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This paper focuses on the critical role of temperature in ultrafast direct laser writing processes, where temperature changes can trigger or exclusively drive certain transformations, such as phase transitions. It is important to consider both the temporal dynamics and spatial temperature distribution for the effective control of material modifications. We present analytical expressions for temperature variations induced by multi-pulse absorption, applicable to pulse durations significantly shorter than nanoseconds within a spherical energy source. The objective is to provide easy-to-use expressions to facilitate engineering tasks. Specifically, the expressions are shown to depend on just two parameters: the initial temperature at the center denoted as T00 and a factor Rτ representing the ratio of the pulse period τp to the diffusion time τd. We show that temperature, oscillating between Tmax and Tmin, reaches a steady state and we calculate the least number of pulses required to reach the steady state. The paper defines the occurrence of heat accumulation precisely and elucidates that a temperature increase does not accompany systematically heat accumulation but depends on a set of laser parameters. It also highlights the temporal differences in temperature at the focus compared to areas outside the focus. Furthermore, the study suggests circumstances under which averaging the temperature over the pulse period can provide an even simpler approach. This work is instrumental in comprehending the diverse temperature effects observed in various experiments and in preparing for experimental setup. It also aids in determining whether temperature plays a role in the processes of direct laser writing. Toward the end of the paper, several application examples are provided. [ABSTRACT FROM AUTHOR]

Featured Application: Functional surfaces of zirconia with antibacterial properties. Femtosecond pulsed laser irradiation was performed to investigate the feasibility and fundamental characteristics of embedding silver nanoparticles onto zirconia ceramic surfaces. By irradiating laser, nanopores were fabricated on the surface of the yttria-stabilized zirconia (YSZ) substrate, and silver nanoparticles were infiltrated and immobilized into the pores using a commercial nano-silver dispersion solution. Numerous nanopores embedded with silver nanoparticles were successfully obtained on the YSZ surface while keeping the grains' shapes unchanged by controlling laser parameters. Optimizing laser fluence and scanning speed near the ablation threshold made it possible to remove only the excess dispersant that remained on the surface while keeping silver in the pores and without causing machining of the surface of the YSZ substrate. In addition, about 60% embedding in the nanopores was achieved. It was found that the shorter pulse width was suitable to avoid evaporating both dispersant and silver. Cross-sectional observation revealed that the silver nanoparticles were agglomerated to form clumps and were embedded without a gap at the bottom of the pores at a depth of about 600 nm. After laser irradiation, no significant laser-induced phase change was observed in the YSZ substrate, indicating that there was no in-process thermal damage to the bulk. These findings demonstrated the possibility of adding a metal nanoparticle to the zirconia surface by using only a laser process without damaging the properties of the base material during the process. New applications of zirconia, such as the generation of functional surfaces with antibacterial properties, are expected. [ABSTRACT FROM AUTHOR]

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Femtosecond pulsed laser irradiation of yttria-stabilized zirconia (YSZ) was performed to investigate the feasibility and fundamental characteristics of nanopore structure fabrication. Numerous nanopores were successfully generated on the YSZ surface with only a single laser pulse shot by controlling laser power near the ablation threshold. The nanopore generation mechanism involves light focusing by the convex shape of a crystal grain and ablation inside the grain. By increasing laser power, the number of nanopores increased. Cross-sectional observation revealed that the depth of nanopores was about 500 nm, and nanopores were generated inside the YSZ grains of the top layer while keeping the grains' shapes unchanged. It was found that higher scanning speed and a small number of scans enabled nanopores fabrication without changing the original surface shape, avoiding the removal of the surface layer. Laser-irradiated surfaces of YSZ were characterized by Raman spectroscopy, and it was found that there was no significant phase change in the specimen after nanopore generation compared with the original YSZ surface, confirming that there was no thermal damage to the bulk material. The surface with nanopores showed an enhancement in surface hydrophilicity. These findings demonstrated the possibility of selectively generating nanopores in the top surface of YSZ for use in functional surfaces without serious thermal damage to the workpiece. It is expected that the nanopore generation will lead to new applications of YSZ.

