This PDF file contains the front matter associated with SPIE Proceedings Volume 9361, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

We report a saturated absorption characteristic of carbon nanowall and Q-switched laser operation using carbon nanowall saturable absorber. Carbon nanowall is vertically aligned nanographite sheets on Si substrate synthesized by plasma-enhanced chemical vapor deposition method. A polyimide thin film, with incorporated carbon nanowall, coated by spin-coating method, is used as saturable absorber. Linear absorption spectrum of carbon nano-walls was observed without absorption peak wavelength range from 1000 to 2000nm. Modulation depth of carbon nanowall saturable absorber was measured with wavelength of about 1560nm. Q-switch laser operation with carbon nanowall saturable absorber and erbium doped optical fiber was demonstrated.

We present an analytical expression for the differential transmission of a delta-shaped light field in Landau-quantized graphene. This enables a direct comparison of experimental spectra to theoretical calculations reflecting the carrier dynamics including all relevant scattering channels. In particular, the relation is used to provide evidence for strong Auger scattering in Landau-quantized graphene.

We demonstrate the arbitrary control of the carrier-envelope phase of intense few-cycle THz pulses by using a simple passive component with high transmission efficiency based on a parallel metal plate waveguide. In this component, the carrier-envelope phase is altered by using the difference between the group and phase velocities. We demonstrate pulseshape- dependent nonlinear spectroscopy using these passive optics for Ge:Sb, where strong transitions between the shallow acceptor levels are located at 2.0 THz.

We demonstrate how diverse femtosecond spectroscopy approaches coalesce to a comprehensive understanding of photochemical reaction pathways, exemplarily for the ring-open isomers of merocyanine compounds. Pump-probe transient absorption spectroscopy discloses photo-induced ring closure, whereas coherent two-dimensional (2D) electronic spectra directly visualize whether there is photoisomerization. We further introduce coherent triggered-exchange 2D electronic spectroscopy, a versatile tool for analyzing excited states and associated reaction pathways, with the information from where the reaction started intrinsically preserved. Beyond that, third-order three-dimensional spectroscopy provides an intuitive picture for which reactants can be turned into which products, additionally exposing the reactive molecular modes connecting them.

The correct understanding of the electronic structure and relaxation behavior in nanosystems is essential for technical applications. We propose a spectroscopic method to measure the dipole-forbidden electronic transitions of quantum dots and trace their relaxation behavior. Therefore, we utilize two-dimensional coherent spectroscopy, which is an advantageous tool to get information about the dynamics of exciton densities and coherences in nanoscopic structures. In combination with nanoplasmonics, it enables excitation of dipole-forbidden states. A nanoplasmonic dolmen structure allows us to dynamically excite either dipole-allowed and dipole forbidden states selectively. In combination with two-dimensional spectroscopy, this gives us additional control over excitation and tracing relaxation involving dipole-forbidden states in nanoscopic systems.

In this manuscript, we study the impact of the two Coulomb induced resonance energy transfer processes, Förster and Dexter coupling, on the spectral signatures obtained by double quantum coherence spectroscopy. We show that the specific coupling characteristics allow us to identify the underlying excitation transfer mechanism by means of specific signatures in coherent spectroscopy. Therefore, we control the microscopic calculated coupling strength of spin preserving and spin flipping Förster transfer processes by varying the mutual orientation of the two quantum emitters. The calculated spectra reveal the optical selection rules altered by Förster and Dexter coupling between two semiconductor quantum dots. We show that Dexter coupling between bright and dark two-exciton states occurs.

We present results on the continuous tuning of the interaction strength between the cyclotron transition in a two dimensional electron gas (2DEG) and the LC mode of THz split ring resonators (SRRs) with ω_LC = 2π× 0.52 THz. The interaction strength is continuously modified in a gated sample by changing the electron density in the 2DEG. We observe an asymmetric emergence of the polaritonic branches at the onset of the ultrastrong coupling. Both, the line widths and transmission amplitudes are modulated when moving from the weak coupling regime to the ultrastrong coupling regime reaching a normalized coupling rate Ω ω= 0.21.

