- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Second harmonic generation at 544a??nm of a femtosecond laser
摘要： We study second harmonic generation (SHG) at 544 nm of the 0-type (e + e - e) quasi-phase-matching based on a femtosecond laser at 1088 nm. The green pulse with the spectrum width of 0.6 nm and the peak power of 17.7 kW is obtained at the pump power density of 2.81 GW/cm2 and the conversion e?ciency is 21 %. As the propagation distance along the PPMgLN crystal increases, the spectrum at 544 nm becomes narrower and narrower and the pulse duration broadens very seriously.
关键词： Group velocity match,544 nm laser,Second harmonic generation,PPMgLN,Ultrafast optics,Femtosecond pulses
更新于2025-09-23 15:21:01
-
Laser machined ultralow water adhesion surface by low pressure processing
摘要： Ultralow water adhesion aluminum surface has been fabricated by eco friendly low pressure processing technique. The laser patterned surface shows interconnected spongy porous nanostructures with micro packets at regular intervals. The micro volume of air present inside the interconnected porous surface structure together with the adsorbed hydrocarbons by low pressure processing leads to ultralow water adhesion surface. Application of bigger droplet volumes to the patterned surface showed a decrease in static contact angle measurement due to larger radius of curvature and axisymmetrical compared to the smaller droplets.
关键词： Sliding angle,Ultrafast laser,Low pressure,Wetting,Adhesion
更新于2025-09-23 15:21:01
-
Determining Orientations of Optical Transition Dipole Moments Using Ultrafast X-ray Scattering
摘要： Identification of the initially prepared, optically active state remains a challenging problem in many studies of ultrafast photoinduced processes. We show that the initially excited electronic state can be determined using the anisotropic component of ultrafast time-resolved X-ray scattering signals. The concept is demonstrated using the time-dependent X-ray scattering of N-methyl morpholine in the gas phase upon excitation by a 200 nm linearly polarized optical pulse. Analysis of the angular dependence of the scattering signal near time zero renders the orientation of the transition dipole moment in the molecular frame and identifies the initially excited state as the 3pz Rydberg state, thus bypassing the need for further experimental studies to determine the starting point of the photoinduced dynamics and clarifying inconsistent computational results.
关键词： time-resolved experiments,ultrafast
更新于2025-09-23 15:21:01
-
Sub-nanosecond multiple-wavelength harmonic mode-locked Tm-Ho co-doped fiber laser
摘要： We demonstrate an all-fiber sub-nanosecond passively mode-locked Tm-Ho co-doped fiber laser. With 1.1-km single-mode fiber (SMF) inserted into the cavity, the laser system can generate 183.4-kHz and 720-ps pulses based on a GaAs saturable absorber (SA). The output spectrum is presented with three wavelengths, which are at 1858.5, 1861.3, and 1864.2 nm, respectively. In addition, with the adjustment of the polarization controller and pump power, the multiple-pulse operation, such as the harmonic mode-locking operation, can also be observed. Higher order of harmonic mode locking is promising but limited by the damage threshold of the SA.
