602 research outputs found
High energy terahertz pulses from organic crystals: DAST and DSTMS pumped at Ti:sapphire wavelength
High energy terahertz pulses are produced by optical rectification (OR) in
organic crystals DAST and DSTMS by a Ti:sapphire amplifier system centered at
0.8 microns. The simple scheme provides broadband spectra between 1 and 5 THz,
when pumped by collimated 60 fs near-infrared pump pulse and it is scalable in
energy. Fluence-dependent conversion efficiency and damage threshold are
reported as well as optimized OR at visible wavelength.Comment: 8 pages, 6 figure
Micromachining of hardened Portland cement pastes using femtosecond laser pulses
Femtosecond laser pulses (30fs in length) of various energies were utilised for production of single and multiple overlapping ablation sites on flat polished surfaces of hardened Portland cement pastes. In order to assess the sizes of the ablation sites and possible subsurface laser-induced damage, the ablation sites were investigated using environmental scanning electron microscopy (ESEM) - both from normal top-down view and in cross-sections. Furthermore, approximately 10-µm wide notches were produced using femtosecond pulses on cylindrical microspecimens (150µm in diameter) of hardened Portland cement pastes. In addition to electron microscopy observations, several microspecimens were investigated using synchrotron-based X-ray computed microtomography (SRμCT). The results suggest that production of "damage-free” samples for micromechanical testing of hardened Portland cements pastes is possibl
Temporal characterization of individual harmonics of an attosecond pulse train by THz streaking
We report on the global temporal pulse characteristics of individual
harmonics in an attosecond pulse train by means of photo-electron streaking in
a strong low-frequency transient. The scheme allows direct retrieval of pulse
durations and first order chirp of individual harmonics without the need of
temporal scanning. The measurements were performed using an intense THz field
generated by tilted phase front technique in LiNbO_3 . Pulse properties for
harmonics of order 23, 25 and 27 show that the individual pulse durations and
linear chirp are decreasing by the harmonic order
Generation of 1.5-octave intense infrared pulses by nonlinear interactions in DAST crystal
Infrared pulses with large spectral width extending from 1.2 to 3.4 μ m are generated in the organic crystal DAST (4-N, N-dimethylamino-4′-N′-methylstilbazolium tosylate). The input pulse has a central wavelength of 1.5 μ m and 65 fs duration. With 2.8 mJ input energy we obtained up to 700 μ J in the broadened spectrum. The output can be easily scaled up in energy by increasing the crystal size together with the energy and the beam size of the pump. The ultra-broad spectrum is ascribed to cascaded second order processes mediated by the exceptionally large effective χ 2 nonlinearity of DAST, but the shape of the spectrum indicates that a delayed χ 3 process may also be involved. Numerical simulations reproduce the experimental results qualitatively and provide an insight in the mechanisms underlying the asymmetric spectral broadening
Field-driven femtosecond magnetization dynamics induced by ultrastrong coupling to THz transients
Controlling ultrafast magnetization dynamics by a femtosecond laser is
attracting interest both in fundamental science and industry because of the
potential to achieve magnetic domain switching at ever advanced speed. Here we
report experiments illustrating the ultrastrong and fully coherent light-matter
coupling of a high-field single-cycle THz transient to the magnetization vector
in a ferromagnetic thin film. We could visualize magnetization dynamics which
occur on a timescale of the THz laser cycle and two orders of magnitude faster
than the natural precession response of electrons to an external magnetic
field, given by the Larmor frequency. We show that for one particular
scattering geometry the strong coherent optical coupling can be described
within the framework of a renormalized Landau Lifshitz equation. In addition to
fundamentally new insights to ultrafast magnetization dynamics the coherent
interaction allows for retrieving the complex time-frequency magnetic
properties and points out new opportunities in data storage technology towards
significantly higher storage speed.Comment: 25 page
Macroscopic effects in attosecond pulse generation
We examine how the generation and propagation of high-order harmonics in a
partly ionized gas medium affect their strength and synchronization. The
temporal properties of the resulting attosecond pulses generated in long gas
targets can be significantly influenced by macroscopic effects, in particular
by the intensity in the medium and the degree of ionization. Under some
conditions, the use of gas targets longer than the absorption length can lead
to the generation of self-compressed attosecond pulses. We show this effect
experimentally, using long argon-filled gas cells as generating medium.Comment: 5 pages 4 figure
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