Abstract The nonlinear optical properties of transparent ocular media have been shown to alter the focused intensity distribution of femtosecond laser pulses, potentially affecting the precision of laser ophthalmic surgery. In this study, the nonlinear refractive index $$n_2$$ of porcine aqueous humor, crystalline lens and vitreous humor was measured using two complementary techniques: the standard Z-scan-derived D4 $$\sigma$$ method and the phase-object imaging method. Both were performed with a tunable femtosecond laser source across the visible to near-infrared range (650–900 nm). All measured $$n_2$$ values were found to be close to $$2 \times 10^{-20}\,m^2/W$$ within experimental uncertainties, with no measurable nonlinear absorption detected. Notably, the phase-object technique proved particularly well-suited for slightly scattering or heterogeneous media, such as the freshly extracted crystalline lens, when calibrated against a reference medium (here, water). These experimental results allow for a quantitative numerical assessment of pulse and beam degradation due to nonlinear refraction during procedures like cataract surgery, as well as an evaluation of its potential impact on photodisruption geometry.

The nonlinear optical properties of transparent ocular media have been shown to alter the focused intensity distribution of femtosecond laser pulses, potentially affecting the precision of laser ophthalmic surgery. In this study, the nonlinear refractive index [Formula: see text] of porcine aqueous humor, crystalline lens and vitreous humor was measured using two complementary techniques: the standard Z-scan-derived D4σ method and the phase-object imaging method. Both were performed with a tunable femtosecond laser source across the visible to near-infrared range (650-900 nm). All measured [Formula: see text] values were found to be close to [Formula: see text] within experimental uncertainties, with no measurable nonlinear absorption detected. Notably, the phase-object technique proved particularly well-suited for slightly scattering or heterogeneous media, such as the freshly extracted crystalline lens, when calibrated against a reference medium (here, water). These experimental results allow for a quantitative numerical assessment of pulse and beam degradation due to nonlinear refraction during procedures like cataract surgery, as well as an evaluation of its potential impact on photodisruption geometry.

Over the past 20 years, endothelial keratoplasty procedures have revolutionized the treatment of corneal endothelial disorders. These conditions have now become the leading indication for corneal transplantation in Western countries and account for half of all donor cornea usage. Despite their undeniable success, the global shortage of donor tissues and major disparities between nations justify the development of alternatives to donor grafts. Cell therapy using injections of suspended endothelial cells has proven effective, and tissue-engineered endothelial keratoplasty (TEEK), comprising a membrane coated with cultured endothelial cells, is under development to better mimic the native endothelial graft. Our team utilizes a femtosecond-laser-cut lens capsule disc as a bioengineering scaffold, taking advantage of this novel tissue's biocompatibility, transparency, curvature, and availability. In the present study, we provide proof of concept, in 12 TEEKs, that it is possible to control the final endothelial cell density (ECD) by varying the seeding density per mm2. Cell characterization was performed through morphometric analysis of the endothelial mosaic stained with anti-NCAM (a lateral membrane marker used as a differentiation marker), using the CellPose artificial intelligence algorithm specifically trained for in vitro endothelium segmentation. Five criteria related to pleomorphism, polymorphism, and elongation were combined into a single endothelial quality score. The median cell viability at 28 days of culture, assessed by Hoechst 33342 and Calcein-AM staining, reached 98% (range: 83-99%). The median viable ECD (number of live cells per surface unit) in the highest-density group was 3.245 cells/mm2 (range: 2.778-3.753), paving the way for the bioengineering of supra-physiological TEEKs, or "super TEEKs".