关键词： Mode-locked lasers,Ultrafast optics,Optical fiber lasers
更新于2025-09-23 15:21:01
-
Analytical solution of dual-phase-lag based heat transfer model in ultrashort pulse laser heating of A6061 and Cu3Zn2 nano film
摘要： The dual-phase-lag model provides the best performance among many existing non-Fourier models and it is particularly more suitable for a short duration of heating. The present literature survey certifies the availability of very few research papers specifically on the development of an exact analytical solution of the dual-phase-lag model illustrating the thermal analysis of ultrashort pulsed laser heating. To address such issues, the present work is intended to develop an exact solution of the thermal response based on the dual-phase-lag heat conduction model utilized for the femtosecond laser heating of nanofilm. The corresponding solution has been derived by a hybrid application of the Duhamel’s theorem and the finite integral transform approach. A comparative thermal analysis has been depicted for the laser heating of 5 nm thin A6061 and Cu3Zn2 nanofilm and the necessity of non-Fourier analysis over the Fourier’s model has been justified. Existing research works are mostly based on gold and chromium nanofilm. As multi-component microstructures of Cu and Al are scientifically proved to be excellent metallic properties (magnetic and optical) and exhibit strong response during energy driven-chemical reactions, the present analysis is focused on these two materials for the femtosecond laser irradiation. In the present analysis, optical properties (absorptivity and reflectivity) of substrate material have been taken into account to develop a better and realistic analytical model than the existing models. The research output notifies that at 0.1 ps of the laser pulse and 100 J m?2 of the laser intensity, developed temperature history reaches the melting point temperature of both the materials in combination with other thermophysical properties. The mathematical modeling also provides the appropriate information about the selection of thermal relaxation time lags for respective materials and this also justifies the experimental observation of relaxation time lags as reported in the literature. The thermal response has been captured for both A6061 and Cu3Zn2 material along the various depths of the nanofilm to evolve the irradiation capacity of the pulsed femtosecond laser source. The present research output is well validated through numerical and experimental research works of existing literature with a negligible variation. The inclusion of optical properties of materials in the present research work plays an important role as it is noticed that the maximum deviation of the temperature difference between with and without optical properties is evidenced as 38.86% and 57.70% for A6061 and Cu3Zn2 nanofilms, respectively.
关键词： Analytical solution,Dual-phase-lag model,Optical properties,Thermal response,Ultrafast pulsed laser
更新于2025-09-23 15:21:01
-
Domain wall dynamics due to femtosecond laser-induced superdiffusive spin transport
摘要： Manipulation of magnetic domain walls via a helicity-independent laser pulse has recently been experimentally demonstrated and various physical mechanisms leading to domain wall dynamics have been discussed. Spin-dependent superdiffusive transport of hot electrons has been identified as one of the possible ways to affect a magnetic domain wall. Here, we develop a model based on superdiffusive spin-dependent transport to study the laser-induced transport of hot electrons through a smooth magnetic domain wall. We show that the spin transfer between neighboring domains can enhance ultrafast demagnetization in the domain wall. More importantly, our calculations reveal that when the laser pulse is properly focused onto the vicinity of the domain wall, it can excite sufficiently strong spin currents to generate a spin-transfer torque that can rapidly move the magnetic domain wall by several nanometers in several hundred femtoseconds, leading to a huge nonequilibrium domain wall velocity.
关键词： spin-transfer torque,ultrafast demagnetization,magnetic domain walls,superdiffusive spin transport,laser-induced dynamics
更新于2025-09-23 15:21:01
-
Theory of photoinduced ultrafast switching to a spin-orbital ordered hidden phase
摘要： Photo-induced hidden phases are often observed in materials with intertwined orders. Understanding the formation of these non-thermal phases is challenging and requires a resolution of the cooperative interplay between different orders on the ultra-short timescale. In this work, we demonstrate that non-equilibrium photo-excitations can induce a state with spin-orbital orders entirely different from the equilibrium state in the three-quarter-filled two-band Hubbard model. We identify a general mechanism governing the transition to the hidden state, which relies on a non-thermal partial melting of the intertwined orders mediated by photoinduced charge excitations in the presence of strong spin-orbital exchange interactions. Our study theoretically confirms the crucial role played by orbital degrees of freedom in the light-induced dynamics of strongly correlated materials and it shows that the switching to hidden states can be controlled already on the fs timescale of the electron dynamics.
