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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3592-3599 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Passive Q switching of an Er:glass laser with the pulse width varying between 14 and 80 ns has been demonstrated, using three resonator vanadium-dioxide-coated (VO2) mirror samples with temperature-dependent reflectivity and differing in the reflectivity contrast. The reflectivity changes because of a phase transition from a semiconductor to a metallic state. Broad band operating characteristics of VO2 mirrors provide Q switching over a wide range of wavelengths. In addition, mode-locked pulses with much shorter time scales have been observed, due to exciton formation and recombination. A simple criterion is derived for the allowable ambient temperatures at which the Q switching operates effectively. A simple relation has also been found relating the duration of the Q-switched pulse to the contrast in reflectivities of the two mirror phases. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5365-5368 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time evolution of the photoluminescence spectra of low current density electrochemically etched porous silicon are studied. When the sample is exposed to light illumination in atmosphere, the luminescence intensity decays initially. However, after a short period of degradation, it starts to enhance gradually. The profiles of the photoluminescence spectra including peak position and line width are very different for the decay and enhancement processes. When the sample is illuminated in vacuum, only a decay process is observed. Infrared spectrum shows that the hydrogen related bonding in the as-anodized sample is replaced by the oxygen related termination. A quantum confinement model together with the activity of nonradiative recombination centers is proposed to explain our observations. After oxidation under light exposure, the intensity of the photoluminescence is strong and stable. Thus, our study also provides a room temperature oxidation method for producing strong and stable luminescent porous silicon. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 8476-8484 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The (1+1) resonance enhanced multiphoton ionization spectra of jet-cooled CS2 were obtained between 45 500 and 48 000 cm−1 (220–208 nm) for the two isotopomers 12C32S2 and 12C34S32S. With the use of different expansion gases which resulted in varying degrees of vibrational cooling and the comparison of the two isotopomer spectra, a partial assignment of the C˜ 1B2–X˜ 1Σg+ transition was obtained. The electronic origin of this transition is confirmed to lie at 46 248.7 cm−1 and values for the predissociation lifetimes for the upper state for 34 vibrational bands and isotopomer shifts of seven vibrational levels of the 1B2 state are presented. The lifetimes of the Σ0 bands were found to be larger than those of corresponding Π1 and Δ2 bands. A simulation of the spectrum, which used the harmonic approximation, is in qualitative agreement with the band positions and shifts, but quantitative disagreement between the values leads us to conclude that a normal mode analysis is not appropriate to describe the low vibrational levels of the 1B2 state. The results presented increase our understanding of the low-lying predissociating levels of CS2, which will be of use in future photofragment studies. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2885-2893 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion-pair upconversion pumped laser emission at 2.7–2.9 μm between the 4I11/2 and 4I13/2 excited states of triply ionized erbium ions (Er3+) has been studied at 300 and 100 K in YLF, YAG, SrF2, and CaF2 hosts. Laser action was obtained by pumping directly into the transition's terminal laser level. In all four hosts, the lifetime of the 4I13/2 state is longer than that of the 4I11/2 state, by factors of 5 and 80 for the first two, and factors of (5)/(2) and 2 for the SrF2 and CaF2, respectively. The absorption coefficient for the 1.533-μm pump radiation is comparable in YLF, SrF2, and CaF2, but is larger by a factor of 3 in YAG. At room temperature the threshold pump energy for YAG is larger by a factor of 10 than for CaF2, SrF2, and YLF. Interpretation of the lasing delay times at threshold pumping levels in terms of a simple analytic model gives for the upconversion coefficients: αYLF =1.2×10−17 cm3 s−1, αYAG =5.4×10−17 cm3 s−1, αSrF2 =2.9×10−15 cm3 s−1, and αCaF2 =3.2×10−15 cm3 s−1. Nonoptimized upconversion pumped laser efficiency in Er:YLF was measured at 110 K to be 17%. A peculiar upconversion pumped lasing behavior was observed in Er:YAG at low temperatures.