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Ultrafast laser processing is a highly versatile tool for creating microscale structures in many materials. The ablation and micromachining characteristics of AISI 304 stainless steel were examined using a femtosecond-pulsed laser. Parameters such as power, scanning speed, transverse overlap, scanning strategies, and shielding gases were systematically varied. The ablation threshold fluence for SS 304 was calculated as 0.16 J/cm2. Two ablation regimes were observed: the gentle regime, where smooth crater walls were formed under low pulse energy (below 20 µJ), and the strong regime, characterized by rough walls created under high pulse energy (above 20 µJ). The optimal parameters for fabricating microchannels on SS 304 surfaces comprised a laser power of 100 mW, a scanning speed of 30 mm/s, a line-to-line distance of 5 µm, and a parallel scan strategy along the major axis. This study provides a practical approach for enhancing the microchannel fabrication process on stainless steel. [ABSTRACT FROM AUTHOR]

One of the main interests of ultrashort pulses at 2 μm will be in medical surgery, lithotripsy, and dentistry. Currently, most reports of ultrashort pulses in this wavelength range are generally of low power, giving outputs in the region of a few tens of milliwatts, which may not be suitable for practical applications. Therefore, it is interesting to generate high-power ultrashort pulses in the region of a few watts. Generally, mode-locked pulses are produced in the solitonic form, capitalizing the anomalous dispersion regime. Soliton pulse has its limitation, as the output pulses are limited to low power due to the pulse breaking effect. In contrast, a stretched pulse is free of this limitation. This work aims to generate ultrashort pulses with a high peak power utilizing the stretched pulse regime, with a net cavity dispersion of 0.03 ps2. The system has a master oscillator, a preamplifier, and a main amplifier. The oscillator was mode-locked by a semiconductor saturable absorber mirror (SESAM) to generate stretched mode-locked pulses, giving a repetition rate of 13.02 MHz at a center wavelength of 1970.1 nm. The average output power and the pulse duration after the main amplifier were 3.14 W and 81 fs, respectively. The pulse energy and the peak power were then calculated as 241 nJ and 3 MW. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) heterogeneous integration has shown great promise in increasing integration density and reducing parasitic capacitance, which micro through vias on insulators are highly desired. In this work, femtosecond laser bidirectional drilling of crack-free micro through-sapphire-vias has been demonstrated. Mechanisms of material removal and defect suppression during the drilling process were studied. The bottom surface was drilled first and followed by the top surface drilling. A blind hole prefabricated by the bottom surface drilling can effectively suppress the edge collapse and extensive ablation damage on the bottom surface during subsequent top surface drilling with high pulse energy laser. Effects of incident laser parameters on the surface quality, morphology, diameter, and taper of the through hole at different drilling stages were systematically studied. Under given strategy, hole diameter down to ~50 μm on 400 μm-thick sapphire wafers can be achieved directly, showing great prospects in 3D heterogeneous integration. [ABSTRACT FROM AUTHOR]

Soliton molecules (SMs) play a crucial role in nonlinear optical systems, enriching our understanding of nonlinear science through the study of their interaction dynamics. While passively mode-locked fiber lasers offer an efficient platform for generating diverse types of SMs, the complex internal dynamics of the laser often pose challenges in achieving predetermined temporal separations between SMs. Here, we implement a delayed optical feedback technique within a femtosecond optical parametric oscillator, enabling the generation of SMs with precise and controllable temporal separations. A theoretical model, which models the intracavity iterations of the signal with a simplified Ikeda map, is proposed to study the impact of parametric gain, intracavity feedback delay, and cavity length on the internal separations of the SMs. Our experimental results confirm that adjusting the cavity length allows for producing desired temporal separations within SMs. To reveal the evolution dynamics of the SMs, we further develop a rigorous numerical model using the carrier-resolved Forward Maxwell Equation, which is capable of modeling ultra-broadband complex dynamics based on a single equation without relying on the slowly-varying envelope approximation. The numerical model unveils the rich formation dynamics of the SMs at various separations, which confirms the critical role of the gain window provided by the pump. This work opens up new opportunities for the on-demand generation of SMs and provides valuable insights into the complex dynamics in femtosecond optical parametric oscillator systems with optical delayed feedback. [ABSTRACT FROM AUTHOR]

The mechanism of formation of laser-induced periodic surface structures (LIPSS) remains unexplored and attracts the attention of researchers. We study the redistribution of laser beam energy along the path from the radiation source to the target surface, specifically in the layer of ionized ablation products formed during processing above the target surface. We take the cloud of ablation products above the target surface as a kind of lens, the material of which has a refractive index different from the refractive index of the surrounding medium. In this article, we consider the process of energy redistribution when a laser beam passes through a plasma lens formed above the target and conclude that LIPSS can be formed due to such a distribution mechanism. The process of femtosecond laser action is considered using computer modeling of the process of laser beam propagation and subsequent temperature ablation of matter from the target surface. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDCs), particularly molybdenum disulfide (MoS2), have gained significant attention in the field of optoelectronics and photonics due to their unique electronic and optical properties. The integration of TMDCs with plasmonic materials allows to tailor the optical response and offers significant advantages for photonic applications. This study presents a novel approach to synthesize MoS2-Au nanocomposites utilizing femtosecond laser ablation in liquid to achieve tunable optical properties in the near-infrared (NIR) region. By adjusting ablation and fragmentation protocols, we successfully synthesize various core–shell and core–shell–satellite nanoparticle composites, such as MoS2/MoSxOy, MoSxOy/Au, and MoS2/MoSxOy/Au. UV-visible absorption spectroscopy unveils considerable changes in the optical response of the particles depending on the fabrication regime due to structural modifications. Hybrid nanoparticles exhibit enhanced photothermal properties when subjected to NIR-I laser irradiation, demonstrating potential benefits for selective photothermal therapy. Our findings underscore that the engineered nanocomposites not only facilitate green synthesis but also pave the way for tailored therapeutic applications, highlighting their role as promising candidates in the field of nanophotonics and cancer treatment. [ABSTRACT FROM AUTHOR]

