Ruth M.J. Benmair

Solar-pumped Er,Tm,Ho:YAG laser.

Direct solar illumination was used to pump a 5-mm-diameter 62-mm exposed-length rod of Er,Tm,Ho:YAG to achieve a quasi-cw lasing of the Ho ion at an average power of 12 W. The solar radiation was chopped at a 20% duty cycle to avoid overloading of the cooling system. The peak power output was more than 65 W during the choppers open times. The slope efficiency is 3.8%, and the threshold input energy is approximately 100 W. The laser was operated for long times (up to hours) while maintaining its performance. This is, to our knowledge, the first directly solar-pumped laser operating at 77 K.

Photochemistry in the electronic ground state. Quantitative electrocyclic isomerization induced by multiphoton absorption of infrared laser radiation

Abstract The electrocyclic isomerization of hexafluorocyclobutene (HFCB) induced by transversely excited infrared laser radiation was studied. A quantitative conversion of HFCB to the less thermodynamically stable hexafluorobutadien (HFB) was achieved in the presence of excess helium gas. The wavelength and light intensity dependence were studied.

Photochemistry in the electronic ground state. Isotope separation by infrared multiphoton isomerization of complex molecules

Abstract Isotope selective isomerization of hexafluorocyclobutene to hexafluorobutadiene by multiphoton absorption of infrared laser light has been studied. All the three possible isotopomers were separated. The wavelength dependence of the reactions, saturation of absorption and the role of inert gas in retaining the selectivity are described.

Threshold of stimulated Brillouin scattering by use of a solar pumped laser

What is to our knowledge the first stimulated Brillouin scattering experiment using a high-power low-gain solar pumped laser is presented. A threshold reflectivity of 0.23% was reached when a peak power of 20.7 kW was used at 7.6 GHz. A cw solar pumped laser was Q-switched with an acousto-optic modulator, and the bandwidth was narrowed with an intracavity etalon. A high polarization ratio (>99.4%) was achieved by use of an intracavity configuration. Higher reflectivity values were limited because of the lack of availability of optical switches.

WATER DETOXIFICATION AND DISINFECTION USING HIGH SOLAR CONCENTRATION AND HOMOGENEOUS PHOTOCATALYSTS

The objectives of the research were to explore the use of concentrated sunlight combined with dissolved photocatalysts to improve water quality. Initial experiments with bromacil using organic-dye photosensitizers indicated that the reaction kinetics were enhanced by concentrated light. Other pesticides (EPTC, Tribufos, Atrazine and Lindane) were also tested in normal and concentrated sunlight. Organic dyes were effective in degrading some of these compounds but did not appear to be promising for complete mineralization. For most target compounds, the reaction rates were approximately proportional to the intensity of light. Iron compounds, especially in combination with hydrogen peroxide as the oxidizer, proved to be effective for degrading all the target pesticides. This system was also shown to mineralize phenol. Reaction rates were again approximately proportional to sunlight intensity. The photoefficiency of this reaction was in a range high enough to indicate that visible light, as well as UV, was participating in the photo-reactions. Preliminary disinfection tests have indicated that either organic dyes or iron compounds are effective. It is concluded from this work that solar irradiation with either organic dyes or the iron-peroxide system are a promising, possibly low cost, means of improving water quality.

Infra-red fluorescence and mode localization of highly excited vibrational states

Abstract The infra-red fluorescence spectrum of hexafluorocyclobutene induced by multiphoton absorption is analyzed. The emitting species are likely to be highly excited mode-localized vibrational states of extreme motion. They are characterized by a dominant configuration in which the excitation is mainly localized in one anharmonic-stretching normal-mode of motion. Two time scales are experimentally observed for the collisional decay of the temporal fluorescence obtained when two lasers excite the system within a short time delay at two distinct wavelengths. The fluorescence monitored is of short wavelength and is coming from highly excited species. The first laser excites the molecule into mode-localized extreme-motion states. Further excitation is induced by the second pulse but in a combination of bending and deformation motions. Two decay time scales exist because different modes of motion are being excited although the total vibrational energy of the molecule is large and it is in the quasi-continuum.

I.R. laser chemistry of allyl phenyl ether

The Claisen rearrangement of allyl phenyl ether to 2-allyl phenol has been investigated by I.R. multiphoton excitation. While the thermal reaction of the same starting material yields only the Claisen isomerization product, the I.R. photochemical excitation initiates both fragmentation and isomerization reactions. The dependence of product distribution on fluence is different at various wavelengths. Two mechanisms are proposed for the I.R. photochemical reaction. One assumes selective absorption, the other assumes wavelength dependent competition between absorption and stimulated emission of the vibrationally excited reaction intermediates.