Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session B04: Coherent Nonlinear Optical Microscopy IFocus
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Sponsoring Units: DCP DSOFT DPOLY DLS Chair: Marcus Cicerone, Georgia Inst of Tech Room: 109 |
Monday, March 2, 2020 11:15AM - 11:51AM |
B04.00001: Coherent Nonlinear Optical Microscopy with Mid-infrared Radiation Invited Speaker: Eric Potma Fundamental vibrational modes are efficiently excited by mid-infrared (MIR) radiation, in a light-matter interaction that is many orders of magnitude stronger than vibrational excitation through the Raman effect. Despite this clear advantage, MIR microscopy is not ubiquitously used for imaging of biological samples due to practical limitations including low spatial resolution, the use of expesensive cameras and the intrinsic limitation of absoprtion-based detection. Some of these limitations can be overcome when using nonlinear upconversion techniques to translate the driven MIR transition into a signal in the visible/NIR range of the spectrum. We will discuss several coherent nonlinear optical approaches that enable rapid laser-scanning microscopy in the MIR with high, three-dimensional resolution. |
Monday, March 2, 2020 11:51AM - 12:03PM |
B04.00002: Multidimensional spectroscopy on the microscale: Development of a multimodal imaging system incorporating 2D white-light spectroscopy, broadband transient absorption, and atomic force microscopy. Andrew Jones, Nicholas Kearns, Miriam Bohlmann Kunz, Jessica Flach, Martin T Zanni The dynamics of electronic transitions in solid-state materials are closely linked to microscopic morphology, but it is often challenging to simultaneously characterize their broadband spectral and temporal response with high spatial resolution. We present a combined coherent multidimensional spectroscopy and microscopy system using visible white-light supercontinuum pulses as a broadband light source. This system correlates ~nm scale sample morphology determined from atomic force topography measurements with broadband transient absorption hyperspectral images and ultrafast multidimensional spectra, all with a spatial resolution of ≤1 μm. We demonstrate the application of this technique to the mapping of spatial heterogeneity in the process of singlet fission within single microcrystals of an organic semiconductor material, TIPS-Pentacene. Here, we identify heterogeneity in the temporal and spectral response corresponding to presence of non-equilibrium molecular packing near edges and morphological defect structures. |
Monday, March 2, 2020 12:03PM - 12:39PM |
B04.00003: Image Formation in Coherent Nonlinear Optical Microscopy Invited Speaker: Lora Ramunno Coherent nonlinear optical microscopy has allowed real-time visualization of objects and biological processes on small length scales, where molecule-specific imaging can be achieved without the use of labels. Given the coherent nature of the nonlinear processes involved (which includes, for example, coherent anti-Stokes Raman scattering, second and third harmonic generation), the images produced are complex and not always straightforward to interpret, especially when object sizes are much smaller than the focal volume. Images are subject to, for example, interference from multiple scatterers, interference due to competing nonlinear processes, and distortion to due inhomegeneities. This can lead to bright spots that appear in the wrong place or are 10x brighter than they should be, unexpected shadows, false dark and bright signals, spectral shifts that depend on the spatial position of objects along the laser axis, and signals that depend on the precise shapes and relative positions of sub-wavelength objects within the focal volume (rather than just the total number of molecules present), to name a few. I will discuss the origin of these strage effects, and review our work and others in this area over the last several years. |
Monday, March 2, 2020 12:39PM - 12:51PM |
B04.00004: Strong-field-driven dynamics and high-harmonic generation in interacting 1D systems Fernando Sols, Sandra de Vega, Joel Cox, Javier Garcia de Abajo We explore the role of electronic band structure and Coulomb interactions in solid-state HHG by studying the optical response of linear atomic chains and carbon nanotubes to intense ultrashort pulses. Specifically, we simulate electron dynamics by solving self-consistently the single-particle density matrix equation of motion in the presence of intense ultrafast optical fields and electron interactions. Our 1D model provides insight on the temporal evolution of electronic states in reciprocal space. We demonstrate that electron interactions play an important role in the HHG yield. This model further predicts that doped semiconductors generate high harmonics more efficiently than their metallic and undoped counterparts. To complement this idealized system we also show results for HHG in more realistic quasi-1D structures such as carbon nanotubes, whose behavior is found to be in good qualitative agreement with that of the atomic chains. Our findings apply directly to extreme nonlinear optical phenomena and can be extended to optimize existing platforms for HHG or identify new solid-state alternatives in the context of nonlinear plasmonics. |