Abstract Soliton molecules (SMs) play a crucial role in nonlinear optical systems, enriching our understanding of nonlinear science through the study of their interaction dynamics. While passively mode-locked fiber lasers offer an efficient platform for generating diverse types of SMs, the complex internal dynamics of the laser often pose challenges in achieving predetermined temporal separations between SMs. Here, we implement a delayed optical feedback technique within a femtosecond optical parametric oscillator, enabling the generation of SMs with precise and controllable temporal separations. A theoretical model, which models the intracavity iterations of the signal with a simplified Ikeda map, is proposed to study the impact of parametric gain, intracavity feedback delay, and cavity length on the internal separations of the SMs. Our experimental results confirm that adjusting the cavity length allows for producing desired temporal separations within SMs. To reveal the evolution dynamics of the SMs, we further develop a rigorous numerical model using the carrier-resolved Forward Maxwell Equation, which is capable of modeling ultra-broadband complex dynamics based on a single equation without relying on the slowly-varying envelope approximation. The numerical model unveils the rich formation dynamics of the SMs at various separations, which confirms the critical role of the gain window provided by the pump. This work opens up new opportunities for the on-demand generation of SMs and provides valuable insights into the complex dynamics in femtosecond optical parametric oscillator systems with optical delayed feedback.

With the intensification of global aging,presbyopia has gradually become a global problem, and presbyopia correction surgery has emerged in recent years. The application of laser technology has brought great convenience to refractive surgery, and it also plays an increasingly important role in the correction of presbyopia. The emergence of excimer laser and femtosecond laser technology has opened a new world of surgical treatment for presbyopia, and brought new hope for surgical correction of presbyopia. In this paper, the application and new progress of excimer laser and femtosecond laser in presbyopia surgery are described.

A large variety of ultrafast laser‐matter interaction regimes and different processed surface finishing qualities of stainless steel can be achieved by varying the laser processing parameters. The optimization of the laser fluence to the most efficient ablation also leads to the lowest surface roughness of the ablated material. High laser fluence together with a high pulse repetition rate leads to heat accumulation, which results in the formation of microstructures with various morphology and scales. The use of GHz bursts allows a rough stainless‐steel surface to be smoothed and even polished. In this work, the fast and high‐quality milling of 2.5D cavities is demonstrated. Laser beam spot optimization is used to increase the throughput of the high‐power femtosecond laser (67.8 W), resulting in an ablation rate of 13 mm3 min−1. The complex cavities are produced by laser milling and cutting in layers. The formation of surface structures on stainless steel because of laser irradiation has been demonstrated. The possibilities of further GHz burst polishing are examined on previously laser‐milled stainless steel using with lowest possible surface roughness. The ability to polish the surface with microstructures below the original roughness is demonstrated by bursts of ultrashort pulses with a repetition rate in the GHz range. It has been demonstrated that mold milling in stainless steel designed for LED diffusers can be fabricated using a modern femtosecond laser source together with beam size optimization technique for efficient ablation with low surface roughness, layer‐by‐layer milling techniques, and GHz burst polishing techniques. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) semiconductor nanoparticles (NPs) have promising applications in many fields of science. In particular, as photocatalysts TiO2 NPs are unique for their special optical and electronic properties. Plasmonic metal doping of TiO2 NPs modifies the optical bandgaps of the composite NPs, due to which their applications will be extended in the visible spectral range. In the present study, gold (Au) doped TiO2 NPs (in powder form) were synthesized in the deposition–precipitation method at two different concentrations of Au (25% and 50%). Subsequently, dispersions were prepared by dispersing the Au-TiO2 NPs in ethanol. Nonlinear optical (NLO) studies of the Au-doped TiO2 dispersions (0.25 Au-TiO2, 0.50 Au-TiO2NPs) were carried out by employing the laser pulses of duration ~ 150 fs at a repetition rate ~ 76 MHz, in open aperture (OA) and closed aperture (CA) Z-scan methods. Wavelength-dependent NLO studies of Au-TiO2 NPs (0.25 Au-TiO2, 0.50 Au-TiO2 NPs) have been carried out at different input wavelengths 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, and 950 nm. It was observed that the recorded OA data fit well to three-photon absorption (3PA) for the 0.25 of Au doping, whereas for 0.50 Au-TiO2NPs data fitting was pretty good for two-photon absorption (2PA), for the input wavelengths starting from 800 nm, 850 nm, 900 nm, and 950 nm. At 700 nm, 0.25 Au-TiO2 NPs demonstrated reverse saturable absorption (RSA) in saturable absorption (SA), and 750 nm normalized transmittance exhibited a W-shaped signature (saturation in 2PA). Similarly, 700 nm, 750 nm, and 0.50 Au-TiO2 NPs have illustrated very strong 3PA at the input wavelengths. However, the pure TiO2 NPs in ethanol have demonstrated pure 2PA. CA traces recorded for both 0.25 Au and 0.50 Au TiO2 NPs in ethanol at all mentioned incident wavelengths, demonstrated a negative signature for the intensity dependent refractive index (n2). [ABSTRACT FROM AUTHOR]

In this study, we present a high precision and high spatial resolution in situ Fe isotope protocol using femtosecond (fs) laser ablation multi‐collector inductively coupled plasma‐mass spectrometry (LA‐MC‐ICP‐MS). The intermediate measurement precision obtained over a period of ca. 3 years for the USGS glass BIR‐1G against the Puratronic reference material is 0.17‰ (2s) for δ56Fe. Uncertainties achieved on individual analyses of glass and olivines were < 0.15‰ for δ56Fe. This high precision is associated with high spatial resolution of about 170 × 25 μm. Our results display good consistency between LA‐MC‐ICP‐MS and solution nebulisation MC‐ICP‐MS data from the literature. Obtained δ56Fe values on different USGS glasses (BIR‐1G, BHVO‐2G and BCR‐2G) show that these reference materials have homogenous Fe isotope ratio and therefore can be used as bracketing calibrators during laser ablation measurement sessions. On the other hand, the San Carlos Olivine displays high Fe isotope heterogeneity, and therefore cannot be considered as a good bracketing standard (calibrator). We also applied our fs‐LA‐MC‐ICP‐MS protocol to olivines and pyroxene from the Kerguelen Archipelago. This technique appears to be a relevant tool to resolve isotopic zoning in chemically zoned silicate phenocrysts, even of small size (< 1 mm). We demonstrate that within single lavas, olivine crystals display various zoning depending on their size, related to their residence time in the magma. Both equilibrium and diffusive processes were observed in olivine crystals from Kerguelen, uncovering complex histories. Hence, iron isotope ratio measurements by fs‐LA‐MC‐ICP‐MS open new possibilities for studying highly zoned silicate minerals in magmatic rocks to better understand their formation. [ABSTRACT FROM AUTHOR]

