Evidence for a wide continuum of polymorphs ina-SiO2

UV-laser-induced densification of fused silica: a molecular dynamics study

“…On the other hand, our densification results are comparable to those from higher-laser-fluence experiments. Fiori and Devine [5] used a 248 nm laser with a fluence of 300 mJ/cm 2 and a pulse duration of 20 ns to study the densification of a-SiO 2 thin film. For an accumulated dose of 30 J/cm 2 (equivalent to an absorbed fluence of 0.16 J/cm 2 ), a densification of approximately 1% was achieved.…”

“…Densification induced by c rays, electrons, protons, and deuterons was also observed [4]. In 1986, for the first time, Fiori and Devine studied 248 nm laser-induced changes in a-SiO 2 thin films with a laser fluence of 300 mJ/cm 2 [5]. Since then, intensive experimental efforts have been undertaken to study UV-laser-induced densification of bulk fused silica [1,[6][7][8][9][10][11].…”

Ablation and compaction of amorphous SiO2 irradiated with ArF excimer laser

“…Takigawa et al [7] developed an Ar 2 excimer laser (k ¼ 126 nm, E ¼ 9:87 eV) and they discovered generation of silicon on a-SiO 2 surface. Fiori and Devine [8][9][10] found that the structural changes were induced in a-SiO 2 by a KrF excimer laser. They demonstrated that oxygen loss was observed by Augerelectron spectroscopy (AES) in a thin ($15 A) SiO 2 film exposed to 248 nm laser irradiation for 1 h at an energy density of 100 mJ/cm 2 (pulse duration 10 ns, repetition frequency 20 Hz) [10].…”

Fibre gratings and devices for sensors and lasers

“…The role of fundamental research remains critical to establishing and optimizing the necessary pathways of achieving the ideal performance parameters many of these new applications demand as well as open new directions previously unconsidered -for example, the observation of the Birnbaum effect [10] within a volume of glass [11,12] irradiated with a femtosecond laser has spurred the notion of using this previously undesirable process to advantage in creating novel extreme polarisation-selective nano structures, whether within the grating period itself or simply as a structure on it own [11,12]. Another important area which has been revisited is the well known photosensitivity phenomena of UV induced densification through excitation of the band edge, which predates Ken Hill's observations in germanosilicate glass by decades [13][14][15][16]. It has become an important tool in writing gratings in pure silica fibres, in particular, structured optical fibres such as photonic crystal fibres [17] and Fresnel fibres [18] where the presence of high index contrast holes prevents direct femtosecond laser grating writing, for example.…”