Femtosecond Laser Research Articles

Selective amplification effect on the diffraction efficiency of a phase grating generated by femtosecond laser pulses

Selective amplification effect on the diffraction efficiency of a phase grating generated by femtosecond laser pulses

Single-Cell Synchro-Subtractive-Additive Nanoscale Surgery with Femtosecond Lasers.

Herein, an in situ "synchro-subtractive-additive" technique of femtosecond laser single-cell surgery (FLSS) is presented to address the inadequacies of existing surgical methods for single-cell manipulation. This process is enabled by synchronized nanoscale three-dimensional (3D) subtractive and additive manufacturing with ultrahigh precision on various parts of the cells, in that the precise removal and modification of a single-cell structure are realized by nonthermal ablation, with synchronously ultrafast solidification of the specially designed hydrogel by two photopolymerizations. FLSS is a minimally invasive technique with a post-operative survival rate of 70% and stable proliferation. It opens avenues for bottom-up synthetic biology, offering new methods for artificially synthesizing organelle-like 3D structures and modifying the physiological activities of cells.

60 Years of Betaine 30─From Solvatochromic Discovery to Future Frontiers.

Betaine-30 (B30) was reported by Karl Dimroth and Christian Reichardt et al. in 1963 as a solvatochromic probe that can be easily synthesized, shows good solubility, and remains stable in various organic solvents and solutions. Its strongly negatively solvatochromic behavior arises from differential solvation between its electronic ground and excited states, making it a valuable tool for assessing solvent polarity using the ET(30) polarity scale, also devised by Dimroth and Reichardt. In addition, advancements in femtosecond laser spectroscopy in the 1990s greatly improved the understanding of B30's relaxation dynamics following photoexcitation. In solvents capable of hydrogen bonding, such as alcohols, intermolecular hydrogen-bond rearrangement contributes to the multiple relaxation components observed. Since the 1990s, the applications of B30 have expanded beyond simple organic solvents to include complex solvent mixtures, such as electrolyte solutions for battery technologies and eutectic solvent mixtures. Given the growing importance of these complex solvent mixtures, B30 is becoming an increasingly valuable tool for studying previously unexplored solvation properties.

Femtosecond laser direct writing wedge metallic microcavities for terahertz sensing

Metallic resonators allow the manipulation of electromagnetic fields in subwavelength volumes for strong light-matter interaction, underpinning emerging flat-optics devices. Metamaterials designed with optimized effective mode volume (Veff) for stimulating and maximizing the utilization of high-density photons are highly desirable for sensing applications. Here, we demonstrate a bowtie-type terahertz (THz) metallic aperture metamaterial structure with low Veff for enhanced biosensing. The device leverages the inherent characteristic of the femtosecond laser fabrication process enabling wedge cavities down to 3 µm by tailoring the pulse energy, whose sensing performance is superior to trapezoidal ones. Such a substrate-free, microcavity metallic metamaterial sensor with extremely strong interactions achieves an experimentally normalized sensitivity of 0.654 RIU−1, and demonstrates the detection of L-proline down to 0.87 nmol. These findings provide new insights into the design and optimization of efficient THz metamaterials with tightly confined fields for ultrasensitive biomolecular detection.

Bioinspired, anti-fogging and de-icing transparent surfaces with flexible property

In cold environments, natural phenomena like icing, frost, and fog can significantly impede the functionality of optical windows. Consequently, there is a growing demand for optical windows that demonstrate anti-fogging and de-icing characteristics while maintaining flexibility and transparency with high optical clarity. The development of cost-effective and straightforward anti-fogging and de-icing elements encounters various challenges. The remarkable visual acuity of polar bear eyes in challenging weather conditions can be attributed to a tear film that covers the cornea and the thermoregulatory characteristics of their eyeballs. Inspired by the anti-fogging and anti-icing properties of polar bear eyes, a new flexible, transparent surface with heating capabilities has been developed. To address the limitations of conventional slippery surfaces that solely offer anti-fouling properties, a flexible internal heating unit is integrated into the slippery surface through a layered nesting technique to emulate the homothermal features of polar bear eyeballs. The slippery property of the PDMS surface can be attributed to a gel layer containing an auto-secretory lubricant. To preserve its optical properties, a new processing method that combines liquid metal microfluidics and femtosecond laser processing is employed. This technique can create narrow channels with a high length-to-diameter ratio, thereby reducing the impact on the transmission rate. The sample demonstrates self-cleaning, resistance to dust and pollution, and efficient electrical heating properties. Testing on fogging and freezing validates the practicality and effectiveness of these substances for applications in anti-fogging and de-icing.