It is well known that Fluorescence Resonance Energy Transfer (FRET), the most common mechanism for electronic energy to migrate between molecular chromophores, has a predominantly inverse sixth power dependence on the rate of transfer as a function of the distance R between the chromophores. However, the unified theory of electronic energy transfer, derived from quantum electrodynamics, predicts an additional contribution with an R^-4 dependence on distance. This intermediate-zone term becomes especially important when the chromophore spacing is similar in magnitude to the reduced wavelength (ƛ= λ 2π ) associated with the mediated energy. In previous theoretical studies we have suggested that inclusion of the intermediate term, through rate equation and quantum dynamical calculations, may be important for describing the exciton diffusion process in some circumstances, and in particular when the distance between the chromophores exceeds 5 nm. In this paper, we focus of the role of the intermediate-zone contribution to distance measurements between chromophores made through the application of spectroscopic ruler techniques. One of the major assumptions made in employing these experimental techniques is that the R⁻⁶ dependence is valid. In this work, we reformulate the spectroscopic ruler principles for intermediate distances to include the inverse fourth power rate component, and compare the results of this reformulation to experimental FRET results from the literature.

Electrical nanosources of surface plasmons will be an integral part of any future plasmonic circuits. Three different types of such nanosources (based on inelastic electron tunneling, high energy electron bombardment, and the electrical injection of a semiconductor device) are briefly described here. An example of a fundamental experiment using an electrical nanosource consisting of the tunnel junction formed between a scanning tunneling microscope (STM) and a metallic sample is given. In this experiment, the temporal coherence of the broadband STM-plasmon source is probed using a variant of Young's double slit experiment, and the coherence time of the broadband source is estimated to be about 5-10 fs.

Far field Super resolution (SR) microscopy, based on the emission of label fluorescent molecules, has become an important tool in life sciences. We present a new, label free, far field SR scheme, aimed towards material science, which is based on ultrafast, nonlinear excitation of materials to non-equilibrium state. In a pump-probe scheme, we optically excite a spatial temperature profile throughout the diffraction limited spot, and probe the material with an overlapping beam. Due to nonlinearities in thermal properties, we demonstrate enhancement of at least x2 better than the diffraction limit. Our approach can be extended to include other temperature dependent physical properties such as Raman scattering, reflection/absorption edge or luminescence. The method is suitable to characterize semiconductor and optoelectronic systems in vacuum, ambient, and liquid, semi-transparent and opaque systems, ultrathin and thick samples alike. In this communication we present the method and discuss some major physical consideration and experimental aspects of its application. We focus the discussion on ultrafast dynamic and thermal properties. We also discuss the applicability of the method in the unique case of VO2 where photo-induced phase transition provides the contrast and present a highly accurate optical edge detection method based on the modulation phase.

In numerous solids exhibiting broken symmetry ground states, changes in electronic (spin) structure are accompanied by structural changes. Femtosecond time-resolved techniques recently contributed many important insights into the origin of their ground states by tracking dynamics of the electronic subsystem with femtosecond light pulses. Moreover, several studies of structural dynamics in systems with periodic lattice modulation (PLD) were performed. Since intensities of the super-lattice diffraction peaks are in the first approximation proportional to the square of the PLD amplitude, their temporal dynamics provides access to cooperative atomic motion. This process takes place on a fraction of a period of the corresponding lattice vibration (typically 100 fs timescale). However, since energy transfer from the excited electronic system to the lattice takes place on a comparable timescale, contribution of the incoherent lattice motion on diffraction intensities has to be taken into account. Furthermore we demonstrate an ultrafast transmission electron diffraction set-up, where relative changes in individual diffraction peaks of less than 1% can be studied. Here we show, that by simultaneously tracking the dynamics of intensities in super-lattice peaks, lattice peaks and in the incoherent background over multiple diffraction orders the two processes can be effectively disentangled.

We propose an ultrafast, all-optical mechanism utilizing ultrashort terahertz electric field pulses to tailor the kinetic energy and directivity of surface plasmon generated electron pulses. By varying the electric field strength of a single applied terahertz pulse, the angular spread, directivity and peak kinetic energy can be controlled. Further control over the kinetic energy range can be obtained through varying the time delay of a second terahertz electric field pulse with respect to the first. It is also observed that the carrier envelope phase dependency of the kinetic energy is maintained in the presence of a terahertz electric field.

