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1. Large-area, high-numerical-aperture multi-level diffractive lens via inverse design: reply

   https://doi.org/10.1364/OPTICA.427037  

   Meem, Monjurul ; Banerji, Sourangsu ; Majumder, Apratim ; Sensale-Rodriguez, Berardi ; Menon, Rajesh ( July 2021 , Optica)

   We proposed the use of relative encircled power as a measure of focusing efficiency [Optica7,252(2020)OPTIC82334-253610.1364/OPTICA.388697]. The comment [Optica8,1009(2021)OPTIC82334-253610.1364/OPTICA.416017] has raised useful questions, which we address briefly here and provide some clarifications.

    

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2. Second-harmonic generation of spatiotemporal optical vortices and conservation of orbital angular momentum

   https://doi.org/10.1364/OPTICA.422743  

   Hancock, S. W. ; Zahedpour, S. ; Milchberg, H. M. ( April 2021 , Optica)

   A spatiotemporal optical vortex (STOV) is an intrinsic optical orbital angular momentum (OAM) structure in which the OAM vector is orthogonal to the propagation direction [Optica6,1547(2019)OPTIC82334-253610.1364/OPTICA.6.001547] and the optical phase circulates in space-time. Here, we experimentally and theoretically demonstrate the generation of the second harmonic of a STOV-carrying pulse along with the conservation of STOV-based OAM. Our experiments verify that photons can have intrinsic orbital angular momentum perpendicular to their propagation direction.

    

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3. Efficiency enhancement of ultrathin CIGS solar cells by optimal bandgap grading. Part III: piecewise-homogeneous grading

   https://doi.org/10.1364/AO.516850  

   Ahmad, Faiz ; Monk, Peter B. ; Lakhtakia, Akhlesh ( April 2024 , Applied Optics)

   In Parts I [Appl. Opt.58,6067(2019)APOPAI0003-693510.1364/AO.58.006067] and II [Appl. Opt.61,10049(2022)APOPAI0003-693510.1364/AO.474920], we used a coupled optoelectronic model to optimize a thin-film CIGS solar cell with a graded-bandgap photon-absorbing layer, periodically corrugated backreflector, and multilayered antireflection coatings. Bandgap grading of the CIGS photon-absorbing layer was continuous and either linear or nonlinear, in the thickness direction. Periodic corrugation and multilayered antireflection coatings were found to engender slight improvements in the efficiency. In contrast, bandgap grading of the CIGS photon-absorbing layer leads to significant enhancement of efficiency, especially when the grading is continuous and nonlinear. However, practical implementation of continuous nonlinear grading is challenging compared to piecewise-homogeneous grading. Hence, for this study, we investigated piecewise-homogeneous approximations of the optimal linear and nonlinear grading profiles, and found that an equivalent efficiency is achieved using piecewise-homogeneous grading. An efficiency of 30.15% is predicted with a three-layered piecewise-homogeneous CIGS photon-absorbing layer. The results will help experimentalists to implement optimal designs for highly efficient CIGS thin-film solar cells.

    

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4. Coherence, entanglement, and complementarity in mixed classical light

   https://doi.org/10.1364/JOSAA.395172  

   Al-Qasimi, Asma ( September 2020 , Journal of the Optical Society of America A)

   The classical analogues of quantum correlations have been the subject of considerable interest in the past few years; however, all of these investigations consider the classical analogue of only pure quantum mechanical states. In this work, we studymixedclassical light states and derive relations between the polarization coherence of the field and the (classical) entanglement between its degrees of freedom. We show, for a specific model of mixed states, where the purity is determined by a single parameter, how the coherence shared between polarization and entanglement shrinks as the level of purity decreases. The sum of the square of polarization and entanglement remains constant, a behavior consistent with previous results [Phys. Rev. Lett.117,153901(2016)PRLTAO0031-900710.1103/PhysRevLett.117.153901] of pure states, even though the constant for the mixed-state case is now smaller in value.

    

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5. Antireflection temporal coatings: comment

   https://doi.org/10.1364/OPTICA.410990  

   Mai, Wending ; Xu, Jingwei ; Werner, Douglas H. ( May 2021 , Optica)

   The quarter-wavelength matching technique is widely used because it minimizes the reflection while it maximizes the transmission. The recently introduced antireflection temporal coatings (ATCs) [Optica7,323(2020)10.1364/OPTICA.381175] have been considered as its temporal analog. However, our study shows that by introducing an ATC, not only will the reflection be reduced but also the transmission. This phenomenon is opposite its spatial counterpart, which indicates that ATCs are more than simply a temporal dual of quarter-wavelength matching. This is a direct consequence of the different physical phenomena that are manifested in the temporal and spatial domains.

    

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