• A femtosecond pulsed laser was used to induce the periodic surface structure of polysilicon on 50 nm thickness a-Si thin films. • By adjusting the laser fluence, scanning speed and polarization, The formation of LIPSS on a-Si thin films was accompanied by the study of its crystallographic variation and potential of the morphology control. • The periodic surface structure of polysilicon was prepared in a large area and uniform, and the color effect was observed in the dark field. • This technology is expected to promote practical applications in areas such as pattern decoration, optical storage and optical anti-counterfeiting. The large area and uniform laser-induced periodic surface structure has a wide range of industrial application potential. The effect of the laser beam scanning velocity and laser fluence on the large-area fabrication of Laser-Induced Periodic Surface Structures (LIPSS), on 50 nm thickness a-Si thin films, is investigated. The results show that the formation and crystallization changes of LIPSS structure are obviously related to the scanning speed and laser fluence. In addition to surface morphology, the crystallinity of polycrystalline silicon can also be controlled by laser parameters. Based on these results, we applied direct laser induced periodic surface structuring to drive the phase transition from amorphous silicon into polycrystalline silicon. And prepare the periodic fringe structure of polycrystalline silicon with good crystallization and regular structure. By changing the polarization direction of the incident laser, the periodic surface structure with specific orientation can be obtained, and the surface of the material can be endowed with significant optical properties. When the prepared polycrystalline silicon periodic structure samples with different orientations are put into dark field microscope, the different color effects of the samples can be observed. [ABSTRACT FROM AUTHOR]

This paper focuses on the critical role of temperature in ultrafast direct laser writing processes, where temperature changes can trigger or exclusively drive certain transformations, such as phase transitions. It is important to consider both the temporal dynamics and spatial temperature distribution for the effective control of material modifications. We present analytical expressions for temperature variations induced by multi-pulse absorption, applicable to pulse durations significantly shorter than nanoseconds within a spherical energy source. The objective is to provide easy-to-use expressions to facilitate engineering tasks. Specifically, the expressions are shown to depend on just two parameters: the initial temperature at the center denoted as T00 and a factor Rτ representing the ratio of the pulse period τp to the diffusion time τd. We show that temperature, oscillating between Tmax and Tmin, reaches a steady state and we calculate the least number of pulses required to reach the steady state. The paper defines the occurrence of heat accumulation precisely and elucidates that a temperature increase does not accompany systematically heat accumulation but depends on a set of laser parameters. It also highlights the temporal differences in temperature at the focus compared to areas outside the focus. Furthermore, the study suggests circumstances under which averaging the temperature over the pulse period can provide an even simpler approach. This work is instrumental in comprehending the diverse temperature effects observed in various experiments and in preparing for experimental setup. It also aids in determining whether temperature plays a role in the processes of direct laser writing. Toward the end of the paper, several application examples are provided.

Femtosecond pulsed laser irradiation was performed to investigate the feasibility and fundamental characteristics of embedding silver nanoparticles onto zirconia ceramic surfaces. By irradiating laser, nanopores were fabricated on the surface of the yttria-stabilized zirconia (YSZ) substrate, and silver nanoparticles were infiltrated and immobilized into the pores using a commercial nano-silver dispersion solution. Numerous nanopores embedded with silver nanoparticles were successfully obtained on the YSZ surface while keeping the grains’ shapes unchanged by controlling laser parameters. Optimizing laser fluence and scanning speed near the ablation threshold made it possible to remove only the excess dispersant that remained on the surface while keeping silver in the pores and without causing machining of the surface of the YSZ substrate. In addition, about 60% embedding in the nanopores was achieved. It was found that the shorter pulse width was suitable to avoid evaporating both dispersant and silver. Cross-sectional observation revealed that the silver nanoparticles were agglomerated to form clumps and were embedded without a gap at the bottom of the pores at a depth of about 600 nm. After laser irradiation, no significant laser-induced phase change was observed in the YSZ substrate, indicating that there was no in-process thermal damage to the bulk. These findings demonstrated the possibility of adding a metal nanoparticle to the zirconia surface by using only a laser process without damaging the properties of the base material during the process. New applications of zirconia, such as the generation of functional surfaces with antibacterial properties, are expected.