The imaging of surface plasmon polariton waves in two photon photoemission microscopy has been intensely studied during the past years, with a focus on contrast mechanisms and light-plasmon interaction. The possibility of photoemission from the plasmonic fields alone has so far not been addressed in such experiments. This was justified, since the intensity of the plasmonic fields at the surface was comparatively weak and nonlinear plasmonic effects were not to be expected. Here we discuss the properties of grating couplers for creation of intense and short plasmon polariton pulses for which the emission of electrons purely from the plasmonic field cannot be neglected any more. Two examples for signatures of such nonlinear plasmoemission effects in experimental two photon photoemission microscopy images are discussed.

We present a theoretical discussion on the feasibility of spasing for a specific spaser setup. For this purpose we develop a numerically exact and feasible solution to the open system Tavis-Cummings model in the Born- Markov Lindblad formalism. The complexity of the solution scales with the third power in the number of two level systems- a considerable advance compared to the exponential scaling of the brute force solution. The question of spasing is answered negatively in agreement with the literature.

Media that are described by extreme electromagnetic parameters, such as very large/small permittivity/permeability, have generated significant fundamental and applied interest in recent years. Notable examples include epsilon-near-zero, ultra-low refractive-index, and ultra-high refractive-index materials. Many photonic structures, such as waveguides, lenses, and photonic band gap materials, benefit greatly from the large index contrast provided by such media. In this paper, I discuss our recent work on media with infinite anisotropy, i.e., infinite permittivity (permeability) in one direction and finite in the other directions. As an illustration of the unusual optical behaviors that result from infinite anisotropy, I describe efficient light transport in deep-subwavelength apertures filled with infinitely anisotropic media. I then point out some of the opportunities that exist for controlling light at the nano-scale using infinitely anisotropic media by themselves. First, I show that a single medium with infinite anisotropy enables diffraction-free propagation of deep-subwavelength beams. Next, I demonstrate interfaces between two infinitely anisotropic media that are impedancematched for complete deep-subwavelength beams and enable reflection-free routing with zero bend radius that is entirely free from diffraction effects even when deep-subwavelength information is encoded on the beams. These behaviors indicate an unprecedented possibility to use media with infinite anisotropy to manipulate beams with deepsubwavelength features, including complete images. To illustrate physical realizability, I demonstrate a metamaterial design using existing materials in a planar geometry, which can be implemented using well-established nanofabrication techniques. This approach provides a path to deep-subwavelength routing of information-carrying beams and far-field imaging unencumbered by diffraction and reflection.

We present the detailed investigation of an ultrafast silicon based nanoplasmonic three terminal device. The device operates on the principle of ponderomotive acceleration of two-photon absorption generated electrons within a nanoplasmonic waveguide structure. Due to high spatial mode confinement, high spatial asymmetry, and high enhancement of the nanoplasmonic electric field, electrons are accelerated to high kinetic energies and are directed towards the copper anode generating an output current. Application of a negative grid voltage modulates an effective energy barrier that restricts the number of electrons reaching the anode, thus reducing the output current. Operating at electric field strengths up to 1×10⁷ V/cm generates a 150 fs output current pulse of 628 mA/μm. Careful consideration of the materials used facilitates monolithic integration with current complementary-metal-oxide-semiconductor nanoelectronics devices.

Dropletons are new highly correlated quasiparticles recently discovered in GaAs quantum wells. The dropleton discovery is verified with a new measurement set and the full identification cycle is presented. The analysis confirms that a dropleton contains four or more electron–hole pairs within a tiny correlation bubble and that dropleton’s electron–hole pairs are in a liquid-like state that is quantized due to quantum confinement.

By using terahertz (THz) pump-THz probe spectroscopy, we investigated ultrafast dynamics of s-wave superconductors NbN. After instantaneous excitation with an intense monocycle THz pulse, transient oscillation of the superconducting order parameter is observed in the transmission of the THz probe pulse, which is interpreted as the collective Higgs amplitude mode associated with spontaneous symmetry breaking. We also found that the Higgs mode can be resonantly excited by a sub-gap multi-cycle THz pump pulse in the nonlinear response regime, resulting in efficient third-order harmonics generation. These results shed new light on the ultrafast optical control of quantum condensates and its application to THz nonlinear optics.