We demonstrate femtosecond ultra-stable green laser generation by an ytterbium-doped polarization-maintaining fiber laser with a 2.4 mm long lithium triborate (LBO) crystal. We generated 5.6 W of femtosecond green light at 520 nm for a fundamental power of 12 W, which corresponds to a conversion efficiency of 46.7%. The fiber chirped-pulse amplifier, which has an environmentally immune front end, delivered 170 fs pulses at a 75 MHz repetition rate centered at 1040 nm. According to the dispersion of the optical material in a double-frequency setup, the introduced dispersion had a negligible effect for the green laser, and the pulse duration of the generated green laser was calculated to be 171 fs, resulting in an excellent power stability, with fluctuation as low as 0.16% of the generated green light. This system could be of great interest in ultrafast optical and photobiology research. [ABSTRACT FROM AUTHOR]

Ytterbium laser sources are state-of-the-art systems that are increasingly replacing Ti:Sapphire lasers in most applications requiring high repetition rate pulse trains. However, extending these laser sources to THz Time-Domain Spectroscopy (THz-TDS) poses several challenges not encountered in conventional, lower-power systems. These challenges include pump rejection, thermal lensing in nonlinear media, and pulse durations exceeding 100 fs, which consequently limit the detection bandwidth in TDS applications. In this article, we describe our design of a THz-TDS beamline that seeks to address these issues. We report on the effectiveness of temperature controlling the Gallium Phosphide (GaP) used to generate the THz radiation and its impact on increasing the generation efficiency and aiding pump rejection while avoiding thermal distortions of the residual pump laser beam. We detail our approach to pump rejection, which can be implemented with off-the-shelf products and minimal customization. Finally, we describe our solution based on a commercial optical parametric amplifier to obtain a temporally compressed probe pulse of 55 fs duration. Our study will prove useful to the increasing number of laboratories seeking to move from the high-energy, low-power THz time-domain spectroscopy systems based on Ti:Sapphire lasers, to medium-energy, high-power systems driven by Yb-doped lasers. [ABSTRACT FROM AUTHOR]

Purpose: To assess the role of femtosecond laser‐assisted capsulotomy centration in the long‐term intraocular positioning of a multifocal intraocular lens. Design: Prospective comparative study. Methods: A total of 60 eyes of 30 patients underwent femtosecond laser‐assisted Refractive Lens Exchange (RLE). For every patient, capsulotomy centration was randomly performed according to pupil centre (PC) in one eye and first Purkinje reflex (FPR) in the other. The intraocular lens (IOL) positioning, visual acuities, spherical equivalent, internal aberrometry and quality of vision were assessed and compared at 3 years' follow‐up between groups (PC and FPR). Results: Intraocular lens positioning showed a statistically significant difference between groups, with a closer centration to the visual axis in the FPR patients (p < 0.001). Internal aberrometry showed higher values in the PC capsulotomy centration group (p < 0.01). Conclusions: FPR centered capsulotomy is associated to a closer centration of the IOL to the visual axis. [ABSTRACT FROM AUTHOR]

Purpose: To describe the use of FLACS (Femtosecond-Laser-Assisted Cataract Surgery) and pupiloplasty technique employed in a cataract surgery associated with iris-lens-zonule coloboma, as well as to report the advantages that FLACS can provide in this type of complicated surgery. Observations: During FLACS (Victus® - TECHNOLAS, Bausch and Lomb Incorporated, USA), after the docking procedure, the parameters of capsulotomy, fragmentation and incisions were manually adjusted. Iris retractors were anchored to the edge of the anterior lens capsule to provide stability to the bag during phacoemulsification maneuvers, and a capsular tension ring and intraocular lens (IOL) were implanted. Iris repair was approached using a modification of the slip-knot technique. For this purpose, a 10.0 Prolene on a straight needle was used and knotted extraocularly, over the conjunctiva. Finally, an anterior vitrectomy was performed as a precaution. Conclusions and importance: In spite of the existing controversy regarding FLACS technology compared to conventional surgery, it seems to be beneficial in complicated cases such as cataracts associated with iris and lens coloboma, since it allows the modification of different parameters that facilitate and ensure surgery safety. On the other hand, the iris repair technique described facilitates manipulation of the iris sutures. In addition, complementary techniques such as the use of a capsular tension ring and pupiloplasty help to center and stabilize the IOL, and to reduce the symptoms derived from iris coloboma, obtaining a better visual quality.

Deep anterior lamellar keratoplasty (DALK) has emerged as a transformative approach in managing corneal pathologies, notably keratoconus (KC), providing a viable alternative to penetrating keratoplasty (PK). This systematic review explores the intricacies of DALK, comparing its preoperative, intraoperative, and postoperative considerations with PK. Extensive literature searches revealed a wealth of data regarding DALK's advantages and challenges, with an emphasis on graft survival, visual outcomes, and complications. In the preoperative phase, DALK showcases its versatility, catering to a wide spectrum of patients, including those with KC and ocular surface disorders. Intraoperatively, it offers innovative techniques to address emphysema, bubble formation, and Descemet's membrane perforation, all while maintaining a strong focus on patient-centered outcomes. Postoperatively, DALK's lower rejection rates and decreased complications underscore its potential superiority over PK, although unique challenges such as graft failure from nonimmunologic factors demand vigilant management. This comprehensive review not only serves as a valuable resource for ophthalmic surgeons but also sheds light on the evolving landscape of corneal transplantation, highlighting DALK's role as a transformative force in the field.