The low‐energy layer edge states (LESs) from quasi 2D hybrid perovskite single crystals have shown great potential because of their nontrivial photoelectrical properties. However, the underlying formation mechanism of the LESs still remains controversial. Also, the presence or creation of the LESs is of high randomness due to the lack of proper techniques to manually generate these LESs. Herein, using a single crystals platform of quasi‐2D (BA)2(MA)n−1PbnI3n+1 (n > 1) perovskites, the femtosecond laser ablation approach to design and write the LESs with a high spatial resolution is reported. Fundamentally, these LESs are of smaller bandgap 3D MAPbI3 nanocrystals which are formed by the laser‐induced BA escaping from the lattice and thus the lattice shrinkage from quasi‐2D to 3D structures. Furthermore, by covering the crystal with tape, an additional high‐energy emission state corresponding to the reformation of (BA)2PbI4 (n = 1) within the irradiation region is generated. This work presents a simple and efficient protocol to manually write LESs on single crystals and thus lays the foundation for utilizing these LESs to further enhance the performance of future photoelectronic devices. [ABSTRACT FROM AUTHOR]

Single event burnout (SEB) is a great threat to gallium nitride (GaN) power devices for aerospace applications. This paper is dedicated to the investigation of the SEB mechanism in a GaN power device using a femtosecond pulsed laser. In the test, the SEB of a commercial p-GaN power device was triggered by a focused laser beam with a wavelength of 620 nm, and the irradiation-sensitive area of the devices was identified. We observed that the damage modes were consistent with the results of heavy ion experiments. The vertical breakdown of the drain is proposed as the dominant mechanism of SEB. We also provide a schematic representation of the leakage path formation using the electrical data obtained following laser-induced SEB. This study provides an important reference for consideration of device reliability and application prospects. [ABSTRACT FROM AUTHOR]

Ag mesh transparent conductive films (TCFs) were prepared on the commercial FTO/Glass substrate by ultrafast laser direct writing, trying to improve its overall photoelectric performances. The effects of laser scanning speed, laser fluence and Ag mesh height on photoelectric properties of the Ag mesh/FTO TCFs were systematically studied. The results indicated that a small scanning speed or a high laser fluence would cause excessive ablation of the FTO film and result in an increased Ag mesh line width, which was detrimental to the photoelectric properties of the resulting TCF. It was found that the optimal parameters for fabricating Ag mesh/FTO TCFs were a laser scanning speed of 2200 mm/s, a laser fluence of 0.050 J/cm2 and an Ag mesh height of 2500 nm. The as-fabricated TCF possessed the highest figure of merit of 13.03 × 10−2 Ω−1, which was significantly superior to that of the commercial FTO film. Finally, transparent heaters (THs) were prepared respectively based on the optimal Ag mesh/FTO TCF and the FTO/Glass substrate. The Ag mesh/FTO TH exhibited a more excellent heating performance than the FTO TH, further confirming that the overall photoelectric performance of the FTO/Glass substrate had been greatly improved. [ABSTRACT FROM AUTHOR]

We propose a point-by-point inscription method for fiber Bragg grating (FBG) fabrication using a femtosecond pulsed laser focused through a fiber polyimide coating, realizing a 2-μm-wavelength-band FBG. A femtosecond laser acts as the inscription laser, focused by a 63× oil lens. A first-order FBG was fabricated with a grating interval of 700 nm. The 15-μW pulsed laser was focused directly on the fiber core through the polyimide coating and cladding. A first-order FBG for 2004.8-nm light with more than 56% reflectances was fabricated. High wavelength sensitivity and linearity of the FBG were demonstrated by temperature and strain-sensing testing. The first-order FBG of 2004.8 and 2000.2 nm resonant wavelengths could be realized simultaneously through parallel inscription method in 3000 μm long grating area.

Single event burnout (SEB) is a great threat to gallium nitride (GaN) power devices for aerospace applications. This paper is dedicated to the investigation of the SEB mechanism in a GaN power device using a femtosecond pulsed laser. In the test, the SEB of a commercial p-GaN power device was triggered by a focused laser beam with a wavelength of 620 nm, and the irradiation-sensitive area of the devices was identified. We observed that the damage modes were consistent with the results of heavy ion experiments. The vertical breakdown of the drain is proposed as the dominant mechanism of SEB. We also provide a schematic representation of the leakage path formation using the electrical data obtained following laser-induced SEB. This study provides an important reference for consideration of device reliability and application prospects.

