Harmonic Of Ti Research Articles

Efficient (∼10%) generation of vacuum ultraviolet femtosecond pulses via four-wave mixing in hollow-core fibers.

We report the generation of the fifth harmonic of Ti:sapphire, at 160 nm, with more than 4 µJ of pulse energy and a pulse length of 37 fs with a 1 kHz repetition rate. The vacuum ultraviolet pulses are produced using four-wave difference frequency mixing in a He-filled stretched hollow-core fiber, driven by a pump at 267 nm and seeded at 800 nm. Guided by simulations using Luna.jl, we are able to optimize the process carefully. The result is a conversion efficiency of ∼10% from the 267 nm pump beam.

Discrete exited states influence on the harmonics spectrum generated in two-colour laser fields

The contribution of excited discrete atomic levels to the generation of high- and low-order harmonics in the interaction of a single atom with a two-color laser field has been studied for the first time. The studies were carried out for two types of atoms with different symmetry of the ground state wave functions (Ag, Ne) and for a two-color laser field consisting of the linearly polarized fundamental and second harmonics of Ti:Sa laser (ω + 2ω). The angle between the polarization of the ω + 2ω laser field components is varied. A significant effect of the symmetry of populated excited levels on the polarization characteristics of the generated harmonics is shown. A new method of control over the polarization state of the generated radiation is proposed.

Toward the possibility of 229Th isomeric nuclear state excitation by two-color laser field

The process of high harmonic generation (HHG) has a wide area of different applications, in particular, in nanoscale imaging, study the nanoscale energy transport in complex molecules and solids, probe the charge and spin dynamics with the femtosecond time resolution, etc. Here we discuss a possible application of HHG effect related with the study of nuclear transition dynamics. We analyse the efficiency of excitation of the isomeric nuclear state 229mTh by the fifth harmonic of Ti: Sa laser generated in thorium by two-color femtosecond pulse consisting of the fundamental and thensecond harmonic of Ti: Sa laser (ω+2ω). It is shown that the rate of isomeric state excitation can be enhanced significantly with respect to other nucleus excitation processes in laser plasma or by an external coherent source at the resonance wavelength. This enhancement is due to the discussing process of “nonlinear laser nuclear excitation”.

Study of the fragmentation phenomena of TiO2 nanoparticles produced by femtosecond laser ablation in aqueous media

Since last decade, Pulsed Laser Ablation in Liquid (PLAL) has become an increasingly important technique for the production of the nanoparticles (NPs) since it usually provides high purity nanoparticle systems. This paper reports on the production and fragmentation of titanium oxide TiO2 nanoparticles by pulsed laser ablation of a titanium target immersed in Sodium Dodecyl Sulfate (SDS) solution using an ultrafast Ti:Sapphire laser. After the production of TiO2 nanoparticles for 30min of laser irradiation, second harmonics of the laser wavelength are re-applied for different energies (180,120, 60µJ) to SDS solution containing TiO2 colloids in order to fragment relatively large pieces to obtain smaller ones. It was found that size of nanoparticles after the treatment is independent of the initial characteristics of colloids, but depends strongly on laser parameters especially pulse energy and on the presence of chemically active species in the solution. It was reported that particle size and size distribution range can be decreased using second harmonics of Ti:Sapphire laser wavelengths by using different values of energy. Re-irradiation process at average energy value of 180μJ decreased average particle size from 185nm to 110nm. Characterization of the NPs was studied by applying various techniques such as UV–visible (UV–vis.), Transmission Electron Microscope (TEM), Dynamic Light Scattering (DLS) and Fourier Transform Infra-Red (FTIR).

Detailed studies of photocathodes based on Y thin films grown by PLD technique

The effects of laser fluence on the morphology of Y films in the regime characteristic of multiple-pulse laser deposition were investigated. Y thin films were deposited on silicon and copper substrates. The samples deposited on silicon substrate were used to deduce the morphology and the thickness of the deposited films. On the contrary, the samples deposited on copper were tested as photocathodes in a DC photodiode cell. The interest to produce Y-based photocathodes is due to the low work function of this metal with the possibility to drive such photocathodes with a visible radiation in the radio-frequency photo-injector. In this way it is possible to reduce the thermal emittance of the photoelectron beam and to increase the photocurrent intensity by utilizing the second harmonic of Ti:Sa driver laser. The quantum efficiency was measured for the first time by using a visible CW laser diode emitting at 406 nm.

Quasi-phase matching of third harmonic generation in corrugated discharge capillary

Abstract Quasi-phase matching third harmonic of Ti:sapphire laser was measured by propagation through corrugated discharge capillaries. The 1 cm long capillary with periodical varying inner radius was used with corrugation frequency of 200 μm. The longitudinal plasma density was periodically varied by a discharge current ablating the inner capillary walls, altering the refractive index accordingly. Average plasma density measured was 10 18 cm −3 at minimum corrugation radius. Peak laser intensity was 10 10 W/cm 2 allowing enough pondermotive energy to the electron for high harmonic generation.

Multiphoton ionization of the calcium atom by linearly and circularly polarized laser fields

We theoretically study multiphoton ionization of the Ca atom irradiated by the second (photon energy 3.1 eV) and third (photon energy 4.65 eV) harmonics of Ti:sapphire laser pulses (photon energy 1.55 eV). Because of the dense energy level structure the second and third harmonics of a Ti:sapphire laser are nearly single-photon resonant with the ${4s4p}$ $^1P^o$ and ${4s5p}$ $^1P^o$ states, respectively. Although two-photon ionization takes place through the near-resonant intermediate states with the same symmetry in both cases, it turns out that there are significant differences between them. The photoelectron energy spectra exhibit the absence/presence of substructures. More interestingly, the photoelectron angular distributions clearly show that the main contribution to the ionization processes by the third harmonic arises from the far off-resonant ${4s4p}$ $^1P^o$ state rather than the near-resonant ${4s5p}$ $^1P^o$ state. These findings can be attributed to the fact that the dipole moment for the ${4s^2}$ $^1S^e$ - ${4s5p}$ $^1P^o$ transition is much smaller than that for the ${4s^2}$ $^1S^e$ - ${4s4p}$ $^1P^o$ transition.

Spectral dependences of conical emission in gases: Minimization of scattering for ultra-short pulsed laser ablation

Parameters of conical emission (CE), at focusing of femtosecond and short picosecond pulses in ambient gases, are characterized in a wide range of experimental conditions. Scattered and absorbed energy, the beam profiles and spectra are compared for different duration and wavelengths of laser radiation (harmonics of Ti:Sa and Yb:YAG laser). Shorter wavelengths were found to be most beneficial for elimination of CE. Nearly no scattering of short picosecond pulses was observed at 515 nm in the energy density range up to 300 J/cm2. The results are analyzed in terms of the contributing ultra-fast phenomena effecting refraction index of gases (the Kerr effect, different mechanisms of ionization). Advantages of the visible pulses are illustrated in deep drilling experiments.

Control of relative carrier-envelope phase slip in femtosecond Ti:sapphire and Cr:forsterite lasers.

We were able to control relative carrier-envelope phase slip among mode-locked Ti:sapphire and Cr:forsterite lasers by employing electronic feedback. The pulse timings of these lasers were passively synchronized with our crossing-beam technique. Since the optical-frequency ratio of Ti:sapphire and Cr:forsterite is approximately 3:2, we can observe the phase relation by superimposing the third harmonic of Cr:forsterite and the second harmonic of Ti:sapphire lasers in time and in space. The spectrum width of the locked beat note was less than 3 kHz, which corresponds to the controlled fluctuation of a cavity-length difference of less than 10 pm.