Purpose: To explore the effect of the variation of pupil diameter (PD) and intraocular pressure (IOP) induced by femtosecond laser treatment on the subsequent phacoemulsfication and intraocular lens implantation. And whether the application of 0.1% pranoprofen could significantly reduce the miosis and increased IOP caused by femtosecond laser treatment in femtosecond laser-assisted cataract surgery (FLACS). Methods: In this study, patients were pretreated with (trial group) or without (control group) topical 0.1% pranoprofen. The PD and IOP were measured at different time points within 30 ​min after the completion of the femtosecond laser treatment. Results: The comparisons of the two groups showed the PD of patients pretreated with 0.1% pranoprofen was significantly larger than that of the control only at 15 ​min after FLACS (P ​= ​0.046), and there was no significant difference in IOP at any time point (P ​> ​0.05). Neither the ratio of significant miosis (PD ​≤ ​5 ​mm) nor intraocular hypertension (IOP ≥30 ​mmHg) was significantly different between the control group (1.72%, 6.67%) and the trial group (1%, 4.17%) (P ​> ​0.05). Conclusions: The PD and IOP of patients undergoing FLACS showed fluctuations within a small range. The rates of significant miosis and intraocular hypertension are very low, it is safe for surgeons to complete the follow-up procedures within 30 ​min after femtosecond laser treatment. Pretreatment with 0.1% pranoprofen exerted a slight, albeit significant prophylactic effect preventing pupil miosis. However, it provided only a limited benefit in patients undergoing FLACS without other complications.

Deep anterior lamellar keratoplasty (DALK) has emerged as a transformative approach in managing corneal pathologies, notably keratoconus (KC), providing a viable alternative to penetrating keratoplasty (PK). This systematic review explores the intricacies of DALK, comparing its preoperative, intraoperative, and postoperative considerations with PK. Extensive literature searches revealed a wealth of data regarding DALK's advantages and challenges, with an emphasis on graft survival, visual outcomes, and complications. In the preoperative phase, DALK showcases its versatility, catering to a wide spectrum of patients, including those with KC and ocular surface disorders. Intraoperatively, it offers innovative techniques to address emphysema, bubble formation, and Descemet's membrane perforation, all while maintaining a strong focus on patient-centered outcomes. Postoperatively, DALK's lower rejection rates and decreased complications underscore its potential superiority over PK, although unique challenges such as graft failure from nonimmunologic factors demand vigilant management. This comprehensive review not only serves as a valuable resource for ophthalmic surgeons but also sheds light on the evolving landscape of corneal transplantation, highlighting DALK's role as a transformative force in the field. [ABSTRACT FROM AUTHOR]

The chirped pulse amplification (CPA) systems based on transition-metal-ion-doped chalcogenide crystals are promising powerful ultrafast laser sources providing access to sub-TW laser pulses in the mid-IR region, which are highly relevant for essential scientific and technological tasks, including high-field physics and attosecond science. The only way to obtain high-peak power few-cycle pulses is through efficient laser amplification, maintaining the gain bandwidth ultrabroad. In this paper, we report on the approaches for mid-IR broadband laser pulse energy scaling and the broadening of the gain bandwidth of iron-doped chalcogenide crystals. The multi-pass chirped pulse amplification in the Fe:ZnSe crystal with 100 mJ level nanosecond optical pumping provided more than 10 mJ of output energy at 4.6 μm. The broadband amplification in the Fe:ZnS crystal in the vicinity of 3.7 μm supports a gain band of more than 300 nm (FWHM). Spectral synthesis combining Fe:ZnSe and Fe:CdSe gain media allows the increase in the gain band (~500 nm (FWHM)) compared to using a single active element, thus opening the route to direct few-cycle laser pulse generation in the prospective mid-IR spectral range. The features of the nonlinear response of carbon nanotubes in the mid-IR range are investigated, including photoinduced absorption under 4.6 μm excitation. The study intends to expand the capabilities and improve the output characteristics of high-power mid-IR laser systems. [ABSTRACT FROM AUTHOR]

PurposeThis study investigated the initial feasibility of using femtosecond laser trabeculotomy (FLT) to create open channels through the trabecular meshwork into Schlemm's canal to lower intraocular pressure (IOP) in a perfused anterior segment model.MethodsHuman anterior segments (12 eyes) were assigned to either treatment (n = 6) or sham treatment (n = 6) groups. Both groups were perfused until a baseline IOP was recorded upon which a direct FLT treatment or a sham treatment was administered. IOP was recorded before and after the treatment. Spectral domain optical coherence tomography and second harmonic generation imaging we used to investigate the FLT channels.ResultsIn the FLT group, there was a significant mean decrease in the IOP of 22% compared with the pre-FLT IOP (7.13 ± 2.95 mm Hg to 5.34 ± 1.62 mm Hg; P < 0.05). In the control group, the post-sham IOP remained relatively unchanged compared with the pre-sham IOP (6.39 ± 3.69 mm Hg to 6.67 ± 4.12 mm Hg).ConclusionsThe results of this study indicate that FLT treatment can significantly decrease the IOP in a perfusion model and may provide a potential noninvasive treatment option for primary open angle glaucoma.Translational relevanceInvestigating the use of femtosecond lasers for photodisrupting the trabecular meshwork can lead to a clinically relevant alternative to current glaucoma procedures.

AIM: To evaluate corneal astigmatic outcomes of femtosecond laser-assisted arcuate keratotomies (FAKs) combined with femtosecond-laser assisted cataract surgery (FLACS) over 12mo follow-up. METHODS: Totally 145 patients with bilateral cataracts and no ocular co-morbidities were recruited to a single-centre, single-masked, prospective randomized controlled trial (RCT) comparing two monofocal hydrophobic acrylic intraocular lenses. Eyes with corneal astigmatism (CA) of >0.8 dioptres (D) received unpaired, unopened, surface penetrating FAKs at the time of FLACS. Visual acuity, subjective refraction and Scheimpflug tomography were recorded at 1, 6, and 12mo. Alpins vectoral analyses were performed. RESULTS: Fifty-one patients (61 eyes), mean age 68.2±9.6y [standard deviation (SD)], received FAKs. Sixty eyes were available for analysis, except at 12mo when 59 attended. There were no complications due to FAKs. Mean pre-operative CA was 1.13±0.20 D. There was a reduction of astigmatism at all post-operative visits (residual CA 1mo: 0.85±0.42 D, P=0.0001; 6mo: 0.86±0.35 D, P=0001; and 12mo: 0.90±0.39, P=0.0001). Alpins indices remained stable over 12mo. Overall, the cohort was under-corrected at all time points. At 12mo, 61% of eyes were within ±15 degrees of pre-operative astigmatic meridian. CONCLUSION: Unpaired unopened penetrating FAKs combined with on-axis phacoemulsification are safe but minimally effective. CA is largely under-corrected in this cohort using an existing unmodified nomogram. The effect of arcuate keratotomies on CA remained stable over 12mo.

