Shaped Femtosecond Laser Research Articles

High-Efficiency Targeted Gene Transfection of Cells Using Temporal and Spatial Shaping Femtosecond Laser Irradiation.

Laser-irradiation-assisted cell gene transfection is sterile and nontoxic, but the low transfection efficiency cannot meet the application requirements. To improve the efficiency, a temporal and spatial shaping method of a femtosecond laser is proposed. Using the time shaping method, we can segment the pulse into subpulses of varying energies and with a defined delay, thereby influencing the interaction between electrons and photons, ultimately enhancing transfection efficiency. The transfection efficiency is further improved by spatially shaping the laser pulse to extend the focusing beam's working distance and reduce the cell's sensitivity to the focal position. Through the characterization of the viability and transfection efficiency of HEK-293T cells, the method achieved efficient and active transfection, with a maximum transfection efficiency of 45.1% and a cell survival rate of 93.6%. This method provides key technical support for femtosecond laser transfection and promotes its further application in clinical practice.

Rapid surface patterning to strengthen adhesive bonding of carbon fiber reinforced polymer by spatial shaping femtosecond laser

Carbon fiber reinforced polymer (CFRP) have become gradually important in the aerospace industry due to their outstanding strength-to-weight ratio. However, traditional mechanical surface treatment methods are challenging to apply to CFRP because of their anisotropic and nonhomogeneous properties. Femtosecond laser offers unique advantages for surface treatment, as it allows processing with very low thermal load due to the extremely short interaction time. This study investigates the effect of different surface structures resulting from surface treatment using a femtosecond laser on adhesive properties of CFRP. The experimental results show that: 1) beam shaping can be realized by using the plano-convex cylindrical mirror, which improves the quality of laser processing and greatly improves processing efficiency. It only takes 20 s to complete the laser processing of a 1 cm*1 cm area, which increases the work efficiency by 49 times. 2) pre-bonding surface treatment significantly enhances the tensile shear strength of the single lap joint, and the shear strength of samples with low spatial frequency LIPSS (LSFL) (14.57 ± 1.58 MPa) is 2.96 times higher than that of the untreated sample (US) (4.92 ± 1.34 MPa). 3) LSFL structure exhibits the best results, because the surface of CFRP with LSFL exhibits a relatively higher surface polarity and surface energy. This study provides an efficient, high-precision, and low-damage surface treatment method for preparing CFRP for adhesive bonding, which may promote the application of femtosecond laser technology in difficult-to-process composite materials and provide new methods and technical support for its application in aerospace, vehicle manufacturing, and other fields.

Facile fabrication of THz metasurfaces by a spatially shaped femtosecond laser printing system

Terahertz (THz) metasurfaces provide unprecedented abilities to realize versatile THz wavefronts manipulations. Nevertheless, these high degree of freedom, non-periodic, densely arranged subwavelength unit cells pose numerous extreme parameter requirements for the fabrication of metasurfaces, presenting significant challenges to their practical application. Herein, a spatial shaping femtosecond laser printing system, based on spatial light modulation (SLM), is proposed for the creation of THz metasurfaces. Through programming the SLM with a sequence of computer-generated holograms (CGH) corresponding to C-shaped Bessel beams with varying opening angles and orientation angles, the C-shaped slit resonant rings with different geometric parameters—fundamental units of the metasurface—were precisely printed onto a gold film. To validate this technique, a THz metalens based on a phased gradient design and a THz holographic plate employing simultaneous phase and amplitude modulation were meticulously fabricated, displaying outstanding performance. Owing to the simple processing flow, high reproducibility, and wide applicability of materials, this technique stands out as a versatile and efficient approach for fabricating THz metasurfaces, with the potential to promote the commercialization of terahertz metasurfaces.

Wide-Size Range and High Robustness Self-Assembly Micropillars for Capturing Microspheres.

