Transmission of XeCl excimer laser pulses through optical fibers: Dependence on fiber and laser parameters

Abstract

Abstract.Measurements of the transmission of XeC1 excimer laser pulses (308 nm) through optical all-silica fibers are reported. The observed photodegradation effects during long time irradiation are dependent on the laser energy density and the laser repetition rate. Also the influence of the fiber drawing parameters and fiber geometry have been investigated. Absorption spectra of the fibers in the wavelength range from 200 nm to 400 nm before and after the irradiation with the excimer laser give some insight in the physical reasons for the changes in transmission properties. A spectral analysis of the fiber fluorescence has been performed. PACS: 78.90, 78.40F, 78.20 Many applications of lasers need the guidance of the laser energy through optical waveguides. Especially most medical applications of XeC1 excimer lasers, e.g. in laser angioplasty [1,2], minimal-invasive surgery [3] and ophthalmology [4] require the use of optical fibers. Most suitable for these purposes are quartz fibers with a core of fused silica and a cladding of doped fused silica. Manufacturing of this kind of fibers became a well established technique. Nevertheless, the interaction of high power UV laser pulses with the fiber material causes specific problems which have been investigated recently by several groups [5][6][7][8][9][10]. The maximum amount of excimer laser energy which can be transmitted is limited by the damage threshold of the fiber front surface [11,12]. But already well below this threshold photodegradation effects are observed which lead to a drop of the fiber transmission. It is well known, that UV radiation causes the formation of color centers in the quartz material. Optical fibers are ideal to study these effects, because the optical path can be made long enough to enable the detection of even weak absorption bands. Especially at 308 nm the effects are usually too small to be observed in experiments with ordinary bulk samples. Getting information on the nature of the absorbing states can help to improve the fiber properties for UV-transmission.The first scope of this work is to evaluate the influence of several laser and fiber properties on the fiber transmission. Most important laser parameters for the photodegradation * Presented at LASERION '91, June 12-14, 1991, Mtinchen (Germany) ** Present address: University of Britisch Columbia, Department of Physics, 6244 Agricultural Road, Vancouver B.C. V6T2A6, Canada are the energy density and the repetition rate. Additionally, the influence of the fiber core diameter and fiber drawing conditions has been evaluated. We have also measured fiber absorption spectra in the wavelength range between 200 nm and 400 nm before and after laser irradiation and performed a spectral analysis of the fiber fluorescence.Of practical and of theoretical interest is the fact, that the photodegradation effects are at least partly reversible. The time scale for the recovery effects is measured and discussed together with the temporal development of the fiber absorption spectra after laser ir...

Single-mode delivery of 250 nm light using a large mode area photonic crystal fiber

“…Our observations are consistent with these studies as the 250 nm irradiation reduced transmission at that wavelength, while transmission of 633 nm light is not affected [15,16,17,18]. Additionally, as shown in the left of Fig.…”

“…As discussed in the introduction, operation for 1s-10s of hours, as demonstrated here, is useful in several applications. There has been some discussion on the possible role of two-photon processes in the damage [15,17] but the low powers used in our experiment suggest this to be unlikely. The transmission data of Fig.…”

<title>Quantitative analysis of aromatic molecules in water by laser-induced fluorescence spectroscopy and multivariate calibration techniques</title>

“…LIF-techniques for fiber-optic sensing operating in the UV spectral range are still restricted by the transmission properties of fused silica optical fibers in this spectral range. Our results concerning fiber transmission have been published elsewhere [8][9][10] After developing and testing the laser fluorometer we have directed our research work to the improvement of the calibration procedure, since we regard quantitative and selective results as a prerequisite for the acceptance of the new technique.…”

<title>Fiber optic aspects of UV laser spectroscopic in situ detection of water pollutants</title>

“…For example, at a given wavelength it depends on laser intensity, laser repetition rate and fiber length. We found that during irradiation interrupts the transmission recovers partly but starting the laser again leads to a new drop8 Photodegradation becomes less important with increasing wavelength. This is demonstrated by the 308 nm transmission curve inFig.…”