We report on manufacturing of a compact beam homogenizer module including two lens arrays and an aperture. Lens arrays are fabricated by an all laser-based technology employing a precise femtosecond pulsed laser ablation and a CO 2 laser polishing step. Each lens array is processed revealing a high contour accuracy and a roughness of 25 nm. The 8x8 lens arrays are designed to have a square footprint to generate a quadratic Top-Hat beam profile and focal length of 10 mm to realize compact packaging. Firstly, the lens arrays are tested in an experimental setup using commercial lens holders with their functionality being demonstrated by shaping a uniform 4.5 mm squared Top-Hat beam profile, as being calculated. Afterwards, a 3D printer is used to additively manufacture the housing for the beam homogenizer module having a length of only 16 mm. After assembling the laser-fabricated lens arrays and a laser-cutted aperture into the housing, the functionality of the miniaturized module is proven. [ABSTRACT FROM AUTHOR]

In order to study the charge characteristics of monocrystalline silicon irradiated by femtosecond pulsed laser, measurement systems of charge and infrared temperature induced by femtosecond pulse laser irradiation monocrystalline silicon are established by using oscilloscope and infrared thermal imager. The monocrystalline silicon (circle disc) irradiated by femtosecond pulse laser are carried out along the thickness direction of monocrystalline silicon. The experimental results show that the thermo-mechanical coupling effect of femtosecond pulsed laser irradiated on monocrystalline silicon will produce polarization in the target. At the initial stage of laser irradiation, the laser damage threshold of the interface between crystal surface and air is low and the charge mainly transfers along the surface of monocrystalline silicon, resulting in a high polarization. With the continuation of laser irradiation, it proves that the charge transfers in monocrystalline silicon gradually, and the polarization degree decreases with the modification of the material internal structure. After laser irradiation for a certain time, the charge transfers tend to be stable. Because the target lies in front of the laser focus, its energy density is insufficient to destroy the macrostructure of the target due to laser-pressure and temperature gradient, the polarization effect tends to be stable, resulting in a stable periodic change of charge transfer and recovery. [ABSTRACT FROM AUTHOR]

We report on Z -scan investigations of the nonlinear optical properties of thin pyrolytic carbon films and two- and three-layer graphene films, utilizing an 800 nm pulsed laser generating ultrashort 180 fs pulses. We analyze the sign and magnitude of nonlinear refraction and absorption in these materials, given contradictory results in this respect in the literature. In particular, we find that nonlinear refraction of graphene changes sign with changing light intensity with concomitant subtle changes in nonlinear absorption, a behavior not reported previously that suggests an interplay of several mechanisms that depend on intensity. Pyrolytic carbon films, on the contrary, exhibit positive refraction, whose magnitude (nonlinear refractive index n 2 ≅ 1 0 − 7 cm2/W) is comparable to that of graphene, and strong negative absorption, i.e., bleaching, contrary to previously reported results. We discuss implications and possible mechanisms of the observed phenomena. [ABSTRACT FROM AUTHOR]

• A 1030 nm fiber femtosecond pulsed laser was used to etch grooves on FTO thin films. • The groove quality was improved by optimizing laser fluence and scanning speed. • The best quality of laser-etched grooves was achieved at 1.1 J/cm2 and 3000 mm/s. • Grooves with a width of 7.92 μm and without shoulder-like protrusions were obtained. • Laser patterning on the touch screen sensor layer was successfully performed. In this study, the fluorine-doped tin oxide (FTO) film on a glass substrate was etched by using a femtosecond pulsed laser with a wavelength of 1030 nm, a repetition rate of 1 MHz and a pulse duration of 262 fs. The effect of laser fluence and scanning speed on the quality of the groove etched on the FTO film surface was systematically studied, trying to improve the groove quality. The results indicated that in order to obtain high quality grooves for use on touch screens, a balance needed to be achieved between laser fluence and scanning speed. Excessive laser fluence caused cracks at the bottom of the groove with shoulder protrusions formed at the edge of the groove, and the scanning speed had a considerable influence on the groove width at the same time. After discussing and comparing the results of five groups of experiments, the best groove quality was determined at the scanning speed of 3000 mm/s and the laser fluence of 1.1 J/cm2. In this case, the edge of the groove was sharp without obvious cracks and shoulder-like protrusions, and the groove width was 7.92 μm, which made it possible to process small etched areas for touch screen. Furthermore, the optimal parameters were confirmed to be available for processing a pattern on the touch screen sensor layer with a line spacing of 5 μm. [ABSTRACT FROM AUTHOR]