Over the past 20 years, endothelial keratoplasty procedures have revolutionized the treatment of corneal endothelial disorders. These conditions have now become the leading indication for corneal transplantation in Western countries and account for half of all donor cornea usage. Despite their undeniable success, the global shortage of donor tissues and major disparities between nations justify the development of alternatives to donor grafts. Cell therapy using injections of suspended endothelial cells has proven effective, and tissue-engineered endothelial keratoplasty (TEEK) comprising a membrane coated with cultured endothelial cells is under development to better mimic the native endothelial graft. Our team utilizes a femtosecond-laser-cut lens capsule disc as a bioengineering scaffold, taking advantage of this novel tissue’s biocompatibility, transparency, curvature, and availability. In the present study, we provide proof of concept, in 12 TEEKs, that it is possible to control the final endothelial cell density (ECD) by varying the seeding density per mm2. Cell characterization was performed through morphometric analysis of the endothelial mosaic stained with anti-NCAM (a lateral membrane marker used as a differentiation marker), using the CellPose artificial intelligence algorithm specifically trained for in vitro endothelium segmentation. Five criteria related to pleomorphism, polymorphism, and elongation were combined into a single endothelial quality score. The median cell viability at 28 days of culture, assessed by Hoechst 33342 and Calcein-AM staining, reached 98% (range: 83–99%). The median viable ECD (number of live cells per surface unit) in the highest-density group was 3,245 cells/mm2 (range: 2,778–3,753), paving the way for the bioengineering of supra-physiological TEEKs, or super TEEKs. Impact statement The process of manufacturing tissue-engineered endothelial keratoplasty (TEEK) allows for the control of endothelial cell density (DCE) and, in particular, the creation of super TEEKs, meaning grafts with supra-physiological DCE that are more likely to better withstand the challenges of surgery and have a prolonged lifespan in recipients. ### Competing Interest Statement The authors have declared no competing interest.

The bioengineering of corneal endothelial grafts consists of seeding in vitro cultured corneal endothelial cells onto a thin, transparent, biocompatible, and sufficiently robust carrier which can withstand surgical manipulations. This is one of the most realistic alternatives to donor corneas, which are in chronic global shortage. The anterior capsule of the crystalline lens has already been identified as one of the best possible carriers, but its challenging manual preparation has limited its use. In this study, we describe a femtosecond laser cutting process of the anterior capsule of whole lenses in order to obtain capsule discs of 8 mm diameter, similar to conventional endothelial grafts. Circular marks made on the periphery of the disc indicate its orientation. Immersion in water for 3 days is sufficient to completely remove the lens epithelial cells and to enable the seeding of corneal endothelial cells, which remain viable after 27 days of culture. Therefore, this method provides a transparent, decellularized disc ready to form viable tissue engineered endothelial grafts.

Laser surface micro machining has attracted a worldwide attention due to the possibility to obtain micro and submicrometric structuring on various substrates with the flexibility of the laser irradiation tool. Many application fields are impacted by the possibility to structure the surface at the micro and submicrometric level, mostly related to adding functions to surfaces like wettability, optical properties and cellular differentiation [1]–[3]. When using ultrafast laser pulses for surface structuring, the low onset of thermal effects at low repetition rate enlarges the laser process parameters that generates a wide variety of micro and nano structures.

Abstract Ultrafast laser processing can induce surface nanostructurating (SNS) in most materials with dimensions close to the irradiation laser wavelength. In-situ SNS characterization could be key for laser parameter’s fine-tuning, essential for the generation of complex and/or hybrid nanostructures. Laser Induced Periodic Surface Structures (LIPSS) created in the ultra-violet (UV) range generate the most fascinating effects. They are however highly challenging to characterize in a non-destructive manner since their dimensions can be as small as 100 nm. Conventional optical imaging methods are indeed limited by diffraction to a resolution of $$\approx 150$$ ≈ 150 nm. Although optical super-resolution techniques can go beyond the diffraction limit, which in theory allows the visualization of LIPSS, most super-resolution methods require the presence of small probes (such as fluorophores) which modifies the sample and is usually incompatible with a direct surface inspection. In this paper, we demonstrate that a modified label-free Confocal Reflectance Microscope (CRM) in a photon reassignment regime (also called re-scan microscopy) can detect sub-diffraction limit LIPSS. SNS generated on a titanium sample irradiated with a $$\lambda =257$$ λ = 257 nm femtosecond UV-laser were characterized with nanostructuring period ranging from 105 to 172 nm. Our label-free, non-destructive optical surface inspection was done at 180 $$\upmu$$ μ m $$^2$$ 2 /s, and the results are compared with commercial SEM showing the metrological efficiency of our approach.

