We are presently investigating the emission of OH radicals by laser-induced fluorescence (LIF) in the H2 + 1/202 → H2O reaction on polycrystalline platinum. Results are obtained for emission yields of OH as functions of pressure (5-500 mTorr), temperature (950-1300 K), and O2/H2 ratios. The rotational temperature distribution of the desorbing OH molecules is determined, showing a significant dependence of the total pressure. The rotational temperature is only 50-75% of the surface temperature of the catalyst, i.e., the emitted OH radicals are not in thermal equilibrium when they are produced. Apparent desorption energies are also achieved. They vary from 30 to 60 kcal/mole for different O2/H2 ratios.
{"title":"Laser spectroscopic detection of OH in catalytic reactions on platinum","authors":"S. Ljungström, A. Rosén, T. Wahnström, B. Kasemo","doi":"10.1063/1.36800","DOIUrl":"https://doi.org/10.1063/1.36800","url":null,"abstract":"We are presently investigating the emission of OH radicals by laser-induced fluorescence (LIF) in the H2 + 1/202 → H2O reaction on polycrystalline platinum. Results are obtained for emission yields of OH as functions of pressure (5-500 mTorr), temperature (950-1300 K), and O2/H2 ratios. The rotational temperature distribution of the desorbing OH molecules is determined, showing a significant dependence of the total pressure. The rotational temperature is only 50-75% of the surface temperature of the catalyst, i.e., the emitted OH radicals are not in thermal equilibrium when they are produced. Apparent desorption energies are also achieved. They vary from 30 to 60 kcal/mole for different O2/H2 ratios.","PeriodicalId":422579,"journal":{"name":"International Laser Science Conference","volume":"110 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125675160","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Solid-state photodimerization reaction of O-methoxy trans cinnamic acid has been studied by laser Raman phonon spectroscopy. The progress of reaction has been estimated by monitoring the monomer 315-nm electronic absorption band which decreases in intensity with reaction progress and disappears in the dimer spectrum. The disappearance of the aliphatic C = C stretching monomer mode 1622 cm−1 in the infrared spectrum of the dimer suggests cyclobutane ring formation. Other infrared features also suggest four center type dimerization. In the monomer crystal, Raman phonon bands are observed at 32.5,57.5,65,89,95.5, and 160 cm−1. With reaction progress the sharp 32.5-cm−1 phonon shifts to lower frequency and finally disappears. This suggests softening of this mode with reaction progress and that the reaction is mediated by this phonon. This is the first example of phonon mode softening in solid state photoreaction. In the partially dimerized crystal, the monomer phonon bands lose their intensity and new phonon bands appear. When the reaction is almost complete, a new phonon spectrum is observed. The appearance of the segregated phonon spectra in the partially dimerized crystal suggests that the reaction is heterogeneous and the reactant and the product form separate lattices.
{"title":"Laser Raman phonon spectroscopy of solid-state photoreactions: photodimerization of O-methoxy trans cinnamic acid","authors":"U. Ghosh, T. N. Misra","doi":"10.1063/1.36823","DOIUrl":"https://doi.org/10.1063/1.36823","url":null,"abstract":"Solid-state photodimerization reaction of O-methoxy trans cinnamic acid has been studied by laser Raman phonon spectroscopy. The progress of reaction has been estimated by monitoring the monomer 315-nm electronic absorption band which decreases in intensity with reaction progress and disappears in the dimer spectrum. The disappearance of the aliphatic C = C stretching monomer mode 1622 cm−1 in the infrared spectrum of the dimer suggests cyclobutane ring formation. Other infrared features also suggest four center type dimerization. In the monomer crystal, Raman phonon bands are observed at 32.5,57.5,65,89,95.5, and 160 cm−1. With reaction progress the sharp 32.5-cm−1 phonon shifts to lower frequency and finally disappears. This suggests softening of this mode with reaction progress and that the reaction is mediated by this phonon. This is the first example of phonon mode softening in solid state photoreaction. In the partially dimerized crystal, the monomer phonon bands lose their intensity and new phonon bands appear. When the reaction is almost complete, a new phonon spectrum is observed. The appearance of the segregated phonon spectra in the partially dimerized crystal suggests that the reaction is heterogeneous and the reactant and the product form separate lattices.","PeriodicalId":422579,"journal":{"name":"International Laser Science Conference","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133395861","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We describe a photoacoustic method for the direct measurement of the energy absorbed by wide-gap optical materials during non-linear interaction with intense laser beams and present results obtained with ultrapure NaCl crystals exposed to 80-ps pulses from a frequency-doubled Nd:YAG laser. The measured temperature rise of the interaction volume depends approximately on the fourth power of the laser peak flux F and exceeds 300 K at F = 1.45 × 1030 photons/cm2s without laser-induced breakdown. We find no evidence of free-electron avalanche formation up to these temperatures and show that the mechanism of energy deposition is four-photon electron-hole pair generation and subsequent single-photon absorption by free electrons and self-trapped holes with small contributions from self-trapped excitons. We report the first photoacoustically measured four-photon absorption cross section: σ(4) = 2 × 10-113cm8s3in NaCl for linearly polarized 532-nm photons. This value is corroborated by σ(4) = 0.94 × 10-113 cm8 s3 obtained in physically similar KBr at 40 K by measuring the recombination luminescence of four-photon-generated self-trapped excitons.