Laser induced periodic surface structures (LIPSS) have been produced at the surface of a WC-Co turning insert by femtosecond pulsed laser ablation. Wavelengths of approx. 500 nm have been obtained with a 1030 nm incident radiation and with a spot size of 30 μm. No thermal damage is induced by following this procedure, although a slight surface stress relaxation is detected as fluence increases. The higher material removal needed for chamfering operations requires accumulated fluences over 1 kJ/cm2. At lower energy densities, material removal is not completed. If fluence is increased by reducing the laser spot size, material removal is also inefficient since signicant amount of debris is accumulated on the irradiated areas. Best chamfering strategy involves the combination of relatively large spot sizes and fluences. Form factors (Κappa) of the chamfered cutting edges range from 4 to 10 although the laser is oriented at 45° of the rake face. Lower Κ values can be obtained by adjusting the laser focus along the machining process. • Surface texturing of turning inserts based on a submicron WC-10wt.%Co hardmetal grade has been carried out by femtosecond pulsed laser machining • Correlation between FIB-DIC and sin2 ψ techniques is excellent for as-ground and low power laser texturing • Chamfering of cutting edges requires higher accumulated fluences (> 1 kJ/cm2). • Κ-factors obtained by focusing the laser beam at the rake face range from 10 to 4 as accumulated fluence increases [ABSTRACT FROM AUTHOR]

We report on manufacturing of a compact beam homogenizer module including two lens arrays and an aperture. Lens arrays are fabricated by an all laser-based technology employing a precise femtosecond pulsed laser ablation and a CO2 laser polishing step. Each lens array is processed revealing a high contour accuracy and a roughness of 25 nm. The 8x8 lens arrays are designed to have a square footprint to generate a quadratic Top-Hat beam profile and focal length of 10 mm to realize compact packaging. Firstly, the lens arrays are tested in an experimental setup using commercial lens holders with their functionality being demonstrated by shaping a uniform 4.5 mm squared Top-Hat beam profile, as being calculated. Afterwards, a 3D printer is used to additively manufacture the housing for the beam homogenizer module having a length of only 16 mm. After assembling the laser-fabricated lens arrays and a laser-cutted aperture into the housing, the functionality of the miniaturized module is proven.

The effect of laser irradiation on surface wettability of cyclic olefin polymer (COP) was investigated. Under different laser parameters, a superhydrophilic or a superhydrophobic COP surface with a water contact angle (WCA) of almost 0° or 163°, respectively, could be achieved by direct femtosecond laser irradiation. The laser power deposition rate (PDR) was found to be a key factor on the wettability of the laser-treated COP surface. The surface roughness and surface chemistry of the laser-irradiated samples were characterized by surface profilometer and X-ray photoelectron spectroscopy, respectively; they were found to be responsible for the changes of the laser-induced surface wettability. The mechanisms involved in the laser surface wettability modification process were discussed.

Highlights • Different carbon morphologies have been produced from MWCNT under pulsed laser irradiation with different pulse duration. • The pseudo-topotactic conversion of MWCNT happened under the irradiation of picosecond and femtosecond pulsed laser. • Carbon nanoparticles, porous nanorods, and diamond nanobundles have been obtained under nanosecond laser irradiation. • The corresponding transformation mechanisms have also been discussed. Abstract Carbon nanowires have many interesting properties in electronic, opto-electronic and nanoelectromechanical devices due to their high aspect ratios. Carbon nanotubes are ideal templates for the synthesis of one-dimensional carbon nanowires. T-carbon nanowires have been recently produced by the pseudo-topotactic conversion of multi-walled carbon nanotubes (MWCNTs) under picosecond laser irradiation. There is no data about the relationship between the carbon product morphology and laser pulse duration reported so far. Pulsed laser induced reaction is a fast and far from equilibrium process. Carbon nanostructures with different morphology have been produced from carbon nanotube suspension in methanol under laser irradiation with different pulse duration. Carbon nanoparticles, porous carbon nanorods, and even diamond nanobundles have been obtained under nanosecond laser irradiation. The one-dimensional template growth from MWCNTs to carbon nanowires is not successful under nanosecond laser irradiation. However, different carbon nanowires with diameters similar to shortened carbon nanotubes have been easily produced from carbon nanotube suspension under the irradiation of picosecond and femtosecond pulsed laser. The morphology-directing transformations of carbon nanotubes have also explained using reported mechanisms. [ABSTRACT FROM AUTHOR]