关键词： spin-orbital orders,photo-induced hidden phases,non-equilibrium photo-excitations,two-band Hubbard model,ultrafast switching
更新于2025-09-23 15:21:01
-
Complementary cathodoluminescence lifetime imaging configurations in a scanning electron microscope
摘要： Cathodoluminescence (CL) spectroscopy provides a powerful way to characterize optical properties of materials with deep-subwavelength spatial resolution. While CL imaging to obtain optical spectra is a well-developed technology, imaging CL lifetimes with nanoscale resolution has only been explored in a few studies. In this paper we compare three different time-resolved CL techniques and compare their characteristics. Two configurations are based on the acquisition of CL decay traces using a pulsed electron beam that is generated either with an ultra-fast beam blanker, which is placed in the electron column, or by photoemission from a laser-driven electron cathode. The third configuration uses measurements of the autocorrelation function g(2) of the CL signal using either a continuous or a pulsed electron beam. The three techniques are compared in terms of complexity of implementation, spatial and temporal resolution, and measurement accuracy as a function of electron dose. A single sample of InGaN/GaN quantum wells is investigated to enable a direct comparison of lifetime measurement characteristics of the three techniques. The g(2)-based method provides decay measurements at the best spatial resolution, as it leaves the electron column configuration unaffected. The pulsed-beam methods provide better detail on the temporal excitation and decay dynamics. The ultra-fast blanker configuration delivers electron pulses as short as 30 ps at 5 keV and 250 ps at 30 keV. The repetition rate can be chosen arbitrarily up to 80 MHz and requires a conjugate plane geometry in the electron column that reduces the spatial resolution in our microscope. The photoemission configuration, pumped with 250-fs 257-nm pulses at a repetition rate from 10 kHz to 25 MHz, allows creation of electron pulses down to a few ps, with some loss in spatial resolution.
关键词： Electron microscopy,Ultrafast,Cathodoluminescence,Time-resolved,Quantum wells
更新于2025-09-23 15:21:01
-
Ultrafast Excited-State Dynamics of Hydrogen-Bonded Cytosine Microsolvated Clusters with Protic and Aprotic Polar Solvents
摘要： Microsolvation effects on the ultrafast excited-state deactivation dynamics of cytosine (Cy) were studied in hydrogen-bonded Cy clusters with protic and aprotic solvents using mass-resolved femtosecond pump-probe ionization spectroscopy. Two protic solvents, water (H2O) and methanol (MeOH), and one aprotic solvent, tetrahydrofuran (THF), were investigated, and transients of Cy·(H2O)1-6, Cy·(MeOH)1-3, and Cy·THF microsolvated clusters produced in supersonic expansions were measured. With the aid of electronic structure calculations, we assigned the observed dynamics to the low-energy isomers of various Cy clusters and discussed the microsolvation effect on the excited-state deactivation dynamics. With the protic solvents only the microsolvated clusters of Cy keto tautomer were observed. The observed decay time constants of Cy·(H2O)n are 0.5 ps for n=1 and ~0.2–0.25 ps for n=2–6. For Cy·(MeOH)n clusters, the decay time constant for n=1 cluster is similar to that of the Cy monohydrate, but for n=2 and 3 the decays are about a factor of two slower than the corresponding microhydrates. With the aprotic solvent, THF, hydrogen-bonded complexes of both keto and enol tautomers are present in the beam. The keto-Cy·THF shows a similar decay as the keto-Cy monomer, whereas the enol-Cy·THF exhibits a two-fold slower decay than the enol-Cy monomer, suggesting an increase in the barrier to excited-state deactivation upon binding of one THF molecule to the enol form of Cy.
关键词： Cytosine,Excited-state deactivation,Hydrogen-bonded clusters,Microsolvation,Ultrafast dynamics
更新于2025-09-23 15:21:01
-
Ultrafast molecular clock with subcycle resolution from correlated electron-nuclear spectra
摘要： To probe ultrafast molecular dynamics, a high spatial-temporal resolution is of crucial importance. Different from the usual pump-probe method, here we present a probing scheme to clock the molecular dynamics with subcycle precision by investigating the correlated electron-nuclear energy spectra in a multicycle laser pulse. The molecular dynamics in the tunneling ionization regime are numerically simulated in a two-dimensional H+2 non-Born-Oppenheimer model. It is found that the asymmetry between the yields of electrons ionized in opposite directions along the laser polarization axis shows peaks and valleys alternately as a function of the nuclear energy. Our results show that the temporally resolved asymmetry of the ionization of electrons can be used as a clock to probe the nuclear Coulomb explosion channel with subcycle resolution and extract the corresponding molecular dynamics accurately. This method can be used even when the intensity averaging of the focused laser beam is considered.
关键词： tunneling ionization regime,subcycle resolution,non-Born-Oppenheimer model,correlated electron-nuclear spectra,ultrafast molecular dynamics
更新于2025-09-23 15:21:01