Intramolecular charge transfer and the associated changes in molecular structure in N,N'-dimethylpiperazine are tracked using femtosecond gas-phase X-ray scattering. The molecules are optically excited to the 3p state at 200 nm. Following rapid relaxation to the 3s state, distinct charge-localized and charge-delocalized species related by charge transfer are observed. The experiment determines the molecular structure of the two species, with the redistribution of electron density accounted for by a scattering correction factor. The initially dominant charge-localized state has a weakened carbon-carbon bond and reorients one methyl group compared with the ground state. Subsequent charge transfer to the charge-delocalized state elongates the carbon-carbon bond further, creating an extended 1.634 Å bond, and also reorients the second methyl group. At the same time, the bond lengths between the nitrogen and the ring-carbon atoms contract from an average of 1.505 to 1.465 Å. The experiment determines the overall charge transfer time constant for approaching the equilibrium between charge-localized and charge-delocalized species to 3.0 ps.

Ytterbium laser sources are state-of-the-art systems that are increasingly replacing Ti:Sapphire lasers in most applications requiring high repetition rate pulse trains. However, extending these laser sources to THz Time-Domain Spectroscopy (THz-TDS) poses several challenges not encountered in conventional, lower-power systems. These challenges include pump rejection, thermal lensing in nonlinear media, and pulse durations exceeding 100 fs, which consequently limit the detection bandwidth in TDS applications. In this article, we describe our design of a THz-TDS beamline that seeks to address these issues. We report on the effectiveness of temperature controlling the Gallium Phosphide (GaP) used to generate the THz radiation and its impact on increasing the generation efficiency and aiding pump rejection while avoiding thermal distortions of the residual pump laser beam. We detail our approach to pump rejection, which can be implemented with off-the-shelf products and minimal customization. Finally, we describe our solution based on a commercial optical parametric amplifier to obtain a temporally compressed probe pulse of 55 fs duration. Our study will prove useful to the increasing number of laboratories seeking to move from the high-energy, low-power THz time-domain spectroscopy systems based on Ti:Sapphire lasers, to medium-energy, high-power systems driven by Yb-doped lasers.

Laser ablation (LA) using nanosecond (ns) or femtosecond (fs) pulse widths is well-established for the volatilization of a liquid or solid for applications ranging from micromachining to sampling for compositional analysis. Far less work has examined laser ablation in the intermediate picosecond regime (ps-LA), which corresponds to the approximate timescale for the transfer of energy from laser-excited electrons to the lattice. 213 and 355 nm ps-LA of silicon (Si) with Gaussian beam profiles is compared here to 800 nm fs-LA with both Gaussian and flat-top beam profiles, all performed at or above the ablation threshold with 20 000–67 000 laser pulses. The morphology and composition of the ablation spots are examined using scanning electron microscopy and energy dispersive x-ray spectroscopy (EDS), respectively. 213 nm ps-LA yields more visible nanostructures compared to those ablated by 355 nm ps-LA, but both form central craters with surrounding nanostructures due to resolidified material. The flat-top fs beam creates protruding nanostructures isolated near the rim of the crater and an inside-out umbrella-like structure at the center. The Gaussian fs-LA region displays a relatively smooth conical crater, albeit with some nanostructure at the rim of the crater. EDS finds that these nanostructures are at least partly composed of silicon oxide or suboxides. The invisibility of these nanostructures to optical profilometry is consistent with black-silicon. The ablation crater results from optical profilometry for 213 nm ps-LA are close to those for 800 nm flat-top fs-LA, and both are consistent with cylindrical craters. [ABSTRACT FROM AUTHOR]

Progress in the field of machine learning has enhanced the development of self-adjusting optical systems capable of autonomously adapting to changing environmental conditions. This study demonstrates the concept of self-adjusting optical systems and presents a new approach based on reinforcement learning methods. We integrated reinforcement learning algorithms into the setup for tuning the laser radiation into the fiber, as well as into the complex for controlling the laser-plasma source. That reduced the dispersion of the generated X-ray signal by 2–3 times through automatic adjustment of the position of the rotating copper target and completely eliminated the linear trend arising from the ablation of the target surface. The adjustment of the system was performed based on feedback signals obtained from the spectrometer, and the movement of the target was achieved using a neural network-controlled stepper motor. As feedback, the second harmonic of femtosecond laser radiation was used, the intensity of which has a square root dependence on the X-ray yield. The developed machine learning methodology allows the considered systems to optimize their performance and adapt in real time, leading to increased efficiency, accuracy, and reliability. [ABSTRACT FROM AUTHOR]

The photophysical properties of Cu(II) complexes with 5,10,15,20-meso-tetrakis(phenyl)porphyrin and 5,10,15,20-meso-tetrakis(N-methylpyridium-4-yl)porphyrin are examined via the luminescence and femtosecond time-resolved absorbance methods, respectively. These studies are supported by DFT and TD-DFT calculations, which highlight the important role played by ligand-to-metal charge-transfer states in directing the system toward either intersystem crossing to the triplet hypersurface or coordinative expansion to a five-coordinate quasi-stable intermediate. The latter processes occur when the porphyrin is photolyzed in the presence of suitably located Lewis bases. Femtosecond time-resolved absorbance measurements of Cu(II)-5,10,15,20-meso-tetrakis(N-methylpyridium-4-yl)porphyrin confirm that the coordinative expansion in water occurs in approximately 700 fs, while crossing to the triplet hypersurface takes approximately 140 fs in the same solvent. These processes are mutually exclusive, although both can occur simultaneously depending on the environment of the porphyrin. The ratio of the two processes depends on the relative orientation of the Lewis base with respect to the copper atom at the time of excitation. As a consequence, copper porphyrins such as these are excellent probes in the environment of the porphyrin and can be used to identify the location of the porphyrin when interacting with DNA fragments. [ABSTRACT FROM AUTHOR]