Capillary force driven self-assembly micropillars (CFSA-MP) holds immense promise for the manipulation and capture of cells/tiny objects, which has great demands of wide size range and high robustness. Here, we propose a novel method to fabricate size-adjustable and highly robust CFSA-MP that can achieve wide size range and high stability to capture microspheres. First, we fabricate a microholes template with an adjustable aspect ratio using the spatial-temporal shaping femtosecond laser double-pulse Bessel beam-assisted chemical etching technique, and then the micropillars with adjustable aspect ratio are demolded by polydimethylsiloxane (PDMS). We fully demonstrated the advantages of the Bessel optical field by using the spatial-temporal shaping femtosecond laser double-pulse Bessel beams to broaden the height range of the micropillars, which in turn expands the size range of the captured microspheres, and finally achieving a wide range of capturing microspheres with a diameter of 5-410 μm. Based on the inverted mold technology, the PDMS micropillars have ultrahigh mechanical robustness, which greatly improves the durability. CFSA-MP has the ability to capture tiny objects with wide range and high stability, which indicates great potential applications in the fields of chemistry, biomedicine, and microfluidics.

Rapid fabrication of antireflective structures on ZnS surface by spatial shaping femtosecond laser

Antireflection performance and fabrication efficiency are key factors that affect the practical application of antireflective structures. Nowadays, how to combine good antireflection performance with highly efficient processing is still a difficult problem. In this work, a novel and scalable method of fabrication of antireflective LIPSS (laser induced periodic surface structure) on ZnS surface by spatial shaping femtosecond laser is proposed. A Gaussian beam is converted to a line beam by a cylindrical lens transformation. The focal long axis of line beam is on the scale of centimeters, and the minor axis is on the scale of micrometers. Hence, the fabrication efficiency can be significantly improved by adjusting the scanning direction perpendicular to the major axis. Notably, the proposed highly efficient method only takes 21 s to complete the fabrication of 1 × 1 cm2 antireflective ZnS surface with excellent antireflective property. At the laser power of 500 mW, scan speed of 1.0 mm/s, scan interval of 0.55 cm, the transmittance of fabricated antireflective structures maintains 78–87.5% at 2.5–10 μm, with the average transmittance of 81.3%, 5.9% higher than that of untreated ZnS. This proposed method may open a revolutionary concept for the rapid antireflective surface laser processing, which has a great application potential in energy, military, aerospace and other fields.

Controllable Photoreduction of Graphene Oxide/Gold Composite Using a Shaped Femtosecond Laser for Multifunctional Sensors.

The mixture of graphene oxide and noble metal nanoparticles has been widely used in flexible multifunctional sensors. Femtosecond lasers are regarded as useful tools for sensor fabrication through direct inscribing. Normally, the laser power is adjusted to optimize the sensing performances. However, the process between the laser and the sample can be effectively altered by the temporal distribution of the pulse and the laser wavelength. This paper proposes a controllable photoreduction of graphene oxide/gold composite method using a shaped femtosecond laser and promotes its application on multifunctional sensors. Different from the strong reliance of the photoreduction process on laser fluence, femtosecond laser shaping expands the controllability range of the photoreduction degree. By combining the parameters of fluence, temporal distribution, laser wavelength, humidity, and strain multifunctional sensors can be both optimized by controlling the laser reduction. The strain sensor exhibits good linearity with a gauge factor of 67.2 in a strain range of 28.2%; the sensitivity of the humidity sensor is improved by 68.4%. The humidity sensor maintains its performance after 28 days, and the strain sensor maintains its stability after 5000 cycles of stretching. The multifunctional sensor can be applied to detect human breath and human pulse and holds value for human health monitoring.

Theoretical Study on the Ultrafast Selective Excitation of Surface-Enhanced Coherent Anti-Stokes Raman Scattering Based on Fano Resonance of Disk-Ring Nanostructures by Shaped Femtosecond Laser Pulses

The enhancement and selective excitation of coherent anti-Stokes Raman scattering (CARS) and the suppression of background noise are very important problems for real-time detection at the single-molecule level. Optimizing the plasmonic substrate to ensure that all the hot spots of the pump, probe, Stokes, and anti-Stokes light are at the same position is the key to increasing the CARS signal to reach the level of single-molecule detection. The selective excitation of the target CARS peak and the suppression of the other peaks are the key to improving the signal-to-noise ratio. In this paper, we present a theoretical study to control the selective excitation and enhancement of any one of the three CARS peaks using the Fano resonance of a disk-ring structure. By optimizing the modulation of the pump, Stokes, and probe pulse, one CARS peak is maximized, while the other two are suppressed to zero. Fano resonance is applied to simultaneously enhance the four surface plasmon modes of the pump, probe, Stokes, and anti-Stokes light and to ensure that all the hot spots are located at the same position by adjusting the size of the disk-ring structure. The hot spots of the four pulses are concentrated in the disk-ring gap with a deviation distance of less than 2 nm, and the intensity of the CARS is enhanced by 1.43 × 1012 times, which is much higher than the requirement of single-molecule detection. The time, frequency, and phase distribution of the input and the response of the four pulses are studied in detail. It was found that the selective excitation and the spectra of CARS are both well preserved.