{"title":"Direct measurement of nonlinear energy deposition from an intense 532-nm photon field into alkali halides","authors":"S. C. Jones, X. A. Shen, P. Bräunlich, P. Kelly","doi":"10.1063/1.36842","DOIUrl":"https://doi.org/10.1063/1.36842","url":null,"abstract":"We describe a photoacoustic method for the direct measurement of the energy absorbed by wide-gap optical materials during non-linear interaction with intense laser beams and present results obtained with ultrapure NaCl crystals exposed to 80-ps pulses from a frequency-doubled Nd:YAG laser. The measured temperature rise of the interaction volume depends approximately on the fourth power of the laser peak flux F and exceeds 300 K at F = 1.45 × 1030 photons/cm2s without laser-induced breakdown. We find no evidence of free-electron avalanche formation up to these temperatures and show that the mechanism of energy deposition is four-photon electron-hole pair generation and subsequent single-photon absorption by free electrons and self-trapped holes with small contributions from self-trapped excitons. We report the first photoacoustically measured four-photon absorption cross section: σ(4) = 2 × 10-113cm8s3in NaCl for linearly polarized 532-nm photons. This value is corroborated by σ(4) = 0.94 × 10-113 cm8 s3 obtained in physically similar KBr at 40 K by measuring the recombination luminescence of four-photon-generated self-trapped excitons.","PeriodicalId":422579,"journal":{"name":"International Laser Science Conference","volume":"114 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116234044","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
One aspect of making a gamma-ray laser concerns the rapid re lease of energy stored in a long-lived nuclear isomer. A proposed method for the release of this energy is to pump the isomerto a nearby, shorter-lived nuclear excited state. This excited state subsequently decays to a lasing transition. In this paper, we consider the dynamical coupling of the nucleon and electron motion using classical dynamics and calculate the perturbation on the spectra. In our model,1 a valence excited proton is bound as an independent particle to the nuclear core using a Woods-Saxon potential. The electron is bound to a core of protons and the valence proton by a Coulomb potential. Initial conditions for the classical trajectories were chosen to be semiclassical states of the separable Hamiltonian. A method2 to extract spectral information from classical trajectories is then used to calculate both transition intensities and frequencies. For some isomers, very strong coupling and chaotic motion were observed.
{"title":"Classical and semiclassical calculation of nuclear-electron coupling","authors":"D. W. Noid, F. Hartmann, M. Koszykowski","doi":"10.1063/1.36804","DOIUrl":"https://doi.org/10.1063/1.36804","url":null,"abstract":"One aspect of making a gamma-ray laser concerns the rapid re lease of energy stored in a long-lived nuclear isomer. A proposed method for the release of this energy is to pump the isomerto a nearby, shorter-lived nuclear excited state. This excited state subsequently decays to a lasing transition. In this paper, we consider the dynamical coupling of the nucleon and electron motion using classical dynamics and calculate the perturbation on the spectra. In our model,1 a valence excited proton is bound as an independent particle to the nuclear core using a Woods-Saxon potential. The electron is bound to a core of protons and the valence proton by a Coulomb potential. Initial conditions for the classical trajectories were chosen to be semiclassical states of the separable Hamiltonian. A method2 to extract spectral information from classical trajectories is then used to calculate both transition intensities and frequencies. For some isomers, very strong coupling and chaotic motion were observed.","PeriodicalId":422579,"journal":{"name":"International Laser Science Conference","volume":"10 20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129437927","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High power chemical lasers present a fascinating array of special environments and associated technology development subjects. Included are: processes to produce the source reactants; supersonic mixing and reacting flow fields; the production and dissipation of multiple vibrational–rotational molecular states; optical gain extraction in complex geometries; media inhomogeneity effects, and waste energy and reaction products removal. Some configurations desire wavelength selectivity, special optical components, and coherent cavity or beam combining. Progress has been made in these areas in recent years in behalf of cw and repetitively pulsed hydrogen fluoride and deuterium fluoride lasers, subsonic and supersonic oxygen-iodine lasers, and potential shorter wavelength chemical lasers based on chemically excited higher electronic states. This paper presents a brief review of the technical approach in some of the technology areas and the status in achieving practical, integrated high power chemical lasers.
