This PDF file contains the front matter associated with SPIE Proceedings Volume 8260, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

We apply ultrafast pump-probe photocurrent spectroscopy to directly probe few Fermion charge and spin dynamics in an artificial molecule formed by vertically stacking a pair of InGaAs self-assembled quantum dots. As the relative energy of the orbital states in the two dots are energetically tuned by applying static electric fields, pronounced anticrossings are observed arising from electron tunnel couplings. Time resolved photocurrent measurements performed in the vicinity of these anticrossings provide direct information on the comparative roles of elastic and inelastic resonant tunneling processes between the two quantum dots forming the molecule. Resonant pumping of the neutral exciton in the upper dot with circularly polarized light facilitates ultrafast initialization of hole spin qubits over timescales limited only by the laser pulse duration (<5ps) and a near perfect Pauli spin-blockade with a near unity suppression of absorption (>96%) for spin forbidden transitions. Such a spin selective photocurrent response opens the way to probe spin dynamics in the system over ultrafast timescales.

We demonstrate an instantaneous all-optical manipulation of optical absorption at the ground state of InGaAs/GaAs quantum dots (QDs) via a quantum-confined Stark effect (QCSE) induced by the electric field of incident THz pulses with peak electric fields reaching 200 kV/cm in the free space. As a result, a THz signal with the full bandwidth of 3 THz can be directly encoded onto an optical signal probing the ground state absorption in QDs, resulting in the encoded temporal features as fast as 460 fs. The optical absorption modulation at highest THz fields reaches about 30% of the total optical absorption in QDs at the ground state. The dependency of electro-absorption modulation depth on the peak THz field is found to be strongly nonlinear, as expected from the QCSE. From this dependency we conclude that the dominant contribution to the observed electro-absorption modulation in our sample is made by the overall optical absorption quenching via a reduction of the overlap integral and hence the probability of inter-band transition, rather than by the Stark shift of the QD absorption peak away from the spectrum of the optical probe. As expected from the three-dimensional geometry of a QD, the THz QCSE was found to be independent of the polarization of the THz field. The instantaneous nature of THz QCSE in QDs enables femtosecond all-optical switching at very high repetition rates. This allowed us to demonstrate the potential for applications in THz-range wireless communication systems with the data rate of at least 0.5 Tbit/s.

The investigation of the intersubband dynamics occurring in the conduction band of doped semiconductor quantum dots (QD's) has emerged as a powerful tool to probe their electronic structure and properties. Here, the temperature, the dephasing and the relaxation dynamics are of interest, both from a fundamental point of view but also regarding the performance of QD-based optoelectronic devices. Whereas the lineshape of QD interband transitions is well described by the independent boson model treating a diagonal electron-phonon coupling. For intraband transitions both diagonal and non-diagonal electron-phonon coupling are relevant. Typically, such problems involving diagonal and non-diagonal coupling are treated within approximate or perturbative approaches. Here, we present a fully quantized theory to calculate the coupled electron-phonon dynamics based on a non-perturbative equation of motion approach reproducing also correct results for limits of known exactly solvable models.

We present a microscopic theory for the time resolved light emission from a semiconductor quantum dot, interacting with LO-phonons. We investigate the emission properties of the QD under strong external laser powers, leading to strongly correlated electron phonon dynamics. We employ an equation of motion approach, which treats the electron phonon interaction with necessary accuracy far beyond the typical bath approximation. We can describe several new non-equilibrium features, like phonon assisted Mollowtriplets and phonon related anti-crossings, which occur in the spectrum in the strong excitation regime.

Using an empirical pseudopoential description of electron states and an adiabatic bond charge model for phonon states, a full band structure calculation is performed for the one- and two-photon indirect optical injection of carriers and spins in bulk silicon. The calculated one- and two-photon absorption coefficients are in agreement with experiments. For σ^- light propagation direction along 001, the carrier and spin injection rates and the degree of spin polarization show strong valley anisotropy. The carrier injection rates in the Z valleys are larger than that in the X valley. Furthermore, the two photon indirect carrier injection shows anisotropy and linear-circular dichroism with respect to the light propagation direction.