A Novel Strategy Achieving GaN Ultra-Smooth Surface via a Square, Flat Top Beam Shaped Femtosecond Laser Processing Combined with Chemical Mechanical Polishing

We propose a strategy for GaN ultra-smooth manufacture by combing of femtosecond laser processing and chemical mechanical polishing. The optimized flat top beam is used to redistribute the laser fluence from Gaussian distribution to square, flat top profile. Surface with high flatness is achieved after femtosecond laser processing through optimization of the technical parameters. The optimum process to control the damages on surface and subsurface reduces negative influence of femtosecond laser processing on chemical mechanical polishing. Roughness (Ra) of processed surface is decreased to less than 0.1 nm when it is be polished for 6 h. In the background of traditional GaN polishing efficiency facing bottleneck, the characteristic of present study is to use a square, flat top beam shaped femtosecond laser to induce surface of GaN. Structures and composition on induced surface are simultaneous removed in chemical mechanical polishing process. It reduces the burden of GaN chemical mechanical polishing. The present method has advantage of high efficiency and easy realization, which has a wide application in GaN ultra-smooth processing.

Superhydrophilic-Superhydrophobic Multifunctional Janus Foam Fabrication Using a Spatially Shaped Femtosecond Laser for Fog Collection and Detection.

Fog collection is an effective method for addressing water shortages in arid areas. By constructing a Janus structure with asymmetric wettability on its two sides, flexible and efficient fog capture can be achieved. However, in situ detection and fog collection on a Janus surface are still challenging tasks. Herein, a novel method for producing a superhydrophilic-superhydrophobic Janus fog collector is proposed; the method utilizes a combined process in which a spatially shaped femtosecond laser treatment (superhydrophilic) is applied to one side of a copper foam and a chemical replacement reaction (superhydrophobic) is applied to the other side of the copper foam. Two configurations of the Janus structure were designed to study different water transport behaviors. Furthermore, the Au micro-nanoparticle prepared adhered to the Janus structure, indicating the effectiveness of surface-enhanced Raman spectroscopy detection. The Janus foam shows excellent sensitivity and stability on testing the fog mixed with rhodamine 6G. This surface allows for the simultaneous collection and detection of fog, which can provide insights into the preparation of Janus multifunction structures and how such structures can play a key role in the subsequent purification and usage of water resources.

Machining of Micro-Optical Elements Using Electrons Dynamics Controlled Temporally/Spatially Shaped Femtosecond Laser

Machining of Micro-Optical Elements Using Electrons Dynamics Controlled Temporally/Spatially Shaped Femtosecond Laser

Efficiency Enhancement by Transient Electron Dynamic Control in Shaped Femtosecond Laser Fabrication of Metals

Efficiency Enhancement by Transient Electron Dynamic Control in Shaped Femtosecond Laser Fabrication of Metals

Spectral Hump Formation in Visible Region of Supercontinuum from Shaped Femtosecond Laser Filamentation in Fused Silica

We investigate experimentally the local intensity control in the visible region of the supercontinuum (SC) generated from femtosecond laser filamentation in fused silica by using pulse shaping technology. Based on the genetic algorithm, we show that a distinct spectral hump at any preset wavelength can be formed in the blue-side extension. The local intensity control in the SC could improve the abilities of the SC applications.

Three-Dimensional Maskless Fabrication of Bionic Unidirectional Liquid Spreading Surfaces Using a Phase Spatially Shaped Femtosecond Laser.

