect. We show that TM polarisation is required for the surface plasmon generation process, while intraband resonances are largely unaffected by the incident polarisation. We also show that the plasmon generation process is strongly intensity dependent, with resonance features washed out for pulse fluences >1 mJ/cm2. This implies a subtle interplay between the nonlinear generation process and sample heating.
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