https://hdl.handle.net/11000/1458 2026-04-19T11:10:15Z https://hdl.handle.net/11000/31240 Título : Customized depolarization spatial patterns with dynamic retardance functions Autor : Marco, David; López Morales, Guadalupe; Sánchez López, María del Mar; Lizana, Ángel; Moreno Soriano, Ignacio; Campos, Juan Resumen : In this work we demonstrate customized depolarization spatial patterns by imaging a dynamical time-dependent pixelated retarder. A proof-of-concept of the proposed method is presented, where a liquid–crystal spatial light modulator is used as a spatial retarder that emulates a controlled spatially variant depolarizing sample by addressing a time-dependent phase pattern. We apply an imaging Mueller polarimetric system based on a polarization camera to verify the effective depolarization effect. Experimental validation is provided by temporal integration on the detection system. The effective depolarizance results are fully described within a simple graphical approach which agrees with standard Mueller matrix decomposition methods. The potential of the method is discussed by means of three practical cases, which include non-reported depolarization spatial patterns, including exotic structures as a spirally shaped depolarization pattern. 2024-02-07T16:40:24Z https://hdl.handle.net/11000/31239 Título : Gouy phase effects on propagation of pure and hybrid vector beams Autor : Sánchez López, María del Mar; Davis, Jeffrey A.; Moreno Soriano, Ignacio; Cofré Henríquez, Aarón; Cottrell, Don M. Resumen : The robustness of the polarization spatial distribution of vector beams upon propagation is crucial for a number of applications, including optical communications and materials processing. This study has been commonly centered on Gouy phase effects on focused vector beams. In this work, we present a theoretical and experimental analysis of the Gouy phase’s effects on the propagation of pure and hybrid vector beams. Experimental results at various axial planes, before and past the focus, are obtained by using a simplified liquid-crystal spatial light modulator-based optical system that allows the easy generation of these beams. Furthermore, a new alternative optical set-up that is devoid of moving elements is demonstrated, which simplifies this study. We experimentally verify the differences between pure and hybrid vector beams upon propagation. While the first ones remain stable, hybrid vector beams show Gouy phase effects that demonstrate an optical activity where the local polarization states rotate by an angle that depends on the propagation distance. Experimental results agree with the theory. 2024-02-07T16:39:28Z https://hdl.handle.net/11000/31238 Título : Measuring the spatial deformation of a liquid-crystal on silicon display with a self-interference effect Autor : Marco, David; Vargas, Asticio; Sánchez López, María del Mar; Moreno Soriano, Ignacio Resumen : We present a simple technique to characterize the spatial non-uniformity of a liquid-crystal on silicon (LCOS) spatial light modulator (SLM). It is based on illuminating the display with a wavelength out of the operation range, so there is a significant reflection at the output surface. As a consequence, a Gires–Tournois interferometer is directly created, without any alignment requirement and insensitive to vibrations. The beam reflected at the output surface is the reference beam, while the beam reflected at the silicon backplane is modulated with the addressed gray level in order to quantitatively derive its deformation.We provide an experimental demonstration using a LCOS-SLM designed to operate in the near-infrared range but illuminated with visible light. 2024-02-07T16:26:15Z https://hdl.handle.net/11000/31237 Título : Efficient on-axis SLM engineering of optical vector modes Autor : García-Martínez, Pascuala; Marco, David; Martínez Fuentes, José Luis; Sánchez López, María del Mar; Moreno Soriano, Ignacio Resumen : This work presents a method for the efficient experimental generation of arbitrary polarized vector beam modes. The optical system employs two liquid-crystal on silicon (LCOS) spatial light modulators (SLM) in a common path architecture, avoiding the use of beam-splitters. Each SLM displays a different phase-only mask, each one encoding a different pattern onto two orthogonal linear polarization components of the input beam. These phase-only masks are designed using a recently proposed random technique to encode complex amplitude values. This encoding technique reconstructs the complex function on-axis, thus avoiding incorporating carrier phases. By addressing such properly designed phase-only holograms we demonstrate arbitrary scalar