Ubiquitous biological processes exhibit the ability to achieve spontaneous directionally guided droplet transport. Maskless three-dimensional (3D) fabrication of various miniature bionic structures, a method applicable to various materials, is subject to processing method limitations. This remains a large obstacle to realizing self-driven, continuous, and controllable unidirectional liquid spreading. Thus, we present a flexible maskless 3D method for fabricating bionic unidirectional liquid spreading surfaces by using a phase spatially shaped femtosecond laser. The laser can be transformed from having Gaussian distributions to having 3D bionic structure field distributions. Furthermore, we fabricated Syntrichia caninervis bionic structures with a spiculate end for unidirectional water spreading; 1 μL droplets had a 16 mm flow length on Si surfaces when the S. caninervis single structure was 34 (length), 8 (width), and 12 μm (height). Furthermore, various bionic structures-Nepenthes, cactus, and moth structures-were fabricated on Si, SiO2, and Ti. We also demonstrated the measurability of two-dimensional (S-shaped) curved flows on Si wafers as well as 3D curved flows on a Ti pipe turning 120° within 2320 ms. Our method can realize high-efficiency maskless 3D processing of various materials and structures (especially asymmetric structures); it is both flexible and fast, effectively expanding the processing capacity of micro-/nanostructures on patterned surfaces. This is of great significance to various domains such as microfluids, fog collection, and chemical reaction control.

Multifunctional 3D Micro-Nanostructures Fabricated through Temporally Shaped Femtosecond Laser Processing for Preventing Thrombosis and Bacterial Infection.

Blood-contacting medical devices that directly inhibit thrombosis and bacterial infection without using dangerous anticoagulant and antibacterial drugs can save countless lives but have proved extremely challenging. Here, a useful methodology is proposed that employs temporally shaped femtosecond laser ablation combined with fluorination to fabricate multifunctional three-dimensional (3D) micro-nanostructures with excellent hemocompatibility, zero cytotoxicity, outstanding biocompatibility, bacterial infection prevention, and long-term effectiveness on NiTi alloys. These multifunctional 3D micro-nanostructures present 0.1% hemolysis ratio and almost no platelet adhesion and activation, repel blood to inhibit blood coagulation in vitro, maintain 100% cell viability, and have exceptional stability over 6 months. Moreover, the multifunctional 3D micro-nanostructures simultaneously suppress bacterial colonization to form biofilm and kill 100% colonized Pseudomonas aeruginosa (P.aeruginosa) and 95.6% colonized Staphylococcus aureus (S.aureus) after 24 h of incubation, and bacterial residues can be easily removed. The fabrication method in this work has the advantages of simple processing, high efficiency, high quality, and high repeatability, and the new multifunctional 3D micro-nanostructures can effectively prevent thrombosis and bacterial infection, which can be widely applied to various clinical needs such as biomedical devices and implants.

Ultrafast selective excitation of surface-enhanced Raman scattering from a single molecule by shaping pump and Stokes pulses

Surface-enhanced Raman scattering (SERS) has attracted much attention as an important technique for studying and monitoring the behavior of molecules. Coherent control by shaping femtosecond pulses is an efficient method for controlling molecular vibration state, rotation state, ionization state, and other molecule dynamics. In this paper, we propose a theoretical scheme of selective excitation of SERS from a single porphycene molecule with two Raman peaks at 327[Formula: see text]cm[Formula: see text] and 367[Formula: see text]cm[Formula: see text] placed in the gap between silver dimer nanospheres. Based on the theory of quantum coherent control, selective excitation of the peak at 327[Formula: see text]cm[Formula: see text] and depression of another at 367[Formula: see text]cm[Formula: see text] are demonstrated by properly shaping femtosecond laser pulses with central frequency of 12500[Formula: see text]cm[Formula: see text] and a full width at half maximum (FWHM) of 300[Formula: see text]cm[Formula: see text]. Ultrafast dynamics of the response of dimer nanospheres to the shaped pump and Stokes pulses are simulated by finite difference time domain (FDTD) method followed by Fourier transform. The enhanced and selected single molecule SERS is realized simultaneously. The SERS probability is enhanced by more than six orders in magnitude compared with the case in air environment, and the FWHMs of the enhanced and the depressed Raman peaks are both larger than 17[Formula: see text]cm[Formula: see text] despite the narrow gap of only 40[Formula: see text]cm[Formula: see text] between the two Raman peaks.