Monday, March 2, 2020 12:51PM - 1:27PM |
B04.00005: Broadband Coherent Anti-Stokes Raman Scattering (BCARS) MicroSpectroscopy Invited Speaker: Charles Henry Camp The ability to noninvasively image the dynamic chemical composition within cells and tissues would revolutionize our understanding of biology and disease. Molecular vibrational imaging techniques detect the small oscillations between bonded atoms, providing dense spectral information about composition and state without the addition of fluorophores or dyes. Technologies, such as Raman and infrared microscopies, have offered this capability for over half a century, but significant limitations in speed, resolution, or sample preparation have prevented their ubiquity. Coherent Raman imaging (CRI) methods, proposed as the solution, have been practically confined to small increments of the vibrational spectrum with limited chemical specificity. Broadband coherent anti-Stokes Raman scattering (BCARS), a particular CRI modality, on the other hand, has demonstrated an unprecedented combination of speed, sensitivity, and spectral breadth, enabling full hyperspectral imagery in minutes rather than hours. Furthermore, as a coherent anti-Stokes Raman scattering (CARS)-based method, a coherent background is generated that is molecularly sensitive and can be used as a built-in internal reference at each pixel; thus, enabling directly comparable results between samples and spectra collected on different microscope systems. |
Monday, March 2, 2020 1:27PM - 1:39PM |
B04.00006: Studying the photodynamics of FRET paired fluorescent molecules near gold nanogratings Jennifer Steele, Chae Ramnarace, WIlliam Farner The plasmonic properties of structured metal surfaces can be engineered to enhance the output of nearby quantum emitters through the manipulation of the local density of optical states (LDOS). Although metal enhanced fluorescence (MEF) has been well understood for decades, the influence of plasmonic modes in Förster resonance energy transfer (FRET) is still a debated issue. Gold nanogratings provide a unique plasmonic substrate to study the effects of altering the LDOS on FRET efficiencies. Gratings support narrow plasmon resonances at a range of wavelengths, allowing for the comparison of FRET efficiencies by increasing the LDOS at donor and acceptor emission wavelengths on a single substrate. Previous work has shown an increase in efficiency when the surface plasmon modes overlapped the acceptor emission spectrum. In this talk, ongoing work on the optimizing the increase in efficiencies will be discussed. Furthering the understanding of the application of MEF to FRET will aid developing methods for the enhancement of FRET, expanding its use in biological systems, photosynthesis, and photovoltaic devices. |
Monday, March 2, 2020 1:39PM - 2:15PM |
B04.00007: Geophotonics: Multimodal Nonlinear Optical Microscopy in Geology Invited Speaker: Adrian Pegoraro Nonlinear optical microscopy offers label-free contrast and enhanced depth penetration in heterogeneous media compared to more traditional optical microscopy techniques. These advantages make it a natural fit for biological imaging where optical microscopy is frequently the tool of choice. For geologic materials, where electron microscopy is much more prevalent than optical imaging, the utility of newly developed nonlinear optical techniques was less obvious. Nonetheless, we show that these techniques, such as second harmonic generation, coherent Raman microscopy, and pump-probe microscopy, provide complementary contrast mechanisms for a host of geological systems. For some applications, the ability to image rapidly in 3D reveals previously unseen spatial correlations. Even in opaque systems, nonlinear optical signals can achieve comparable contrast to electron microscopy techniques which are inherently confined to the surface. This allows for much more rapid screening of samples with less sample preparation. We believe that by leveraging ongoing developments in biophotonics, it is possible to offer new and improved imaging tools for many other systems that are not traditionally studied using optical microscopy. |
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