In order to diminish the occurrence of cavitation bubbles during the liquid-assisted laser machining, ultrasound-assisted underwater femtosecond laser drilling on stainless steel is adopted. This method greatly diminishes the optical disturbance of cavitation bubbles. By investigating and analyzing the effect of laser pulse energy and pulse number on the morphology of the holes, it has been found that ultrasound not only has a remarkable function of forming a hole with clean and flat bottom, but also reduces debris redeposition around the processing area. This method improves the machining quality. Besides, it also improves the depth-to-diameter ratio of the hole about 20%. [ABSTRACT FROM AUTHOR]

A femtosecond (fs) pulsed laser was employed to drill microholes in TiC ceramic. The Morphologies of microholes drilled at different assisted gas pressures and laser feeding speeds were investigated. Chemical compositions and chemical bonds of laser treated debris and untreated specimen were analysed. The mechanism of interaction between the femtosecond laser and the TiC ceramic was discussed. The results indicated that the assisted gas pressure had a greater effect on the morphologies of microholes, compared with the feeding speed. The entrance diameter of microholes was smaller than the exit diameter. The entrance roundness was more perfect than the exit roundness, and the entrance roundness decreased slightly with increasing gas pressure and feeding speed. Higher feeding speed was unfavourable to the morphologies of microholes. Ti, C and O were detected in laser treated debris. X-ray photoelectron spectroscopy (XPS) investigation showed that the C-Ti bond was broken and Ti2 O3 and TiO2 were formed during drilling. [ABSTRACT FROM AUTHOR]

Diamond is widely used in a series of industrial and scientific applications, including the micro-electro-mechanical systems, optical elements, ultra-precision machining tools, etc. Femtosecond laser beam machining is promising for high precision and high accuracy machining diamond material for its famous non-thermal machining regime. Initially, the laser ablation threshold was determined for the low and high laser fluence stage, respectively. Then, the ionization regime of femtosecond pulsed laser beam machining mono-crystalline diamond with different laser power was discussed. The influence of the ionization regime on laser machining also was analyzed basing on Raman analysis and laser machined surface topography. The laser ablation threshold was 0.29 J/cm 2 for the low laser fluence stage and 2.35 J/cm 2 for the high laser fluence stage, respectively. The calculation of the Keldysh parameter indicated that the multi-photon ionization prevailed in the low laser fluence stage while the tunneling ionization became dominant in the high laser fluence stage. The transition of the ionization regime from the multi-photon ionization to the tunneling ionization occurred around the laser fluence 3.2 J/cm 2 . Graphitization of diamond material was discovered on laser machined diamond surface by means of Raman analysis. Graphitization would be enhanced by the tunneling ionization regime in the high laser fluence stage. A strong surface cracking tendency was also observed in laser machining in the high fluence stage. [ABSTRACT FROM AUTHOR]

The infrared thermal imaging system was used in order to investigate the temperature field distributions for optical glass lenses irradiated by femtosecond pulsed laser. The experimental research of the temperature field distributions on the surface of the H-K9L optical glass lenses with anti-reflection film and film free have been accomplished by this system combining with the irradiation at different frequencies and actuation duration by the femtosecond pulsed laser. The angle between the normal direction of the mirror surface and the laser output was 45 degrees. Experimental results showed that the coating of the lens on surface increases the distortion of the heat-affected zone and the temperature field, the penetration time increases as well as the temperature gradient decreases at the same time, which was caused by the reflection reducing coating on the surface of the lenses and this kind of coating has a certain protective effect to the optical lenses. The output frequencies of the laser presented a positive correlation linearly to the maximum surface temperatures of the lens in a certain range when the output energy of single laser pulse was constant. The spectral of temperature field was dominated by low frequency signals, the higher the laser output frequency was, the larger the amplitude of the spectrum signals was. The evolutionary processes of temperature for feature points at the edge of heat-affected zone were basically the same, therefore the laser irradiation in a small angle less than 45 degrees had little influence on the distributions and the evolutionary processes of the surface temperature fields in the heat-affected zone for thin targets. [ABSTRACT FROM AUTHOR]