{"title":"Advances in chemical lasers","authors":"Joseph Miller","doi":"10.1063/1.36732","DOIUrl":"https://doi.org/10.1063/1.36732","url":null,"abstract":"High power chemical lasers present a fascinating array of special environments and associated technology development subjects. Included are: processes to produce the source reactants; supersonic mixing and reacting flow fields; the production and dissipation of multiple vibrational–rotational molecular states; optical gain extraction in complex geometries; media inhomogeneity effects, and waste energy and reaction products removal. Some configurations desire wavelength selectivity, special optical components, and coherent cavity or beam combining. Progress has been made in these areas in recent years in behalf of cw and repetitively pulsed hydrogen fluoride and deuterium fluoride lasers, subsonic and supersonic oxygen-iodine lasers, and potential shorter wavelength chemical lasers based on chemically excited higher electronic states. This paper presents a brief review of the technical approach in some of the technology areas and the status in achieving practical, integrated high power chemical lasers.","PeriodicalId":422579,"journal":{"name":"International Laser Science Conference","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123413967","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Simple physical pictures using the dressed atom approach are introduced for understanding atomic motion in laser beams.1 New cooling schemes are suggested.
介绍了用修饰原子的方法来理解激光束中原子运动的简单物理图像提出了新的冷却方案。
{"title":"Theory of atomic motion in laser light","authors":"C. cohen-tannoudji","doi":"10.1063/1.36783","DOIUrl":"https://doi.org/10.1063/1.36783","url":null,"abstract":"Simple physical pictures using the dressed atom approach are introduced for understanding atomic motion in laser beams.1 New cooling schemes are suggested.","PeriodicalId":422579,"journal":{"name":"International Laser Science Conference","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128540035","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Y. Zhu, R. Sauerbrey, F. Tittel, W. Wilson, W. Nighan
Highly efficient and extremely narrow spectral output has been demonstrated for an injection controlled electrically excited XeF (C → A) and Xe2Ci laser media. Amplification of an injected tunable dye laser pulse was achieved throughout the entire blue-green spectral region. Experiments were performed by exciting optimized gas mixtures with an intense electron beam. Several different confocal unstable resonator geometries were investigated. In the case of the XeF (C → A) excimer transition, a maximum output of ~ 150 mJ was measured at 482.5 nm for a cavity with magnification M = 1.08, which corresponds to an energy density and intrinsic efficiency of ~8J/liter and ~ 6%, respectively. The tuning range was from 435 to 535 nm.1 An analytical model of the injection process was developed. A set of nonlinear coupled rate equations described the laser process. This model was used to describe the injection controlled excimer laser performance as a function of delay time between the dye laser injection and e-beam pumping pulse, as well as to assist the optimization of the confocal unstable resonator design.
