- 标题
- 摘要
- 关键词
- 实验方案
- 产品
过滤筛选
- 2020
- fast processes in solids
- femtosecond interferometry
- femtosecond laser radiation
- Optoelectronic Information Science and Engineering
- Prokhorov General Physics Institute, Russian Academy of Sciences; National Research Nuclear University MEPhI
-
Resolving fine spectral features in lattice vibrational modes using femtosecond coherent spectroscopy
摘要： We show resolution of fine spectral features within several Raman active vibrational modes in potassium titanyl phosphate (KTP) crystal. Measurements are performed using a femtosecond time-domain coherent anti-Stokes Raman scattering spectroscopy technique that is capable of delivering equivalent spectral resolution of 0.1 cm?1. The Raman spectra retrieved from our measurements show several spectral components corresponding to vibrations of different symmetry with distinctly different damping rates. In particular, linewidths for unassigned optical phonon mode triplet centered at around 820 cm?1 are found to be 7.5±0.2 cm?1, 9.1±0.3 cm?1, and 11.2±0.3 cm?1. Results of our experiments will ultimately help to design an all-solid-state source for sub-optical-wavelength waveform generation that is based on stimulated Raman scattering.
关键词： damping rates,potassium titanyl phosphate,Raman active vibrational modes,femtosecond coherent spectroscopy,spectral resolution
更新于2025-09-23 15:21:01
-
Laser-assisted in-situ keratomileusis (LASIK) with a mechanical microkeratome compared to LASIK with a femtosecond laser for LASIK in adults with myopia or myopic astigmatism
摘要： Laser-assisted in-situ keratomileusis (LASIK) is a surgical procedure that corrects refractive errors. This technique creates a flap of the outermost parts of the cornea (epithelium, bowman layer, and anterior stroma) to expose the middle part of the cornea (stromal bed) and reshape it with excimer laser using photoablation. The flaps can be created by a mechanical microkeratome or a femtosecond laser.
关键词： mechanical microkeratome,femtosecond laser,myopic astigmatism,LASIK,myopia
更新于2025-09-23 15:21:01
-
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
-
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
-
Enhancing Perovskite Solar Cell Performance through Femtosecond Laser Polishing
摘要： Nonradiative recombination loss is a key process that determines the performance of perovskite solar cells, and how to control it is significant for the research and development of perovskites. Generally, traditional chemical modification/passivation methods are complicated and prone to secondary contamination. Here, we demonstrate femtosecond (fs) laser polishing as a promising technique to ameliorate the surface of perovskite films, to reduce nonradiative recombination loss and improve solar cell performance. The high-intensity fs laser pulses can remove around 20-nm thick perovskite top-layer through ionization process, help to decrease the grain boundary density and enlarge the grain size of perovskite films after recrystallization. We believe that fs laser polishing is a time-effective and highly precise technique which is suitable for large-scaled device production, thus will trigger more applications in optoelectronics.
关键词： femtosecond lasers,perovskites,recombination,passivation,solar cells
更新于2025-09-23 15:21:01
-
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
-
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
-
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
-
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
-
Non-Fourier Estimate of Electron Temperature in Case of Femtosecond Laser Pulses Interaction with Metals
摘要： This work is devoted to the electron temperature variation in metals through interaction with femtosecond laser pulses. Our study was inspired by the last mathematical breakthroughs regarding the exact analytical solutions of the heat equation in the case of flash laser-matter interaction. To this purpose, the classical Anisimov’s two temperature model was extended via the 3D telegraph Zhukovsky equation. Based upon this new approach, the computational plots of electron thermal fields during the first laser pulse interaction with a gold surface were inferred. It is shown that relaxation times and coupling factors over electron thermal conductivities (g/K) govern the interaction between the laser pulse and metal sample during the first picoseconds. The lower the factor g/K, the higher the electron temperature becomes. In contrast, the lower the relaxation time, the lower the electron temperature.
关键词： two temperature model,3D telegraph equation,femtosecond lasers-metal interaction,metals
更新于2025-09-23 15:21:01