This thesis reports experiments and theory on intrinsic mirrorless bistability in the luminescenc... more This thesis reports experiments and theory on intrinsic mirrorless bistability in the luminescence of ytterbium- doped crystals and glasses. The main results are the observation of intrinsically bistable luminescence at room temperature and chromatic switching at low temperature, reported here for the first time. The nonlinear dynamics responsible for these optical phenomena are shown to arise from ion-ion interactions controlled by the application of resonant electromagnetic fields. On the theoretical side, the classical Lorentz local field correction is shown to be the lowest order term of radiation-driven correlation contributions to local polarization which arise from inter-ion coherences and cooperative relaxation and frequency shifts beyond the dynamic shift are predicted. The nonlinear Maxwell-Bloch equations are extended to describe energy transfer between different species of ions predicting bistability in excited state populations which then emit bistable luminescence as a consequence, and an intensity dependent transfer rate is predicted. Diffusive excitation migration in space is also explored as a possible mechanism for generating multiple instabilities, but is not predicted to give rise to hysteresis loops by itself. On the experimental side, original observations of intrinsic optical switching and hysteresis are reported in the luminescence of Yb:CsCdBr 3 and Yb, Tm:glass. Evidence of cross-coupling between different impurities is also presented, together with spectroscopic details of intrinsic chromatic switching between different luminescent transitions of the acceptor species in Yb, Er:CsCdBr3 excited at the infrared Yb resonance wavelength. Conclusive spectroscopic evidence that excludes thermal effects as responsible for low temperature intrinsic switching is also presented. Room temperature intrinsic optical switching and hysteresis are reported for the first time in bulk Yb,Tm:glass samples. Switching, hysteresis, and clamping of laser output from waveguide channels fabricated in the glass material are also reported and indicate fundamental design limitations for compact optical amplifiers and oscillators.
This chapter describes designs and experiments that apply the Raman effect to wideband amplifiers... more This chapter describes designs and experiments that apply the Raman effect to wideband amplifiers (WBAs). In the context of this chapter, wideband corresponds to a bandwidth of approximately 50 to 100 nm or more. We start by explaining the need for WBAs, and briefly review some of the key enabling technologies for wideband systems. Section 14.2 describes several approaches for WBA, including the erbium-doped fiber amplifier (EDFA) and Raman amplifier combinations as well as all-Raman amplifiers. Section 14.3 summarizes the advantages and challenges of the all-Raman approach, the focus of this chapter. Section 14.4 identifies the key physical principles that need to be considered in the design of all-Raman WBAs. Then, perhaps the most important section of this chapter, Section 14.5 describes engineering design rules for construction of all-Raman WBAs that satisfy gain and noise figure performance requirements of typical long-haul and ultra-long-haul fiber-optic transmission systems. Several WBA experiments that use either EDFA/Raman amplifier combinations or all-Raman amplifiers are illustrated in Section 14.6, and exemplary wideband system experiments are described in Section 14.7. Finally, we summarize and conclude the chapter in Section 14.8.
Cascaded Raman wavelength shifting up to three orders from 1553 nm to 1867 nm is demonstrated in ... more Cascaded Raman wavelength shifting up to three orders from 1553 nm to 1867 nm is demonstrated in As 2 S 3 -chalcogenide fibers. Due to a long zero dispersion wavelength for the sulfide fiber (>4.5 µm), pumping the fiber at 1553 nm results in generation of cascaded Stokes orders based on stimulated Raman scattering. Using the threshold power for the Raman orders, we estimate the Raman gain coefficient for the As 2 S 3 fibers to be ~5.7x10 -12 m/W at 1550 nm. Observation of higher Raman orders is limited by damage to the fiber at input intensities >1 GW/cm 2 .
Cascaded Raman wavelength shifting up to three orders from 1553 nm to 1867 nm is demonstrated in ... more Cascaded Raman wavelength shifting up to three orders from 1553 nm to 1867 nm is demonstrated in As 2 S 3 -chalcogenide fibers. Due to a long zero dispersion wavelength for the sulfide fiber (>4.5 µm), pumping the fiber at 1553 nm results in generation of cascaded Stokes orders based on stimulated Raman scattering. Using the threshold power for the Raman orders, we estimate the Raman gain coefficient for the As 2 S 3 fibers to be ~5.7x10 -12 m/W at 1550 nm. Observation of higher Raman orders is limited by damage to the fiber at input intensities >1 GW/cm 2 .