Short-length nanosecond pulsed 1.653-μm DBR fiber Raman laser oscillator fabricated by femtosecond laser direct-writing

We demonstrate a nanosecond pulsed 1.653-μm fiber Raman laser (FRL) oscillator in a short-length distributed Bragg reflector (DBR) cavity made by femtosecond laser direct-writing technique. The DBR FRL cavity is composed of commercial ultrahigh NA germanium-doped silica fiber with a short length of 10 m and a pair of fiber Bragg gratings (FBGs). The FBGs were directly inscribed on the ends of the Raman gain fiber, using femtosecond-laser point-by-point (PbP) writing method. A home-made 1.55-μm nanosecond fiber laser source was used as the pump of the FRL. 1.653-μm nanosecond pulsed laser oscillation with maximum average output power of 125 mW (corresponding to peak power of 6.6 W), 3 dB linewidth of ≤ 0.15 nm, and slope efficiency of 48 % was obtained under 1.55-μm pump with optimized repetition rate of 10 MHz. The optical signal-to-noise-ratio (OSNR) of the 1.653-μm narrow-linewidth Raman lasing is above 70 dB. The short-length DBR FRL output exhibits decently high degree of polarization (DOP) and high degree of linear polarization (DOLP) above 80 % in 3-hour period, benefitted from the birefringent FBGs made by femtosecond laser direct-writing method. It is expected that by further reducing the cavity length to < 1 m, the 1.653-μm DBR FRL oscillator made by femtosecond laser direct-writing method is promising as single-frequency narrow-linewidth, highly linearly polarized, high-OSNR laser sources for high-sensitivity CH4 gas detection.

Bowman Layer Transplantation With Stromal Inclusion Using Femtosecond Laser: 3-year Results.

The aim of this study was to evaluate the 3-year clinical results of Bowman layer with stromal inclusion (Bowman layer) transplantation using femtosecond laser for patients with advanced keratoconus. This single-center retrospective study included 7 eyes of 7 patients diagnosed with progressive keratoconus who underwent Bowman layer transplantation with stromal inclusion between 2018 and 2020. Follow-up was carried out from the date of surgery until 36 months later. Bowman layer grafts were positioned into a mid-stromal pocket performed by a femtosecond laser and patients were evaluated up to 3 years after surgery. Corneal flattening of 5.49 D (P = 0.0020) in Kmax was observed, increased in corneal pachymetry, and an improvement best-corrected visual acuity measured in logarithm of minimum angle of resolution (LogMAR) from 0.89 to 0.60 and tolerance to contact lens from 42% of the patients to 100% of them. Stabilization of the cornea was achieved in 100% with no further progression of the keratoconus; all surgical procedures were uneventful, and no complications were observed during the 3 years of follow-up. Bowman layer transplantation with stromal inclusion flattened the cornea improving best-corrected visual acuity and contact lens tolerance and stabilized keratoconus in 100% of the patients during 3 years of follow-up and may be a feasible option in patients with advanced and progressive KC to delay or avoid the need for PK or DALK.

Advanced manufacturing of high conductive graphene coatings on polyethylene terephthalate substrate through laser-induced processes and thermal optimization

Graphene holds immense promise for applications in sensors due to its exceptional properties such as large carrier mobility and high electrical and thermal conductivities. Nevertheless, the manufacture of high conductive graphene films onto flexible substrates remains a formidable challenge. This paper presented a novel method for the precise incorporation of high conductive graphene coatings onto polyethylene terephthalate (PET) through the back transfer of laser-reduced graphene oxide (LRGO) from Al2O3 ceramic to PET. A record-low sheet resistance for LRGO so far, approximately 12 Ω/sq. was achieved, meantime exhibiting 5B level adhesion performance with PET substrate. The sheet resistance of the transferred LRGO was measured and demonstrated to be adjustable by manipulating laser power, scanning speed, and hatch distance. The analysis of reduction of graphene oxide (GO) involved a comprehensive examination of alterations in topography image, chemical bond content, C/O atomic ratio, and ID/IG intensity ratio. These observations provided insights into the factors contributing to the decrease of sheet resistance within LRGO. The adoption of a continuous gigahertz (GHz) femtosecond laser as the light source, coupled with the incorporation of thermally conductive Al2O3 plate as a heat sink, facilitated the manufacturing processes including reduction and transfer of GO. The manufacture of graphene coatings with high electrical conductivity on PET in a versatile and cost-effective manner, presents significant potential for diverse applications, particularly in conductive-coatings-based sensors.

