Localized Dynamics during Laser-Induced Damage in Optical Materials

Abstract

Laser-induced damage in wide band-gap optical materials is the result of material modifications arising from extreme conditions occurring during this process. The material absorbs energy from the laser pulse and produces an ionized region that gives rise to broadband emission. By performing a time-resolved investigation of this emission, we demonstrate both that it is blackbody in nature and that it provides the first direct measurement of the localized temperature of the material during and following laser damage initiation for various optical materials. For excitation using nanosecond laser pulses, the plasma, when confined in the bulk, is in thermal equilibrium with the lattice. These results allow for a detailed characterization of temperature, pressure, and electron densities occurring during laser-induced damage.

Synchrotron radiation infrared microscopic study of non-bridging oxygen modes associated with laser-induced breakdown of fused silica

“…A time-dependent runaway absorption process is thought to take place with collapse of the ~9eV band gap 3 and transient temperatures and pressures as high as 10,000 K and 10 GPa, respectively. 4 Phase transformations, 5 shock-induced densification, 6 and the creation of electronic defects [7][8][9][10] have been observed following a laser-breakdown event. Because the onset of breakdown is strongly coupled to laser pulse characteristics, 11 additional insight might be achieved by probing a-SiO 2 as a function of laser pulse length .…”

Thermal Approaches to Interpret Laser Damage Experiments

“…Indeed, for large enough values of k whatever the value of n,t h es h a p eo fQ abs with respect to a remains almost the same that imposes the value of x. Now, the optical constants can be determined from experimental data F c = 10 ± 1 J/cm 2 (Carr et al, 2004) and x = 0.35 ± 0.05 (Burnham et al, 2003). The theoretical index range providing these two values is obtained by performing a superposition of Figs.…”

“…It is worth noting that the associated Mie absorption efficiency with the latter optical indices is Q abs (a c )=6.5 % where a c ≃ 100 nm. In order to compare to experiments where the ionized region size is estimated to 30 μm (Carr et al, 2004) in conditions where the fluence is twice the critical fluence (for such a high energy, the plasma spreads over the whole focal laser spot), we have evaluated Q abs with the above found index and a = 30 μm.I nt h a tc a se,Q abs ≃ 10 % which is close to the 12 % experimental value (Carr et al, 2004). It is noteworthy that Q abs saturates with respect to a for such values of the optical index and absorber size.…”

“…The plot of F as a function of a exhibits a minimum (Hopper & Uhlmann, 1970) (see Fig. 1) and since the existence of at least one absorber of size a is assumed, the critical fluence necessary to reach the critical temperature T c (set to 10000 K in all the calculations (Carr et al, 2004)) can thus be written as :…”

Evaluation of UV absorption coefficient in laser-modified fused silica

“…1,2 In large bandgap materials, such as fused silica (SiO 2 ), laser intensities in excess of 10 12 W/cm 2 are required to achieve intrinsic breakdown. 3 However, defects in the material can initiate localized breakdown at more than two orders of magnitude lower intensities.…”