Norbert Leclerc

The UV-induced 210 nm absorption band in fused silica with different thermal history and stoichiometry

Abstract In high-purity, OH-rich fused silica, the generation rate of the 210 nm absorption band under irradiation with 248 nm laser photons was determined. The density of D2 ‘defects’ was determined by Raman spectroscopy as a measure of the fictive temperatures of the fused silica samples. The data show a correlation between the generation rate of the 210 nm absorption band and the D2 intensity in samples with differing thermal histories. It was assumed that the generation rate of the 210 nm absorption band is related to the concentration of a precursor defect. By taking the energy of formation of the D2 ‘defect’ reported by Geissberger and Galeener, the energy of formation of the precursor defect to 2.3 (±0.5) eV was estimated. It is shown that the generation rate of the 210 nm absorption band is higher in samples synthetized under higher oxygen partial pressure and that the D2 ‘defect’ is not the predominant precursor defect in flame pyrolyzed fused silica.

Transient absorption and fluorescence spectroscopy in fused silica induced by pulsed KrF excimer laser irradiation

We have carried out in situ transient absorption and fluorescence spectroscopy measurements in two ‘‘wet’’(OH content ∼0.1%) fused silica samples (Suprasil II from Heraeus Amersil and P‐30 from Shin‐Etsu Quartz Product) during KrF laser irradiation. Both samples exhibit an absorption peak at 210 nm corresponding to the E’ center. For Suprasil II, there is also a 265 nm absorption peak, and both peaks increase with the number of irradiated pulses showing little relaxation after the laser was turned off. The region irradiated with three million pulses at 400 mJ/cm2 fluence ten months ago has a residual absorption of about 10%/cm at 210 nm. On the other hand, the P‐30 shows a rapid increase in the 210 nm absorption in both the unirradiated and previously irradiated regions during the initial irradiation and levels off after a few thousand pulses. There is no residual absorption at the spot irradiated for 63 million pulses ten months ago. However, the initial rate of increase in the previously irradiated spot...

Luminescence and transient absorption bands in fused SiO2 induced by KrF laser radiation at various temperatures

Abstract High purity fused silica with about 800 ppm OH content was irradiated with KrF laser radiation (248 nm) at temperatures between −180°C and room temperature. The laser-induced absorption at 215 nm (due to E′ centers) was investigated. The generation rate of E′ centers from a precursor state depends linearly on the applied energy density, indicating the presence of a one-photon generation process for E′ centers in addition to the two-photon generation process from the silica network. The generation rate and relaxation of the 215 nm band is reduced at temperatures below room temperature. A luminescence band centered at 650 nm is excited during irradiation. A transient non-bridging oxygen center is postulated to explain the observed increase of the luminescence intensity with decreasing temperatures and with increasing radiation energy density.

KrF-laser irradiation induced defects in all silica optical fibers

Abstract High power UV laser irradiation of synthetic fused silica material induces transient absorption bands centered at 215 and 265 nm. The temporal behaviour of the 215 and the 265 nm absorption bands and also of the 248 nm laser transmission were measured with a transient absorption spectrometer during KrF excimer laser irradiation. Fiber samples made from stoichiometric and non-stoichiometric fused silica core material were irradiated at room temperature. The absorption at 215 nm correlates with the laser absorption in stoichiometric materials, whereas in the sample with oxygen rich core material a linear correlation is observed for 265 and 248 nm. The experimental data give evidence that the laser induced decrease in transmission at the laser wavelength can be reduced by using stoichiometric material.

KrF-excimer-laser-induced absorption and fluorescence bands in fused silica related to the manufacturing process

Transient and permanent UV absorption bands and fluorescence bands induced by 248 nm excimer laser radiation in fused silica are reported. It is shown that the permanent absorption measurements are not suitable to characterize the material with respect to transmission of high power laser pulses. In fused silica samples with high OH - content recovery of the 210 nm absorption band is observed after the end of irradiation. In samples with low OH - content no quick re covery is observed. 1 .

Optical Fiber Transmission Of Excimer Laser Pulses

The use of optical fibers to transmit high power UV pulses from an excimer laser is desirable for many applications. We have tested different tapered and untapered fibers with regard to power transmission properties and lifetime at 308 nm from a XeCl excimer laser with unstable resonator (8 nsec pulse length). The transmitted power density in a 600 μm tapered fiber decreases from initally 1.25 to 1.0 GW/cm2 over a period of 105 pulses. This is sufficient for a lot of applications, such as medical surgery or etching of selected types of ceramics.

Bundle of tapered fibers for the transmission of high-power excimer laser pulses

For the transmission of high-power excimer laser radiation in the kilowatt range, a flexible bundle of tapered quartz fibers is presented. Thirty fibers with a tapered coupling section are assembled in a bundle, which is tested with an excimer laser providing 2 J pulse energy at repetition rates of up to 20 pulses per second. The bundle showed good transmission qualities at 308 nm wavelength with an output power of 0.5 J/pulse. Catastrophic damage of fibers or other bundle elements did not occur during irradiation. The transmitted energy remained constant over the energy range tested with short irradiation times and low frequencies and is sufficient for material processing. At present, the transmission efficiency of the bundle is about 25%.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.