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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 7227-7239 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4906-4906 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3592-3599 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 869-871 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Lasing action at 1.73, 1.23, and 0.85 μm was obtained by a threefold upconversion process in Er:YLF at 110 K using a 1.53 μm Er:glass pump laser. The 1.73 μm transition had the lowest threshold and highest pump conversion efficiency.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2885-2893 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 4077-4086 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 648-653 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Emission and absorption spectra of (5% Er) BaY2F8 were studied at 300, 77, and 4.2 °K. Stark-level positions were determined from the liquid-helium absorption spectra. Emission spectra were excited with a UV flash lamp and 1.53-μm radiation from an Er:glass laser; in the latter case, the visible and near-IR fluorescence of the Er3+ ions was excited through a multiphoton upconversion process. The lifetimes of Er3+-ion-excited states were measured at 300 and 77 °K. Laser action was stimulated at 0.85, 1.73, and 2.796 μm in a (5% Er) BaY2F8 laser rod using the transitions 4S3/2→4IJ, where J=13/2, 9/2, and 4I11/2→4I13/2, respectively. A Xe flash lamp was used for optical pumping. The latter two laser transitions were also pumped through upconversion of 1.53-μm radiation of the Er:glass laser. The cross-relaxation ion-pair conversion coefficient for the 4I13/2 levels of the Er3+ ions in BaY2F8 was calculated to be α=3.7×10−17 cm−3 s−1.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Optical and quantum electronics 22 (1990), S. S75 
    ISSN: 1572-817X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract Population kinetics of the upper4I11/2 and lower4I13/2 laser states of the Er3+ ion were studied experimentally and theoretically in (Er)BaY2F8, (Er)YLF, (Er)YSGG, (Er)CaF2 and (Er)YALO. Fluorescence from these states to the4I15/2 ground state was excited through upconversion simultaneously with the4I11/2 →4I13/2 lasing using 1.53 µm radiation from an erbium : glass laser for optical pumping. Lifetimes of both states are altered during lasing by co-operative energy transfer processes: the lifetime of the lower state τ1 is shortened and that of the upper state τ2 increased with the resultant ratio τ2/τ1〉1. After lasing the lifetime ratio returns to the ‘normal’ value τ2/τ1 〈1; that is, one obtained under weak ultraviolet excitation. Kinetic rate equations for the population density functions for both laser states were set up and solved by approximation in three time domains. It was assumed that only one co-operative energy transfer process operates in the laser crystals and determines the population inversion kinetics. Consistency relationships for comparison of the theoretical results with the experiment were developed. Only (Er)BaY2F8 spectral features showed close agreement with theory, resulting in a high score of 94% for the overall correlation in the consistency test, whereas all other crystals scored 〈50%. As a result of this high correlation, a close match between theoretical and experimental population decay curves was shown for (Er)BaY2F8. Most probably, more than one energy transfer process shapes the decay curves and determines the population inversion kinetics for the other laser crystals. (Er)YALO showed little lifetime change for the laser states, apparently due to inefficient co-operative energy transfer processes. As a result it probably lased in a self-terminating short-pulse mode.
    Materialart: Digitale Medien
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