Polymethylpentene (PMP) polymers can be used to make advanced optics, especially for midinfrared (MIR) ultrafast optics. In this study, an optical parametric converter pumped by a Ti sapphire femtosecond laser was used to investigate the polymer. The thermal effect generated by loosely focused femtosecond near mid-infrared (MIR) pulses in bulky materials is observed in real-time, and the polymer exhibits thermal stability and conformability. To avoid strong linear absorption and to increase the nonlinear damage threshold, the spectral region for ultrafast applications is 1310 nm (0.95 eV)–1350 nm (0.92 eV). For the process in region VI, there is a sign of stronger coupling for short-wavelength photons, and the pulse duration is recommended to be lower than 160 fs. In the ultraviolet (UV) region, filamentary writing using a low-focused beam, the laser peak power was selected in the range of 2.2 MW–9.2 MW. High-density bulky gratings were written. The refractive-index modulation was significant, and the polymer exhibited highly nonlinear features. This study provides insights into the applications and production of PMP polymers in laser optics and laser engineering. • In situ thermal observation on filamentation built by near MIR femtosecond pulses in polymer. • Using super-continuum spectra to characterise filamentary process of PMP. • Writing bulky gratings with tightly focused beam. [ABSTRACT FROM AUTHOR]

Since binder-less polycrystalline diamond (BLPCD) has no macro cleavage planes and highest hardness, it is desirable material for micro milling tools. However, fabricating micro tools made of BLPCD by conventional method such as grinding is very time consuming due to its extremely high hardness. This paper describes the successful results obtained in our recent study on productive machining of BLPCD using femtosecond-pulsed laser (FSPL). The ablation effect of BLPCD by FSPL has been studied by conducting a series of experiments. Also, the predictability of ablation effect of FSPL when machining BLPCD has been evaluated by introducing numerical analysis model. [ABSTRACT FROM AUTHOR]

Laser shock imprinting is highly efficient to manufacture functional thin films. However, the manufacturing process and the service life of the mold were the main issues that restrict its large-scale application. In this study, high-quality and high-precision periodic patterns were manufactured on aluminum foils of thickness 4 μm by laser shock imprinting with femtosecond pulsed laser etched Si and SiC molds. It proved that the micro molds with different patterns fabricated by variant femtosecond pulsed laser were able to tailor the optical function performance of the films. The effects of shock imprinting times on the abrasion resistance of different material mold were studied. The SiC mold with higher hardness has better wear resistance. The reflection rate attenuation of the film based on the SiC mold was obviously smaller than that on the Si mold after 100 times of imprinting. The difference performance caused by different molds was analyzed by elastoplastic mechanics of finite element method. The higher hardness of SiC suffer less wear and plastic deformation in the imprinting process, so it can mitigate the mold microstructure size degradation, which fabricates more accurate surface microstructures on the aluminum foils. The SiC is more suitable for making laser shock imprinting mold for future large-scale industrial application. • Femtosecond pulsed laser machines hard micro molds for laser shock imprinting. • Accuracy of the micro molds after repeated use is analyzed. • Performance of silicon carbide mold is still good after many times of use. • Excellent wear resistance of silicon carbide reduces size change of micro mold. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we report the fabrication of a large area uniformly distributed periodic nano-ripple structure on silicon substrate through the proper scanning of a line-shaped femtosecond laser beam. The fabricated nano-ripple structure has a periodicity of ∼600nm and a ripple depth of ∼300nm. The modulation depth is much deeper than the one previously reported. The developed structure is demonstrated to be able to substantially reduce light reflection due to the effective optical coupling between the incident sunlight with the nano-ripple structure and exhibit an absorption enhancement of ∼41% compared with planar silicon wafer. The physics underlying the formation of the nano-ripple structure is also discussed. [Copyright &y& Elsevier]