Spin-optoelectronic devices have become a field of intensive research in the past few years. Here we present electrical spin injection into spin light-emitting diodes both at room temperature and in magnetic remanence. Our devices consist of a Fe/Tb multilayer spin injection structure with remanent out-of-plane magnetization, a MgO tunnel barrier for efficient spin injection and an InAs quantum dot light-emitting diode. The ground state emission and first excited state emission both show circularly polarized emission in remanence, i.e. without external magnetic fields which is due to spin injection from our ferromagnetic contact. Using a series of samples with varying transport path lengths between the spin injector and the active region, we investigate the spin relaxation length during vertical carrier transport through our devices. Due to our spin injector with remanent out-of-plane magnetization this spin relaxation can be investigated without the need for external magnetic fields which would possibly influence the spin relaxation process. The decrease in circular polarization with increasing injection path length is found to be exponential, indicating drift-based transport which is in accordance with theoretic calculations. From the exponential decay the spin relaxation length of 26 nm as well as a lower bound for the spin injection efficiency of 25% are calculated. Additionally, influences of magnetic field, temperature and current density in the devices on the spin relaxation process are discussed.

With the aid of Maker fringe technique, we have observed two nonlinear optical (NLO) phenomena separately on diameter and length of ZnO nanorod (NR). One is second harmonic generation (SHG) saturation in rod diameter, and the other is SHG enhancement in rod length. Besides that, the model based on Lorentz local field is proposed for the first time to elucidate the above phenomena. The deduced second order susceptibility _χ⁽²⁾ with various sizes of ZnO NR matches well to our theory, demonstrating that the size effect on _χ⁽²⁾ is governed by Lorentz local field. Our theory provides a theoretical basis to explain the mechanism of light-material interaction in nano-dimensions and is readily to be extended to other kind of semiconductor nanostructures when addressing NLO properties in them.

InAs nanowires have been previously shown to be efficient emitters of THz radiation, upon excitation with NIR pulses. In this work we report complementary measurements of THz radiation and reflectometry together with DC transport measurements that point to a unifying picture of low-energy acoustic-like longitudinal surface plasmons as being the origin of this THz emission from the nanowires.

We report on nonlinear propagation of single-cycle THz pulses with peak electric fields reaching 300 kV/cm in n-type semiconductors at room temperature. Dramatic THz saturable absorption effects are observed in GaAs, GaP, and Ge, which are caused by the nonlinear electron transport in THz fields. The semiconductor conductivity, and hence the THz absorption, is modulated due to the acceleration of carriers in strong THz fields, leading to an increase of the effective mass of the electron population, as the electrons are redistributed from the low-momentum, low-effective-mass states to the high-momentum, high-effective-mass states in the energy-momentum space of the conduction band. Further, we observe the typical accompanying effects of saturable absorption on the THz pulses, such as an increase of the group delay, as the peak electric field of the pulse increases. In this paper we present the results of nonlinear THz time-domain spectroscopy, and of THz pump - THz probe spectroscopy.

We describe a unique mathematical/numerical model to analyze ultrafast laser experimental data and obtain two-photon (TPA) and multi-photon (MPA) absorption parameter(s). The material used to demonstrate the numerical method is a hybrid organic-inorganic nano-structured semiconductor quantum dot-polymer composite. Chemical, biological and engineering studies require advancements in TPA/MPA absorbers for microscopy, fluorescence, imaging, and microprocessing of materials. We illustrate the numerical method by fitting data from the well-known z-scan experimental method. Often an analytical model is used to analyze data from such experiments, which is limited in scope with certain restrictions on laser intensity and material thickness. A more general mathematical/numerical method that includes TPA/MPA and can be extended to free carrier absorption and stimulated emission is described. Under certain circumstances, we can also calculate the electron population density on every electronic level to demonstrate physical effects such as saturation. Additionally, we include diffraction in our numerical calculation so that the TPA/MPA can be obtained even for thick optical samples. We use the numerical method to calculate published z-scan measurements on quantum-dot CdS-polymer composites, and show excellent agreement with published analytical results.

We show by experiments and simulations that properly chirped laser pulses enable efficient and broadband sum frequency generation in nonlinear crystals. We achieved high energy, picosecond deep-UV pulses with spectral width one order of magnitude greater than the acceptance bandwidth of the nonlinear interaction. The broad spectrum supports shaping of ps flat-top deep-UV pulses with short rise- and fall-time, which are optimal for driving high brightness photocathode electron guns.

We review the recent progress made by us on power scaling of terahertz (THz) waves and development of compact and portable THz sources. By reversely stacking GaP plates, we were able to improve the photon conversion efficiency from 25% to 40%, which is the record-high value. As the number of the stacked GaP plates was increased from 4 to 5, the output power was decreased. This is the evidence on back conversion. In order to make our THz source truly compact and portable, we investigated a new route to THz generation by mixing two frequencies generated by a single Nd:YLF solid-state laser. After two Nd:YLF crystals were introduced in the laser cavity, the output power was scaled up to 4.5 μW. Such a configuration exhibits versatile characteristics such as the generation of different THz frequencies by combining two different laser crystals. Our recent investigation of THz generation based on passively Q-switched dual-frequency pulses may help us with further reducing the dimension of our compact and portable THz source.