{"title":"Injection controlled operation of broadband excimer lasers","authors":"Y. Zhu, R. Sauerbrey, F. Tittel, W. Wilson, W. Nighan","doi":"10.1063/1.36858","DOIUrl":"https://doi.org/10.1063/1.36858","url":null,"abstract":"Highly efficient and extremely narrow spectral output has been demonstrated for an injection controlled electrically excited XeF (C → A) and Xe2Ci laser media. Amplification of an injected tunable dye laser pulse was achieved throughout the entire blue-green spectral region. Experiments were performed by exciting optimized gas mixtures with an intense electron beam. Several different confocal unstable resonator geometries were investigated. In the case of the XeF (C → A) excimer transition, a maximum output of ~ 150 mJ was measured at 482.5 nm for a cavity with magnification M = 1.08, which corresponds to an energy density and intrinsic efficiency of ~8J/liter and ~ 6%, respectively. The tuning range was from 435 to 535 nm.1 An analytical model of the injection process was developed. A set of nonlinear coupled rate equations described the laser process. This model was used to describe the injection controlled excimer laser performance as a function of delay time between the dye laser injection and e-beam pumping pulse, as well as to assist the optimization of the confocal unstable resonator design.","PeriodicalId":422579,"journal":{"name":"International Laser Science Conference","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114309099","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We have developed a self-referencing interferometer that will allow phase measurements of the near field of diode arrays. The method uses a double-slit aperture that is scanned across a magnified image of the diode near field. The far-field double-slit fringe locations then give a direct measurement of the phase difference between the two slits. We can then reconstruct the phase using the sampled difference data. The method has several advantages over other interferometric techniques including (1) the wavefront is interfered with itself, so that a separate reference wavefront is not needed; (2) the method is insensitive to array near-field intensity variations so that fringe maps need not be deconvolved from intensity variations; (3) the method works well in the presence of broadband radiation. The source needs very little coherence length which is quite an important consideration for diode lasers. Data from several commercially available devices are presented. (Poster paper)
{"title":"Near-field phase measurements of diode laser arrays","authors":"G. Dente, K. Wilson, D. Depatie, John Querns","doi":"10.1063/1.36714","DOIUrl":"https://doi.org/10.1063/1.36714","url":null,"abstract":"We have developed a self-referencing interferometer that will allow phase measurements of the near field of diode arrays. The method uses a double-slit aperture that is scanned across a magnified image of the diode near field. The far-field double-slit fringe locations then give a direct measurement of the phase difference between the two slits. We can then reconstruct the phase using the sampled difference data. The method has several advantages over other interferometric techniques including (1) the wavefront is interfered with itself, so that a separate reference wavefront is not needed; (2) the method is insensitive to array near-field intensity variations so that fringe maps need not be deconvolved from intensity variations; (3) the method works well in the presence of broadband radiation. The source needs very little coherence length which is quite an important consideration for diode lasers. Data from several commercially available devices are presented. (Poster paper)","PeriodicalId":422579,"journal":{"name":"International Laser Science Conference","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133938728","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In models of nonradiative energy transfer applied to doped solid-state laser materials, the distance between excited donors and neighboring acceptors critically affects the calculated energy transfer rates. In the generally successful formulation of nonradiative transfer theory,1 the donors and acceptors are taken to be distributed evenly throughout the crystal and are independent (uncorrelated) in position. We derive a general expression to treat donor-acceptor transfer rates for locally correlated donor-acceptor placement. Several specific cases appropriate to actual laser materials are (1) an excluded volume around a donor diminished in acceptor concentration and (2) an enhanced volume around a donor in which acceptors preferentially locate. Physical effects which can lead to such microscopic distributions are discussed.
{"title":"Extended Foerster-Dexter model for correlated donor-acceptor placement in solid-state materials","authors":"S. Rotman, F. Hartmann","doi":"10.1063/1.36733","DOIUrl":"https://doi.org/10.1063/1.36733","url":null,"abstract":"In models of nonradiative energy transfer applied to doped solid-state laser materials, the distance between excited donors and neighboring acceptors critically affects the calculated energy transfer rates. In the generally successful formulation of nonradiative transfer theory,1 the donors and acceptors are taken to be distributed evenly throughout the crystal and are independent (uncorrelated) in position. We derive a general expression to treat donor-acceptor transfer rates for locally correlated donor-acceptor placement. Several specific cases appropriate to actual laser materials are (1) an excluded volume around a donor diminished in acceptor concentration and (2) an enhanced volume around a donor in which acceptors preferentially locate. Physical effects which can lead to such microscopic distributions are discussed.","PeriodicalId":422579,"journal":{"name":"International Laser Science Conference","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126507617","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We have used the method of coherent anti-Stokes Raman scattering (CARS) in our study of double base propellants containing varying ratios of nitrocellulose and nitroglycerine. We have chosen N2 and H2, among other major combustion products, to measure the temperatures of the propellant flames in air and in inert atmospheric conditions.
{"title":"Propellant combustion study by coherent anti-Stokes Raman scattering","authors":"T. H. Vu, R. Field","doi":"10.1063/1.36802","DOIUrl":"https://doi.org/10.1063/1.36802","url":null,"abstract":"We have used the method of coherent anti-Stokes Raman scattering (CARS) in our study of double base propellants containing varying ratios of nitrocellulose and nitroglycerine. We have chosen N2 and H2, among other major combustion products, to measure the temperatures of the propellant flames in air and in inert atmospheric conditions.","PeriodicalId":422579,"journal":{"name":"International Laser Science Conference","volume":"74 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134594199","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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