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1. Coherent light filter

   https://doi.org/10.1364/OL.447393  

   Bergthold, Morgan; Stewart_Jr, Keith; Duggar, Nicholas; Muhowski, Aaron_J; Wasserman, Daniel (May 2022, Optics Letters)

   We demonstrate efficient filtering of coherent light from a broad spectral background. A Michelson interferometer is used to effectively filter out the coherent emission of mid-infrared lasers from the co-propagating incoherent emission of a broadband thermal source. We show coherent light suppression as high as 16.9 dB without any modification of the broadband incoherent background spectrum. In addition, we demonstrate the ability to measure the spatially dependent (incoherent) thermal emission from a patterned surface, using our filter to remove a coherent signal which would otherwise overload our detection system. The demonstrated filter is rapidly tunable and wavelength-flexible, and has potential for imaging and spectroscopy applications in the presence of an otherwise overpowering coherent signal. 

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2. A Comprehensive Investigation of the Two-Phonon Characteristics of Heat Conduction in Superlattices

   https://doi.org/10.3390/cryst15070654  

   Chakraborty, Pranay; Nasiri, Milad; Cui, Haoran; Maranets, Theodore; Wang, Yan (July 2025, Crystals)

   The Anderson localization of phonons in disordered superlattices has been proposed as a route to suppress thermal conductivity beyond the limits imposed by conventional scattering mechanisms. A commonly used signature of phonon localization is the emergence of the nonmonotonic dependence of thermal conductivity κ on system length L, i.e., a κ-L maximum. However, such behavior has rarely been observed. In this work, we conduct extensive non-equilibrium molecular dynamics (NEMD) simulations, using the LAMMPS package, on both periodic superlattices (SLs) and aperiodic random multilayers (RMLs) constructed from Si/Ge and Lennard-Jones materials. By systematically varying acoustic contrast, interatomic bond strength, and average layer thickness, we examine the interplay between coherent and incoherent phonon transport in these systems. Our two-phonon model decomposition reveals that coherent phonons alone consistently exhibit a strong nonmonotonic κ-L. This localization signature is often masked by the diffusive, monotonically increasing contribution from incoherent phonons. We further extract the ballistic-limit mean free paths for both phonon types, and demonstrate that incoherent transport often dominates, thereby concealing localization effects. Our findings highlight the importance of decoupling coherent and incoherent phonon contributions in both simulations and experiments. This work provides new insights and design principles for achieving phonon Anderson localization in superlattice structures. 

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3. Identifying incoherent mixing effects in the coherent two-dimensional photocurrent excitation spectra of semiconductors

   https://doi.org/10.1063/5.0121635  

   Bargigia, Ilaria; Gutiérrez-Meza, Elizabeth; Valverde-Chávez, David A.; Marques, Sarah R.; Srimath Kandada, Ajay Ram; Silva, Carlos (November 2022, The Journal of Chemical Physics)

   We have previously demonstrated that in the context of two-dimensional (2D) coherent electronic spectroscopy measured by phase modulation and phase-sensitive detection, an incoherent nonlinear response due to pairs of photoexcitations produced via linear excitation pathways contributes to the measured signal as an unexpected background [Grégoire et al., J. Chem. Phys. 147, 114201 (2017)]. Here, we simulate the effect of such incoherent population mixing in the photocurrent signal collected from a GaAs solar cell by acting externally on the transimpedance amplifier circuit used for phase-sensitive detection, and we identify an effective strategy to recognize the presence of incoherent population mixing in 2D data. While we find that incoherent mixing is reflected by the crosstalk between the linear amplitudes at the two time-delay variables in the four-pulse excitation sequence, we do not observe any strict phase correlations between the coherent and incoherent contributions, as expected from modeling of a simple system. 

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4. Thermal disruption of a Luttinger liquid

   https://doi.org/10.1038/s41467-023-38767-0  

   Cavazos-Cavazos, Danyel; Senaratne, Ruwan; Kafle, Aashish; Hulet, Randall G. (May 2023, Nature Communications)

   Abstract The Tomonaga–Luttinger liquid (TLL) theory describes the low-energy excitations of strongly correlated one-dimensional (1D) fermions. In the past years, a number of studies have provided a detailed understanding of this universality class. More recently, theoretical investigations that go beyond the standard low-temperature, linear-response TLL regime have been developed. While these provide a basis for understanding the dynamics of the spin-incoherent Luttinger liquid, there are few experimental investigations in this regime. Here we report the observation of a thermally induced, spin-incoherent Luttinger liquid in a⁶Li atomic Fermi gas confined to 1D. We use Bragg spectroscopy to measure the suppression of spin-charge separation and the decay of correlations as the temperature is increased. Our results probe the crossover between the coherent and incoherent regimes of the Luttinger liquid and elucidate the roles of the charge and the spin degrees of freedom in this regime. 

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5. Comparison of Coherent and Incoherent Donut Beams for Deep Tissue STED Microscopy

   https://doi.org/10.1364/CLEO_SI.2023.SM1I.2  

   Shanavas, Thariq; McLeod, Robert R.; Siemens, Mark E.; Gopinath, Juliet T. (January 2023, Conference on Lasers and Electro-Optics (CLEO))

   We numerically compare the null quality for STED microscopy generated by Laguerre-Gaussian beams with orbital angular momentum and donut beams generated by incoherent addition of orthogonal Hermite Gaussian beams when imaging deep biological tissue. 

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