In this study, the amplification of Ti: sapphire laser pulses in a regenerative amplifier with Z geometric arrangement has been demonstrated based on chirped pulse amplification method. Two pocket cells were used to transfer the seed pulses to the amplifier cavity and extract the amplified pulses. Build up time of the amplified pulses according to the energy of the pump laser has been studied, and the dynamic evolution of the pulses inside the amplifier cavity has been investigated. The pulse duration of the generated pulses inside the cavity without seed pulses is about 80 ns, and the buildup time is 38 ns. The 2 mJ amplified femtosecond laser pulses at a repetition rate of 10 Hz are obtained after 17 round trips using pump energy of 15 mJ at 532 nm. The amplified laser wavelength is 800 nm with 30 nm spectral bandwidth, which is 30 nm narrower than the oscillator bandwidth. The amplification efficiency relative to the pump energy is obtained at about 13%, and the amplification coefficient in this scheme reached 106.

Abstract Background Differences between programmed capsulorhexis diameter and actual resulting capsulorhexis diameter (ARCD) are commonly encountered in femtosecond laser-assisted cataract surgery (FLACS). The purpose of this study was to identify the preoperative ophthalmic variables influencing capsulorhexis diameter index (CDI) in FLACS for adults and create a multiple linear regression model for obtaining a more accurate capsulorhexis diameter. Methods This retrospective study involved sixty-seven eyes of 44 patients who received FLACS and intraocular lens implantation. The ARCD was measured using anterior segment swept-source optical coherence tomography (CASIA 2). Keratometry (K1, K2 and average K), anterior chamber depth (ACD), lens thickness (LT), anterior chamber width (ACW), white-to-white (WTW), curvature radius of anterior lens capsule (Front R) and axial length (AL) were all measured preoperatively. Based on the derived data, LT/ACW, LT/AL, LT/ACD and LT/ACW/Front R were calculated. The ratio of the programmed capsulorhexis diameter and ARCD was defined as the CDI. Correlation analysis was conducted to examine the relationship between preoperative variables listed above and the CDI. Multiple linear regression analysis was applied to select the most influential preoperative variables on CDI. Results ACD, LT, ACW, Front R, AL, LT/ACW, LT/AL, LT/ACD, and LT/ACW/Front R showed significant correlation with CDI. Front R and LT/ACW/Front R were selected as constants in the multiple linear regression model using stepwise variable selection. The following equation represents the multiple linear regression model: CDI = 1.306–4.516 × LT/ACW/FrontR-0.011 × Front R, when P

Purpose: To determine the safety and efficacy of low-energy settings in small incision lenticule extraction (SMILE) for correcting myopia and myopic astigmatism. Methods: We included patients aged ≥18 years with the myopia of −0.5 to −10 D and myopic astigmatism of −0.5 to −5 Dcyl in this retrospective case series performed at a private eye hospital in South India. All patients had preoperative best-corrected visual acuity of LogMar 0.0 ± 0, with stable refraction for 1 year and normal corneal topography. Ocular surface disease and other pathology cases were excluded. The repetition rate of the laser was 500 kHz, and the pulse energy was 110 nJ. The lenticule diameter was set at 6.5 mm, cap diameter was 7.20 mm, and intended cap thickness was 110–130 μ. The spot distance was 4.5 μm. All patients were evaluated immediately postoperation and on postoperative days 1, 8, and 30. Results: Overall, 541 eyes were included. The mean patient age was 25.03 ± 4.1 years. The mean spherical error was -3.76 ± 1.84 Ds. The mean cylinder was -1.24 ± 0.91. The mean spherical equivalent of refraction was −4.22 ±1.94 D. The logMAR on postoperative day 1 was 0.0 ± 0. The mean spherical equivalent at 1 month was 0.28 ± 1.06 D. There was no loss of Snellen's lines after the procedure. The mean spherical equivalent of refraction to the target was 95% within ± 0.50 D. The postoperative astigmatism was within 0.5 Dycl. No intraoperative complications of SMILE including retained lenticule fragments, tears of incision, or improper dissection occurred. Conclusion: Low-energy settings in SMILE are safe and effective in correcting myopia and myopic astigmatism including high cylinders (>3 Dcyl).

Purpose: To compare visual outcomes of early enhancement following small incision lenticule extraction (SMILE) versus laser in situ keratomileusis (LASIK). Methods: Retrospective analysis of eyes (patients operated in the setting of a tertiary eye care hospital between 2014 and 2020) requiring early enhancement (within one year of primary surgery) was conducted. Stability of refractive error, corneal tomography, and anterior segment Optical Coherence Tomography (AS-OCT) for epithelial thickness was performed. The correction post regression was done using photorefractive keratectomy and flap lift in eyes, wherein the primary procedure was SMILE and LASIK, respectively. Pre- and post enhancement corrected and uncorrected distance visual acuity (CDVA and UDVA), mean refractive spherical equivalent (MRSE), and cylinder were analyzed. IBM SPSS statistical software. Results: In total, 6350 and 8176 eyes post SMILE and LASIK, respectively, were analyzed. Of these, 32 eyes of 26 patients (0.5%) post SMILE and 36 eyes of 32 patients (0.44%) post-LASIK required enhancement. Post enhancement (flap lift in LASIK, and PRK in SMILE group) UDVA was logMAR 0.02 ± 0.05 and 0.09 ± 0.16 (P = 0.009), respectively. There was no significant difference between the refractive sphere (P = 0.33) and MRSE (P = 0.09). In total, 62.5% of the eyes in the SMILE group and 80.5% in the LASIK group had a UDVA of 20/20 or better (P = 0.04). Conclusion: PRK post SMILE demonstrated comparable results to flap lift post LASIK and is a safe and effective approach for early enhancement post SMILE.

