Dispersion anomalies of tuning characteristics and spectrum of an optical parametric oscillator

Abstract

Recently, it has been shown that if we consider the higher derivative correction, the viscosity bound conjectured to be η/s = 1/4π is violated and so is the causality. In this paper, we consider medium effect and the higher derivative correction simultaneously by adding charge and Gauss-Bonnet terms. We find that the viscosity bound violation is not changed by the charge. However, we find that two effects together create another instability for large momentum regime. We argue the presence of tachyonic modes and show it numerically. We draw a phase diagram relevant to the instability in charge-coupling space. Correspondence. chemical potential in the theory was figured out in [8,9]. Phases of these theories were also discussed in D3/D7 setup [10 -12] as well as in D4D8D8 [9].More recently, it had been conjectured that the viscosity value of theories with gravity dual may give a lower bound for the η/s = 1/4π for all possible liquid [13]. However, the authors of [14] and [15] showed that if we consider the stringy correction to α ′ order, the viscosity bound is violated and causality is also [16] violated as a consequence (See also for more recent paper [17]).The α ′ terms are also related to the (in)stability issues of black holes. The instability of D-dimensional asymptotically flat Einstein-Gauss-Bonnet black holes has been discussed by several authors [18,19]. Their results show that for the gravitational perturbations of Schwarzschild black holes in D = (from 5 to 11) Gauss-Bonnet gravity, the instability occurs only for D = 5 and D = 6 cases at large value of α ′ [19].In this paper, we add charge together with the Gauss-Bonnet term, and calculate η/s and consider the stability issue including the causality violation. We find that the viscosity bound violation is not changed by the charge. However, we find that for large momenta regime, there exists a new instability due to the charge effect. The linearized perturbation has a negative frequency squared signaling an instability. We draw the phase diagram relevant to the instability. We emphasize that the new instability present only if both charge and Gauss-Bonnet term present.

Femtosecond nonlinear frequency conversion based on BiB3O6

“…57b in comparison to Fig. 57a, it can be concluded that in the spectral range where the spectral gain bandwidth is determined by higher-order dispersion terms, the effect of the gain coefficient, Γ , is rather weak [111,142]. Figs.…”

“…It is clear that for collinear type-I interaction, the third-order term (10) also vanishes near degeneracy, and this makes it necessary to consider the fourth-order term [111]. From our consideration, this term is given by Eq.…”

“…Many other nonlinear crystals with sufficient birefringence in fact possess the same property, provided the three wavelengths lie within the transparency range. This is related to the existence of retracing behavior of the phase-matching curves [111,112], which can be traced back to the material dispersive properties. In any case, it happens at a certain pump wavelength that does not necessarily coincide with the wavelengths of the available femtosecond sources that can be used for pumping OPAs or OPGs.…”

Broadband continuum generation in GaAs

“…Also, an OP-GaAs optical parametric oscillator (OPO) of ns pulse duration was built and produced tunable output from 2-11 µm [5]. We recently demonstrated optical parametric generation (OPG) in OP-GaAs that produced an ultrabroad infrared continuum [6].Extremely wide tuning bandwidths for parametric processes are associated with the zero-GVD wavelength [7]. For an interaction where d 2 k/dω 2 = 0 at the degenerate signal-idler wavelength, then detuning the signal and idler away from degeneracy will, to third order, leave the phase-mismatch (∆k) unchanged so that the tuning bandwidth near degeneracy will be wide.…”

“…Extremely wide tuning bandwidths for parametric processes are associated with the zero-GVD wavelength [7]. For an interaction where d 2 k/dω 2 = 0 at the degenerate signal-idler wavelength, then detuning the signal and idler away from degeneracy will, to third order, leave the phase-mismatch (∆k) unchanged so that the tuning bandwidth near degeneracy will be wide.…”