Search Results (43)

This study elucidates the critical role of pulse repetition frequency (PRF) in optimizing laser inhibition of Microcystis aeruginosa. Using a 355 nm laser (20 ns pulse width, 5 W average power) at 20–65 kHz, 50 kHz is identified as the optimal parameter, achieving 70.6% growth suppression by day 6 (p < 0.001) and reducing cell viability to 28.0 ± 1.6% by day 5 (p < 0.001). Photosynthetic analysis reveals severe PSII dysfunction with Fᵥ/Fₘ of 0.028, representing 91% inhibition (p < 0.001). Biochemical assays demonstrate peak reactive oxygen species generation at 1.59 (p < 0.001) and progressive lipid peroxidation with MDA of 45 nmol/L protein. Transmission electron microscopy and Evans Blue staining corroborate the complete thylakoid disintegration in abundant cells after laser treatment at 50 kHz. These findings establish PRF-dependent photothermal–photomechanical synergy as a deterministic mechanism for efficient, chemical-free algal control. Full article

The use of excimer laser atherectomy (ELA) has significantly evolved from the mid-1990s to the present, showing substantial improvements in both coronary and peripheral artery interventions. Initially associated with suboptimal outcomes due to low-energy settings and limited techniques, advancements such as high-energy delivery, improved catheter designs, contrast injection protocols, and refined procedural approaches have greatly enhanced clinical efficacy. In coronary applications, ELA has become an established technique for treating intracoronary thrombus, under-expanded stents, in-stent restenosis, and heavily calcified lesions, offering favorable procedural and clinical outcomes with low complication rates. The excimer laser operates through photochemical, photothermal, and photomechanical mechanisms, enabling precise plaque ablation with minimal collateral damage. In peripheral interventions, especially in critical limb ischemia (CLI), ELA has emerged as a viable option for complex, non-crossable lesions and in-stent restenosis, demonstrating high technical success, improved patency, and promising limb salvage rates. Multiple clinical trials and registries support the safety and effectiveness of ELA, particularly in high-risk patient populations. This narrative review summarizes current evidence and practical considerations on the use of excimer laser atherectomy in coronary and peripheral interventions. Full article

Polydimethylsiloxane (PDMS) films doped with graphene nanoplatelets (GNP) with an embossed surface-relief grating were investigated as photothermal actuated sensors. The films were initially characterized using controlled environmental heating where the wavelength of a diffracted white-light probe beam measured at a fixed angle increased monotonically with temperature due to thermal expansion of the grating. An asymmetric double sigmoidal function tracked the shift in peak diffraction wavelength. The observed thermal response is consistent with the thermal expansion of a freestanding PDMS composite film. When a continuous-wave (CW) laser was incident on the film, intensity-dependent photothermal expansion caused a transient deformation in the grating. The photomechanical behavior of the grating, tracked by the diffracted probe beam with a miniature spectrometer, was then shown to act as a laser power meter. These results demonstrate that photomechanical materials can be used as add-ons to existing optical spectroscopy devices for power-sensing applications. Full article

Excimer Laser Coronary Atherectomy (ELCA) has re-emerged as a valuable adjunctive modality in percutaneous coronary intervention (PCI), particularly in the context of increasingly complex coronary anatomy and rising procedural expectations. By delivering pulsed ultraviolet energy at 308 nm through flexible fiber-optic catheters, ELCA enables precise photochemical, photothermal, and photomechanical ablation of atherosclerotic, fibrotic, calcified, and thrombotic tissue while minimizing thermal injury to surrounding structures. Recent technical refinements, simplified catheter designs, and improved safety profiles have enhanced its feasibility and utility across a range of challenging lesion subsets. This review summarizes the fundamental principles underlying excimer laser–tissue interaction, discusses available equipment and key procedural considerations, and examines the expanding clinical evidence supporting ELCA in contemporary practice. Data from observational studies and multicenter registries suggest that ELCA may enhance device crossability, restore coronary flow, and reduce distal embolization in thrombus-rich lesions, particularly during primary PCI. In device-uncrossable lesions, ELCA facilitates plaque modification and improves procedural success, including in chronic total occlusions. Furthermore, ELCA—especially when performed with simultaneous contrast injection—has demonstrated efficacy in treating stent underexpansion refractory to high-pressure balloon dilation, improving minimal stent area and enabling optimal post-dilatation. As lesion complexity continues to increase, ELCA is gaining recognition as an important tool within the interventional armamentarium. While generally safe in experienced hands, ELCA carries a risk of procedural complications that must be carefully considered. Ongoing investigations are expected to further define its optimal use and reinforce its relevance in modern interventional cardiology. Full article

