Femtosecond

About: Femtosecond is a research topic. Over the lifetime, 35106 publications have been published within this topic receiving 691405 citations. The topic is also known as: 1 E-15 s & fs.

Ultrafast nanoporous silica formation driven by femtosecond laser irradiation

Abstract: A type of glass modifications occurring after femto- second laser irradiation gives rise to strong (10 −2 ). This form birefringence is thought to be related to index nanostructure (called nanogratings). Analyzing induced tracks in fused silica using scanning electron microscopy (SEM) with nm resolution shows that nanostructures are porous nanoplanes with an av- erage index lower than typical silica (� n ∼ -0.20). Their origin is explained as arising from fast decomposition of the glass un- der localized, high-intensity femtosecond laser radiation where strong nonlinear, multiphoton-induced photoionization leads to plasma generation. Mechanistic details include Coulom- bic explosions characteristic of strong photoionization and the production of self-trapped exciton (STE). Rapid relaxation of these STE prevents recombination and dissociated atomic oxy- gen instead recombines with each other to form molecular oxygen pointed out using Raman microscopy. Some of it is dissolved in the condensed glass whilst the rest is trapped within nanovoids. A chemical recombination can only occur at 1200 ◦ C for many hours. This explains the thermal stability

Femtosecond Time-Resolved Optical and Raman Spectroscopy of Photoinduced Spin Crossover: Temporal Resolution of Low-to-High Spin Optical Switching

Abstract: A combination of femtosecond electronic absorption and stimulated Raman spectroscopies has been employed to determine the kinetics associated with low-spin to high-spin conversion following charge-transfer excitation of a FeII spin-crossover system in solution. A time constant of τ = 190 ± 50 fs for the formation of the 5T2 ligand-field state was assigned based on the establishment of two isosbestic points in the ultraviolet in conjunction with changes in ligand stretching frequencies and Raman scattering amplitudes; additional dynamics observed in both the electronic and vibrational spectra further indicate that vibrational relaxation in the high-spin state occurs with a time constant of ca. 10 ps. The results set an important precedent for extremely rapid, formally forbidden (ΔS = 2) nonradiative relaxation as well as defining the time scale for intramolecular optical switching between two electronic states possessing vastly different spectroscopic, geometric, and magnetic properties.

Bioinspired Design of Underwater Superaerophobic and Superaerophilic Surfaces by Femtosecond Laser Ablation for Anti- or Capturing Bubbles.

Abstract: A micro-/nanoscale hierarchical rough structure inspired by the underwater superaerophobicity of fish scales was fabricated by ablation of a silicon surface by a femtosecond laser. The resultant silicon surface showed superhydrophilicity in air and became superaerophobic after immersion in water. Additionally, inspired by the underwater superaerophilicity of lotus leaves, we showed that the polydimethylsiloxane surface after femtosecond laser ablation exhibits superhydrophobicity in air and becomes superaerophilic in water. The underwater superaerophobic surface showed excellent antibubble ability, whereas the underwater superaerophilic surface could absorb and capture air bubbles in a water medium. The experimental results revealed that the in-air superhydrophilic surface generally shows superaerophobicity in water and that the in-air superhydrophobic surface generally shows underwater superaerophilicity. An underwater superaerophobic porous aluminum sheet with through microholes was prepared, and this s...

Observation of extremely efficient terahertz generation from mid-infrared two-color laser filaments

Abstract: Extreme nonlinear interactions of THz electromagnetic fields with matter are the next frontier in nonlinear optics. However, reaching this frontier in free space is limited by the existing lack of appropriate powerful THz sources. Here, we experimentally demonstrate that two-color filamentation of femtosecond mid-infrared laser pulses at 3.9 μm allows one to generate ultrashort sub-cycle THz pulses with sub-milijoule energy and THz conversion efficiency of 2.36%, resulting in THz field amplitudes above 100 MV cm−1. Our numerical simulations predict that the observed THz yield can be significantly upscaled by further optimizing the experimental setup. Finally, in order to demonstrate the strength of our THz source, we show that the generated THz pulses are powerful enough to induce nonlinear cross-phase modulation in electro-optic crystals. Our work paves the way toward free space extreme nonlinear THz optics using affordable table-top laser systems. Powerful terahertz pulses are generated during the nonlinear propagation of ultrashort laser pulses in gases. Here, the authors demonstrate efficient sub-cycle THz pulse generation by using two-color midinfrared femtosecond laser filaments in ambient air.

Nanosecond and femtosecond laser ablation of brass: Particulate and ICPMS measurements

Abstract: Femtosecond and nanosecond lasers were compared for ablating brass alloys. All operating parameters from both lasers were equal except for the pulse duration. The ablated aerosol vapor was collected on silicon substrates for particle size measurements or sent into an inductively coupled plasma mass spectrometer. The diameters and size distribution of particulates were measured from scanning electron microscope (SEM) images of the collected ablated aerosol. SEM measurements showed that particles ablated using nanosecond pulses were single spherical entities ranging in diameter from several micrometers to several hundred nanometers. Primary particles ablated using femtosecond ablation were ∼100 nm in diameter but formed large agglomerates. ICPMS showed enhanced signal intensity and stability using femtosecond compared to nanosecond laser ablation.