We discuss equilibrium and ultrafast optical pump-THz probe spectroscopy of the model stripe-ordered system La_1.75Sr_0.25NiO₄. We present a multi-oscillator analysis of the phonon bending mode splitting observed at low temperatures in equilibrium, along with a variational model for the transient THz reflectivity variations. The low temperature splitting is directly related to the formation of the long-range stripe-order, while the background conductivity is reminiscent of the opening of the mid-IR pseudogap. Ultrafast experiments in the multi-THz spectral range show strong THz reflectivity variations around the phonon bending mode frequency (≈11 THz).

The transient dynamics of transition-metal dichalcogenides is of significant interest for clarifying fundamental manyparticle interactions at the nanoscale as well as for novel applications. We report an ultrafast terahertz study up to 7 THz of the lamellar semiconductor MoS₂ to access the non-equilibrium conductivity of photo-excited indirect e-h pairs in this multi-layered parent compound. While the equilibrium transport is Drude-like, near-IR optical excitation results in a complex photo-induced conductivity that consists of two components. Mobile charge carriers dominate the low frequency response below 2 THz, while at low temperatures an additional excess conductivity is observed that is enhanced around 4 THz. Two time scales appear in the dynamics: a slow ns relaxation due to non-radiative recombination and a faster sub-100 ps decay connected to the high-frequency THz feature. We discuss the broad THz peak within a model of intra-excitonic transitions in MoS₂. It agrees well with the expected binding energy and oscillator strength, yet results in an anomalous temperature dependence of the exciton fraction requiring an electronically inhomogeneous phase.

By means of THz pump and optical probe spectroscopy, we observed that the incident THz pulse induces a strong spectral modulation of the 1s heavy-hole exciton peak of GaAs quantum wells due to Rabi splitting. Our precise measurements in the time domain show that the Rabi splitting follows the instantaneous THz electric pulse at extremely strong fields but persists up to a negative delay time of ~1 ps at weak fields. This field dependent dynamics of the Rabi splitting indicates that the excitonic field ionization governs a nonperturbative nonlinear dynamics of excitons by causing a reduction of the dephasing time

In the previous work we presented results demonstrating the ability of transmission mode terahertz time domain spectroscopy (THz-TDS) to detect doping profile differences and deviations in silicon. This capability is potentially useful for quality control in the semiconductor and photovoltaic industry. We shared subsequent experimental results revealing that terahertz interactions with both electrons and holes are strong enough to recognize both n- and p-type doping profile changes. We also displayed that the relatively long wavelength (~ 1 mm) of THz radiation allows this approach to be compatible with surface treatments like for instance the texturing (scattering layer) typically used in the solar industry. In this work we continuously demonstrate the accuracy with which current terahertz optical models can simulate the power spectrum of terahertz radiation transmitted through junctions with known doping profiles (as determined with SIMS). We conclude that current optical models predict the terahertz transmission and absorption in silicon junctions well.

Shift currents in bulk GaAs are computed and analyzed using a microscopic model. Our approach combines k.p band structure calculations with the multisubband Bloch equations and provides a transparent description of the generation and the dynamics of optical material excitations. The description of shift currents requires to include o-resonant excitations into the analysis. Besides sketching our theoretical approach, numerical results on the shift current dynamics are presented and discussed.

We demonstrate the generation of waveform-controlled THz radiation from air plasma that is produced when carrier envelope phase (CEP) stabilized few-cycle laser pulses undergoes filamentation in ambient air. Elliptically polarized THz waves are generated from air plasma induced by circularly polarized few-cycle laser pulses. Our results reveal that electric field asymmetry in rotating directions of the circularly polarized few-cycle laser pulses produces the enhanced broadband transient currents, and the phase difference of perpendicular laser field components is partially inherited in the generation process of THz emission.

Through combined three-dimensional electromagnetic and particle tracking simulations we demonstrate a THz driven electron streak camera featuring a temporal resolution down to a femtosecond. The ultrafast streaking field is generated in a resonant THz sub-wavelength antenna, which is illuminated by an intense single-cycle THz pulse. Since electron bunches and THz pulses are generated by the same laser system, synchronization between the two is inherently guaranteed.