Active plasmonics combines the manipulation of light on both sub-wavelength length and ultrashort time scales, a unique meld that holds promise for developments in many scientific fields. This thesis reports on a novel approach to ultrafast, all-optical control of grating-assisted excitation of surface plasmon polaritons based on opto-thermally modifying the optical properties of gold. In contrast to prior works, this approach results in plasmonic modulation on picosecond and even sub-picosecond time scales, and is compatible with modern, multi-GHz information processing technology. Finally, an analytic model is developed that allows for the rapid and accurate calculation of the coupling efficiency of beams with arbitrary spatial profile. First, the ultrafast dynamics of existing plasmonic coupling resonances, on gold films with grating overlayers, are studied with spectrally resolved pump-probe measurements. Irradiation of the metal by 700 fs, 775 nm laser pulses results in modulations of the plasmonic coupling efficiency of ~20% near the center, or ~60% off-center, of resonances centered between 540 nm and 700 nm. The modulations decay with a time constant of 770 +/- 70 fs. The experimental results are consistent with simulations based on the thermal-dynamics of the electron-lattice gold system, coupled with numerical modeling of light-grating interactions. Next, two 150 fs, 810 nm laser beams are interfered on the surface of a planar gold film, leading to an absorption/refraction grating in the metal. Optical pump-probe spectroscopy measurements of the first (-1) diffracted order in transmission identify plasmonic coupling resonances between 520 nm and 570 nm. The observed coupling efficiency is ~10^{-5}, and the launch window decays with a time constant of 620 +/- 100 fs. Lastly, a Green function-based analytic model is developed to describe grating assisted plasmonic coupling, culminating in a first-order differential equation with coefficients that have both clear physical significance as well as analytic forms. Comparison of this technique with standard numerical modeling methods shows that plasmonic coupling efficiencies in excess of 0.8 are predicted within an error of 15%. This model is used to study plasmonic excitation by finite-size beams, showing the spatial evolution of the intensity of both the surface plasmon polariton and the reflected beam.

Active plasmonics combines the manipulation of light on both sub-wavelength length and ultrashort time scales, a unique meld that holds promise for developments in many scientific fields. This thesis reports on a novel approach to ultrafast, all-optical control of grating-assisted excitation of surface plasmon polaritons based on opto-thermally modifying the optical properties of gold. In contrast to prior works, this approach results in plasmonic modulation on picosecond and even sub-picosecond time scales, and is compatible with modern, multi-GHz information processing technology. Finally, an analytic model is developed that allows for the rapid and accurate calculation of the coupling efficiency of beams with arbitrary spatial profile. First, the ultrafast dynamics of existing plasmonic coupling resonances, on gold films with grating overlayers, are studied with spectrally resolved pump-probe measurements. Irradiation of the metal by 700 fs, 775 nm laser pulses results in modulations of the plasmonic coupling efficiency of ~20% near the center, or ~60% off-center, of resonances centered between 540 nm and 700 nm. The modulations decay with a time constant of 770 +/- 70 fs. The experimental results are consistent with simulations based on the thermal-dynamics of the electron-lattice gold system, coupled with numerical modeling of light-grating interactions. Next, two 150 fs, 810 nm laser beams are interfered on the surface of a planar gold film, leading to an absorption/refraction grating in the metal. Optical pump-probe spectroscopy measurements of the first (-1) diffracted order in transmission identify plasmonic coupling resonances between 520 nm and 570 nm. The observed coupling efficiency is ~10^{-5}, and the launch window decays with a time constant of 620 +/- 100 fs. Lastly, a Green function-based analytic model is developed to describe grating assisted plasmonic coupling, culminating in a first-order differential equation with coefficients that have both clear physical significance as well as analytic forms. Comparison of this technique with standard numerical modeling methods shows that plasmonic coupling efficiencies in excess of 0.8 are predicted within an error of 15%. This model is used to study plasmonic excitation by finite-size beams, showing the spatial evolution of the intensity of both the surface plasmon polariton and the reflected beam.