Femtosecond laser-assisted astigmatic keratotomy (FSAK) is recognized as a safe and effective therapeutic option for addressing high corneal astigmatism in corneal transplants. Although the incidence of corneal infection after FSAK in corneal transplants is very low, early detection and treatment is necessary to optimize visual outcomes and prevent devastating sequelae. This report describes a rare case of an early-onset infectious keratitis occurring in a corneal transplant after FSAK. A 38-year-old man with previous history of penetrating keratoplasty and FSAK presented to emergency department with deep corneal infiltration at the FASK incision site along with a decline in his baseline best corrected visual acuity 1 month after FSAK. Corneal scraping was performed, and topical fortified antibiotic eyedrops were started. Culture results showed no growth. Three weeks later, the corneal infiltrate resolved with residual scarring at the FSAK incision site, and the patient regained his baseline best corrected visual acuity with no sequelae.

Alizarin red S is a sulfonated, water-soluble derivative of alizarin. This work presents femtosecond studies of alizarin red S (ARS) nanoparticles in comparison to ARS in aqueous solution and to alizarin in DMSO. The femtosecond studies cover a probing spectral range of 350–750 nm using different excitation wavelengths, taking into account the variation of the absorption spectra with the pH values of the solvent. Stationary absorption spectra show slight differences between solution and nanoparticles. Excitation at 530 nm results in low and noisy responses, therefore, we additionally recorded transient spectra of the nanoparticles at λex = 267 nm. While the results in DMSO are comparable to previous studies in non-aqueous solvents, we report a relatively fast relaxation of 14 ps in [La(OH)2][ARS] nanoparticles in aqueous solution after excitation at 530 nm, which is similar to Na(ARS) solution (19 ps). The dynamics changed with lower pH, but still without significant differences between nanoparticles and solution. We propose [La(OH)2][ARS] nanoparticles as a suitable alternative to dissolved molecules with similar spectroscopic properties, for example, with regard to biomarker applications. [ABSTRACT FROM AUTHOR]

The impact of group velocity dispersion (GVD) on femtosecond laser filamentation with the higher-order Kerr effect is studied at different atmospheric pressures. The results show that GVD makes the collapse distance to not meet the semi-empirical formula proposed by Dawes and Marburger, suppresses multiple focusing and splitting in time during the propagation process, and reduces the length of filament. In addition, we also compared the results with those considering only the third-order Kerr effect. This provides some information for the study of whether the defocus effect in the femtosecond laser filamentation is the higher-order Kerr effect or the plasma effect. [ABSTRACT FROM AUTHOR]

Edge-functionalization of graphene is emerging as a powerful chemical method for the construction of π-delocalized highly-planar graphene nanoconjugates that are not accessible through surface-supported syntheses. Herein, a graphene-porphyrin nanoconjugate via a robust pyrazine (pz) linkage has been obtained by condensing 2,3-diamino-5,10,15,20-tetraphenylporphyrin (DA-TPP) with ortho-quinone (o-quinone) moieties at edge sites of graphene oxide (GO). The as-prepared GO-pz-TPP exhibits an intense absorption extending from 375 to 900 nm and a high quenching yield (98%) of fluorescence, indicating a strong electronic coupling effect between GO and TPP units. GO-pz-TPP displays strong nonlinear optical (NLO) absorption and giant NLO coefficients with 800 and 1,030 nm fs laser, in sharp contrast to traditional graphene-porphyrin nanohybrids only NLO-active towards ns laser. Such a dramatic NLO performance towards femtosecond pulsed laser has not been achieved in any carbon-chromophores nanohybridized materials to date. This work validates the π-extended edge-functionalization strategy as a means to tune the NLO properties of graphene, thereby providing a new paradigm for the assembly of versatile optoelectronic materials. [ABSTRACT FROM AUTHOR]

In this study, we evaluate and compare the outcomes of conventional phacoemulsification cataract surgery (CPS) and femtosecond laser-assisted cataract surgery (FLACS) with the implantation of an extended depth of field (EDOF) intraocular lens (IOL). A prospective, consecutive cohort study was conducted. Patients were given the option to choose FLACS or CPS and were implanted with an EDOF IOL. Refractive data, visual acuity data, ocular aberration measured with a wavefront aberrometer, and optical quality measured with an optical quality analysis system II were collected at one month postoperatively. A total of 92 eyes of 64 patients were enrolled in this study; 35 eyes of 26 patients were treated with FLACS, whereas 57 eyes of 38 patients were treated with CPS. Uncorrected visual acuity at far, intermediate, and near distance and best-spectacle-corrected visual acuity were not statistically significantly different between the groups (all p > 0.05), nor were the mean cylinder and mean spherical equivalent refraction (both p > 0.05). The FLACS group had a lower ocular trefoil than the CPS group (p = 0.033), and there was no significant difference between the two groups considering other aberration parameters, whether ocular or internal (all p > 0.05). Optical-quality-related parameters showed also no significant difference between the two groups (all p > 0.05). In conclusion, there was no significant difference between FLACS and CPS with implantation of EDOF IOLs in postoperative ocular parameters, refractive outcomes, ocular aberration, optical quality, and aberration parameters, except a lower ocular trefoil in the FLACS group. In terms of these indicators, FLACS does not provide an additional clinical benefit for patients over CPS. [ABSTRACT FROM AUTHOR]

Introduction: The purpose of this study is to investigate and compare the effects of the antimicrobial agents Moringa oleifera and bioactive glass nanoparticles activated by femtosecond laser light on the biomimetic dentin remineralization using teeth having carious dentin ICDAS code 3. Methods and Materials: A total of 27 dentin surface samples were divided into three groups: the first group was treated with a Moringa oleifera extract, while the second group was treated with bioactive glass nanoparticles, and as for the control group, the third group received no additional agent. All groups were subjected to femtosecond laser light at three different wavelengths: 390 nm, 445 nm, and 780 nm. The photoactivation of each sample was achieved using the femtosecond laser light for 5 min with an average power rating of 300 mW, a pulse duration of 100 fs, and a pulse repetition rate of 80 Hz. The mineral content of the samples was obtained and analyzed using the laser-induced breakdown spectroscopy (LIBS). The LIBS analysis was conducted with the following laser light parameters: average power of ~215 mW, wavelength of 532 nm, pulse duration of 10 ns, and a pulse repetition rate of 10 Hz. Results: Most studied samples exhibited a relative increase in the mineral content that may enhance biomimetic remineralization. Moringa oleifera photoactivated by femtosecond laser light at 445 nm achieved a significant increase in mineral content. Conclusion: Using the femtosecond laser light to activate the relatively cheap and commercially available antimicrobial agent Moringa oleifera supports the strategy of minimal invasive approaches for the treatment and biomimetic remineralization of carious dentin ICDAS code 3. [ABSTRACT FROM AUTHOR]