spectrum when the laser is tuned into resonance with the 2 F7/2(0)! 2 F5/2(28) absorption of Yb 3... more spectrum when the laser is tuned into resonance with the 2 F7/2(0)! 2 F5/2(28) absorption of Yb 31 , providing direct confirmation of its assignment. The observation of the first and second members of a Franck-Condon progression for both the local and the bulk totally symmetric modes indicates that a D process, rather than an M process, induces the vibronic
We report the first observation of intrinsic optical bistability in CsCdBr3:1% Yb3+ and show, usi... more We report the first observation of intrinsic optical bistability in CsCdBr3:1% Yb3+ and show, using site-selective spectroscopy, that only the asymmetric, strongly coupled Yb3+ ion-pair minority site gives rise to hysteresis of near-infrared and cooperative up-conversion luminescence as a function of incident laser intensity below 15 K.
4 emission. Our analysis indicates that individual thermally activated Stark levels dominate cros... more 4 emission. Our analysis indicates that individual thermally activated Stark levels dominate cross-relaxation dynamics, revealing unexpected specificity for off-resonant, dark processes in this material. Energy migration in the lower level of the avalanche absorption transition is also sufficiently rapid to explain the magnitude and comparative efficiency of avalanche emission in this material vis-a ` -vis Tm:YAG. Based on these findings,
Pronounced electron-phonon coupling is observed for the 2 F 7/2 ↔ 2 F 5/2 4 f transitions of Yb 3... more Pronounced electron-phonon coupling is observed for the 2 F 7/2 ↔ 2 F 5/2 4 f transitions of Yb 3ϩ doped into CsCdBr 3 . A comparison of the Raman spectrum and the luminescence excitation sideband accompanying the 2 F 7/2 (0)→ 2 F 5/2 (2Ј) crystal-field transition reveals vibrational properties of the ͓YbBr 6 ͔ coordination unit that differ markedly from those of the CsCdBr 3 host. In particular, the vibronic transition associated with the totally symmetric ͓YbBr 6 ͔ stretching mode appears as a very weak feature at 191 cm Ϫ1 in the Raman spectrum, whereas the totally symmetric ͓CdBr 6 ͔ stretching mode of the CsCdBr 3 bulk, which appears as a strong feature at 162.5 cm Ϫ1 in the Raman spectrum, is only weakly discernible in the sideband. This is direct evidence for a large contribution from ͓YbBr 6 ͔ local modes and a small contribution from bulk modes to the vibronic intensity. The intensity of the local mode is enhanced by approximately a factor of 2 in the Raman spectrum when the laser is tuned into resonance with the 2 F 7/2 (0)→ 2 F 5/2 (2Ј) absorption of Yb 3ϩ , providing direct confirmation of its assignment. The observation of the first and second members of a Franck-Condon progression for both the local and the bulk totally symmetric modes indicates that a ⌬ process, rather than an M process, induces the vibronic intensity. Huang-Rhys factors of S local ϭ0.010Ϯ0.002 and S bulk ϭ0.15Ϯ0.03 were determined from the data, and reflect quite different electron-phonon coupling strengths. These results suggest that multiphonon relaxation of excited electronic states proceeds by the excitation of local modes of ͓YbBr 6 ͔ followed by energy transfer to bulk modes of the lattice, possibly through a nonlinear coupling mechanism which is discussed briefly.
Intrinsic bistability and hysteresis have been observed in the photoluminescence of bulk glass do... more Intrinsic bistability and hysteresis have been observed in the photoluminescence of bulk glass doped with Yb 31 and Tm 31 impurities at room temperature. Multiple instabilities also occur in channel waveguide lasers in this material. Consequently, local field effects exhibit more degrees of freedom than expected and have important implications for compact optical amplifiers and oscillators. PACS numbers: 42.65.Pc Nearly a century ago, Lorentz developed an elegant theory for the optical polarization of matter [1] which introduced the concept of local fields. He calculated a correction for fields incident on a solid which yielded the internal field value using a simple, approximate procedure applicable to many materials. This theory was reformulated and extended for specific crystal structures subsequently by a number of authors . With the advent of nonlinear optics [4] and the discovery of phenomena such as surface-enhanced Raman scattering [5], local field corrections were gradually recognized as being important for quantitative explanations of some optical interactions with matter because of the multiplicative dependence of output intensity on several fields, and, consequently, several local field factors. On the other hand, new nonlinear phenomena specifically mediated by local field corrections were not reported, although dramatic nonlinearities originating from dynamic local field modifications were predicted to occur in dense collections of radiating atoms driven by resonant electromagnetic fields . It was shown theoretically-for example, by incorporation of the local field correction in the Maxwell-Bloch equations for two-level systems subject to resonant light-that intrinsic switching of optical emission could take place. Recently, these predictions were confirmed by the observation of intrinsically bistable emission of rare-earth impurities at low temperature in the compounds Cs 3 Y 2 Br 9 :10% Yb 31 , Cs 3 Lu 2 Br 9 :10% Yb 31 , and CsCdBr 3 :1% Yb 31 [7-9]. Nonlinearities mediated by local field effects have also been reported in composite dielectrics .
