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

Abstract

Nanosecond pulse laser-driven optical breakdown at SiO2 surfaces as probed by synchrotron-based Fourier transform infrared (SRFTIR) and photoluminescence (PL) microscopies is presented. SRFTIR mapping of laser damage identified localized non-bridging Si-O vibrational modes at ∼950 cm−1 which became stiffer as 355 nm laser pulse lengths were increased from 5 to 20 ns. The bridging Si-O-Si transverse optic mode frequency varied significantly across damaged regions indicating a wide range of average bond angles, softening slightly with increasing pulse length. 355 nm-excited PL images of laser modified regions could be directly correlated with the structural modifications identified through SRFTIR.

Morphology of ejected particles and impact sites on intercepting substrates following exit-surface laser damage with nanosecond pulses in silica

“…[1][2][3][4][5][6][7][8] Experimental evidence and modeling suggest that the material is exposed to pressures of the order of 10 GPa and temperatures of the order of 1 eV. [9][10][11][12] Considerably less information exists on the relaxation of the metastable superheated material and the surrounding "cold" material that was exposed to high pressures and stresses generated during the process. The relaxation process may include vaporization, particle ejection, radiative cooling, and phase transformation.…”

Phase modulation in high power optical systems caused by pulsed laser-driven particle ablation events

“…When this wave impinges on the silica surface, it can densify the underlying material and is a likely source of the pitting found in these experiments and similar to the shock densification of silica observed from 3 ns laser damage events. 5,10 At pressures >7 GPa, higher pressure phases of silica are expected, 11 though from our FTIR analysis detected no discernible variation in the Si bond coordination that would support this. However, the small increase in T F shown in Fig.…”

Correlation of UV damage threshold with post-annealing in CVD-grown SiO2 overlayers on etched fused silica substrates

“…The presence of a NB mode in the FTIR reflectance spectra suggested there may be a population of optically-active NBOHCs -in addition to other defects -in the CVD films that have previously been associated with optical damage [6,20]. In order to observe more directly the electronic transitions that may be associated with these defect vibrational states, we performed confocal PL microscopy with near-UV (400 nm) laser excitation, and a 430 nm long pass filter at the collection side.…”

“…A lateral step size of 50 m was used to measure variations in IR reflectance as a function of local thermal treatment. Additional details of the SR-FTIR system are described elsewhere [6].…”

“…Photoluminescence (PL) from electronic transitions has been observed from these structures but with much shorter life-time than the known point intrinsic defects [2]. At the same time, intrinsic point defects associated with nonbridging oxygen hole centers (NBOHC) and oxygen deficient centers (ODC) have also been associated to laser damage in silica [4] [5] [6]. In addition to these intrinsic defects, extrinsic defects in the form of impurities left by the polishing process, or introduced through environmental contamination, can also lead to absorption of laser light and damage [7].…”