Effect of two-beam coupling in strong-field optical pump-probe experiments

Abstract

Nonlinear optics experiments measuring phase shifts induced in a weak probe pulse by a strong pump pulse must account for coherent effects that only occur when the pump and probe pulses are temporally overlapped. It is well known that a weak probe beam experiences a greater phase shift from a strong pump beam than the pump beam induces on itself. The physical mechanism behind the enhanced phase shift is diffraction of pump light into the probe direction by a nonlinear refractive index grating produced by interference between the two beams. For an instantaneous third-order response, the effect of the grating is to simply double the probe phase shift, but when delayed nonlinearities are considered, the effect is more complex. A comprehensive treatment is given for both degenerate and nondegenerate pump-probe experiments in noble and diatomic gases. Results of numerical calculations are compared to a recent transient birefringence measurement [Loriot et al., Opt. Express 17, 13429 (2009)] and a recent spectral interferometry experiment [Wahlstrand et al., Phys. Rev. A 85, 043820 (2012)]. We also present results from two new experiments using spectrally-resolved transient birefringence with 800 nm pulses in Ar and air and degenerate chirped pulse spectral interferometry in Ar. Both experiments support the interpretation of the negative birefringence at high intensity as arising from a plasma grating. arXiv:1302.3208v2 [physics.optics]

Sensitivity of propagation and energy deposition in femtosecond filamentation to the nonlinear refractive index

“…As an example, extracted 2 n values for the major constituents of air, N 2 and O 2 , show a range of variation exceeding ~100%. Some of this variation can be attributed to nonlinear 3D propagation effects [8,11], unintentional two-beam coupling in degenerate pump-probe experiments owing to the presence of laser-induced Kerr, plasma, and rotational gratings [10,11,13,14], and the laser pulsewidth dependence of the nonlinear response, which had not been directly resolved [8,[10][11][12].…”

Interpretation of negative birefringence observed in strong-field optical pump-probe experiments: High-order Kerr and plasma grating effects

“…3 (c)]. However, it was recently suggested that the absence of asymmetry could be the result of the the PG effect when considering temporally chirped pulses [42]. Although all our experiments so far were performed for compressed pump and probe beams, a set of data recorded with chirped pump and probe pulses around the region of inversion are compared to numerical simulations in Fig.…”

“…The fact that the symmetry of the observed signals is preserved while the pulses are chirped and also that the HOK model does not predict any symmetry reversal of the signal allows to exclude the chirp as a possible artifact from our measurements. Finally, it should be pointed that large chirps, as those responsible for symmetric PG signal [42], lead at constant energy level to a dramatic drop of intensity and consequently to a significant decrease of the birefringence signal above the inversion threshold. This along with a temporal broadening of the signal could have been straightly noticed in the previous studies [1,5] so that any unforeseen significant chirp would have been corrected.…”

Dynamic-grating-assisted energy transfer between ultrashort laser pulses in lithium niobate

“…Quite quickly the developed approaches were extended for the description of the interaction of light pulses. The term "two-beam coupling" was still used to define the interaction of pulses (see, e.g., [5][6][7]), but it became often replaced by "pulse energy transfer" [8][9][10][11][12] or "energy exchange" [13]. The researchers dealing with pump-probe techniques were facing the problem of so called "coherent peaks" [14,15], which is a consequence of pump and probe pulse coupling via a dynamic grating, too [16].…”