Intrinsic bistability and hysteresis have been observed in the photoluminescence of bulk glass do... more Intrinsic bistability and hysteresis have been observed in the photoluminescence of bulk glass doped with Yb3+ and Tm3+ impurities at room temperature. Multiple instabilities also occur in channel waveguide lasers in this material. Consequently, local field effects exhibit more degrees of freedom than expected and have important implications for compact optical amplifiers and oscillators.
A simple upconversion scheme utilizing 40-fs pulses is shown to permit high-contrast imaging of o... more A simple upconversion scheme utilizing 40-fs pulses is shown to permit high-contrast imaging of objects obscured by a highly scattering medium when no ballistic component is evident in the scattered light and imaging is performed with any portion of the scattered light pulse. We present a time-gated, inherently low-pass spatially filtered imaging method that minimizes signal-averaging requirements and greatly facilitates imaging under severe scattering ͑turbid͒ conditions.
Pronounced electron-phonon coupling is observed for the 2 F 7/2 ↔ 2 F 5/2 4 f transitions of Yb 3... more Pronounced electron-phonon coupling is observed for the 2 F 7/2 ↔ 2 F 5/2 4 f transitions of Yb 3ϩ doped into CsCdBr 3 . A comparison of the Raman spectrum and the luminescence excitation sideband accompanying the 2 F 7/2 (0)→ 2 F 5/2 (2Ј) crystal-field transition reveals vibrational properties of the ͓YbBr 6 ͔ coordination unit that differ markedly from those of the CsCdBr 3 host. In particular, the vibronic transition associated with the totally symmetric ͓YbBr 6 ͔ stretching mode appears as a very weak feature at 191 cm Ϫ1 in the Raman spectrum, whereas the totally symmetric ͓CdBr 6 ͔ stretching mode of the CsCdBr 3 bulk, which appears as a strong feature at 162.5 cm Ϫ1 in the Raman spectrum, is only weakly discernible in the sideband. This is direct evidence for a large contribution from ͓YbBr 6 ͔ local modes and a small contribution from bulk modes to the vibronic intensity. The intensity of the local mode is enhanced by approximately a factor of 2 in the Raman spectrum when the laser is tuned into resonance with the 2 F 7/2 (0)→ 2 F 5/2 (2Ј) absorption of Yb 3ϩ , providing direct confirmation of its assignment. The observation of the first and second members of a Franck-Condon progression for both the local and the bulk totally symmetric modes indicates that a ⌬ process, rather than an M process, induces the vibronic intensity. Huang-Rhys factors of S local ϭ0.010Ϯ0.002 and S bulk ϭ0.15Ϯ0.03 were determined from the data, and reflect quite different electron-phonon coupling strengths. These results suggest that multiphonon relaxation of excited electronic states proceeds by the excitation of local modes of ͓YbBr 6 ͔ followed by energy transfer to bulk modes of the lattice, possibly through a nonlinear coupling mechanism which is discussed briefly.
A simple upconversion scheme utilizing 40-fs pulses is shown to permit high-contrast imaging of o... more A simple upconversion scheme utilizing 40-fs pulses is shown to permit high-contrast imaging of objects obscured by a highly scattering medium when no ballistic component is evident in the scattered light and imaging is performed with any portion of the scattered light pulse. We present a time-gated, inherently low-pass spatially filtered imaging method that minimizes signal-averaging requirements and greatly facilitates imaging under severe scattering ͑turbid͒ conditions.
... Figure 2, top, shows unpolarized luminescence excita-tion spectra of the 2F72 0 ! 2F52 20 tra... more ... Figure 2, top, shows unpolarized luminescence excita-tion spectra of the 2F72 0 ! 2F52 20 transition in a CsCdBr3:1% Yb31 single crystal at 7 K recorded by fre-quency ... We as-sign this line to the undistorted Yb-V-Yb symmetric ion pair on the basis of its high abundance [16]. ...