A tunable polarization modulator based on the periodic metal strips embedded in a polymer waveguide is presented. The periodic metallic structure is analyzed by Finite Element simulation (COMSOL). The calculation results show that the giant birefringence is formed by the selective cut-off of TE polarization over TM polarization, which makes it possible to design an efficient polarization modulator with a short conversion length. The metallic strips are made by using four-layer lift-off fabrication technology. The transmission and group indices of TE and TM modes are measured. However, it is observed that TE and TM modes cut off at same time, which does not agree with our predictions. The reason for failure is that the change in refractive indices is different from what we expected, which makes the device perform in opposite way. Finally, further suggestions are provided to modify the design so that the device can achieve its expected function.

A tunable polarization modulator based on the periodic metal strips embedded in a polymer waveguide is presented. The periodic metallic structure is analyzed by Finite Element simulation (COMSOL). The calculation results show that the giant birefringence is formed by the selective cut-off of TE polarization over TM polarization, which makes it possible to design an efficient polarization modulator with a short conversion length. The metallic strips are made by using four-layer lift-off fabrication technology. The transmission and group indices of TE and TM modes are measured. However, it is observed that TE and TM modes cut off at same time, which does not agree with our predictions. The reason for failure is that the change in refractive indices is different from what we expected, which makes the device perform in opposite way. Finally, further suggestions are provided to modify the design so that the device can achieve its expected function.

Surface plasmon polaritons are electromagnetic surface waves coupled to electron plasma oscillation of metals at a metal-dielectric interface. At optical frequencies, these modes are of great interest because of their high confinement to a metal-dielectric interface. Due to the field enhancement at the interface, they have been used in different applications such as sensors, second harmonic generation and enhanced Raman scattering. Surface plasmon resonance based sensors are being used for detection of molecular adsorption such as DNA and proteins. These sensors are known to be highly sensitive and have successfully become commercialized. Terahertz (THz) frequency band of electromagnetic spectrum has attracted researchers in the last few years mostly because of sensing and imaging applications. Many important chemical and biological molecules have their vibrational and rotational resonance frequencies in the THz range that makes the THz sensing one of the most important applications of THz technology. Considering above mentioned facts, extending the concept of surface plasmon sensors to THz frequencies can result in sensitive sensors. In this work the possibility of this extension has been investigated. After reviewing optical surface plasmon polariton waves and a basic sensor configuration, surface plasmon polariton waves propagating on at metallic and doped semiconductor surfaces have been examined for this purpose. It has been shown that these waves on metallic surfaces are loosely confined to the metal-dielectric interface and doped semiconductors are also too lossy and cannot meet the requirements for sensing applications. Afterwards, it is shown that periodically patterned metallic surfaces can guide surface waves that resemble surface plasmon polariton waves. A periodically patterned metallic surface is used to guide THz surface plasmon polariton-like surface waves and a highly sensitive sensor is proposed based on that. The quasi-optical continuous wave (CW) THz radiation is coupled to this structure using the Otto's attenuated total reflection (ATR) configuration and the sensitivity of the device is discussed. A general scattering parameter based model for prism coupling has been proposed and verified. It is shown that a critical coupling condition can happen by changing the gap size between the prim and periodic surface. Details of fabrication of the periodic structure and experimental setup have also been presented.

Surface plasmon polaritons are electromagnetic surface waves coupled to electron plasma oscillation of metals at a metal-dielectric interface. At optical frequencies, these modes are of great interest because of their high confinement to a metal-dielectric interface. Due to the field enhancement at the interface, they have been used in different applications such as sensors, second harmonic generation and enhanced Raman scattering. Surface plasmon resonance based sensors are being used for detection of molecular adsorption such as DNA and proteins. These sensors are known to be highly sensitive and have successfully become commercialized. Terahertz (THz) frequency band of electromagnetic spectrum has attracted researchers in the last few years mostly because of sensing and imaging applications. Many important chemical and biological molecules have their vibrational and rotational resonance frequencies in the THz range that makes the THz sensing one of the most important applications of THz technology. Considering above mentioned facts, extending the concept of surface plasmon sensors to THz frequencies can result in sensitive sensors. In this work the possibility of this extension has been investigated. After reviewing optical surface plasmon polariton waves and a basic sensor configuration, surface plasmon polariton waves propagating on at metallic and doped semiconductor surfaces have been examined for this purpose. It has been shown that these waves on metallic surfaces are loosely confined to the metal-dielectric interface and doped semiconductors are also too lossy and cannot meet the requirements for sensing applications. Afterwards, it is shown that periodically patterned metallic surfaces can guide surface waves that resemble surface plasmon polariton waves. A periodically patterned metallic surface is used to guide THz surface plasmon polariton-like surface waves and a highly sensitive sensor is proposed based on that. The quasi-optical continuous wave (CW) THz radiation is coupled to this structure using the Otto's attenuated total reflection (ATR) configuration and the sensitivity of the device is discussed. A general scattering parameter based model for prism coupling has been proposed and verified. It is shown that a critical coupling condition can happen by changing the gap size between the prim and periodic surface. Details of fabrication of the periodic structure and experimental setup have also been presented.