Femtosecond Laser Double Pulses Nanofabrication on Silicon

The temporal shaping femtosecond (fs) laser is realized by dividing a fs laser pulse into two identical sub-pulses. The double-pulse fs laser can be used to effectively control the initial free electron state such as electron temperature, capacity and density, etc. to improve the surface morphology quality. In this experiment, silicon was fabricated using the double-pulse fs laser. It was found that the average diameter of ablated micro-or nanoholes decreases with the increasing pulse delay (up to 1.5 ps) under the same laser fluence and the phenomenon was explained quantitatively by the plasma model. Furthermore, nanoholes were achieved using the double-pulse fs laser, which cannot be obtained by single pulse laser, and the processing size can be reduced to below 200 nm.

基于整形飞秒激光脉冲的三维微纳制备

基于整形飞秒激光脉冲的三维微纳制备

Selective Excitation on Tip-Enhanced Raman Spectroscopy by Pulse Shaping Femtosecond Laser

In this paper, we propose a scheme for achieving ultrafast coherent control of the selective excitation among three excited states in stimulated Raman scattering process on a tip-enhanced Raman spectroscopy (TERS). The center frequencies of the pump and Stokes laser pulses are 14,000 cm−1 and 12,500 cm−1, and their spectral bandwidths are both 700 cm−1. By properly modulating the spectral phase distribution and cutting the frequency components, the stimulated Raman transition probabilities of two excited state keep maximal, while the other one can be suppressed to zero. The shaped pump and Stokes pulse irradiate obliquely into the TERS nanostructure containing a single layer molecule. The impulse response in temporal and frequency domain is calculated by using finite-difference time-domain (FDTD) simulation followed by Fourier transform. The frequency components and the relative phase are same with the corresponding input pulses, but the intensities are enhanced by more than 10 times. Compared with the case without the TERS nanostructure, the probability of selective excited Raman transition increases by more than 4 orders of magnitude, and the selective depressed Raman peak keeps at 0.

Preparation of Monolayer MoS2 Quantum Dots using Temporally Shaped Femtosecond Laser Ablation of Bulk MoS2 Targets in Water

Zero-dimensional MoS2 quantum dots (QDs) possess distinct physical and chemical properties, which have garnered them considerable attention and facilitates their use in a broad range of applications. In this study, we prepared monolayer MoS2 QDs using temporally shaped femtosecond laser ablation of bulk MoS2 targets in water. The morphology, crystal structures, chemical, and optical properties of the MoS2 QDs were characterized by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, UV–vis absorption spectra, and photoluminescence spectra. The analysis results show that highly pure, uniform, and monolayer MoS2 QDs can be successfully prepared. Moreover, by temporally shaping a conventional single pulse into a two-subpulse train, the production rate of MoS2 nanomaterials (including nanosheets, nanoparticles, and QDs) and the ratio of small size MoS2 QDs can be substantially improved. The underlying mechanism is a combination of multilevel photoexfoliation of monolayer MoS2 and water photoionization–enhanced light absorption. The as-prepared MoS2 QDs exhibit excellent electrocatalytic activity for hydrogen evolution reactions because of the abundant active edge sites, high specific surface area, and excellent electrical conductivity. Thus, this study provides a simple and green alternative strategy for the preparation of monolayer QDs of transition metal dichalcogenides or other layered materials.

High-aspect-ratio, high-quality microdrilling by electron density control using a femtosecond laser Bessel beam

We propose an efficient microdrilling method of high-aspect-ratio, high-quality microholes in polymethyl methacrylate by controlling localized transient spatial electron density using single-pulse femtosecond laser Bessel beams. The microholes fabricated with diameters of 1.5–2.4 μm are taper-free, which are of much better quality in the entrances and sidewalls, as compared with those fabricated by Gaussian beams. The aspect ratio of the microholes is up to 330:1. It takes 42 min to fabricate a 501 × 501 microhole array (with 251,001 holes in total, about 100 holes per second under a repetition rate of 100 Hz) in a 1 cm × 1 cm area, which is very uniform in size and shape. For single-pulse drilling of a microhole array, the number of ultrahigh-aspect-ratio microholes processed per second is theoretically determined by the repetition rate. The liquid infiltration method and cross-sectional profile tests confirm hollow microhole drillings rather than material modifications. The theoretical simulation of optical intensity distribution and intensified charge-coupled device detection shows that fabricating such thin, long, uniform microholes using Bessel beams is attributed to electron density control by spatially shaping femtosecond laser pulses.