This work aims to determine the mechanism of the photomechanical response of poly(Methyl methacrylate) polymer doped with the photo-isomerizable dye Disperse Red 1 using the non-isomerizable dye Disperse Orange 11 as a control to isolate photoisomerization. Samples are free-standing thin films with thickness that is small compared with the optical skin depth to assure uniform illumination and photomechanical response throughout their volume, which differentiates these studies from most others. Polarization-dependent measurements of the photomechanical stress response are used to deconvolute the contributions of angular hole burning, molecular reorientation and photothermal heating. While photo-isomerization of dopant molecules is commonly observed in dye-doped polymers, the shape changes of a molecule might not couple strongly to the host polymer through steric mechanical interactions, thus not contributing substantially to a macroscopic shape change. To gain insights into the effectiveness of such mechanical coupling, we directly probe the dopant molecules using dichroism measurements simultaneously while measuring the photomechanical response and find mechanical coupling to be small enough to make photothermal heating—mediated by the transfer of optical energy as heat to the polymer—the dominant mechanism. We also predict the fraction of light energy converted to mechanical energy using a model whose parameters are thermodynamic material properties that are measured with independent experiments. We find that in the thin-film geometry, these dye-doped glassy polymers are as efficient as any other material but their large Young’s modulus relative to other organic materials, such as liquid crystal elastomers, makes them suitable in applications that require mechanically strong materials. The mechanical properties and the photomechanical response of thin films are observed to be significantly different than in fibers, suggesting that the geometry of the material and surface effects might play an important role. Full article

Azo-containing liquid crystal elastomers are photomechanical materials that can be actuated via illumination. The photomechanical response is a result of the photoisomerization of the azo moiety, which produces bulk stresses in the material. These stresses arise via two distinct and competing mechanisms: order parameter change induced stress and direct contractile stress. We describe thermomechanical and photomechanical experiments aimed at assessing the relative contributions of these. We show that the details of the attachment of azo dyes to the network can greatly influence the photoresponse. We discuss our results and summarize our findings. Full article

Photomechanical molecular crystals, actuated by solid-state photochemical reactions, manifest a spectrum of mechanical motions upon light exposure, underscoring their prospective integration into the next generation of intelligent materials and devices. Utilizing the solid-state photodimerization of naphthyl acrylic acid as a paradigm, this study delved into the interplay between crystal morphology and reaction dynamics on the photomechanical responses of molecular crystals. Distinct crystal forms—bulk, microrods, and microplates—were cultivated through tailored crystallization conditions. While bulk crystals of naphthyl acrylic acid (NA) underwent shattering and splintering upon UV light exposure, the microplate counterparts displayed unique cracking patterns with fissures yet retained their overall structural integrity. In contrast, NA microrods underwent pronounced bending under identical irradiation conditions. These phenomena are attributed to the efficient lattice reconfiguration stemming from the [2 + 2] cycloaddition photochemical reaction within the crystals. An intermediate fluorescence enhancement was observed across all crystal types upon light exposure. Collectively, our results underscore the pivotal role of crystal shape in dictating photomechanical behavior, thereby heralding novel strategies for developing advanced photomechanical materials. Full article