modes on each polarization component, whose superposition results in a vector beam mode. Different superpositions of Laguerre–Gaussian and Hermite–Gaussian modes are obtained and the generated vector beam modes are analyzed. Moreover, the addition of a phase-bias proves itself useful to perform a phase-shifting technique in order to evaluate the correct phase of the generated vector beam. 2024-02-07T16:24:49Z https://hdl.handle.net/11000/31236 Título : Spectral performance of a zero-order liquid-crystal polymer commercial q-plate for the generation of vector beams at different wavelengths Autor : Sánchez López, María del Mar; Abella, Isaiah; Puerto García, Daniel; Davis, Jeffrey A.; Moreno Soriano, Ignacio Resumen : Liquid-crystal polymer q-plates are commercial devices for generating vector beams at the design wavelength where the device exhibits half-wave (HW) retardance. Since they are not voltage addressable, the operational wavelength remains fixed. In this work we perform a broadband spectral characterization of the q-plate retardance as a function of wavelength, /(k), and identify the wavelengths with retardance values relevant for vector beam generation (p, p/2, and 3p/2). The wavelength is then used as a tuning parameter to change the device performance from a HW q-plate to a positive-QW or a negative-QW q-plate. These performances are analyzed using the Jones matrix formalism. We present a simple procedure to derive the polarization distribution of the vector beams expected at these QW wavelengths, as a superposition of the input polarization state and the output state of a HW q-plate. Experimental results using the red and blue lines of an Ar-Kr laser and an IR laser diode of 980 nm confirm the theoretical predictions. We show that for input linearly polarized light of 980 nm and 488 nm the device generates hybrid vector beams (where the ellipticity varies with the azimuthal angle), while for 647 nm pure radial vector beams with constant ellipticity are obtained. These results could extend the use of commercial q-plates for multicolour vector beam applications. 2024-02-07T16:23:43Z https://hdl.handle.net/11000/31235 Título : Achromatic linear retarder with tunable retardance Autor : Messaadi, Abdelghafour; Sánchez López, María del Mar; Vargas, Asticio; García-Martínez, Pascuala; Moreno Soriano, Ignacio Resumen : We present a universal design and proof-of-concept of a tunable linear retarder of uniform wavelength response in a broad spectral range. It consists of two half-wave retarders (HWR) between two quarter-wave retarders (QWRs), where the uniform retardance can be tuned continuously by simply rotating one of the HWRs. A proof-of-concept of this design is built by using commercially available Fresnel rhomb retarders that provide retardation with almost wavelength uniformity in the visible and near infrared from 450 to 1550 nm. The design is universal, since other achromatic QWRs and HWRs could also be employed. The system is experimentally demonstrated to control the state of polarization of a supercontinuum laser. 2024-02-07T16:21:56Z https://hdl.handle.net/11000/30968 Título : The loss of function of PhaC1 is a survival mechanism that counteracts the stress caused by the overproduction of poly-3-hydroxyalkanoates in Pseudomonas putidaΔfadBA Autor : Obeso, José I.; Maestro García-Donas, Beatriz; Jesús M., Sanz; Olivera, Elías R.; Luengo, José M. Resumen : The poly-3-hydroxylkanoate (PHA)-overproducing mutant Pseudomonas putida U ΔfadBA (PpΔfadBA) lacks the genes encoding the main β-oxidation pathway (FadBA). This strain accumulates enormous amounts of bioplastics when cultured in chemically defined media containing PHA precursors (different n-alkanoic or n-aryl-alkanoic acids) and an additional carbon source. In medium containing glucose or 4-hydroxy-phenylacetate, the mutant does not accumulate PHAs and grows just as the wild type (P. putida U). However, when the carbon source is octanoate, growth is severely impaired, suggesting that in PpΔfadBA, the metabolic imbalance resulting from a lower rate of β-oxidation, together with the accumulation of bioplastics, causes severe physiological stress. Here, we show that PpΔfadBA efficiently counteracts this latter effect via a survival mechanism involving the introduction of spontaneous mutations that block PHA accumulation. Surprisingly, genetic analyses of the whole pha cluster revealed that these mutations occurred only in the gene encoding one of the polymerases (phaC1) and that the loss of PhaC1 function was enough to prevent PHA synthesis. The influence of these mutations on the structure of PhaC1 and the existence of a protein-protein (PhaC1-PhaC2) interaction that explains the functionality of the polymerization system are discussed herein. 