We utilize quantum-confined Stark-effect in asymmetric double quantum wells (ADQW) to realize coherent detection of broadband THz pulses. For that, broadband THz transients formed by a two-color air plasma are focused onto ADQW, in turn dynamically shifting the ADQW bands, with the bandedge at ~ 825 nm. Spectrally-resolved detection scheme analyzes absorption modulation signatures imprinted onto the transmitted NIR probe spectrum. Use of only few micron thick samples ensures large detection bandwidth, currently demonstrated up to ~ 15 THz. Time-domain analysis of this signal shows pronounced bi-polar (coherent) as well as small unipolar components of the signal.

We present a review of our recent nonlinear spectroscopy experiments on bulk semiconductors performed using a novel source of ultra-intense multi-THz transients. The field-induced interband optical absorption in InP is studied on subcycle timescales. Our simulations corroborate the Franz-Keldysh effect as the main reason for the observed optical anomalies. The time-resolved four-wave mixing signals generated in InSb demonstrate clear signatures of a nonperturbative excitation regime and can be qualitatively reproduced by a simplified model of a two-level system driven far from the resonance.

Nonlinear terahertz (THz) spectroscopy gives insight into high-field charge transport in semiconductors. Strong THz transients with field amplitudes of up to megavolts/cm serve as a driving field for free carriers and the resulting transport behavior is directly inferred from the field radiated by the moving charges. We study the transition from a ballistic to a drift-like transport regime of electrons in bulk GaAs. While electrons in the lowest conduction band of an n-type sample display ballistic transport, a transition to a drift-like behavior is found in an optically generated electron-hole plasma. Time-resolved measurements reveal the onset of friction on a time scale of a few picoseconds, mainly due to interactions of electrons with the hole distribution heated by the intense THz driving field. Experiments in which photoexcited electrons undergo intervalley scattering from the Γ to the L valley reveal characteristic changes of the transport behavior due to the picosecond backscattering to the Γ valley. The experimental results are in agreement with theoretical calculations of the time-dependent friction including both electron-hole scattering and local-field effects.

We create an optically imprinted gain-trapped polariton wire with a length of 15 μm and a width of 2μm by modulating the shape of a non-resonant excitation spot using a high-resolution spatial light modulator (SLM). We study the spatially, spectrally and temporally resolved emission from the wire and find that the system passes several regimes, starting with an intense emission peak originating from the wire center and develops towards longer living emission from its side. The temporal development of the emission wavelengths corresponding to these peaks allow us to characterize these different emission regimes in terms of photon lasing and polariton condensation.

Characteristic low-threshold polariton lasing of organic and inorganic microcavity systems can only be achieved with efficient population of the lower polariton ground state. In this regard, the key role undertaken by vibronic replicas and molecular phonon it has been shown experimentally and theoretically predicted by various works. We report here, direct observation of critical enhancement of polariton population density in strongly coupled J-aggregate based organic microcavities. The process highlighted in our study is manifested by discrete maxima of the angular-resolved photoluminescence intensity and interpreted by the mediation of molecular vibrations quanta characteristic of the active material. By measuring the reduced time scale of vibrations driven relaxation dynamics, manifested by sub 100fs buildup times, we emphasized the efficiency of the mechanism to overcome losses channel in disordered J-aggregate systems. Hence, the realization of amplified polariton population with improved relaxation rates paves the way for the observation of low threshold lasing, primary step for developing room temperature organic laser sources and ultra-fast optoelectronic devices with less fabrication complexity than their crystalline counterparts.

The biexciton cascade within semiconductor quantum dots is known to be a useful source of polarizationentangled photon pairs. An analytical solution in the weak-coupling regime for quantum-state tomography matrix elements, i.e. the two-photon correlation function, is presented. It is demonstrated that with the inclusion of pure dephasing and considering degenerate exciton levels, the entanglement is not affected, and a convenient formula to calculate the degree of entanglement in an experiment is derived.

