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Femtosecond laser irradiation of titanium oxide thin films: accumulation effect under IR beam
摘要： This paper discusses the mechanisms of laser-induced periodic surface structures (LIPSS) formation using a high repetition rate femtosecond laser beam irradiation of magnetron-sputtered titanium oxide thin films (TiO1.8) grown onto SiO2/Si substrates. An Yb:YKW 500 fs linearly polarized laser emitting at a wavelength, λ, of 1030 nm, was used to irradiate the films (300 nm thickness) at a repetition rate of 100 kHz under both static and dynamic (scanning) conditions. Under static beam conditions, an incubation behavior related to materials in thin film form was established with a damage threshold of 72 mJ/cm2. Close to this fluence value and increasing the number of laser shots from 1 to 1000, micro-cracking occurred and propagated inside the beam waist diameter zone estimated close to 60 μm. In addition, using a higher fluence value of 280 mJ/cm2, i.e., well above the damage threshold, a melting occurred in an intermediate zone within the irradiated area, with a surprising ‘cure effect’ that contributes to the micro-cracks stabilization. Simultaneously, at the center of the Gaussian laser beam spot, the entire film ablation was observed. Furthermore, irradiation under dynamic mode with a scanning speed of 4 mm/s and a repetition rate of 100 kHz were achieved for the large-scale processing of the TiO1.8 films up to surface area of 25 × 25 mm2. For these irradiation conditions case that correspond to a fluence of 110 mJ/cm2 and a cumulative number of shots of 3000, 2D-LIPSS nano-cracks (200 nm length and λ/8 to λ/9 period) are obtained over the whole irradiated surface, a phenomenon that is mainly attributed to a thermo-mechanical ablation mechanism.
关键词： Femtosecond laser beam,Titanium oxide film,Micro/nano-cracks,High repetition rate,Incubation,LIPSS
更新于2025-09-23 15:21:01
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Slit beam shaping technique for femtosecond laser inscription of enhanced plane-by-plane FBGs
摘要： In this work, the development of plane-by-plane (Pl-b-Pl) fiber Bragg gratings (FBGs) by using a single pulse is reported. A slit oriented along the longitudinal axis of the fiber is employed for this. The purpose is to shape the beam so that the focal volume is spatially wider in the transverse direction of the fiber. In this way, it is possible to make 2-D modifications of the refractive index whose width and height depends on the slit width and the pulse energy, respectively. Through an analytical mathematical modelling, the relationship between the diameter of the Gaussian laser beam (Dx) and the slit width (s = Dy) is determined in order to obtain a circular cross-section. In the experimental results carried out, it can be observed that Dx/Dy=3 ratio cause positive and uniform refractive index changes, compared to the negative and inhomogeneous refractive index changes corresponding to point-by-point (PbP) FBGs. Likewise, Pl-b-Pl FBGs, presenting a broader modification of the core cross-section, show significantly lower losses in transmission (0.3 dB), as well as better reflectivity and FWHM. It is observed that these three parameters (losses, reflectivity and FWHM) have a monotonous tendency according to the slit width. Polarization-dependence is also evaluated.
关键词： Optical Fiber Sensor,Slit beam technique,Femtosecond laser,Plane-by-Plane,Fiber Bragg grating
更新于2025-09-23 15:21:01
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Particulars of Femtosecond Laser Modification of Antimony-Silicate Glass
摘要： The particulars of the effect of focused femtosecond laser pulses on antimony silicate glass with the composition 25Sb2O3–75SiO2 % (molar content) in thermal and athermal regimes were studied. It was found that in contrast to quartz, alkali silicate, and some borosilicate glasses the birefringence of the form characteristic for the formation of nanogratings does not arise in the laser-modified zones of the studied glass. Weak birefringence with slow axis parallel to the polarization plane of the writing laser beam, accompanied by precipitation of crystalline phases, seemingly including the cubic modification of Sb2O3, arises in the modified zones under irradiation by 106 pulses with energy > 100 nJ and repetition frequency 10 and 200 kHz.
