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F. Vallée and N. Del Fatti
and interactions in the material. This versatility opens a broad field of technological
applications but also raises many fundamental questions on the involved processes
at the origin of the observed properties. In the optical domain, a large interest has
been devoted to plasmonic effects in metallic nanoparticles or nanomaterials. They
show-up by the appearance of new optical resonances in their linear and nonlinear
optical responses [1–6]. These are associated to localized or propagating surface
plasmon resonances (SPR) depending of the system dimensionality, e.g., in metal
nanoparticles or in nanowires and at surfaces, respectively. SPR are concomitant
with strong enhancement and spatial localization of the electromagnetic field in and
around metallic nanostructures due to dielectric confinement or local field effect.
Their spectral properties, wavelength, width, and amplitude reflect the characteristics
of the nanoobjects (composition, size, shape), of their environment, and of their
coupling in a nanomaterial [3, 5, 7–11]. They have been exploited to design new
optical devices, with many applications, as in sensing [12, 13], and also offers a
large potential for sub-wavelength light manipulation and guiding in plasmonic metamaterials [14–17].
The optical response of a plasmonic material being directly connected to those
of its nano-components, it can be actively modified and controlled modifying their
dielectric function. This can be done optically with a light pulse exploiting the optical
nonlinearities component materials, and in particular the large nonlinearity of metals.
Using femtosecond pulses, it opens the way to ultrafast active control of light propagation or transmission [18–24]. The ultrafast optical nonlinearity of metal nanostructures also provides a unique way to investigate their electronic and vibrational
properties. Time-resolved spectroscopy has been extensively used in this context, first
in metal films [25–31], and, subsequently, in metal nanostructures [32–37], and in
single nanoparticles [38–45]. It has provided information on electronic motion coherence losses or SPR polarization decay [46–49], on electron energy redistribution in
nanoobjects (electron-electron scattering and electron-lattice energy transfer) [33,
50–53], on their acoustic vibrations [33, 37, 44, 54–57] and on metal-environment
energy exchanges [58, 59]. These studies also yield information on the physical origins of the third order nonlinearity of metallic materials, disentangling them using
their different spectral and temporal signatures [60].
Fully exploiting the potentialities offered by the optical nonlinearities of metallic
nanomaterials requires modeling of their nonlinear optical response at a nanoscale
including plasmonic effects. In this chapter we describe ultrafast third order Kerrtype nonlinearity of metallic nanomaterials and its impact of their observable optical
response, e.g., light absorption, transmission, or reflection. It is based on modeling
ultrafast modification of the dielectric function of metal due to its interaction with
a short light pulse. Even for pulses as short as 20 fs, this is dominated by resonant
incoherent processes associated to energy absorption by the electrons of the metal
[26, 37, 43, 47, 61]. Note that it is not the case for optical nonlinearity leading to
creation of new frequencies, such as second, third or high-harmonic generations,
that mostly involves coherent processes [48, 62–64]. The nonlinear mechanisms
considered here are associated to energy absorption by the material and show a
time dependence following its electronic, vibrational and thermal relaxation. The
F. Vallée and N. Del Fatti
and interactions in the material. This versatility opens a broad field of technological
applications but also raises many fundamental questions on the involved processes
at the origin of the observed properties. In the optical domain, a large interest has
been devoted to plasmonic effects in metallic nanoparticles or nanomaterials. They
show-up by the appearance of new optical resonances in their linear and nonlinear
optical responses [1–6]. These are associated to localized or propagating surface
plasmon resonances (SPR) depending of the system dimensionality, e.g., in metal
nanoparticles or in nanowires and at surfaces, respectively. SPR are concomitant
with strong enhancement and spatial localization of the electromagnetic field in and
around metallic nanostructures due to dielectric confinement or local field effect.
Their spectral properties, wavelength, width, and amplitude reflect the characteristics
of the nanoobjects (composition, size, shape), of their environment, and of their
coupling in a nanomaterial [3, 5, 7–11]. They have been exploited to design new
optical devices, with many applications, as in sensing [12, 13], and also offers a
large potential for sub-wavelength light manipulation and guiding in plasmonic metamaterials [14–17].
The optical response of a plasmonic material being directly connected to those
of its nano-components, it can be actively modified and controlled modifying their
dielectric function. This can be done optically with a light pulse exploiting the optical
nonlinearities component materials, and in particular the large nonlinearity of metals.
Using femtosecond pulses, it opens the way to ultrafast active control of light propagation or transmission [18–24]. The ultrafast optical nonlinearity of metal nanostructures also provides a unique way to investigate their electronic and vibrational
properties. Time-resolved spectroscopy has been extensively used in this context, first
in metal films [25–31], and, subsequently, in metal nanostructures [32–37], and in
single nanoparticles [38–45]. It has provided information on electronic motion coherence losses or SPR polarization decay [46–49], on electron energy redistribution in
nanoobjects (electron-electron scattering and electron-lattice energy transfer) [33,
50–53], on their acoustic vibrations [33, 37, 44, 54–57] and on metal-environment
energy exchanges [58, 59]. These studies also yield information on the physical origins of the third order nonlinearity of metallic materials, disentangling them using
their different spectral and temporal signatures [60].
Fully exploiting the potentialities offered by the optical nonlinearities of metallic
nanomaterials requires modeling of their nonlinear optical response at a nanoscale
including plasmonic effects. In this chapter we describe ultrafast third order Kerrtype nonlinearity of metallic nanomaterials and its impact of their observable optical
response, e.g., light absorption, transmission, or reflection. It is based on modeling
ultrafast modification of the dielectric function of metal due to its interaction with
a short light pulse. Even for pulses as short as 20 fs, this is dominated by resonant
incoherent processes associated to energy absorption by the electrons of the metal
[26, 37, 43, 47, 61]. Note that it is not the case for optical nonlinearity leading to
creation of new frequencies, such as second, third or high-harmonic generations,
that mostly involves coherent processes [48, 62–64]. The nonlinear mechanisms
considered here are associated to energy absorption by the material and show a
time dependence following its electronic, vibrational and thermal relaxation. The