Critics have frequently employed strict binary schemes to explain Abstract Expressionism’s singular contributions to art history: the victory of abstraction over figuration, avant-garde over kitsch, pure art over anecdotal illustration, action over premeditation, or escapist detachment over direct political engagement. Taking Willem de Kooning’s Easter Monday as a case study, this paper will question the efficacy of such dyadic explanations to encapsulate the diversity of New York School practice. Easter Monday includes both figural and abstract elements, some that parade the work’s impulsive and spontaneous character and others that were created by a photo-mechanical process. Some celebrate the artist’s personal and idiosyncratic touch, others the impersonality of popular forms of advertising. In contradistinction, the semiotic terminology of C.S. Pierce reveals not only multiple points of intersection with de Kooning’s work; it also effectively identifies and differentiates the plurality of elements the artist conjoined in a single visual field, some of which qualify as iconic, indexical, symbolic, or even as hybrid combinations of the above. These more elastic descriptors, it will be argued, are well-suited to address de Kooning’s variegated surfaces: they can address his accommodation of diverse techniques, as well as the multiple ways the artist constructed meaning and responded to popular culture. Full article

This article analyzes the phenomenon of multi-sensorial, digital, and immersive art exhibitions of popular artists, which has been widely neglected in academic research, from a historical perspective. Reflecting the significance of lived experience in art consumption, this 21st-century phenomenon can be confronted productively with early-20th-century art reproductions. The article focuses on the characteristics of both popular phenomena and on their advertisement, as well as on the discourse around them, documenting reactions from resistance to persistence and accommodation. The analysis shows noticeable similarities between the two types of popularization of high art, positioning the new immersive exhibitions in a traditional line of technical innovative art popularization. Whereas photomechanical art reproduction had an immense influence on the popular art canon, being also dependent on ‘photogenic’ conditions of artworks and thus focusing predominantly on painting, the contemporary canon is predisposed by the immersible characteristics of artists’ oeuvres. Full article

Azobenzene-containing polymers (azo-polymers) have been a subject of extensive investigations during the last two and half decades, due to their remarkable ability to undergo pronounced alignment and deformation under irradiation with light. The molecular ordering and deformation in azo-polymers of various structures under irradiation with linearly polarized light was described in a series of theoretical works, based on the effect of the reorientation of azobenzene moieties due to the anisotropic character of the photoisomerization processes. In the present study, we generalize the previous orientation approach to describe the photo-alignment and deformation of azo-polymer networks under irradiation with elliptically polarized light. We demonstrate that, in general, the light-induced ordering and deformation have a biaxial symmetry defined by the polarization ellipse. Azobenzene chromophores have a tendency to align along the direction of light propagation, the orientation in the other two directions being dependent of the aspect ratio of the polarization ellipse. This causes deformation of azo-polymer networks along the direction of light propagation, the sign of which (expansion/contraction) is defined by a chemical structure of network strands. Theoretical results are in agreement with experiments and have a practical importance to predict the photo-mechanical response of azo-polymers depending on their structure and on the polarization of light. Full article

Photoactive polymers are important for fundamental studies and applications in several area of photonics such as data storage and holography and nonlinear optics and photomechanics. The latter is perhaps one of the most important applications of such materials, since they act as light to mechanical energy transducers and move under light action. For example, azo-polymers irradiated by inhomogeneous resonant ultra-violet or visible light undergo molecular and macroscopic motion, at sub-glass transition temperatures by photoisomerization of the azo dyes. Our recent research in this field highlighted the fundamentals of mobility enhancement by light, including light-induced viscosity change and acceleration of relaxation times, and photomechanics, encompassing motions in gradients of actinic light leading to surface structuring and actuation. In this paper, we present an original model which predicts the creation of mechanical pressure, i.e., motion, by a photo-induced change in the occupied volume and length of anisometric isomers, and we give simple analytical expressions describing the dynamics of volume as well as strain change upon polarized light irradiation of photomechanic samples. Full article