We report on the observation of ultrafast in-plane charge oscillations resulting from simultaneous optical excitation of heavy- and light-hole excitons in (110)-oriented GaAs quantum wells. These charge oscillations arise from a displacement between heavy and light-hole states in the plane of the quantum well, and, thus, differ significantly from previously observed charge oscillations directed along the growth direction of a quantum well. Our observations are evidence for the existence of a strong far-infrared inter-subband transition dipole moment between heavy- and light-hole subbands for in-plane wave vectors which we estimate to be ~0.5 eA for the quantum wells under investigation. We attribute this in-plane transition dipole moment to strong band mixing in the (110)-oriented structures.

Exciton dephasing and relaxation dynamics are studied in a GaAs quantum dot ensemble using optical twodimensional Fourier transform spectroscopy. We measure the temperature and excitation-density dependence of the exciton ground-state homogeneous lineshape of quantum dots within the ensemble and show that acoustic phonon sidebands are absent. The linewidth increases nonlinearly with temperature from 6 to 50 K and the behavior is well-described by an Arrhenius equation with an offset. The absence of a phonon-activation peak in the spectra reveals that elastic exciton-phonon scattering is the primary dephasing mechanism and the results can be explained qualitatively using an extension of the independent Boson model that includes quadratic coupling in the phonon displacement coordinates. At temperatures ≥ 35 K, spectral features associated with phonon-assisted population transfer of excitons out of the quantum dots and into quantum wells states begin to appear.

Photoemission spectroscopy using femtosecond XUV light pulses is applied to probe the isomerization state of the molecular switch 3-(4-(4-hexyl-phenylazo)-phenoxy)-propane-1-thiol deposited by liquid phase self-assembly on Au(111). Spectral shifts of valence-electronic signatures that we associate with the carbon C2s orbital enable us to distinguish the trans and the cis isomerization state of the adsorbed molecules. These preliminary results envision the potential to probe reversible switching processes of surface-mounted molecules in real time by tracking the temporal evolution of the electronic and nuclear degrees of freedom in a femtosecond XUV photoemission experiment.

We demonstrate THz imaging and time-domain spectroscopy of a single-layer graphene film. The large-area graphene was grown by chemical vapor deposition on Cu-foil and subsequently transferred to a Si substrate. We took a transmission image of the graphene/Si sample measured by a Si:bolometer (pixel size is 0.4-mm). The graphene film (transmission: 36 - 41%) is clearly resolved against the background of the Si substrate (average transmission: 56.6%). The strong THz absorption by the graphene layer indicates that THz carrier dynamics are dominated by intraband transitions. A theoretical analysis based on the Fresnel coefficients for a metallic thin film shows that the local sheet resistance varies across the sample from 420 to 590 Ohm, consistent with electron mobility ~ 3,000 cm²V^-1s^-1. We also measured time-resolved THz waveforms through the Si substrate and the graphene/Si sample. The waveforms consist of a series of single-cycle THz pulses: a directly transmitted pulse, then subsequent "echos" corresponding to multiple reflections from the substrate. The amplitude difference between graphene/Si pulses and Si pulses becomes more pronounced as the pulses undergo more reflections. From these measurements, we obtained spectrally flat transmission spectra of the transmitted pulses and the average sheet resistance 480 Ohm, consistent with the results of the power transmission measurement. The flat spectral responses indicate that the carrier scattering time in our graphene sample is much shorter than the THz pulse duration.

A new technique, ultrafast refractometry, is introduced for probing the refractive, absorptive, and diffractive conditions in nanocomposite assemblies. It is shown that the physical characteristics of nanocomposites-nanoparticle sizes and volumetric ratios in the polymer host-are decisive factors in determining the material's overall optical properties. Ultrashort optical pulses (100 fs) act as an in-situ probe for temporal phase, optical attenuation, and spatial coherence in these discrete materials. This technique is demonstrated for numerous samples of 20 nm SiC nanoparticle/polymer nanocomposites. A close link between the physical properties and the ultimate refraction, absorption, and diffraction characteristics of these nanocomposite optical materials is shown.

We examine planar double split-ring resonators (SRRs) consisting of two concentric rings with either opposite, similar, or asymmetric gap orientation. Depending on the geometry we observe resonance hybridization, metamaterial induced transparency, or the excitation of dark resonances. These properties can be used for SRR based sensing applications, to realize strongly dispersive behavior, or for determining the optical properties of metals. We further find that THz SRRs featuring very narrow gaps on the micro- or nanoscale can provide in-gap enhancement factors of several 10,000, a property particularly useful for the realization of nonlinear THz experiments.