This thesis reports experiments and theory on intrinsic mirrorless bistability in the luminescenc... more This thesis reports experiments and theory on intrinsic mirrorless bistability in the luminescence of ytterbium- doped crystals and glasses. The main results are the observation of intrinsically bistable luminescence at room temperature and chromatic switching at low temperature, reported here for the first time. The nonlinear dynamics responsible for these optical phenomena are shown to arise from ion-ion interactions controlled by the application of resonant electromagnetic fields. On the theoretical side, the classical Lorentz local field correction is shown to be the lowest order term of radiation-driven correlation contributions to local polarization which arise from inter-ion coherences and cooperative relaxation and frequency shifts beyond the dynamic shift are predicted. The nonlinear Maxwell-Bloch equations are extended to describe energy transfer between different species of ions predicting bistability in excited state populations which then emit bistable luminescence as a consequence, and an intensity dependent transfer rate is predicted. Diffusive excitation migration in space is also explored as a possible mechanism for generating multiple instabilities, but is not predicted to give rise to hysteresis loops by itself. On the experimental side, original observations of intrinsic optical switching and hysteresis are reported in the luminescence of Yb:CsCdBr 3 and Yb, Tm:glass. Evidence of cross-coupling between different impurities is also presented, together with spectroscopic details of intrinsic chromatic switching between different luminescent transitions of the acceptor species in Yb, Er:CsCdBr3 excited at the infrared Yb resonance wavelength. Conclusive spectroscopic evidence that excludes thermal effects as responsible for low temperature intrinsic switching is also presented. Room temperature intrinsic optical switching and hysteresis are reported for the first time in bulk Yb,Tm:glass samples. Switching, hysteresis, and clamping of laser output from waveguide channels fabricated in the glass material are also reported and indicate fundamental design limitations for compact optical amplifiers and oscillators.
This chapter describes designs and experiments that apply the Raman effect to wideband amplifiers... more This chapter describes designs and experiments that apply the Raman effect to wideband amplifiers (WBAs). In the context of this chapter, wideband corresponds to a bandwidth of approximately 50 to 100 nm or more. We start by explaining the need for WBAs, and briefly review some of the key enabling technologies for wideband systems. Section 14.2 describes several approaches for WBA, including the erbium-doped fiber amplifier (EDFA) and Raman amplifier combinations as well as all-Raman amplifiers. Section 14.3 summarizes the advantages and challenges of the all-Raman approach, the focus of this chapter. Section 14.4 identifies the key physical principles that need to be considered in the design of all-Raman WBAs. Then, perhaps the most important section of this chapter, Section 14.5 describes engineering design rules for construction of all-Raman WBAs that satisfy gain and noise figure performance requirements of typical long-haul and ultra-long-haul fiber-optic transmission systems. Several WBA experiments that use either EDFA/Raman amplifier combinations or all-Raman amplifiers are illustrated in Section 14.6, and exemplary wideband system experiments are described in Section 14.7. Finally, we summarize and conclude the chapter in Section 14.8.
Cascaded Raman wavelength shifting up to three orders from 1553 nm to 1867 nm is demonstrated in ... more Cascaded Raman wavelength shifting up to three orders from 1553 nm to 1867 nm is demonstrated in As 2 S 3 -chalcogenide fibers. Due to a long zero dispersion wavelength for the sulfide fiber (>4.5 µm), pumping the fiber at 1553 nm results in generation of cascaded Stokes orders based on stimulated Raman scattering. Using the threshold power for the Raman orders, we estimate the Raman gain coefficient for the As 2 S 3 fibers to be ~5.7x10 -12 m/W at 1550 nm. Observation of higher Raman orders is limited by damage to the fiber at input intensities >1 GW/cm 2 .
Cascaded Raman wavelength shifting up to three orders from 1553 nm to 1867 nm is demonstrated in ... more Cascaded Raman wavelength shifting up to three orders from 1553 nm to 1867 nm is demonstrated in As 2 S 3 -chalcogenide fibers. Due to a long zero dispersion wavelength for the sulfide fiber (>4.5 µm), pumping the fiber at 1553 nm results in generation of cascaded Stokes orders based on stimulated Raman scattering. Using the threshold power for the Raman orders, we estimate the Raman gain coefficient for the As 2 S 3 fibers to be ~5.7x10 -12 m/W at 1550 nm. Observation of higher Raman orders is limited by damage to the fiber at input intensities >1 GW/cm 2 .
