18 research outputs found
Nonlinear Optical Effects Due to Magnetization Dynamics In a Ferromagnet
We theoretically consider magnetization dynamics in a ferromagnetic slab
induced by the magnetic field of a strong femtosecond laser pulse. The
longitudinal geometry, in which the initial magnetization lies in both the
plane of incidence and the sample plane, is studied. The magnetization
oscillations at the optical wave frequency are calculated with the use of the
Kapitza pendulum approach taking into account that the optical frequency is
much greater than the magnetization oscillation eigenfrequency. We study the
reflection of the electromagnetic wave from a ferromagnet %with such a dynamics
and show that this laser-induced low-frequency magnetization dynamics leads to
the appearance of the second-order nonlinearity in the Maxwell's equations,
which in turn gives rise to both the second harmonic generation (SHG) and
rectification effect. Although the amplitude of the magnetization oscillations
is small, the considered effect may be responsible for the SHG with the
efficiency comparable to that of nonmagnetic SHG from metal surfaces. Our
estimations show that the suggested mechanism may explain the recent
experiments on magnetization induced modulation of the SHG intensity in a
``forbidden'' combination of incident and reflected waves in
cobalt/heavy metal systems, where it can be even more pronounced due to the
spin current flow through the ferromagnet/ heavy metal interface.Comment: 8 pages, 3 figure
Multiphoton Effects Enhanced Due to Ultrafast Photon-Number Fluctuations
Multi-photon processes are the essence of nonlinear optics. Optical harmonics
generation and multi-photon absorption, ionization, polymerization or
spectroscopy are widely used in practical applications. Generally, the rate of
an n-photon effect scales as the n-th order autocorrelation function of the
incident light, which is high for light with strong photon-number fluctuations.
Therefore `noisy' light sources are much more efficient for multi-photon
effects than coherent sources with the same mean power, pulse duration and
repetition rate. Here we generate optical harmonics of order 2-4 from bright
squeezed vacuum (BSV), a state of light consisting of only quantum noise with
no coherent component. We observe up to two orders of magnitude enhancement in
the generation of optical harmonics due to ultrafast photon-number
fluctuations. This feature is especially important for the nonlinear optics of
fragile structures where the use of a `noisy' pump can considerably increase
the effect without overcoming the damage threshold
Surface plasmon-mediated nanoscale localization of laser-driven sub-THz spin dynamics in magnetic dielectrics
Ultrafast all-optical control of spins with femtosecond laser pulses is one
of the hot topics at the crossroads of photonics and magnetism with a direct
impact on future magnetic recording. Unveiling light-assisted recording
mechanisms for an increase of the bit density beyond the diffraction limit
without excessive heating of the recording medium is an open challenge. Here we
show that surface plasmon-polaritons in hybrid metal-dielectric structures can
provide spatial confinement of the inverse Faraday effect, mediating the
excitation of localized coherent spin precession with 0.41 THz frequency. We
demonstrate a two orders of magnitude enhancement of the excitation efficiency
at the surface plasmon resonance within the 100 nm layer in dielectric garnet.
Our findings broaden the horizons of ultrafast spin-plasmonics and open
pathways towards non-thermal opto-magnetic recording at the nano-scale
Second harmonic generation in multilayer graphene induced by direct electric current
Optical second harmonic generation (SHG) is studied from multilayer graphene
films in the presence of DC electric current flowing in the sample plane.
Graphene layers are manufactured by chemical vapour deposition (CVD) technique
and deposited on an oxidised Si(001) substrate. SHG intensity from graphene
layer is found to be negligible in the absence of the DC current, while it
increases dramatically with the application of the electric current. The
current-induced change of the SHG intensity rises linearly with the current
amplitude and changes its sign under the reversal of the current direction to
the opposite. The observed effect is explained in terms of the interference of
second harmonic radiation reflected from the Si surface and that induced by the
DC current in multilayer graphene
Experimental Correlation between Nonlinear Optical and Magnetotransport Properties Observed in Au-Co Thin Films
Magnetic materials where at least one dimension is in the nanometer scale typically exhibit different magnetic, magnetotransport, and magnetooptical properties compared to bulk materials. Composite magnetic thin films where the matrix composition, magnetic cluster size, and overall composite film thickness can be experimentally tailored via adequate processing or growth parameters offer a viable nanoscale platform to investigate possible correlations between nonlinear magnetooptical and magnetotransport properties, since both types of properties are sensitive to the local magnetization landscape. It has been shown that the local magnetization contrast affects the nonlinear magnetooptical properties as well as the magnetotransport properties in magnetic-metal/nonmagnetic metal multilayers; thus, nanocomposite films showcase another path to investigate possible correlations between these distinct properties which may prove useful for sensing applications
Coherent lattice dynamics in topological insulator Bi2 Te3 probed with time-resolved optical second-harmonic generation
Size Effects in Optical and Magneto-Optical Response of Opal-Cobalt Heterostructures
Search for new types of efficient magnetoplasmonic structures that combine high transparency with strong magneto-optical (MO) activity is an actual problem. Here, we demonstrate that composite heterostructures based on thin perfectly-arranged opal films and a perforated cobalt nanolayer meet these requirements. Anomalous transmission appears due to periodic perforation of Co consistent with the regular set of voids between opal spheres, while resonantly enhanced MO response involves the effects of surface plasmon-polariton (SPP) excitation at opal/Co interface or those associated with photonic band gap (PBG) in opal photonic crrystals. We observed the enhancement of the MO effect of up to 0.6% in the spectral vicinity of the SPP excitation, and several times less strong effect close to the PBG, while the combined appearance of PBG and SPP decreases the resultant MO response. Observed resonant magneto-optical properties of opal/Co heterostructures show that they can be treated as functional self-assembled magnetoplasmonic crystals with resonantly enhanced and controllable MO effect