Bulletin of the American Physical Society
2021 Joint Spring Meeting of the Texas Sections of APS, AAPT and Zone 13 of the SPS
Volume 66, Number 2
Thursday–Sunday, April 8–11, 2021; Virtual
Session C16: APS: Optics and Laser Science |
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Saturday, April 10, 2021 2:00PM - 2:12PM |
C16.00001: Shifted Excitation Raman Difference Spectroscopy for spore detection Zehua Han, Benjamin Strycker, Blake Commer, Kai Wang, Brain Shaw, Marlan Scully, Alexei Sokolov The presence of fluorescence emission leads to several problems for Raman detection in bio-samples. One is ``fake'' spectral structure which could be easily considered as spontaneous Raman peaks. One approach to get rid of fluorescence is Shifted Excitation Raman Difference Spectroscopy (SERDS), in which a tunable laser produces two spectra with slightly different excitation frequencies. The difference between the two generated spectra can suppress fluorescence contribution significantly. Here, we combine the SERDS strategy with genetic breeding of Aspergillus nidulans mutants and illustrate that the Raman signal originates from pigment molecules. Moreover, we observe fine-structure in fluorescence at room temperature, possibly resulting from the formation of molecular cages in the bio-polymer matrix of the cell wall. We also utilize the technique to study the conidia of 8 different mold species. The results demonstrate that the pure Raman spectra correlate with the melanin biosynthesis pathway, such that species exhibiting a negative response to DHN chemical inhibitors have similar Raman spectra, which in turn differ from those of species exhibiting a positive response. [Preview Abstract] |
Saturday, April 10, 2021 2:12PM - 2:24PM |
C16.00002: $\backslash $pardApplications of Low Frequency Raman Spectroscopy on Amino Acid Crystals$\backslash $pard Ming Che Lee, Zhenhuan Yi, Alexei. V. Sokolov, Marlan. O. Scully h $-abstract-$\backslash $pardBoth Stokes and anti-Stokes Raman spectra at low frequency (\textless 200 cm$^{\mathrm{-1\thinspace }}$range, LF) can be relatively easily accessed with the help of volume Bragg filters. We presented two applications of these spectra from amino acid (AA) crystals. We first used the peak ratio between Stokes and anti-Stokes signal to obtain the local temperature of a sample. Second, due to the distinct intermolecular interactions in AA crystals, vibration modes such as hydrogen bond stretching and shear modes can be easily distinguished with LF Raman. Second, We examined the LF-Raman mapping on different surfaces of crystallized L-alanine. The mapping shows strong dependence on relative orientations between the polarization of the probe light and the orientations of the AA crystals. By changing the polarization of probe light, we were able to differentiate surfaces on the crystals through the analysis of LF-Raman mapping. To conclude, LF-Raman mapping provides an efficient way to identify the orientation of micro AA crystals. $\backslash $pard-/abstract-$\backslash $\tex [Preview Abstract] |
Saturday, April 10, 2021 2:24PM - 2:36PM |
C16.00003: Generation and Characterization of Near-Single-Cycle Pulses Aysan Bahari, Alexandra Zhdanova, Mariia Shutova, Alexei Sokolov Ultrashort laser pulses are widely used to study the properties of the material and fabricate complex structures for a variety of applications. These pulses usually are generated with mode-locked lasers, by passive or active mode-locking. There are also other methods that involve compressing slightly longer pulses by applying several experimental techniques. Here, we demonstrate producing these high-demand near single-cycle pulses, utilizing our coherently-generated Raman sidebands. Our femtosecond pulses consist of a few optical cycles and allow not only synthesis of shaped waveforms with tunable amplitude and frequency as a function of time, but also an arbitrary electric field as a function of time (not necessarily sinusoidal). These pulses are perfect candidates for direct control of electron trajectories in photoionization and high harmonic generation (HHG) processes. We aim to use our pulses to study multi-photon ionization in atomic and molecular gases. [Preview Abstract] |
Saturday, April 10, 2021 2:36PM - 2:48PM |
C16.00004: Minimizing the Lasing Frequency Fluctuations Arising from Temperature Variations in Terahertz Quantum Cascade Lasers Christopher Baird, Marissa Lafferty A terahertz quantum cascade laser (QCL) is designed to emit coherent terahertz radiation. We built and validated numerical code that calculates the electron wavefunctions, energy levels, and lasing frequency for any QCL structure when the space charge, doping, and temperature effects are included. The code accomplishes this by self-consistently solving the Schroedinger, Poisson, space charge, and doping equations. The laser power of terahertz QCL's is limited by internal thermal effects. We therefore used our code to determine how small changes to the QCL structure can reduce the lasing frequency fluctuations across a range of lattice temperatures from 50 K to 150 K. Less lasing frequency fluctuation indicates a structure that is more resistant to thermal effects. The structure used in this project is known as the 2.9 THz Barbieri structure. The small changes consisted of varying the width of the first quantum well from 80{\%} to 120{\%} of its original width. The first well was chosen because this is the well where much of the lasing and the detrimental thermal effects occur. We found that the lasing frequency fluctuation across different temperatures can indeed be reduced, helping to develop structures that are more resistant to thermal effects. [Preview Abstract] |
Saturday, April 10, 2021 2:48PM - 3:00PM |
C16.00005: Interfacing Optical Fiber with Plasmonic Nanoantenna for Enhanced Light Nanofocusing Khant Minn, Blake Birmingham, Brian Ko, Howard Lee, Zhenrong Zhang The major challenges in the study of light-matter interaction in the deep subwavelength regime are the inefficient conversion of far-field to nearfield energy, low signal-to-noise ratio, complicated device designs requiring complex multi-step fabrication processes. Metallic nanowires supporting surface plasmon polaritons can localize optical fields at nanoscale tapered ends for near-field imaging. We propose a fiber-plasmonic hybrid device that efficiently couples linearly polarized fiber core mode to radial plasmons on plasmonic tip for nano-scale confinement of light. First, we report the numerical analysis of the light-coupling and focusing mechanism. Next, we report the fabrication and far-field characterization of the device. The needle-shaped platinum tip is grown by electron beam assisted chemical deposition on the photonic crystal fiber's end facet. By controlling the deposition parameters, height and base diameter of the antenna can be tuned to optimize plasmonic resonance conditions. The cross-polarization analysis of far-field emission to the side of the tip demonstrates the excitation of surface plasmons. The proposed device is highly desirable for applications in medical procedures, biomedical imaging and near-field spectroscopy. [Preview Abstract] |
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