FIBER OPTIC LASER BEAMS COMBINER FOR THREE DIFFERENT WAVELENGTHS

Abstract

In this work we describe a simple fiber optic laser beams combiner prototype for three different wavelengths. The qualitative results described here concern only two of the input branches of the combiner, i.e., only the combination of two beams will be analyzed. The preliminary results obtained are discussed and compared with those obtained from a conventional lumped beam combiner that uses seven mirrors and four beam splitters. These show the feasibility of using the present device to combine laser beams with different wavelengths. Furthermore, the results are better than those obtained with the conventional beams combiner, so far as stability and transmission coefficients are concerned. Since the 80´s decade Brazil has been investing in research and development of techniques to obtain enriched uranium, to be used as nuclear fuel. These works have been focused chiefly on the Atomic Vapor Laser Isotope Separation (AVLIS) and the centrifugation techniques. The research on AVLIS is being performed in the Photonics Division of the Advanced Studies Institute (IEAv/EFO) (1-3). The physical principle of the laser methods for uranium isotope separation is the differentiated capacities possessed by the different isotopes of absorbing light of particular frequencies. The isotopic differences in the absorption spectra are caused by the volume effect of the nucleus and by the nuclear spin of the isotopes. The electronic energy levels present shifts in the visible range of the spectrum, and such shifts allow one of the isotopes to be selectively excited by a monochromatic laser beam. Thus, if a mixture of two isotopes is irradiated by a laser, at a resonant frequency and with an enough narrow linewidth, the light of the laser may be preferentially absorbed by one of the isotopes. AVLIS is based on this fact. First, the material that is formed by an isotopic mixture is vaporized by an electron beam gun or by other techniques, such as laser ablation or cathode sputtering. The desired isotope, present in this vapor, is selectively excited by a laser beam that passes through it. In order to be ionized, at the visible spectrum range, the atoms must absorb at least three different photons so that the total energy of these photons together is greater than the first ionization limit, 6.18 eV for uranium. These three-photons are supplied by three dye laser systems pumped by copper vapor lasers in a MOPA configuration. These three-photons are combined into one single laser beam that interacts with the atoms to lead them to photoionization. After the photoionization, the ions can be deflected by electric and/or magnetic fields and guided up to a collector located in a place not accessible to the neutral 238U isotope. AVLIS more detailed description can be found in the literature (1, 2). In this work we describe a simple fiber optic laser beams combiner prototype for three different wavelengths. The qualitative results described in this work concern experiments on just two branches of the beam combiner i.e., only the combination of two beams will be analyzed. The preliminary results are discussed and compared with those obtained from a conventional beam combiner using seven mirrors and four beam splitters. These show that is possible to use fiber optic device to combine laser beams with different wavelengths. Furthermore, the results are better than those obtained with the conventional beams combiner, so far as stability and transmission coefficients are concerned.