关键词： senarmontite,Raman scattering spectroscopy,crystallization,antimony silicate glass,femtosecond laser modification
更新于2025-09-23 15:21:01
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exposed to an intense laser pulse
摘要： We investigate the role of the rotational excitation in the coherent and unidirectional B 2Σ+u emission of N2+ at 391 nm called air lasing generated when N2 is irradiated with intense femtosecond near-infrared laser pulses at 800 nm. We simulate the time-dependent population transfer process of N2+, which is assumed to be generated suddenly in an intense ultrashort laser pulse, by including vibrational and rotational degrees of freedom, and reveal that, when the light field intensity is below ≈ 4 × 1014 W cm?2, the population inversion can be achieved in N2+ only between rotationally highly excited levels in the vibrational ground (v' = 0) state of the B 2Σ+u state and those in the vibrational ground (v'' = 0) state of the electronic ground X 2Σ+g state, so that the lasing at 391 nm is realized even when the total population in the v' = 0 state of the electronically excited B 2Σ+u state is not inverted with respect to the total population in the v'' = 0 state of the electronic ground X 2Σ+g state.
关键词： air lasing,N2+,rotational excitation,population inversion,femtosecond laser pulses
更新于2025-09-23 15:21:01
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Femtosecond laser surface engineering of biopolymer ceramic scaffolds coated with ZnO by low temperature atomic layer deposition method
摘要： Surface femtosecond laser texturing of biopolymer and biopolymer/ceramic composites with subsequent ZnO film deposition on the samples by low temperature Atomic Layer Deposition (ALD) method was performed. In the current study, the deposition of ZnO layers was implemented at temperature 50 °C under pressure of 2 mbar. In order to investigate the effect of diverse ZnO thin films thickness, 100 or 500 repeating ALD cycles were applied. The samples were exposed to ultra-short laser pulses of 130 fs duration generated by a CPA (chirped pulse amplifier) Ti:Sapphire laser system. The artificial scaffolds were irradiated by varying the laser fluence (0.2 J/cm2, 0.41 J/cm2 and 2.07 J/cm2) and the number of applied laser pulses (N = 1, 2, 5 and 10). The morphology and chemical properties of the treated samples were evaluated by Scanning Electronic Microscopy, Energy-Dispersive X-ray Spectroscopy and X-ray photoelectron spectroscopy. By combining fs laser modification with low temperature ALD method, essentially improved bioactivity properties of hybrid organic–inorganic bone tissue scaffolds could be achieved, which is of great importance for future tissue engineering application of the samples.
关键词： Atomic layer deposition,Biopolymer/ceramic composites,Femtosecond laser modification,Tissue engineering
更新于2025-09-23 15:21:01
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Uniform LIPSS on titanium irradiated by two-color double-pulse beam of femtosecond laser
摘要： The authors have investigated the uniformity of laser-induced periodic surface structures (LIPSSs) generated on titanium surfaces irradiated with a two-color double-pulse cross-polarized beam with a time delay of Δt = 0–200 ps. The double-pulse beam consisted of 800 nm pulses with a duration of 150 fs and 400 nm pulses with a duration of >150 fs. The fundamental-pulse fluence F800 and the second-harmonic pulse fluence F400 were set to be near the corresponding ablation thresholds of F800th = 0.108 J/cm2 and F400th = 0.090 J/cm2, respectively. The authors found that uniform LIPSSs could be produced on titanium surfaces using laser fluences of 1.5F400th + 0.9F800th and a delay of Δt = 0–2 ps. The periodicity and direction of the LIPSSs were characterized by the wavelength and electric field of the fundamental (800 nm) pulse. The results suggest that the longer-wavelength pulse influences surface plasma wave generation and improves uniformity by the second harmonic pulse even though laser plasma is produced on the surface.
