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We experimentally and numerically characterize multiple filamentation of laser pulses with incident intensities of a few TW/cm2. Propagating 100 TW laser pulses over 42 m in air, we observe a new propagation regime where the filament density saturates. As also evidenced by numerical simulations in the same intensity range, the total number of filaments is governed by geometric constraints and mutual interactions among filaments rather than by the available power in the beam.

Owing to an erroneous value of the multiphoton ionization coefficient σK , the action of the plasma response was underestimated in the numerical simulations discussed in Appendix B of our original paper. This mistake led us to conclude that almost no plasma-induced intensity saturation effect takes place when pump and Stokes peak intensities stay less than 5 TW/cm2. The corrected Fig. 14 below should replace Fig. 14 of our original paper. The new Fig. 14 clearly shows that both pump and Stokes pulses are affected by the self-generated plasma in this high-intensity regime. Dark blue and green curves follow from the numerical integration of the complete system including the corrected plasma contributions, whereas bright curves refer to the initial system discarding plasma generation (unchanged from the previous version). We observe that the plasma response reduces the maximum intensity of the pump pulse (dark blue curve) by about 1–2 TW/cm2 and keeps the intensity of the Stokes pulse (dark green curve) clamped at ∼2 TW/cm2. A second qualitative change introduced by the plasma is shown in Fig. 14(d): the Stokes intensity is amplified earlier in the middle of the sample for the unmodulated 27Pcr pump pulse. Apart from these differences, the nonlinear dynamics are, however, analogous to those where plasma generation is neglected. Therefore, the self-focusing properties of the unmodulated and modulated pulses discussed in the main body of our paper remain valid.

The coupling between Kerr filamentation and stimulated Brillouin scattering (SBS) is investigated for nanosecond laser pulses propagating in bulk silica. Phase modulated pulses with moderate spectral bandwidth may not prevent backscattering. We demonstrate the existence of a critical bandwidth above which SBS is efficiently suppressed at any pump power.

We numerically investigate the interplay between Kerr self-focusing (SF) and transient stimulated Brillouin scattering (SBS) for nanosecond pulses in bulk silica. The influences of the input power, phase, or amplitude modulations in the pump pulse together with the incident beam shape on the filamentation dynamics are discussed. We show that appropriate amplitude modulations dividing nanosecond laser pumps into picosecond-long pulse trains inhibit SBS at any power. In contrast, phase-modulated pulses with comparable spectral width undergo multiple filamentation and earlier beam collapse due to modulational instabilities. We demonstrate, however, the existence of a critical pump bandwidth above which SBS can be efficiently suppressed by phase modulations even at high powers. This observation also holds for squared beam shapes with much broader spatial spectra, which decay more easily into multiple filaments over short distances. Intensity profiles of the reflected Stokes waves for such broad pumps are finally discussed.

The propagation of powerful nanosecond optical pulses at the wavelength of 355 nm in thick silica windows usually gives rise to Kerr-induced multiple filamentation, which breaks the homogeneity of the energy distribution and can initiate surface or bulk damage. Part of the incident beam is furthermore back-reflected by stimulated Brillouin scattering (SBS), leading to the creation of a Stokes wave which is also source of damage at the front surface of the sample [1,2]. To address this problem, we study the interaction of these two nonlinear effects from coupled envelope equations in full (3+1)-dimensional geometry. Emphasis is put on the influence of the incident pulse spatial profile and of phase or amplitude modulations applied to the pump wave.

The multiple filamentation of powerful light pulses in fused silica is numerically investigated for central wavelengths at 355 nm and 1550 nm. We consider different values for beam waist and pulse duration and compare the numerical results with behaviors expected from the plane-wave modulational instability theory. Before the nonlinear focus, the spatiotemporal intensity patterns can be explained in the framework of this theory. Once the clamping intensity is reached, for long input pulse durations (approx1 ps), the ionization front defocuses all trailing components within a collective dynamic, and a spatial replenishment scenario takes place upon further propagation. Short pulses (approx50 fs) undergo similar ionization fronts, before an optically turbulent regime sets in. We observe moderate changes in the total temporal extent of ultraviolet pulses and in the corresponding spectra. In contrast, infrared pulses may undergo strong temporal compression and important spectral broadening. For short input pulses, anomalous dispersion and self-steepening push all pulse components to the trailing edge, where many small-scaled filaments are nucleated. In the leading part of the pulse, different spatial landscapes, e.g., broad ring patterns, may survive and follow their own propagation dynamics.

The coupling between Kerr filamentation and stimulated Brillouin scattering (SBS) is numerically investigated for nanosecond laser pulses in silica. In self-focusing regime, phase-modulated broadband pumps may not weaken backscattering, which appropriate amplitude modulations can achieve.

In Saccharomyces cerevisiae , double-strand breaks (DSBs) activate DNA checkpoint pathways that trigger several responses including a strong G 2 /M arrest. We have previously provided evidence that the phosphatases Ptc2 and Ptc3 of the protein phosphatase 2C type are required for DNA checkpoint inactivation after a DSB and probably dephosphorylate the checkpoint kinase Rad53. In this article we have investigated further the interactions between Ptc2 and Rad53. We showed that forkhead-associated domain 1 (FHA1) of Rad53 interacts with a specific threonine of Ptc2, T376, located outside its catalytic domain in a TXXD motif which constitutes an optimal FHA1 binding sequence in vitro. Mutating T376 abolishes Ptc2 interaction with the Rad53 FHA1 domain and results in adaptation and recovery defects following a DSB. We found that Ckb1 and Ckb2, the regulatory subunits of the protein kinase CK2, are necessary for the in vivo interaction between Ptc2 and the Rad53 FHA1 domain, that Ckb1 binds Ptc2 in vitro and that ckb1 Δ and ckb2 Δ mutants are defective in adaptation and recovery after a DSB. Our data thus strongly suggest that CK2 is the kinase responsible for the in vivo phosphorylation of Ptc2 T376.

We report on the all-optical detection of Rydberg states in a effusive atomic beam of strontium atoms using electromagnetically induced transparency (EIT). Using narrow-linewidth CW lasers we obtain an EIT linewidth of 5 MHz. To illustrate the high spectroscopic resolution offered by this method, we have measured isotope shifts of the 5s18d ^1D_2 and 5s19s ^1S_0 Rydberg states. This technique could be applied to high-resolution, non-destructive measurements of ultra-cold Rydberg gases and plasmas., Comment: 8 pages, 4 figures