Full‐Color and High‐Resolution Femtosecond Laser Patterning of Perovskite Quantum Dots in Polyacrylonitrile Matrix

AbstractLaser patterning of perovskite quantum dots (PQDs) in polymer matrix enables in situ synthesis, easy integration, and much improved long‐term stability, holding great promises for varieties of photonics, and optoelectronics applications. Although multi‐color PQD patterns have been demonstrated through tuning the halide stoichiometry, it remains significantly challenging to achieve full‐color patterns due to the slow and spontaneous crystallization of the chlorinated perovskite precursor at room temperature. Herein, polyacrylonitrile (PAN) is introduced to serve as the matrix material, the excess cyano groups of which would coordinate with dissociative cesium and lead cations in the precursor film, leading to the suppression of the unprompted crystallization process. Taking advantage of the nonthermal and contactless ultrafast femtosecond laser, full‐color PQDs are in situ fabricated by tuning the halide stoichiometry in the PAN matrix, with the emission wavelength in the range of 425–685 nm, spanning from deep blue to deep red color, and a sub‐diffraction feature size of ≈400 nm. The approach allows ultrafine and programmable fabrication of full‐color PQD arrays and arbitrary patterns with high resolution and stability. This facile, efficient, and reliable technique believed to offer a novel pathway for precise manufacturing of various photonic or optoelectronic devices based on patterned PQDs.

Dynamics of non–identical coupled Chialvo neuron maps

We study numerically the dynamics of low–dimensional ensembles of discrete neuron models - Chialvo maps. We are focused on choosing the autonomous map parameters corresponding to the invariant curve. We consider two cases of coupling organization: (i) via a nonlinear function of models; (ii) linear coupling, which is an analog of electrical neuron interaction. For the first case, the possibility of invariant curve doublings and the emergence of quasi-periodicity within Arnold tongues as a result of the secondary Neimark-Sacker bifurcation are found. For the second case, we discover an area of three-frequency quasi-periodicity for the case of two neurons. It arises softly as a result of quasi-periodic Hopf bifurcation. We demonstrate a set of resonant two-frequency regimes tongues embedded in this area and bounded by lines of saddle-node bifurcations of invariant curves. For ensemble of three linearly coupled maps, four-frequency quasi-periodicity becomes possible with a built-in system of tongues of three-frequency regimes (tori). We discuss the effect of noise and the evolution of “noise quasi-periodic” regimes, resonant regimes of this type and bifurcations of invariant tori with increasing of noise intensity.

Metal Material Processing Using Femtosecond Lasers: Theories, Principles, and Applications

Metal material processing using femtosecond lasers is a useful technique, and it has been widely employed in many applications including laser microfabrication, laser surgery, and micromachining. The basic mechanisms of metal processing using femtosecond lasers are reviewed in this paper and the characteristics and theory of laser processing are considered. In addition to well-known processes, the recent progress relating to metals processing with femtosecond lasers, including metal material drilling, metal ablation thresholds, micro/nano-surface modification, printed circuit board (PCB) micromachining, and liquid metal (LM) processing using femtosecond lasers, is described in detail. Meanwhile, the application of femtosecond laser technology in different fields is also briefly discussed. This review concludes by highlighting the current challenges and presenting a forward-looking perspective on the future of the metal laser processing field.

Metal Material Processing Using Femtosecond Lasers: Theories, Principles, and Applications

Metal material processing using femtosecond lasers is a useful technique, and it has been widely employed in many applications including laser microfabrication, laser surgery, and micromachining. The basic mechanisms of metal processing using femtosecond lasers are reviewed in this paper and the characteristics and theory of laser processing are considered. In addition to well-known processes, the recent progress relating to metals processing with femtosecond lasers, including metal material drilling, metal ablation thresholds, micro/nano-surface modification, printed circuit board (PCB) micromachining, and liquid metal (LM) processing using femtosecond lasers, is described in detail. Meanwhile, the application of femtosecond laser technology in different fields is also briefly discussed. This review concludes by highlighting the current challenges and presenting a forward-looking perspective on the future of the metal laser processing field.