A terahertz plasmonic waveguide sensor is experimentally demonstrated to utilize surface waves propagated in a onedimension metal grating that constructed on a plastic ribbon waveguide. The grating conformation couples evanescent waves of a subwavelength terahertz waveguide onto the metal surface and highly confines the extended powers within λ/22-range for the phase-matching condition. The confined terahertz waveguiding waves resemble surface plasmonpolaritons but transmit with almost zero dispersion when the coupled surface waves interfere along the metal grating. Based on the dispersion-free guidance, there is Bragg reflection dominated by grating periods and strongly dependent on the refractive index of surface plasmon-polaritions. We successfully detect different thicknesses of polyethylene layers covered on the metal grating with thickness resolution of 1μm when the effective waveguide indices are modified in the vicinity of the metal grating, corresponding to 0.01-index variation. Potentially, terahertz subwavelength ribbon waveguide based plasmonic sensors could be manipulated to detect molecules with extremely low-density or small thickness in the metal-dielectric interface for probing pollution particles and any label-free detection.

The feed-forward technique has recently revolutionized carrier-envelope phase stabilization, enabling unprecedented values of residual phase jitter. Nevertheless, in its original demonstrations the stabilized beam exhibited angular and temporal dispersion. We demonstrate that these problems can be solved, resulting in few-cycle pulses with good beam quality. This in turn enables the use of monolithic interferometers, providing excellent long-term stability of the system. Out-of-loop RMS phase noise of less than 80 mrad over 33 minutes (0.5 mHz to 5 kHz) is measured, i.e., a value that has previously been reported for a few seconds integration time. The current method promises to enable reliable operation of CEP-stable systems over several days.

In tiny metallic nanostructures, quantum confinement and nonlocal response change the collective plasmonic behaviour with resulting important consequences for e.g. field-enhancement and extinction cross sections. Here we report on nonlocal resonances in the hydrodynamical Drude model for plasmonic nanostructures that have no counterpart in the local-response Drude model. Even though there are no additional resonances in the visible due to nonlocal response, plasmonic field enhancements are affected by nonlocal response. We present both analytical results for simple geometries and our numerical implementation for arbitrary geometries, and address computational issues related to the several length scales involved.

We report on the evaluation of lattice thermal conductivity of GeTe/Sb₂Te₃ superlattice (SL) by using a coherent phonon spectroscopy at various lattice temperatures. The time-resolved transient reflectivity obtained in amorphous and crystalline GeTe/Sb₂Te₃ SL films exhibits the coherent A1 optical modes at terahertz (THz) frequencies with picoseconds dephasing time. The relaxation time and frequency of the coherent A1 modes are used to compute the lattice thermal conductivity based on the Debye theory, including scattering by grain boundary and point defect, umklapp process, and phonon resonant scattering. The results indicate that the thermal conductivity in the amorphous SL film is less temperature dependent, due to the dominant phonon-defect scattering, while in the crystalline SL it is temperature dependent because of the main contributions from umklapp and phonon resonant scatterings. We argue the higher thermal conductivity in the GeTe/Sb₂Te₃ SL films than that in the Ge₂Sb₂Te₅ alloy films implies that the phase change in GeTe/Sb₂Te₃ SL is not purely promoted by thermal process, i.e., lattice heating, but rather by nonthermal process, i.e., coherent lattice excitation, because the thermal process generally requires lower thermal conductivity.

Seeking for the new opportunities to efficiently excite GHz-THz coherent acoustic phonons by femtosecond lasers is an active field of research. Several fundamental objectives have to be addressed in order to achieve this acoustic phonons manipulation by femtosecond laser. Among them, the understanding of femtosecond generation of coherent acoustic phonons remains a key route. Several electron-phonon, photon-phonon and phonon-phonon interaction mechanisms are involved in the processes of generation and remain only partially understood up to now. In this paper, we will present a survey of ultrafast photo-generation of coherent acoustic phonon in semiconductors. We will focus first on the generation of the phonons by fs-laser excitation through the photoinduced modifications of nanoscopic internal electric fields (deformation potential) in non-piezo-active [100] GaAs semiconductor. We will show secondly how it is possible to develop more efficient sources by using piezo-active [111], [-1-1-1] and [411] GaAs semiconductors. In that case, generation of GHz acoustic phonon due to inverse piezoelectrical effect is based on ultrafast light-induced screening of the near surface built-in electric field.

