In doing so we resort here to the lowest-order QED processes, that is nonlinear Compton and nonlinear Breit–Wheeler (BW). A prerequisite would be to find observables which display the typical dependence ∝ αχ 2/3, where we denote by α the above quoted fine-structure constant at. With respect to increasing laser intensities the quest for the possible break-down of the Furry picture expansion in line with the RN conjecture becomes, besides its principal challenge, also of 'practical' interest, whether one can explore experimentally this yet uncharted regime of QED. (In QED itself, an analog situation is meet in the Coulomb field of nuclear systems with proton numbers Z > Z crit ≈ 173: if αZ crit > 1 the QED vacuum break-down sets in cf for the actual status of that field). in evaluations of observables in the soft sector where α QCD > 1, cf. The latter requires adequate calculation procedures, as the lattice regularized approaches, which are standard since many years in QCD, e.g. However, the Ritus–Narozhny (RN) conjecture argues that the effective coupling becomes αχ 2/3, meaning that the Furry picture expansion beaks down at αχ 2/3 > 1 (for the definition of χ see below) and one enters a genuinely non-perturbative regime. an electron) with the background are accounted for in all orders, and the interactions with the quantized photon field remains perturbatively in powers of α. The situation in QED becomes special when considering processes in external (or background) fields: one can resort to the Furry (or bound-state) picture, where the (tree-level) interactions of an elementary charge (e.g. In QED, however, is not such a strict limit, nevertheless, predictions/calculations of some observables agree with measurements within 13 digits, see for some examples. ![]() In contrast, quantum chromo-dynamics (QCD) as another SM pillar possesses a negative beta-function due to the non-Abelian gauge group, giving rise to the asymptotic freedom,, i.e. Want to learn more on LIDT measurements and evaluation? Check out different testing regimes at Laser-Induced Damage Threshold (LIDT) Testing.Quantum electro-dynamics (QED) as pillar of the standard model (SM) of particle physics possesses a positive beta-function which makes the running coupling strength increasingly with increasing energy/momentum scale. Thus, laser peak power value can be always calculated, if necessary. It should be noted, that Laser-Induced Damage Threshold (LIDT) expressed as laser peak fluence is always quoted with the pulse duration used for the testing. Sometimes (in community of nonlinear optics) intensity of peak irradiance is used instead of fluence: Then it is converted to the units of square centimeters at the I0/e level of maximal intensity. In the case of Gaussian beams, effective focal spot area is registered by CCDs. To calculate fluence use the following equation or download free app Lidaris Calc: ![]() Within the community of laser scientists and technicians, it is very common to define fluence in units of J/cm2. Laser fluence describes the energy delivered per unit (or effective) area. Let us take a closer look how it is evaluated. Laser-Induced Damage Threshold (LIDT) is frequently expressed in units of laser peak fluence or laser peak power density.
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