spectrum when the laser is tuned into resonance with the 2 F7/2(0)! 2 F5/2(28) absorption of Yb 3... more spectrum when the laser is tuned into resonance with the 2 F7/2(0)! 2 F5/2(28) absorption of Yb 31 , providing direct confirmation of its assignment. The observation of the first and second members of a Franck-Condon progression for both the local and the bulk totally symmetric modes indicates that a D process, rather than an M process, induces the vibronic
We report the first observation of intrinsic optical bistability in CsCdBr3:1% Yb3+ and show, usi... more We report the first observation of intrinsic optical bistability in CsCdBr3:1% Yb3+ and show, using site-selective spectroscopy, that only the asymmetric, strongly coupled Yb3+ ion-pair minority site gives rise to hysteresis of near-infrared and cooperative up-conversion luminescence as a function of incident laser intensity below 15 K.
4 emission. Our analysis indicates that individual thermally activated Stark levels dominate cros... more 4 emission. Our analysis indicates that individual thermally activated Stark levels dominate cross-relaxation dynamics, revealing unexpected specificity for off-resonant, dark processes in this material. Energy migration in the lower level of the avalanche absorption transition is also sufficiently rapid to explain the magnitude and comparative efficiency of avalanche emission in this material vis-a ` -vis Tm:YAG. Based on these findings,
Pronounced electron-phonon coupling is observed for the 2 F 7/2 ↔ 2 F 5/2 4 f transitions of Yb 3... more Pronounced electron-phonon coupling is observed for the 2 F 7/2 ↔ 2 F 5/2 4 f transitions of Yb 3ϩ doped into CsCdBr 3 . A comparison of the Raman spectrum and the luminescence excitation sideband accompanying the 2 F 7/2 (0)→ 2 F 5/2 (2Ј) crystal-field transition reveals vibrational properties of the ͓YbBr 6 ͔ coordination unit that differ markedly from those of the CsCdBr 3 host. In particular, the vibronic transition associated with the totally symmetric ͓YbBr 6 ͔ stretching mode appears as a very weak feature at 191 cm Ϫ1 in the Raman spectrum, whereas the totally symmetric ͓CdBr 6 ͔ stretching mode of the CsCdBr 3 bulk, which appears as a strong feature at 162.5 cm Ϫ1 in the Raman spectrum, is only weakly discernible in the sideband. This is direct evidence for a large contribution from ͓YbBr 6 ͔ local modes and a small contribution from bulk modes to the vibronic intensity. The intensity of the local mode is enhanced by approximately a factor of 2 in the Raman spectrum when the laser is tuned into resonance with the 2 F 7/2 (0)→ 2 F 5/2 (2Ј) absorption of Yb 3ϩ , providing direct confirmation of its assignment. The observation of the first and second members of a Franck-Condon progression for both the local and the bulk totally symmetric modes indicates that a ⌬ process, rather than an M process, induces the vibronic intensity. Huang-Rhys factors of S local ϭ0.010Ϯ0.002 and S bulk ϭ0.15Ϯ0.03 were determined from the data, and reflect quite different electron-phonon coupling strengths. These results suggest that multiphonon relaxation of excited electronic states proceeds by the excitation of local modes of ͓YbBr 6 ͔ followed by energy transfer to bulk modes of the lattice, possibly through a nonlinear coupling mechanism which is discussed briefly.
Intrinsic bistability and hysteresis have been observed in the photoluminescence of bulk glass do... more Intrinsic bistability and hysteresis have been observed in the photoluminescence of bulk glass doped with Yb 31 and Tm 31 impurities at room temperature. Multiple instabilities also occur in channel waveguide lasers in this material. Consequently, local field effects exhibit more degrees of freedom than expected and have important implications for compact optical amplifiers and oscillators. PACS numbers: 42.65.Pc Nearly a century ago, Lorentz developed an elegant theory for the optical polarization of matter [1] which introduced the concept of local fields. He calculated a correction for fields incident on a solid which yielded the internal field value using a simple, approximate procedure applicable to many materials. This theory was reformulated and extended for specific crystal structures subsequently by a number of authors . With the advent of nonlinear optics [4] and the discovery of phenomena such as surface-enhanced Raman scattering [5], local field corrections were gradually recognized as being important for quantitative explanations of some optical interactions with matter because of the multiplicative dependence of output intensity on several fields, and, consequently, several local field factors. On the other hand, new nonlinear phenomena specifically mediated by local field corrections were not reported, although dramatic nonlinearities originating from dynamic local field modifications were predicted to occur in dense collections of radiating atoms driven by resonant electromagnetic fields . It was shown theoretically-for example, by incorporation of the local field correction in the Maxwell-Bloch equations for two-level systems subject to resonant light-that intrinsic switching of optical emission could take place. Recently, these predictions were confirmed by the observation of intrinsically bistable emission of rare-earth impurities at low temperature in the compounds Cs 3 Y 2 Br 9 :10% Yb 31 , Cs 3 Lu 2 Br 9 :10% Yb 31 , and CsCdBr 3 :1% Yb 31 [7-9]. Nonlinearities mediated by local field effects have also been reported in composite dielectrics .