High harmonic generation is investigated for a two-band model of a semiconductor nanostructure. Similar to an atomic two-level system, the semiconductor emits high harmonic radiation. We show how one can specifically enhance the emission for a given frequency by applying a non-trivially shaped laser pulse. Therefore, the semiconductor Bloch equations including the interband and additionally the intraband dynamics are solved numerically and the spectral shape of the input pulse is computed via an optimization algorithm. It is demonstrated that desired emission frequencies can be favored even though the overall input power is kept constant. We also suggest special metallic nano geometries to achieve enhanced localized optical fields. They are found by geometric optimization.

Revealing the ultimate speed limit at which magnetic order can be controlled, is a fundamental challenge of modern magnetism having far reaching implications for magnetic recording industry. Exchange interaction is the strongest force in magnetism, being responsible for ferromagnetic or antiferromagnetic spin order. How do spins react after being optically perturbed on an ultrashort timescales pertinent to the characteristic time of the exchange interaction? Here we demonstrate that femtosecond measurements of X-ray magnetic circular dichroism provide revolutionary new insights into the problem of ultrafast magnetism. In particular, we show that upon femtosecond optical excitation the ultrafast spin reversal of Gd(FeCo) - a material with antiferromagnetic coupling of spins - occurs via a transient ferromagnetic state. The latter one emerges due to different dynamics of Gd and Fe magnetic moments: Gd switches within 1.5 ps while it takes only 300 fs for Fe. Thus, by using a single fs laser pulse one can force the spin system to evolve via an energetically unfavorable way and temporary switch from an antiferromagnetic to ferromagnetic type of ordering. These observations supported by atomistic simulations, present a novel concept of manipulating magnetic order on different classes of magnetic materials on timescales of the exchange interaction.

We report on the recent progress of terahertz magneto-optical measurement combined with terahertz time-domain spectroscopy. The detailed experimental scheme for the observation of optical quantum Hall effect in a two dimensional electron gas system in the integer-quantum Hall effect regime is described.

We investigate the charge transport in nickel-titanium (Ni-Ti) alloy thin films using terahertz (THz) transmission spectroscopy. Ni-Ti alloys have peculiar mechanical properties such as shape memory effects. Electrical conductivity can be a good measure to characterize the alloy phase transitions, yet the carrier transport properties of this material are relatively unexplored in the thin film regime. We grew 60-80-nm Ni-Ti alloy films of various Ti concentrations (0- 100%) on intrinsic Si substrates by Ar plasma sputtering. We carried out THz transmission spectroscopy of the samples using broadband THz pulses. The broadband THz pulses were generated by optical rectification of femtosecond laser pulses in a 1-mm ZnTe crystal. The light source was a 1-kHz Ti:sapphire amplifier producing 800-nm femtosecond pulses (pulse energy, 1 mJ; pulse duration, 90 fs). The transmitted THz pulses were measured by either a L-He-cooled Si:Bolometer (sensitive to time-averaged THz power) or by electro-optic (EO) sampling using a 1-mm ZnTe crystal. Analyzing the power transmission data and the transmitted waveforms, we obtained the alloy resistivity as a function of Ti concentration. Sharp changes in the resistivity were observed at the Ti fractions of 22%, 44% and 62%, indicating that structural disorder is greatly enhanced when the alloy undergoes a phase transition.

For nanostructures such as semiconductor quantum dot emitters or biological systems like light harvesting complexes (photosynthesis) the coupling between individual constituents leads to the formation of delocalized exciton states. Coherent two dimensional spectroscopy is a versatile tool to investigate the structure of the excitonic states, whereas nanoplasmonics allows to localize optical fields on a nanoscale: We combine these two methods in a theoretical study and propose new experiments, such as the two dimensional spectra containing spatial resolution via localized fields. Using post processing of different spectra with localized fields, we can enhance certain spectroscopic features in standard coherent spectroscopy, e.g. by suppressing unwanted resonances.

An antenna geometry that represents the contour of a traditional bowtie antenna is proposed and investigated via finitedifference time-domain simulations. A parameter space consisting of the antenna length and the contour thickness is explored and design principles for this geometry are presented. It is demonstrated that a continuous red-shift of the resonant wavelength relative to the resonant wavelength of a bowtie antenna is possible by decreasing the contour thickness of the antenna. In the parameter space examined, it is found that the antenna footprint may be reduced by a factor of 3.6 and the gap enhancement factor may be increased by 28%. A conceptual understanding of the antenna behavior is built up by drawing a parallel between the plasmonic nanoshell and the nanoplasmonic contour bowtie antenna. Three other variations of this geometry are investigated in order to gain a deeper understanding of the underlying physics.