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1. Experimental realization of an additively manufactured monatomic lattice for studying wave propagation

   https://doi.org/10.1119/5.0085124  

   Mork, Nehemiah; Kuchibhatla, Sai A. R.; Leamy, Michael J.; Fronk, Matthew D. (January 2023, American Journal of Physics)

   Increasing interest in wave propagation in phononic systems and metamaterials motivates the development of experimental designs, measurement techniques, and fabrication methods for use in basic research and classroom demonstrations. The simplest phononic system, the monatomic chain, exhibits rich physics such as dispersion and frequency-domain filtering. However, a limited number of experimental studies showcase monatomic chains for macroscale observation of phonons. Herein, we discuss the design, fabrication, and testing of monatomic lattices as enabled by three-dimensional (3D) printing. Using this widely available technology, we provide design guidelines for realization of a monatomic chain composed of 3D printed serpentine springs and press-fitted cylindrical masses. We also present measurement techniques that record propagating waves and algorithms for the experimental determination of dispersion behavior. 

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2. Dispersion-engineered χ(2) nanophotonics: a flexible tool for nonclassical light

   https://doi.org/10.1088/2515-7647/ac1729  

   Jankowski, Marc; Mishra, Jatadhari; Fejer, M. M. (September 2021, Journal of Physics: Photonics)

   Abstract This article reviews recent progress in quasi-phasematched ${\chi }^{\left(2\right)}$nonlinear nanophotonics, with a particular focus on dispersion-engineered nonlinear interactions. Throughout this article, we establish design rules for the bandwidth and interaction lengths of various nonlinear processes, and provide examples for how these processes can be engineered in nanophotonic devices. In particular, we apply these rules towards the design of sources of non-classical light and show that dispersion-engineered devices can outperform their conventional counterparts. Examples include ultra-broadband optical parametric amplification as a resource for measurement-based quantum computation, dispersion-engineered spontaneous parametric downconversion as a source of separable biphotons, and synchronously pumped nonlinear resonators as a potential route towards single-photon nonlinearities. 

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3. Multi-mode root preserving ptychographic phase retrieval algorithm for dispersion scan

   https://doi.org/10.1364/OE.426859  

   Wilhelm, Alex_M; Schmidt, David_D; Adams, Daniel_E; Durfee, Charles_G (June 2021, Optics Express)

   We present a phase retrieval algorithm for dispersion scan (d-scan), inspired by ptychography, which is capable of characterizing multiple mutually-incoherent ultrafast pulses (or modes) in a pulse train simultaneously from a single d-scan trace. In addition, a form of Newton’s method is employed as a solution to the square root problem commonly encountered in second harmonic pulse measurement techniques. Simulated and experimental phase retrievals of both single-mode and multi-mode d-scan traces are shown to demonstrate the accuracy and robustness of the root preserving ptychographic algorithm (RPPA). 

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4. An Improved Ptychographic Algorithm for Multi-Pulse Phase Retrieval

   https://doi.org/10.1364/FIO.2020.FM2A.6  

   Wilhelm, Alex M.; Schmidt, David D.; Adams, Daniel E.; Durfee, Charles G. (September 2020, Frontiers in Optics)

   B. Lee, C. Mazzali (Ed.)

   We present a ptychographic phase retrieval algorithm which solves the square root problem in second order pulse measurement techniques and reconstructs the fields of multiple incoherent pulses simultaneously from a single dispersion scan trace. 

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5. Global reference seismological data sets: multimode surface wave dispersion

   https://doi.org/10.1093/gji/ggab418  

   Moulik, P; Lekic, V; Romanowicz, B; Ma, Z; Schaeffer, A; Ho, T; Beucler, E; Debayle, E; Deuss, A; Durand, S; et al (December 2021, Geophysical Journal International)

   SUMMARY Global variations in the propagation of fundamental-mode and overtone surface waves provide unique constraints on the low-frequency source properties and structure of the Earth’s upper mantle, transition zone and mid mantle. We construct a reference data set of multimode dispersion measurements by reconciling large and diverse catalogues of Love-wave (49.65 million) and Rayleigh-wave dispersion (177.66 million) from eight groups worldwide. The reference data set summarizes measurements of dispersion of fundamental-mode surface waves and up to six overtone branches from 44 871 earthquakes recorded on 12 222 globally distributed seismographic stations. Dispersion curves are specified at a set of reference periods between 25 and 250 s to determine propagation-phase anomalies with respect to a reference Earth model. Our procedures for reconciling data sets include: (1) controlling quality and salvaging missing metadata; (2) identifying discrepant measurements and reasons for discrepancies; (3) equalizing geographic coverage by constructing summary rays for travel-time observations and (4) constructing phase velocity maps at various wavelengths with combination of data types to evaluate inter-dataset consistency. We retrieved missing station and earthquake metadata in several legacy compilations and codified scalable formats to facilitate reproducibility, easy storage and fast input/output on high-performance-computing systems. Outliers can be attributed to cycle skipping, station polarity issues or overtone interference at specific epicentral distances. By assessing inter-dataset consistency across similar paths, we empirically quantified uncertainties in traveltime measurements. More than 95 per cent measurements of fundamental-mode dispersion are internally consistent, but agreement deteriorates for overtones especially branches 5 and 6. Systematic discrepancies between raw phase anomalies from various techniques can be attributed to discrepant theoretical approximations, reference Earth models and processing schemes. Phase-velocity variations yielded by the inversion of the summary data set are highly correlated (R ≥ 0.8) with those from the quality-controlled contributing data sets. Long-wavelength variations in fundamental-mode dispersion (50–100 s) are largely independent of the measurement technique with high correlations extending up to degree ∼25. Agreement degrades with increasing branch number and period; highly correlated structure is found only up to degree ∼10 at longer periods (T > 150 s) and up to degree ∼8 for overtones. Only 2ζ azimuthal variations in phase velocity of fundamental-mode Rayleigh waves were required by the reference data set; maps of 2ζ azimuthal variations are highly consistent between catalogues ( R = 0.6–0.8). Reference data with uncertainties are useful for improving existing measurement techniques, validating models of interior structure, calculating teleseismic data corrections in local or multiscale investigations and developing a 3-D reference Earth model. 

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