In order to correlate laser damaging fluence with the pertinent theoretical considerations, there were many attempts in the past to establish reliable damage predicting criterion. Such criterion then could be used to estimate laser fluence that triggers the damage process in various optical materials. For example, reaching of materials critical property such as - temperature (melting point), - thermoelastic stress, - electron density are good examples. On the other hand, however, it is already clear that damage mechanism is irradiation condition (wavelengths, pulse duration) and material property dependent. There are no physical restrictions of causing damage by reaching critical stress without critical electron density and vice versa. Accordingly, total absorbed energy or absorbed energy density is likely more suited candidate of universal damage criteria as a common denominator for all critical processes. To our best knowledge, it was never estimated experimentally in the vicinity of the damaging fluence of optical materials. In this study, we present a novel approach based on pump- probe digital holographic microscopy that enables quantitative assessment of absorbed energy during the damage process in transparent dielectric media. By using this method, a case study is conducted in fused silica glass with sharply focused infrared laser pulses at 1030 nm central wavelength and 450 fs pulse duration. By doing so we were able to estimate energy fraction of the incident pulse that is needed to trigger optical damage.
Over the last decade there has been a continuing interest in slow and stored light based on the electromagnetically
induced transparency (EIT) effect, because of their potential applications in quantum information manipulation.
However, previous experimental works all dealt with the single-component slow light which cannot be employed as a
qubit. In this work, we report the first experimental demonstration of two-component or spinor slow light (SSL) using a
double tripod (DT) atom-light coupling scheme. The oscillations between the two components, similar to the Rabi
oscillation of a two-level system or a qubit, were observed. Single-photon SSL can be considered as two-color qubits.
We experimentally demonstrated a possible application of the DT scheme as quantum memory and quantum rotator for
the two-color qubits. This work opens up a new direction in the slow light research.
Nonlinear losses experienced by the self-focusing femtosecond pulse is shown to have an important effect on the
refractive index modifications in fused silica. The region of the maximum induced change is found to coincide
with that of the maximum nonlinear losses of the pulse. It is found as well that material densification and the
formation of color centers both contribute to the index change in that zone. Experimental results are supported
by numerical simulations using model that takes into account accumulation of the permanent refractive index
changes and their influence back on the pulse. Both the color
center- and compaction-induced changes cause the
modification to develop into a waveguide and lead to the narrowing of supercontinuum spectra.
We report on the refractive index grating formation by filamentary propagation of femtosecond pulses in fused
silica. The relevant exposure and work cycles are considered both experimentally and through numerical study,
involving a model of light filaments supported by conical wave, capable to capture permanent glass refraction
index changes.
For high intensity lasers it is very important to choose appropriate optical elements. Since invention of high power lasers laser-induced damage of optical coatings was subject of extensive investigations. At high laser intensities the self-focusing in optical elements appears and intensity at rear optics surface can be much higher than at the front surface. Due to this damage of rear-surface can be reached much faster than damage of the front surface. We investigated the influence of self-focusing on damage threshold in fused-silica windows with anti-reflective coatings on both sides. In our experiments we used titanium-sapphire chirped pulse amplification system (130 fs, 2 mJ, 1 kHz repetition rate pulses at 800 nm). We have tested 1 mm, 3 mm and 6 mm thickness fused-silica windows with identical anti-reflective coatings. The front surface of the samples was placed in the waist of focused beam. The experiments were performed for effective spot diameters on the front 145 μm, 95 μm and 43 μm respectively. The experiments showed the self-focusing of beam inside the fused silica window and self-focusing dependence on initial beam diameter. The damage behavior was dependent on irradiation history. Also we found quite strong nonlinear absorption in fused silica.
Dynamics of damage formation by focusing intense femtosecond pulses inside the fused silica glass is studied in wide energy range. Damage usually is initiated in the zone near geometrical focus, which is preceded by the zone where beam propagates in the form of multiple filaments. For high repetition rate pulses damage appears as an extended narrow track along the beam path, which forms due to the propagation of the initial damage zone toward the laser source. For low repetition rate pulses extended damage tracks don't form.
We report experimental observation of modification and damage in bulk of fused silica induced by intense multiple femtosecond pulses. At power levels several times exceeding critical power for self-focusing the modification is in the form of some permanent changes inside the material and these effects are closely correlated with the beam filamentation process. Longer distances of propagation and much higher pulse energies produce bulk damage in the form of scattering zones. The formation of damage in anti-reflective-coated fused silica windows is also reported. Numerical simulations involving self-focusing, multiphoton absorption and permanent change of the refractive index of the bulk material were found to be in agreement with the experimental results.
The dynamics of multiple pulse laser-induced damage in the form of cracking or nonlinear coloration in bulk materials (fused silica and borosilicate K8 glass) was studied under the irradiation by femtosecond pulses at 800 nm wavelength. A Ti:sapphire chirped pulse amplification system with ~130-fs pulse duration and ~1-mJ pulse energy at 1-kHz repetition rate was used in the experiment. Self-guided propagation of femtosecond pulses over greater than 1-cm lengths accompanied by intensive supercontinuum generation was observed and studied in an interaction geometry where the laser beam was focused in the middle of the thick (~4 cm) sample. The pulse energy value at which self-guided propagation and supercontinuum generation in fused silica was observed was ~60 times lower than the laser-induced damage threshold. The nonlinear coloration in K8 glass was present at pulse energy values which exceeded the threshold for self-guided propagation. Numerical simulations involving self-focusing, temporal dispersion and multiphoton absorption were found to be in good agreement with the experimental results.
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