2024-02-02T10:00:45Z https://hdl.handle.net/11000/30961 Título : Recognition of peptidoglycan and b-lactam antibiotics by the extracellular domain of the Ser/Thr protein kinase StkP from Streptococcus pneumoniae Autor : Maestro García-Donas, Beatriz; Novaková, Linda; Hesek, Dusan; Leyva, Eduardo; Mobashery, Shahriar; Sanz, Jesús M.; Branny, Pavel Resumen : The eukaryotic-type serine/threonine kinase StkP from Streptococcus pneumoniae is an important signal-transduction element that regulates the expression of numerous pneumococcal genes. We have expressed the extracellular C-terminal domain of StkP kinase (C-StkP), elaborated a three-dimensional structural model and performed a spectroscopical characterization of its structure and stability. Biophysical experiments show that C-StkP binds to synthetic samples of the cell wall peptidoglycan (PGN) and to β-lactam antibiotics, which mimic the terminal portions of the PGN stem peptide. This is the first experimental report on the recognition of a minimal PGN unit by a PASTA-containing kinase, suggesting that non-crosslinked PGN may act as a signal for StkP function and pointing to this protein as an interesting target for β-lactam antibiotics. 2024-02-02T09:52:08Z https://hdl.handle.net/11000/30960 Título : Rational stabilization of the C-LytA affinity tag by protein engineering Autor : Hernández-Rocamora, Víctor M.; Maestro, Beatriz; Mollá-Morales, Almudena; Sanz, Jesús M. Resumen : The C-LytA protein constitutes the choline-binding module of the LytA amidase from Streptococcus pneumoniae. Owing to its affinity for choline and analogs, it is regularly used as an affinity tag for the purification of proteins in a single chromatographic step. In an attempt to build a robust variant against thermal denaturation, we have engineered several salt bridges on the protein surface. All the stabilizing mutations were pooled in a single variant, C-LytAm7, which contained seven changes: Y25K, F27K, M33E, N51K, S52K, T85K and T108K. The mutant displays a 7 degrees C thermal stabilization compared with the wild-type form, together with a complete reversibility upon heating and a higher kinetic stability. Moreover, the accumulation of intermediates in the unfolding of C-LytA is virtually abolished for C-LytAm7. The differences in stability become more evident when the proteins are bound to a DEAE-cellulose affinity column, as most of wild-type C-LytA is denatured at approximately 65 degrees C, whereas C-LytAm7 may stand temperatures up to 90 degrees C. Finally, the change in the isoelectric point of C-LytAm7 enhances its solubility at acidic pHs. Therefore, C-LytAm7 behaves as an improved affinity tag and supports the engineering of surface salt bridges as an effective approach for protein stabilization. 2024-02-02T09:51:02Z https://hdl.handle.net/11000/30959 Título : Poly-3-hydroxyalkanoate synthases from Pseudomonas putida U: substrate specificity and ultrastructural studies Autor : Arias, Sagrario; Sandoval, Ángel; Arcos, Mario; Cañedo, Librada María; Maestro García-Donas, Beatriz; Sanz, Jesús M.; Naharro, Germán; Luengo, José M. Resumen : The substrate specificity of the two polymerases (PhaC1 and PhaC2) involved in the biosynthesis of medium-chain-length poly-hydroxyalkanoates (mcl PHAs) in Pseudomonas putida U has been studied in vivo. For these kind of experiments, two recombinant strains derived from a genetically engineered mutant in which the whole pha locus had been deleted (P. putida U Δpha) were employed. These bacteria, which expresses only phaC1 (P. putida U Δpha pMC-phaC1) or only phaC2 (P. putida U Δpha pMC-phaC2), accumulated different PHAs in function of the precursor supplemented to the culture broth. Thus, the P. putida U Δpha pMC-phaC1 strain was able to synthesize several aliphatic and aromatic PHAs when hexanoic, heptanoic, octanoic decanoic, 5-phenylvaleric, 6-phenylhexanoic, 7-phenylheptanoic, 8-phenyloctanoic or 9-phenylnonanoic acid were used as precursors; the highest accumulation of polymers was observed when the precursor used were decanoic acid (aliphatic PHAs) or 6-phenylhexanoic acid (aromatic PHAs). However, although it synthesizes similar aliphatic PHAs (the highest accumulation was observed when hexanoic acid was the precursor) the other recombinant strain (P. putida U Δpha pMC-phaC2) only accumulated aromatic PHAs when the monomer to be polymerized was 3-hydroxy-5-phenylvaleryl-CoA. The possible influence of the putative three-dimensional structures on the different catalytic behaviour of PhaC1 and PhaC2 is discussed. 2024-02-02T09:44:29Z