Laser processing of material surfaces has been very known for the last five decades. Femtosecond LIPSS, are created generally on the surface, they could be classified into two groups depending on the periodicity of the structures: LSFL showing a periodicity lower than the incident wavelength (λ_l), and HSFL with a periodicity well below λ_l that could sit below the optical diffraction limit. In this paper, we show an unprecedented resolution of a noninvasive label-free optical method to observe such structures, that does not require a priori knowledge of the surface. We demonstrate that using a modified reflectance confocal microscope reflection (CMR), the characterization of HSFL(̴Λ_HSFL∽120 nm @ λ_l=257 nm) is possible and efficient. These results, pave the way toward a new, better, and more resolved optical technique to observe nanostructures below the diffraction limit.

Ultrafast laser ablation is widely used as a versatile method for accurate micro-machining of polymers, glasses and metals for a variety of industrial and biomedical applications. We report on the use of a novel process parameter, the modulation of the laser pulse energy during the multi-scan texturing of surfaces. We show that this new and straightforward control method allows us to attain higher and lower roughness (Ra) values than the conventional constant pulse energy irradiation sequence. This new multi-scanning laser ablation strategy was conducted on metals that are commonly used in the biomedical industry, such as stainless steel, titanium, brass and silver samples, using a linear (increasing or decreasing) gradient of pulse energy, i.e., varying the pulse energy across successive laser scans. The effects of ablation were studied in terms of roughness, developed interfacial area ratio, skewness and ablation efficiency of the processed surfaces. Significantly, the investigation has shown a global trend for all samples that the roughness is minimum when a decreasing energy pulse sequence is employed, i.e., the irradiation sequence ends up with the applied laser fluences close to threshold laser fluences and is maximum with increasing energy distribution. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis on single craters with the three different energy deposition conditions revealed a chaotic and random material redistribution in the cases of uniform and increasing energy distributions and the presence of regular laser-induced periodic surface structures (LIPSS) at the bottom of the ablation region in the case of decreasing energy distribution. It is also shown that the ablation efficiency of the ablated surfaces does not significantly change between the three cases. Therefore, this novel energy control strategy permits the control of the roughness of the processed surfaces without losing the ablation efficiency.

Femtosecond lasers emit short pulses whose temporal width is in the range of less than a picosecond to a few femtoseconds (fs), thereby enabling extremely high peak-power machining with minimum thermal damages. Herein we employed femtosecond laser pulses as a versatile tool for surface processing of textiles made of 2 polymers commonly used in textile industry, Polyethylene terephthalate (PET), and Polyamide66 (PA66). This work focuses on a comparison of ultraviolet (UV, 257 nm) and infrared (IR, 800 and 1030 nm) femtosecond laser irradiation at the surface of the polymers PET and PA66, possible hybridization with chemical grafting, as well as the resulting liquid repellency from different process scenarios. The study highlights the different responses of the polymers to the laser irradiations and possible routines for surface functionalization of the textiles.