This thesis details the fabrication of three different plasmon-polariton based devices: a plasmon-polariton Bragg grating (PPBG) biosensor, an intensity modulator incorporating grating couplers, and optically separated electrical contact, and finally an array of nanoholes in an ultrasmooth Au film. The biosensor involves a 35 nm Au stripe, lithographically stepped in width to produce a Bragg reflector. The waveguide is embedded in symmetric, Cytop claddings 8 µm thick. Channels are etched into the top cladding, exposing the waveguides and allowing for the integration of fluidics. The modulator involves a 20 nm Au pad, overlaid with 80 nm Au diffraction gratings, supported by an ultrathin (~3 nm) SiO2 insulator, on a p-doped Silicon wafer backed by an Al Ohmic contact. Electrical contact pads are separated from the waveguide by a thick dielectric (700 nm PMMA), and 2.5 µm vias in-filled with Au allow for electrical connection between the contact pads and waveguides. The nanohole array is machined by focused ion beam into an ultrasmooth Au film revealed by template stripping. The Au film is stacked on a thick film of Cytop between ~5 µm thick.

Graphene nanoribbons, graphene based optical sensors, and grating based plasmonics are explored experimentally. Graphene nanoribbons exhibit highly insulating states that may allow for graphene based digital applications. We investigate the sensitivity of these states to local charged impurities in ultra high vacuum. We look into the possibility of isolating two-dimensional films of H-BN and BSCCO, and test for any interesting phenomena. We also assess graphene*s applicability for optical sensing by implementing a new style of spectral detector. Utilizing surface plasmon excitations nearby a graphene field-effect transistor we are able to produce a detector with wavelength sensitivity and selectivity in the visible range. Finally, we study another plasmonic phenomenon, and observe the resonant enhancement of diffraction into a symmetry-prohibited order in silver gratings.

No description available.

Plasmonic nanostructures provide unique opportunities to improve the detection limits of chiroptical spectroscopies by enhancing chiral light-matter interactions. The most significant of such interaction occur in ultraviolet (UV) range of the electromagnetic spectrum that remains challenging to access by conventional localized plasmon resonance based sensors. Although Surface Plasmon Polaritons (SPPs) on noble metal films can sustain resonances in the desired spectral range, their transverse magnetic nature has been an obstacle for enhancing chiroptical effects. We demonstrate, both analytically and numerically, that SPPs excited by near-field sources can exhibit rich and non-trivial chiral characteristics. In particular, we show that the excitation of SPPs by a chiral source not only results in a locally enhanced optical chirality but also achieves manifold enhancement of net optical chirality. Our finding that SPPs facilitate a plasmonic enhancement of optical chirality in the UV part of the spectrum is of great interest in chiral bio-sensing. Next we focus on the new concepts of transverse spin angular momentum and Belinfante spin momentum of evanescent waves, which have recently drawn considerable attention. We investigate these novel physical properties of electromagnetic fields in the context of chiral surface plasmon polaritons. We demonstrate, both analytically and numerically, that locally excited surface plasmon polaritons possess transverse Spin angular momentum and Belinfante momentum with rich and non-trivial characteristics. We also show that the transverse spin angular momentum of locally excited surface plasmon polaritons leads to the emergence of transverse chiral forces in opposite directions for chiral objects of different handedness. The magnitude of such a transverse force is comparable to the optical gradient force and scattering forces. This finding may pave the way for realization of optical separation of chiral biomolecules