Color Generation and Polarization-Sensitive Encryption by Laser Writing on Plasmonic Reflector Arrays.

Plasmonic color printing presents a sustainable solution for vibrant and durable color reproduction by leveraging the light-manipulating properties of nanostructures. However, the fabrication of plasmonic nanostructures has posed challenges, hindering widespread adoption. In this paper, we introduce plasmonic reflector arrays (PRAs) composed of three layers─Ag nanoparticles (NPs), an Al2O3 spacer, and an Ag reflector─deposited via physical vapor deposition (PVD). By employing nanosecond and femtosecond laser writing techniques, we manipulate the surface morphology of silver nanoparticles on PRAs, resulting in a diverse range of structural colors that are both polarization-insensitive and polarization-sensitive. Furthermore, we demonstrate the versatility of nanosecond laser writing in creating intricate patterns on PRAs. Additionally, we propose a novel two-step method combining nanosecond and femtosecond laser processing to embed QR code patterns into PRAs, showcasing their potential for secure data encryption and transmission. This research underscores the promising applications of PRAs in advanced color printing and secure optical data encoding.

Color Generation and Polarization-Sensitive Encryption by Laser Writing on Plasmonic Reflector Arrays.

Plasmonic color printing presents a sustainable solution for vibrant and durable color reproduction by leveraging the light-manipulating properties of nanostructures. However, the fabrication of plasmonic nanostructures has posed challenges, hindering widespread adoption. In this paper, we introduce plasmonic reflector arrays (PRAs) composed of three layers─Ag nanoparticles (NPs), an Al2O3 spacer, and an Ag reflector─deposited via physical vapor deposition (PVD). By employing nanosecond and femtosecond laser writing techniques, we manipulate the surface morphology of silver nanoparticles on PRAs, resulting in a diverse range of structural colors that are both polarization-insensitive and polarization-sensitive. Furthermore, we demonstrate the versatility of nanosecond laser writing in creating intricate patterns on PRAs. Additionally, we propose a novel two-step method combining nanosecond and femtosecond laser processing to embed QR code patterns into PRAs, showcasing their potential for secure data encryption and transmission. This research underscores the promising applications of PRAs in advanced color printing and secure optical data encoding.

Mid-infrared supercontinuum generation in As2S3-circular photonic crystal fibers pumped by 4.5 μm and 6 μm femtosecond lasers

Mid-infrared supercontinuum generation in As2S3-circular photonic crystal fibers pumped by 4.5 μm and 6 μm femtosecond lasers

Mid-infrared supercontinuum generation in As2S3-circular photonic crystal fibers pumped by 4.5 μm and 6 μm femtosecond lasers

Mid-infrared supercontinuum generation in As2S3-circular photonic crystal fibers pumped by 4.5 μm and 6 μm femtosecond lasers

Pulse repetition-rate effect on the critical power for self-focusing of femtosecond laser in air

Pulse repetition-rate effect on the critical power for self-focusing of femtosecond laser in air

Femtosecond laser direct writing annular small-period long-period fiber gratings for simultaneous refractive index and temperature sensing

Femtosecond laser direct writing annular small-period long-period fiber gratings for simultaneous refractive index and temperature sensing

Femtosecond laser direct writing annular small-period long-period fiber gratings for simultaneous refractive index and temperature sensing

Femtosecond laser direct writing annular small-period long-period fiber gratings for simultaneous refractive index and temperature sensing

Separation of the topographical and chemical components of the wettability of textured surfaces by femtosecond laser

Contrary to what is usually found in the literature, we show in this work that the contribution of ripples (LSFL LIPSS) to the increase in hydrophobicity of femtosecond laser-textured metal surfaces is negligible. Following the demonstration of wettability according to the Wenzel regime, a methodology for decorrelating the chemical and the topographical components of wettability is implemented. This makes it possible to quantify the respective responsibilities of the chemical and topographical contributions to the increase in contact angle. For femtosecond laser-textured 304L steel, it is shown that the topographical contribution made by ripples is around 6% of the increase in hydrophobicity. In contrast, the chemical contribution accounts for 94% of the increase in contact angle after texturing. The chemistry/topography decorrelation approach is validated by comparing wettability results on PDMS as test-materials.