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  • 1
    Electronic Resource
    Electronic Resource
    Laser pointing stabilization and control in the submicroradian regime with neural networks (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 1339-1342 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The possibility of controling the pointing stability of a slowly pulsed Ti:Sapphire laser system by lowpass filters and artificial neural networks (NN) is investigated by performing time series analysis and computer simulations on experimentally measured datasets. The simulations show that at pulse repetition rates of 20 Hz it is possible to use a feedforward algorithm to reduce the angular standard deviation from 0.7 to 0.3 μrad. The properties and advantages of NN methods such as automatic adaptation characteristics of a time series are discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1334624
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  • 2
    Electronic Resource
    Electronic Resource
    A new contribution to spin-forbidden rare earth optical transition intensities: Gd3+ and Eu3+ (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 1787-1797 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quantitative calculations show that numerous spin-forbidden linear optical transitions observed in trivalent rare earth ions acquire a major fraction of their intensity from hitherto neglected contributions involving spin–orbit linkages within excited configurations. Motivated by the importance of analogous linkages previously demonstrated in two-photon absorption, we derive a general expression applicable for all lN→lN transitions which can be incorporated into a revised Judd–Ofelt analysis of observed intensities. Presenting this revised analysis of observed linear absorption intensities for Gd3+ and Eu3+, we show that the new contribution is often comparable to standard contributions. With substantial modification of previously fitted phenomenological parameters, an improved fit to observed intensities is achieved, suggesting that reanalysis of linear intensity data for all trivalent rare earths is warranted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455125
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  • 3
    Electronic Resource
    Electronic Resource
    A new contribution to spin-forbidden rare earth optical transition intensities: Analysis of all trivalent lanthanides (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 1511-1520 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We expand upon recent quantitative calculations which show that numerous parity- and spin-forbidden linear optical transitions observed in trivalent rare earth ions acquire a major fraction of their intensity from hitherto neglected contributions involving spin–orbit linkages within excited configurations. Extending our revised analysis of observed linear absorption intensities for Gd3+ and Eu3+ to the other nine trivalent lanthanides with visible wavelength transitions, we find that the new contributions are at least as important in these other lanthanides, and are often comparable to standard contributions. We also show that spin-forbidden ΔS=1 transitions are selectively modified over the spin-allowed ΔS=0 transitions. In addition, we examine contributions from linkages with g orbital excited states in the light of recent electronic Raman scattering data for lanthanide phosphates, and show that these long neglected terms may actualy dominate the transition intensity. With substantial modification of previously fitted phenomenological parameters, however, the good fit with observed intensities is retained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457111
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of laser pulse duration on short wavelength emission from femtosecond and picosecond laser-produced Ta plasmas (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 654-656 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The efficiency, duration, and spectral content of the emission from laser-produced Ta plasmas in the 10–71 nm spectral region have been measured for laser pulse durations ranging from 100 fs to 70 ps. Efficiencies from 0.3% for 100 fs pulses to 2.65% for 70 ps pulses, x-ray pulse durations from less than 10 ps for 100 fs excitation pulses to 105 ps for 70 ps excitation pulses, and spectral content peaking in the 17–35 nm region were measured for 1 mJ pulses at intensities from 1011 to 5×1014 W/cm2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99842
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  • 5
    Electronic Resource
    Electronic Resource
    Production and characterization of a fully ionized He plasma channel (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 4112-4114 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report guiding of intense (I=1.3±0.7×1017 W/cm2) 80 fs laser pulses with negligible spectral distortion through 1.5-cm-long preformed helium plasma channels. Channels were formed by axicon-focused laser pulses of either 0.3 J energy, 100 ps duration, after preionizing a 200–700 Torr backfill of He gas to ne∼1016 cm−3 with a pulsed electrical discharge; or 0.6–1.1 J energy, 400 ps duration, which required neither preionization nor intentional impurities for seeding. Transverse interferometry showed that He was fully ionized on the channel axis in both cases. Identical femtosecond pulses suffered substantial ionization-induced blueshifts after propagating through Ar and Ne channels of similar dimensions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1329323
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  • 6
    Electronic Resource
    Electronic Resource
    Second-harmonic generation from silicon nanocrystals embedded in SiO2 (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 766-768 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present observations of optical second-harmonic generation (SHG) from silicon nanocrystals embedded in SiO2. SHG sensitivity to Si/SiO2 interface states, charge on the nanocrystals, and particle density gradients is demonstrated. SHG is proven to be a powerful noncontact nondestructive diagnosis tool for characterization of Si-nanocrystal-based devices and materials. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1345825
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  • 7
    Electronic Resource
    Electronic Resource
    Second-harmonic spectroscopy of bulk boron-doped Si(001) (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 181-183 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of bulk boron incorporation on the second-harmonic generation (SHG) spectrum of Si(001) films grown epitaxially by chemical vapor deposition is studied as a function of doping level and temperature. At room temperature, boron doping (NA∼1018 cm−3) strongly enhances and blueshifts the E1 resonance of the second-harmonic generation spectra to 3.4 eV. Surface hydrogen termination reverses this effect. The observed doping and temperature dependence are modeled as electric-field-induced SHG in the bulk depletion region. The results suggest applications of SHG as an in situ, noninvasive probe of electrically active dopants. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126917
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  • 8
    Electronic Resource
    Electronic Resource
    Evolution of subsurface hydrogen from boron-doped Si(100) (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2184-2186 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The reactions of atomic hydrogen with boron-doped Si(100) were studied using temperature programmed desorption (TPD). In addition to adsorbing at surface sites, hydrogen penetrates into boron-doped Si(100) samples and gets trapped by forming subsurface boron–hydrogen complexes. H2-TPD spectra, taken after exposure to atomic hydrogen, showed, in addition to the well known dihydride (680 K) and monohydride (795 K) desorption features, two peaks at 600 and 630 K due to decomposition of subsurface boron–hydrogen complexes. Increasing total hydrogen uptake with increasing dosing temperature (1.7 ML at 300 K, 4.2 ML at 500 K), suggests an activation barrier for subsurface hydrogen uptake. A quantitative correlation between boron concentration and subsurface hydrogen uptake is shown. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119375
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  • 9
    Electronic Resource
    Electronic Resource
    In situ optical second-harmonic-generation monitoring of disilane adsorption and hydrogen desorption during epitaxial growth on Si(001) (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 1376-1378 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The kinetics of disilane adsorption and hydrogen desorption during low-temperature, ultrahigh vacuum chemical vapor deposition on Si(001) is investigated in situ in real time by monitoring the instantaneous hydrogen coverage using optical second-harmonic generation. A simple two-site adsorption model and first-order desorption are used to establish a reactive sticking coefficient and to predict the Si(001) epitaxial growth rate. The reactive sticking coefficient is temperature independent between 740 and 920 K and equal to 0.04±0.01. Predicted growth rates are in agreement with published growth rates obtained from gas-source molecular-beam epitaxy of Si(001). © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119927
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  • 10
    Electronic Resource
    Electronic Resource
    Guiding characteristics of an acoustic standing wave in a piezoelectric tube (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2902-2904 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Propagation of an He–Ne laser beam through a gas filled piezoelectric tube is used to characterize the guiding properties of a radially driven acoustic standing wave. Impedance matched driving at 1 MHz of the 5-cm-long piezotube yields radial density perturbations of 0.005 at 40 V driving voltage. The frequency spectrum of the cavity resonances is used to measure the damping of the standing wave due to shear viscosity in Ar. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122624
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