A highly efficient drilling process is found in non-transparent metallic materials enabled by the use of non-diffractive ultrafast Bessel beams. Applied for deep drilling through a 200 μm-thick steel plate, the Bessel beam demonstrates twofold higher drilling efficiency compared to a Gaussian beam of similar fluence and spot size. Notwithstanding that surface ablation occurs with the same efficiency for both beams, the drilling booster results from a self-replication and reconstruction of the beam along the axis, driven by internal reflections within the crater at quasi-grazing incidence, bypassing potential obstacles. The mechanism is the consequence of an oblique wavevectors geometry with low angular dispersion and generates a propagation length beyond the projection range allowed by the geometry of the channel. With only the main lobe being selected by the channel entrance, side-wall reflection determines the refolding of the lobe on the axis, enhancing and replicating the beam multiple times inside the channel. The process is critically assisted by the reduction of particle shielding enabled by the intrinsic self-healing of the Bessel beam. Thus the drilling process is sustained in a way which is uniquely different from that of the conventional Gaussian beam, the latter being damped within its Rayleigh range. These mechanisms are supported and quantified by Finite Difference Time Domain calculations of the beam propagation. The results show key advantages for the quest towards efficient laser drilling and fabrication processes.

Ultrafast laser processing considerably gains in efficiency when using liquid crystal based spatial light modulators (LCSLM) to tailor the laser beam shape for upgradedsurface or bulk structuring.The fidelity of the experimental beam shape when compared to the target intensity distribution is of great importance for precise and controlled machining. Due to the physical characteristics of LCSLM, their non-perfect optical response has to be taken into account when designing phase masks. In this contribution, we'll discuss phase mask optimization for LCSLM for several beam shapes and present some applications in surface, bulk processing as well as in ophthalmology.

The use of ultrafast laser pulses for eye anterior segment surgery has seen a tremendous growth of interest as the technique has revolutionized the field, from the treatment of myopia, hyperopia, and presbyopia in the cornea to laser-assisted cataract surgery of the crystalline lens. For the latter, a comprehensive understanding of the laser–tissue interaction has yet to be achieved, mainly because of the challenge of observing the interaction zone in situ with sufficient spatial and temporal resolution in the complex and multi-layered tissue of the crystalline lens. We report here on the dedicated characterization results of the laser–tissue interaction zone in the ex vivo porcine lens using three different methods: in situ and real-time microscopy, wide-field optical imaging, and phase-contrast microscopy of the histological cross sections. These complementary approaches together revealed new physical and biological consequences of laser irradiation: a low-energy interaction regime (pulse energy below ~1 µJ) with very limited cavitation effects and a stronger photo-disruption regime (pulse energy above 1 µJ) with a long cavitation duration from seconds to minutes, resulting in elongated spots. These advances in the understanding of the ultrafast laser’s interactions with the lens are of the utmost importance for the preparation of the next-generation treatments that will be applied to the lens.

Spatial beam shaping is becoming an essential technique for optimized surface and bulk laser processing with ultrafast laser pulses. In this contribution, we discuss the interest of non-diffractive intensity distributions for transparent material processing but also for surface drilling where specific physical removal mechanisms are in play. Parallel irradiation with arrays of focused spots is also evoked especially in the context of ophthalmology where the drastic speed increase of the laser treatment have led to a change of paradigm of the most widespread surgery worldwide, the cataract surgery.

When an ultrafast laser pulse is focused in water, non linear absorption mechanisms such as multiphotonic and avalanche ionizations may take place leading to the formation of a local transient electronic plasma. The subsequent energy relaxation eventually generates a localized cavitation bubble whose properties are directly linked to the coupled photonic energy [1] . This process of the so-called Laser induced-optical breakdown (LIOB) using femtosecond laser has gained interest due to many applications particularly in the biomedical fields [2] . LIOB depends on different parameters of the laser radiation, such as the pulse duration, laser polarization and pulse energy. There is a great interest in precisely tuning the laser energy with respect to the LIOB threshold, especially for ophtalmic surgeries assisted by femtosecond laser pulses, such as the LASIK (laser-assisted in situ keratomileusis), FLACS (femtosecond laser assisted cataract surgery) and more recently the FemtoMatrix [3] procedure that proposes a new paradigm for the cataract surgery, acheiving a full lens photoemulsification® with no phacoemulsifier.