In the context of the two-temperature thermoelasticity theory, a novel mathematical–physical model is introduced that describes the influence of moisture diffusivity in the semiconductor material. The two-dimensional (2D) Cartesian coordinate is used to study the coupling between the thermo-elastic plasma waves and moisture diffusivity. Dimensionless quantities are taken for the main physical fields with some initial conditions in the Laplace transform domain. The linear solutions are obtained analytically along with unknown variables when some conditions are loaded at the surface of the homogenous medium according to the two-temperature theory. The Laplace transform technique in inversion form is utilized with some numerical algebraic approximations in the time domain to observe the exact expressions. Due to the effects of the two-temperature parameter and moisture diffusivity, the numerical results of silicon material have been introduced. The impacts of thermoelectric, thermoelastic, and reference moisture parameters are discussed graphically with some physical explanations. Full article

The well-known effect of bending of acicular crystals undergoing photochemical reactions is associated with the transformation gradient across the crystal thickness caused by the absorption of light. It is believed that the direction of bending is unambiguously dictated by the sign of the axial component of the reaction strain and due to the higher light intensity on the irradiated side of the crystal. In this study, it is shown experimentally and theoretically that thin crystals with a convex irradiated surface bend in the opposite direction if their thickness is less than the light penetration depth. The reversal of the bending direction is due to the lens effect, able to overcome the absorption of light in a thin crystal and provide a higher light intensity on the rear side of the crystal. A crystal of [Co(NO₃)₅NO₂]Cl(NO₃) experiencing nitro-nitrito photoisomerization, begins to bend in the opposite direction after it is thinned by etching to 2 µm when irradiated at the wavelengths of 523 nm, 465 nm, and 403 nm, absorbed at a depth of more than 10 µm in the crystal, but bends in the normal direction under 350 nm light absorbed at a depth of about 1 µm. The experimental results are fully confirmed by modeling the interaction of plane EM wave with crystals of various cross sections. Full article

A method to determine the power of a continuous wave laser from photothermal heating of a poly(dimethyl siloxane) film is reported. The base was doped with oil red O and cured on a surface relief grating. The grating period was shown to increase proportional to the temperature by monitoring the decrease in diffraction angle of a probe beam. A $10$s illumination period of a continuous wave (CW) pump beam absorbed by the film increased the film’s temperature, which resulted in a local strain that could be modeled using the two-dimensional heat kernel. The amplitude of the transient response was found to be linearly correlated with the pump laser power. Full article

The purpose of this study is to evaluate the efficacy of the combination of ozone gel and Er:YAG laser treatment in respect of medication-related osteonecrosis of the jaw (MRONJ) for normal procedures. Consequently, the following techniques are compared in the study: medical therapy (MT); MT + conservative surgery with rotary/piezoelectric instruments; MT + ozone therapy; MT + surgical treatment + laser Er:YAG; and MT + ozone therapy + surgical treatment + laser Er:YAG. Fifty-seven patients with MRONJ stages I, II, and III were treated. The protocol was different for each group of patients and included MT, the application of an ozone gel, an Er:YAG laser surgery session, conservative surgery with rotary/piezoelectric instruments, or surgical treatment, and then the monitoring of healing for at least 12 months. The protocols were performed once a week until complete recovery. Patients were reassessed weekly for the first month after treatment, monthly for the following quarter, and then every 3 months until the end of one year. The radiographic surveys were carried out 6 and 12 months after the last treatment. All of the patients in Group 4 (treated with medical therapy + ozone therapy + surgical treatment + laser Er:YAG) achieved complete clinical and radiographic recovery (100%) with complete remission of osteonecrosis. The proposed combined treatment of ozone therapy using laser Er:YAG and the MT + surgical treatment allowed us to obtain excellent results in the resolution of MRONJ. This success was explained by a series of characteristics specific to laser technology; in fact, thanks to its photoacoustic, photochemical, photothermal, and photomechanical properties, the laser made it possible to reduce the bacterial load at the intervention site. Full article