关键词： femtosecond laser,double pulse beam,titanium,LIPSS
更新于2025-09-23 15:21:01
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Fabrication of large-scale freestanding THz wire grid polarizers by femtosecond laser micromachining
摘要： High-performance THz polarizers, as a quasi-optical device to manipulate THz waves, are highly demanded for THz spectroscopy and imaging applications. In this work, we have employed the femtosecond laser micro-machining technique to fabricate freestanding THz wire grid polarizers with two kinds of reinforced line structures which weaken the e?ects of gravity sagging and entanglement of long free wires, thus enabling large-scale processing. The e?ect of the reinforced lines on the polarizers were simulated by the Finite-Di?erence Time-Domain (FDTD) method, and the performances of the polarizer were characterized by THz time-domain spectroscopy and compared with that of a commercial wire gird polarizer. The calculated transmittance is in good agreement with the FDTD results. The degree of polarization and the extinction ratio of the polarizer with discontinuous reinforced lines are better than those of a commercial wire grid polarizer.
关键词： Time-domain THz spectroscopy,THz,Femtosecond laser micro-machining,Wire grid polarizer
更新于2025-09-23 15:21:01
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Engineering of high quality factor THz metasurfaces by femtosecond laser ablation
摘要： We report on the realization of high Q metasurfaces operating in the THz frequency range by femtosecond laser ablation applied to a nanometric metallic layer over a silicon substrate. Two different fabrication methods are used to develop periodic patterns whose basic elements are in form of an array of through-holes or metallic islands. The response of the resulting structures is characterized using a time-domain spectrometer in the frequency range 0.3–1.5 THz. The experimental findings are compared with the predictions of full wave electromagnetic simulations. The fairly good agreement between simulation predictions and experimental findings evidences that the proposed approach can offer a facile way to the elaboration of THz metasurfaces.
关键词： Femtosecond laser ablation,THz,High quality factor,Metasurfaces
更新于2025-09-23 15:21:01
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Simultaneous Nano-Texturing onto a CVD-Diamond Coated Piercing Punch with Femtosecond Laser Trimming
摘要： In this study, a CVD (Chemical Vapor Deposition)-diamond coated tungsten carbide cobalt (WC (Co)) punch was trimmed to adjust its surface roughness and to significantly reduce its edge curvature for fine piercing by femtosecond laser processing. Through this laser trimming, the surface quality of the diamond coating and the punch edge profile were improved to less than 0.5 μm at the maximum roughness and 2 μm in the edge width, respectively. In parallel with this improvement of surface quality, the side surface of the diamond coating was modified to include nano-textures via the LIPSS (Laser Induced Periodic Surface Structuring) process. Through the fine piercing process, this nanotexture was transcribed onto the pierced hole surface together with fine shearing of the hole by piercing. WLI (White-Light Interferometry) and SEM (Scanning Electron Microscopy) were utilized to describe this transcription of nanotextures during the piercing process. These semi-regular nanotextures with an LIPSS period of 300 nm on the pierced hole surface induced a blue colored surface plasmon.
关键词： diamond-coated WC (Co) punch,concurrent transcription of nanotextures,surface plasmon,simultaneous nanotexturing,femtosecond laser trimming,fine piercing
更新于2025-09-23 15:21:01
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Investigation and Prediction on Regulation of Hydrophobicity of Polymethyl Methacrylate (PMMA) Surface by Femtosecond Laser Irradiation
摘要： This study presents the contact angle prediction model of a trapezoidal groove structure based on the laser irradiation on polymethyl methacrylate (PMMA). The trapezoidal groove structure was designed and proposed according to the characteristics of a femtosecond laser. First, the complete wetting model and incomplete wetting model which were compatible with the characteristics of the laser mechanism were constructed based on the Gibbs free energy and the structural parameters of the trapezoidal groove structure. Then, based on the contact angle prediction models constructed, the samples were divided into two groups according to the designed structural parameters, and the experimental investigations were carried out. The result demonstrated that the incomplete wetting prediction model was more in line with the actual situation. The convex width and the top edge length of spacing of the trapezoidal groove structure both affected the contact angle prediction results. From both the experimental contact angles and the contact angles predicted by the incomplete wetting model, it could be known that the contact angle reached 138.09° when the ratio of the convex width to the top edge length of spacing was 0.25, indicating that the smaller the ratio of the convex width to the top edge length of spacing, the better the hydrophobicity of PMMA.
关键词： femtosecond laser,trapezoidal groove structure,polymethyl methacrylate,hydrophobicity
更新于2025-09-23 15:21:01