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 4077-4086 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A study of upconversion processes in Er3+ ions in CaF2 has led to an unambiguous demonstration of IR lasing produced by upconversion pumping alone. The study has shown: (1) strong upconversion lines originating from the 4I11/2 state; (2) the existence of both two-photon and three-photon upconversion processes; (3) an optimum concentration of 5–10 mol % for Er3+; and (4) upconversion efficiencies for the visible bands as high as 10% at 77 K and 1% at 300 K. Measurements of lasing between the 4I11/2 and 4I13/2 levels show that even though the lifetime of the upper (4I11/2) state is only half that of the lower state, self-quenching does not occur. Upconversion is implicated for this transition both by the nonpersistence of a "red shift'' during a lasing pulse, and by the opposite dependence on concentration of laser threshold energy and upconversion-produced fluorescent intensity. A simple theoretical model shows that a 2.8-μm laser operating between the 4I11/2 and 4I13/2 levels can be pumped solely by upconversion of ions in the excited 4I13/2 state produced by absorption of a 1.54-μm pulse. In addition, (1) a minimum of 1.54-μm pump energy is required; (2) lasing occurs with a delay inversely proportional to the pump energy; and (3) lasing can persist for as long as the lifetime of the lower (4I13/2) state. These predictions have been experimentally verified. The lasing experiments give a lower limit for the upconversion coefficient of α=10−16 cm3 s−1.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 7227-7239 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Upconversion-pumped lasing characteristics near 3 μm on the 4I11/2-4I13/2 transition of the Er3+ ion in Er:YSGG (erbium-yttrium-scandium-gallium garnet) and Er:YAG (erbium-yttrium-aluminum-garnet), laser state spectroscopy, and population kinetics, are the main subjects discussed. The wide difference in lasing patterns of both garnets can be attributed to the difference in population inversion kinetics which was studied by analyzing the rise and decay of fluorescence starting from the laser states. It is shown that the effective decay times, τ1 and τ2 of the lower and upper laser states, are changed during lasing by the nonlinear energy-transfer processes such that the resulting ratio becomes τ1/τ2〈1. In Er:YSGG this condition is established during the declining phase of the 4I11/2 population, whereas in Er:YAG it occurs only for a short time during the rising phase. Consequently Er:YAG lases in a self-terminating pulsed mode. The role of various energy-transfer processes in the upconversion-pumped population inversion kinetics is discussed and analyzed. It is experimentally shown that the lower 4I13/2 laser state in both garnets is depopulated by the cooperative energy summing due to the di- and tri-ionic interactions. Because of these interactions, the 4I11/2 and 4S3/2 states are populated with ensuing fluorescence from these states at 980 and 550 nm, respectively. The indication that the latter state is populated directly by the tri-ionic interaction, rather than via the former state by two sequential ion-pair interactions, follows from the experimental fact that the 550-nm fluorescence rises faster and reaches its maximum sooner than the 980-nm fluorescence. The previously proposed kinetic rate equations for Er:YAG and Er:YSGG were modified by adding a cubic term to represent the tri-ionic interaction. The steady-state solutions yielded approximately cubic dependence of green fluorescence intensity on the intensity of pump radiation in agreement with the experiment. These solutions also explained deviations from cubic dependence observed experimentally in several erbium-doped crystals.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4906-4906 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 1067-1067 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high-current, high-energy, and long-pulse positive ion source for the KSTAR neutral beam system is being developed on the basis of proven technology. The original prototype ion source was the TFTR developed by LBNL, but the accelerator slit grid brazed with shaped molybdenum tubes was a barrier for success of the copied work. In order to cover the technical and economical problems caused by the molybdenum tubes, a new OFH copper grid with circular apertures has been designed and manufactured. Cooling circuits aligned along every line of the aperture arrays are made with the help of gun drills. The test and the first experimental results of the upgraded ion source, such as high-voltage characteristics, cooling characteristics, discharge characteristics, and first beam extraction characteristics are described. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 33 (1992), S. 3710-3715 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Quantum superalgebras suq(m||n) are studied in the framework of R-matrix formalism. Explicit parametrization of L(+) and L(−) matrices in terms of suq(m||n) generators are presented. We also show that quantum deformation of nonsimple superalgebra su(n||n) requires its extension to u(n||n).
    Type of Medium: Electronic Resource
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