This study reported the synthetic structural colors obtained by femtosecond laser-induced periodic bidirectional ripples on titanium film. Bidirectional ripples were obtained by secondary laser induction on the secondary deposited metal films. The pulse energy 1.5 μJ and the scanning speeds from 600 to 800 mm/s were selected as the best processing parameters to prepare bidirectional ripples. Considering that the ripple orientation affected the intensity of the color, the induced angle between the bidirectional ripples could be selected according to the range of information displayed. Moreover, the bidirectional ripples with an included angle of 90° were selected for color synthesis. The spectra of synthetic structural colors showed that abundant colors could be obtained through the simultaneous diffraction of bidirectional ripples. In addition, the synthetic structural colors changed with the lightness of the original structural colors. Therefore, this study provided a new idea to enrich the information display and realize the information security. • Bidirectional ripples were obtained by secondary laser induction on the secondary deposited metal films. • Abundant structural colors could be obtained through the simultaneous diffraction of bidirectional ripples. • The synthetic structural colors changed with the lightness of original structural colors. [ABSTRACT FROM AUTHOR]

The demand for precise and high-quality machining of wide-bandgap materials, such as glasses and crystals, is of considerable significance in science and industry. Among these materials, sapphire stands out as an appealing choice due to its exceptional mechanical and optical attributes, high thermal conductivity and stability, low electrical conductivity, and resilience against harsh chemicals. Despite its hardness, sapphire is brittle, making it prone to cracking during conventional machining attempts. Recently, alternative non-contact approaches, like laser ablation, have emerged as potential solutions to improve the machining quality. However research of laser processing of wide-bandgap materials, especially utilizing the high harmonics of femtosecond solid-state laser systems, remains incomplete. Our study focuses on investigating the nonthermal laser ablation of c-cut sapphire crystals using femtosecond (300 fs) deep UV (206 nm) laser pulses and comparing the results with traditional IR femtosecond ablation. The publication encompasses a comprehensive depiction of the ablation process and a review of the various achieved morphologies with accompanying scanning electron microscope images. Our findings indicate that efficient ablation with surface roughness below 100 nm can be achieved through a single-step process within specific laser processing parameter ranges. The ablation process of sapphire encompasses a strong incubation effect, hence the pulses need to be tightly overlapped. Additionally, we provide a detailed description of methodology used to extract surface roughness which was utilized in all the presented research and offers a practical framework for characterizing ablation results obtained from diverse laser systems. • Deep ultraviolet femtosecond pulses minimize thermal effects in sapphire ablation. • Ultraviolet wavelengths surpass infrared for achieving low surface roughness. • The ablation process exhibits a significant incubation effect. • Efficient ablation regime produces deep structures with low roughness. • Ablation originates from impurities and breakup mechanism is photomechanical. [ABSTRACT FROM AUTHOR]

Astigmatism management is a frequently encountered challenge in the world of modern cataract surgery. This review article investigates the importance of astigmatic correction and seeks to uncover the critical components of preoperative evaluation. With the rapid growth of new technologies and techniques, this article aims to also catalogue and clarify the multitude of astigmatism treatment options available for the cataract surgeon.

The chirped pulse amplification (CPA) systems based on transition-metal-ion-doped chalcogenide crystals are promising powerful ultrafast laser sources providing access to sub-TW laser pulses in the mid-IR region, which are highly relevant for essential scientific and technological tasks, including high-field physics and attosecond science. The only way to obtain high-peak power few-cycle pulses is through efficient laser amplification, maintaining the gain bandwidth ultrabroad. In this paper, we report on the approaches for mid-IR broadband laser pulse energy scaling and the broadening of the gain bandwidth of iron-doped chalcogenide crystals. The multi-pass chirped pulse amplification in the Fe:ZnSe crystal with 100 mJ level nanosecond optical pumping provided more than 10 mJ of output energy at 4.6 μm. The broadband amplification in the Fe:ZnS crystal in the vicinity of 3.7 μm supports a gain band of more than 300 nm (FWHM). Spectral synthesis combining Fe:ZnSe and Fe:CdSe gain media allows the increase in the gain band (~500 nm (FWHM)) compared to using a single active element, thus opening the route to direct few-cycle laser pulse generation in the prospective mid-IR spectral range. The features of the nonlinear response of carbon nanotubes in the mid-IR range are investigated, including photoinduced absorption under 4.6 μm excitation. The study intends to expand the capabilities and improve the output characteristics of high-power mid-IR laser systems.

An experimental investigation on nitrogen fluorescence emissions pumped by a single 800 nm fs optical vortex (OV) beam with different topological charges (TC) is reported. The intensity of the two prototype emission lines from neutral nitrogen molecules (N2) and molecular nitrogen ions (N2+), i.e., 337 nm and 391 nm, respectively, shows different TC dependences: the former slightly decreases as the TC increases, while the latter sharply decreases as the TC changes from zero to a non-zero value. The dependences of the 337-nm and 391-nm emission intensity on pulse energy are also different: the former shows a linear variation for different TCs, while the latter has an abrupt change in the slope when changing the TC. Furthermore, the dependence of the 337-nm emission intensity on gas pressure exhibits a plateau which is universal for different TCs. In contrast, the dependence of the 391-nm emission intensity on gas pressure shows an apparent hump which is respective of the TC. These actual new results will facilitate further theoretical study on the formation dynamics of the nitrogen fluorescence emissions induced by the OV beam, and inspire that such beam can been taken as a unique pure optical tool to manipulate the transitions between different electronic-vibrational states.