More Like this

1. Laser THz emission nanoscopy and THz nanoscopy

   https://doi.org/10.1364/OE.382130  

   Pizzuto, Angela ; Mittleman, Daniel M. ; Klarskov, Pernille ( June 2020 , Optics Express)

   We present an experimental and theoretical comparison of two different scattering-type scanning near-field optical microscopy (s-SNOM) based techniques in the terahertz regime; nanoscale reflection-type terahertz time-domain spectroscopy (THz nanoscopy) and nanoscale laser terahertz emission microscopy, or laser terahertz emission nanoscopy (LTEN). We show that complementary information regarding a material’s charge carriers can be gained from these techniques when employed back-to-back. For the specific case of THz nanoscopy and LTEN imaging performed on a lightly p-doped InAs sample, we were able to record waveforms with detector signal components demodulated up to the 6^thand the 10^thharmonic of the tip oscillation frequency, and measure a THz near-field confinement down to 11 nm. A computational approach for determining the spatial confinement of the enhanced electric field in the near-field region of the conductive probe is presented, which manifests an effective “tip sharpening” in the case of nanoscale LTEN due to the alternative geometry and optical nonlinearity of the THz generation mechanism. Finally, we demonstrate the utility of the finite dipole model (FDM) in predicting the broadband scattered THz electric field, and present the first use of this model for predicting a near-field response from LTEN.

    

   more » « less
2. Imaging of surface plasmon polaritons in low-loss highly metallic titanium nitride thin films in visible and infrared regimes

   https://doi.org/10.1364/OE.391482  

   Gadalla, Mena N. ; Chaudhary, Kundan ; Zgrabik, Christine M. ; Capasso, Federico ; Hu, Evelyn L. ( April 2020 , Optics Express)

   Titanium nitride (TiN) has been identified as a promising refractory material for high temperature plasmonic applications such as surface plasmon polaritons (SPPs) waveguides, lasers and light sources, and near field optics. Such SPPs are sensitive not only to the highly metallic nature of the TiN, but also to its low loss. We have formed highly metallic, low-loss TiN thin films on MgO substrates to create SPPs with resonances between 775-825 nm. Scanning near-field optical microscopy (SNOM) allowed imaging of the SPP fringes, the accurate determination of the effective wavelength of the SPP modes, and propagation lengths greater than 10 microns. Further, we show the engineering of the band structure of the plasmonic modes in TiN in the mid-IR regime and experimentally demonstrate, for the first time, the ability of TiN to support Spoof Surface Plasmon Polaritons in the mid-IR (6 microns wavelength).

    

   more » « less
3. Near-field terahertz nonlinear optics with blue light

   https://doi.org/10.1038/s41377-023-01137-y  

   Pizzuto, Angela ; Ma, Pingchuan ; Mittleman, Daniel M. ( April 2023 , Light: Science & Applications)

   The coupling of terahertz optical techniques to scattering-type scanning near-field microscopy (s-SNOM) has recently emerged as a valuable new paradigm for probing the properties of semiconductors and other materials on the nanoscale. Researchers have demonstrated a family of related techniques, including terahertz nanoscopy (elastic scattering, based on linear optics), time-resolved methods, and nanoscale terahertz emission spectroscopy. However, as with nearly all examples of s-SNOM since the technique’s inception in the mid-1990s, the wavelength of the optical source coupled to the near-field tip is long, usually at energies of 2.5 eV or less. Challenges in coupling of shorter wavelengths (i.e., blue light) to the nanotip has greatly inhibited the study of nanoscale phenomena in wide bandgap materials such as Si and GaN. Here, we describe the first experimental demonstration of s-SNOM using blue light. With femtosecond pulses at 410 nm, we generate terahertz pulses directly from bulk silicon, spatially resolved with nanoscale resolution, and show that these signals provide spectroscopic information that cannot be obtained using near-infrared excitation. We develop a new theoretical framework to account for this nonlinear interaction, which enables accurate extraction of material parameters. This work establishes a new realm of possibilities for the study of technologically relevant wide-bandgap materials using s-SNOM methods.

    

   more » « less
4. Infrared Permittivity of the Biaxial van der Waals Semiconductor α‐MoO 3 from Near‐ and Far‐Field Correlative Studies

   https://doi.org/10.1002/adma.201908176  

   Álvarez‐Pérez, Gonzalo ; Folland, Thomas G. ; Errea, Ion ; Taboada‐Gutiérrez, Javier ; Duan, Jiahua ; Martín‐Sánchez, Javier ; Tresguerres‐Mata, Ana I. F. ; Matson, Joseph R. ; Bylinkin, Andrei ; He, Mingze ; et al ( June 2020 , Advanced Materials)

   The biaxial van der Waals semiconductor α‐phase molybdenum trioxide (α‐MoO₃) has recently received significant attention due to its ability to support highly anisotropic phonon polaritons (PhPs)—infrared (IR) light coupled to lattice vibrations—offering an unprecedented platform for controlling the flow of energy at the nanoscale. However, to fully exploit the extraordinary IR response of this material, an accurate dielectric function is required. Here, the accurate IR dielectric function of α‐MoO₃is reported by modeling far‐field polarized IR reflectance spectra acquired on a single thick flake of this material. Unique to this work, the far‐field model is refined by contrasting the experimental dispersion and damping of PhPs, revealed by polariton interferometry using scattering‐type scanning near‐field optical microscopy (s‐SNOM) on thin flakes of α‐MoO₃, with analytical and transfer‐matrix calculations, as well as full‐wave simulations. Through these correlative efforts, exceptional quantitative agreement is attained to both far‐ and near‐field properties for multiple flakes, thus providing strong verification of the accuracy of this model, while offering a novel approach to extracting dielectric functions of nanomaterials. In addition, by employing density functional theory (DFT), insights into the various vibrational states dictating the dielectric function model and the intriguing optical properties of α‐MoO₃are provided.

    

   more » « less
5. Tip-enhanced strong coupling spectroscopy, imaging, and control of a single quantum emitter

   https://doi.org/10.1126/sciadv.aav5931  

   Park, Kyoung-Duck ; May, Molly A. ; Leng, Haixu ; Wang, Jiarong ; Kropp, Jaron A. ; Gougousi, Theodosia ; Pelton, Matthew ; Raschke, Markus B. ( July 2019 , Science Advances)

   Optical cavities can enhance and control light-matter interactions. This level of control has recently been extended to the nanoscale with single emitter strong coupling even at room temperature using plasmonic nanostructures. However, emitters in static geometries, limit the ability to tune the coupling strength or to couple different emitters to the same cavity. Here, we present tip-enhanced strong coupling (TESC) with a nanocavity formed between a scanning plasmonic antenna tip and the substrate. By reversibly and dynamically addressing single quantum dots, we observe mode splitting up to 160 meV and anticrossing over a detuning range of ~100 meV, and with subnanometer precision over the deep subdiffraction-limited mode volume. Thus, TESC enables previously inaccessible control over emitter-nanocavity coupling and mode volume based on near-field microscopy. This opens pathways to induce, probe, and control single-emitter plasmon hybrid quantum states for applications from optoelectronics to quantum information science at room temperature. 

   more » « less