Intrinsic bistability and hysteresis have been observed in the photoluminescence of bulk glass do... more Intrinsic bistability and hysteresis have been observed in the photoluminescence of bulk glass doped with Yb3+ and Tm3+ impurities at room temperature. Multiple instabilities also occur in channel waveguide lasers in this material. Consequently, local field effects exhibit more degrees of freedom than expected and have important implications for compact optical amplifiers and oscillators.
A simple upconversion scheme utilizing 40-fs pulses is shown to permit high-contrast imaging of o... more A simple upconversion scheme utilizing 40-fs pulses is shown to permit high-contrast imaging of objects obscured by a highly scattering medium when no ballistic component is evident in the scattered light and imaging is performed with any portion of the scattered light pulse. We present a time-gated, inherently low-pass spatially filtered imaging method that minimizes signal-averaging requirements and greatly facilitates imaging under severe scattering ͑turbid͒ conditions.
Pronounced electron-phonon coupling is observed for the 2 F 7/2 ↔ 2 F 5/2 4 f transitions of Yb 3... more Pronounced electron-phonon coupling is observed for the 2 F 7/2 ↔ 2 F 5/2 4 f transitions of Yb 3ϩ doped into CsCdBr 3 . A comparison of the Raman spectrum and the luminescence excitation sideband accompanying the 2 F 7/2 (0)→ 2 F 5/2 (2Ј) crystal-field transition reveals vibrational properties of the ͓YbBr 6 ͔ coordination unit that differ markedly from those of the CsCdBr 3 host. In particular, the vibronic transition associated with the totally symmetric ͓YbBr 6 ͔ stretching mode appears as a very weak feature at 191 cm Ϫ1 in the Raman spectrum, whereas the totally symmetric ͓CdBr 6 ͔ stretching mode of the CsCdBr 3 bulk, which appears as a strong feature at 162.5 cm Ϫ1 in the Raman spectrum, is only weakly discernible in the sideband. This is direct evidence for a large contribution from ͓YbBr 6 ͔ local modes and a small contribution from bulk modes to the vibronic intensity. The intensity of the local mode is enhanced by approximately a factor of 2 in the Raman spectrum when the laser is tuned into resonance with the 2 F 7/2 (0)→ 2 F 5/2 (2Ј) absorption of Yb 3ϩ , providing direct confirmation of its assignment. The observation of the first and second members of a Franck-Condon progression for both the local and the bulk totally symmetric modes indicates that a ⌬ process, rather than an M process, induces the vibronic intensity. Huang-Rhys factors of S local ϭ0.010Ϯ0.002 and S bulk ϭ0.15Ϯ0.03 were determined from the data, and reflect quite different electron-phonon coupling strengths. These results suggest that multiphonon relaxation of excited electronic states proceeds by the excitation of local modes of ͓YbBr 6 ͔ followed by energy transfer to bulk modes of the lattice, possibly through a nonlinear coupling mechanism which is discussed briefly.
A simple upconversion scheme utilizing 40-fs pulses is shown to permit high-contrast imaging of o... more A simple upconversion scheme utilizing 40-fs pulses is shown to permit high-contrast imaging of objects obscured by a highly scattering medium when no ballistic component is evident in the scattered light and imaging is performed with any portion of the scattered light pulse. We present a time-gated, inherently low-pass spatially filtered imaging method that minimizes signal-averaging requirements and greatly facilitates imaging under severe scattering ͑turbid͒ conditions.
... Figure 2, top, shows unpolarized luminescence excita-tion spectra of the 2F72 0 ! 2F52 20 tra... more ... Figure 2, top, shows unpolarized luminescence excita-tion spectra of the 2F72 0 ! 2F52 20 transition in a CsCdBr3:1% Yb31 single crystal at 7 K recorded by fre-quency ... We as-sign this line to the undistorted Yb-V-Yb symmetric ion pair on the basis of its high abundance [16]. ...
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Papers by Amos Kuditcher