Highlights: [•] Femtosecond pulsed laser nanotexturing of Si3N4/TiC ceramic was investigated. [•] The optimum processing parameters for the formation of ripples were identified. [•] Surface morphology, ablation dimension and surface roughness were measured. [•] Formation mechanism of ripples on Si3N4/TiC ceramic surface was discussed. [Copyright &y& Elsevier]

Systemic delivery of bioactive molecules in the CNS is hampered by the blood-brain barrier, which has bottlenecked noninvasive physiological study of the brain and the development of CNS drugs. Here we report that irradiation with an ultrashort pulsed laser to the blood vessel wall induces transient leakage of blood plasma without compromising vascular integrity. By combining this method with a systemic injection, we delivered target molecules in various tissues, including the brain cortex. This tool allows minimally invasive local delivery of chemical probes, nanoparticles, and viral vectors into the brain cortex. Furthermore, we demonstrated astrocyte-mediated vasodilation in vivo without opening the skull, using this method to load a calcium indicator in conjunction with label-free photoactivation of astrocytes. [ABSTRACT FROM AUTHOR]

Abstract: We report on a femtosecond-laser induced photoluminescence (PL) in poly(methyl methacrylate) and its potential application to three-dimensional optical storage. Irradiation with a focused 800nm, 1kHz, 100fs pulsed laser induced a strong PL change in UV–visible region. Absorption spectra and Fourier-transform infrared spectra before and after laser irradiation indicate the PL may result from the emissive oxidized products of photo-degradation reaction of PMMA. This makes it possible to read out the stored data by detecting the PL change. The pulse energy threshold of the light-induced PL change of PMMA is found to be at ∼2μJ/pulse and the optimal recording energy is ∼3μJ/pulse. A ten-layer pattern inside the bulk sample recorded by tightly focusing a pulsed laser beam was read out by a reflection-type fluorescent confocal microscope, which detected the emission in visible range as the signal. High-contract fluorescent images with a much higher signal-to-noise ratio were obtained without crosstalk in comparison with the ordinary reflection mode. [ABSTRACT FROM AUTHOR]

Pulsed laser illumination constitutes an excellent tool to emulate the effects produced by the impact of highly energetic particles on electronic circuits. Numerical simulation techniques could be used to study these effects and to establish accurate relationships between the laser parameters and the particle characteristics. Unfortunately, although particle incidence can be accurately simulated, up to now, there not exist a simulation technique able to reproduce completely the effects in electronics produced by a femtosecond pulsed laser. In this paper, we explore the Synopsys Sentaurus TCAD ability to simulate the effects of pulsed laser illumination. Theoretical study of the physics of the laser–semiconductor interactions leads us to design a new simulation tool. Modifying the heavy ion generation rate included in Sentaurus TCAD, we can take into account all the theoretical predicted characteristics of femtosecond laser illumination, and reproduce the single event effects (SEE) found in experimental tests. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: We study the surface chemicals and structures of aluminum plates irradiated by scanning femtosecond laser pulses in air for a wide range of laser fluence from 0.38 to 33.6J/cm2. X-ray photoelectron spectroscopy and X-ray diffraction analyses indicate clearly that crystalline anorthic Al(OH)3 is formed under femtosecond laser pulse irradiation. Besides aluminum hydroxide, crystalline Al2O3 is also found in the samples irradiated at high laser fluence. Field emission scanning electron microscopy demonstrates that the surfaces of the samples irradiated with low laser fluence are colloidal-like and that nanoparticles with a few nanometers in size are embedded in glue-like substances. For high laser fluence irradiated samples, the surfaces are highly porous and covered by nanoparticles with uniform size of less than 20nm. [Copyright &y& Elsevier]

Abstract: Irradiation of Si(100), Si(111), Si(110), Ge(100), and Ge(111) is compared for 150fs, 800nm wavelength pulses in a rough vacuum atmosphere. The surface crystalline orientation of the material is found to affect the final morphology, with (111)- and (110)-surface orientations exhibiting a much higher tendency for conical structure formation under multiple-pulse irradiation. Using cross-sectional transmission electron microscopy, the structures on Si(111) are found to have primarily crystalline cores with the same crystalline orientation as the substrate. The results show that the crystalline orientation of the target should be considered in laser machining applications. [Copyright &y& Elsevier]