52 research outputs found
Parametric Nonlinear Optics with Layered Materials and Related Heterostructures
Nonlinear optics is of crucial importance in several fields of science and technology with applications in frequency conversion, entangledâphoton generation, selfâreferencing of frequency combs, crystal characterization, sensing, and ultraâshort light pulse generation and characterization. In recent years, layered materials and related heterostructures have attracted huge attention in this field, due to their huge nonlinear optical susceptibilities, their ease of integration on photonic platforms, and their 2D nature which relaxes the phaseâmatching constraints and thus offers a practically unlimited bandwidth for parametric nonlinear processes. In this review the most recent advances in this field, highlighting their importance and impact both for fundamental and technological aspects, are reported and explained, and an outlook on future research directions for nonlinear optics with atomically thin materials is provided
Ultrafast Photophysics of Single-Walled Carbon Nanotubes
Single-walled carbon nanotubes (SWNTs) are nanocylinders obtained by wrapping one layer of graphene; due to their very high aspect ratio, they are the prototypical quantum confined one-dimensional systems. The unique mechanical, electronic, and optical properties of SWNTs open up transversal application possibilities in many fields of science and technology, with particular emphasis on optoelectronics and photonics. A prerequisite for many of these applications is a thorough understanding of the nature and dynamics of their elementary excitations. This review aims at summarizing the current understanding of the ultrafast photophysics of SWNTs, based on two decades of experimental investigations. After discussing the morphological and electronic properties of SWNTs and introducing the different photogenerated species, we will briefly describe the ultrafast spectroscopic techniques most commonly used for their characterization. Finally, we present the experimental evidence that has led to establish the nature (singlet and triplet excitons, bi-excitons, trions, and free charges) and the relaxation pathways of photoexcitations in SWNTs
Wavelength tunable soliton rains in a nanotube-mode locked Tm-doped fiber laser
We report soliton rains in a tunable Tm-doped fiber laser mode locked by carbon nanotubes. We also detect their second- and third-harmonics. We achieve a tunability of over 56ânm, from 1877 to 1933ânm, by introducing a polarization-maintaining isolator and two in-line polarization controllers. This makes our system promising as a tunable filter for ultrafast spectroscopy.We acknowledge funding from ERC Grant Hetero2D, EPSRC Grants Nos. EP/L016087/1, EP/K017144/1, EP/K01711X/1 and the China Scholarship Council
Valley Polarization-Electric Dipole Interference and Nonlinear Chiral Selection Rules in Monolayer WSe
In monolayer transition metal dichalcogenides time-reversal symmetry,
combined with space-inversion symmetry, defines the spin-valley degree of
freedom. As such, engineering and control of time-reversal symmetry by optical
or magnetic fields constitutes the foundation of valleytronics. Here, we
propose a new approach for the detection of broken time-reversal symmetry and
valley polarization in monolayer WSe based on second harmonic generation.
Our method can selectively and simultaneously generate and detect a valley
polarization at the valleys of transition metal dichalcogenides at room
temperature. Furthermore, it allows to measure the interference between the
real and imaginary parts of the intrinsic (electric dipole) and valley terms of
the second order nonlinear susceptibility. This work demonstrates the potential
and unique capabilities of nonlinear optics as a probe of broken time-reversal
symmetry and as a tool for ultrafast and non-destructive valleytronic
operations.Comment: 27 pages 6 figure
Exciton-phonon coupling strength in single-layer MoSe2 at room temperature
Single-layer transition metal dichalcogenides are at the center of an ever
increasing research effort both in terms of fundamental physics and
applications. Exciton-phonon coupling plays a key role in determining the
(opto)electronic properties of these materials. However, the exciton-phonon
coupling strength has not been measured at room temperature. Here, we develop
two-dimensional micro-spectroscopy to determine exciton-phonon coupling of
single-layer MoSe2. We detect beating signals as a function of waiting time T,
induced by the coupling between the A exciton and the A'1 optical phonon.
Analysis of two-dimensional beating maps combined with simulations provides the
exciton-phonon coupling. The Huang-Rhys factor of ~1 is larger than in most
other inorganic semiconductor nanostructures. Our technique offers a unique
tool to measure exciton-phonon coupling also in other heterogeneous
semiconducting systems with a spatial resolution ~260 nm, and will provide
design-relevant parameters for the development of optoelectronic devices
Nonlinear Dispersion Relation and Out-of-Plane Second Harmonic Generation in MoSSe and WSSe Janus Monolayers
Janus transition metal dichalcogenides are an emerging class of atomically
thin materials with engineered broken mirror symmetry that gives rise to
long-lived dipolar excitons, Rashba splitting, and topologically protected
solitons. They hold great promise as a versatile nonlinear optical platform due
to their broadband harmonic generation tunability, ease of integration on
photonic structures, and nonlinearities beyond the basal crystal plane. Here,
we study second and third harmonic generation in MoSSe and WSSe Janus
monolayers. We use polarization-resolved spectroscopy to map the full
second-order susceptibility tensor of MoSSe, including its out-of-plane
components. In addition, we measure the effective third-order susceptibility,
and the second-order nonlinear dispersion close to exciton resonances for both
MoSSe and WSSe at room and cryogenic temperatures. Our work sets a bedrock for
understanding the nonlinear optical properties of Janus transition metal
dichalcogenides and probing their use in the next-generation on-chip
multifaceted photonic devices.Comment: 10 pages, 3 figures. SI: 8 pages, 5 figure
Excitonâphonon coupling strength in single-layer MoSe 2 at room temperature
Funder: EC | EC Seventh Framework Programm | FP7 Ideas: European Research Council (FP7-IDEAS-ERC - Specific Programme: "Ideas" Implementing the Seventh Framework Programme of the European Community for Research, Technological Development and Demonstration Activities (2007 to 2013)); doi: https://doi.org/10.13039/100011199; Grant(s): 319277Abstract: Single-layer transition metal dichalcogenides are at the center of an ever increasing research effort both in terms of fundamental physics and applications. Excitonâphonon coupling plays a key role in determining the (opto)electronic properties of these materials. However, the excitonâphonon coupling strength has not been measured at room temperature. Here, we use two-dimensional micro-spectroscopy to determine excitonâphonon coupling of single-layer MoSe2. We detect beating signals as a function of waiting time induced by the coupling between A excitons and AâČ1 optical phonons. Analysis of beating maps combined with simulations provides the excitonâphonon coupling. We get a HuangâRhys factor ~1, larger than in most other inorganic semiconductor nanostructures. Our technique offers a unique tool to measure excitonâphonon coupling also in other heterogeneous semiconducting systems, with a spatial resolution ~260 nm, and provides design-relevant parameters for the development of optoelectronic devices
Tunable broadband light emission from graphene
Graphene is an ideal material for integrated nonlinear optics thanks to its
strong light-matter interaction and large nonlinear optical susceptibility.
Graphene has been used in optical modulators, saturable absorbers, nonlinear
frequency converters, and broadband light emitters. For the latter application,
a key requirement is the ability to control and engineer the emission
wavelength and bandwidth, as well as the electronic temperature of graphene.
Here, we demonstrate that the emission wavelength of graphene s broadband
hot carrier photoluminescence can be tuned by integration on photonic cavities,
while thermal management can be achieved by out-of-plane heat transfer to
hexagonal boron nitride. Our results pave the way to graphene-based ultrafast
broadband light emitters with tunable emission.Comment: 22 pages, 5 Figure
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