This content will become publicly available on September 22, 2023

Mid-IR spectroscopy of Er 3+ doped low-phonon CsCdCl 3 and CsPbCl 3 crystals

The mid-IR spectroscopic properties of$Er3+$doped low-phonon$CsCdCl3$and$CsPbCl3$crystals grown by the Bridgman technique have been investigated. Using optical excitations at$∼<#comment/>800nm$and$∼<#comment/>660nm$, both crystals exhibited IR emissions at$∼<#comment/>1.55$,$∼<#comment/>2.75$,$∼<#comment/>3.5$, and$∼<#comment/>4.5µ<#comment/>m$at room temperature. The mid-IR emission at 4.5 µm, originating from the$4I9/2→<#comment/>4I11/2$transition, showed a long emission lifetime of$∼<#comment/>11.6ms$for$Er3+$doped$CsCdCl3$, whereas$Er3+$doped$CsPbCl3$exhibited a shorter lifetime of$∼<#comment/>1.8ms$. The measured emission lifetimes of the$4I9/2$state were nearly independent of the temperature, indicating a negligibly small nonradiative decay rate through multiphonon relaxation, as predicted by the energy-gap law for low-maximum-phonon energy hosts. The room temperature stimulated more »

Authors:
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Publication Date:
NSF-PAR ID:
10372091
Journal Name:
Journal of the Optical Society of America B
Volume:
40
Issue:
1
Page Range or eLocation-ID:
Article No. A1
ISSN:
0740-3224; JOBPDE
Publisher:
Optical Society of America
1. We report on spectroscopic measurements on the$4f76s28S7/2∘<#comment/>→<#comment/>4f7(8S∘<#comment/>)6s6p(1P∘<#comment/>)8P9/2$transition in neutral europium-151 and europium-153 at 459.4 nm. The center of gravity frequencies for the 151 and 153 isotopes, reported for the first time in this paper, to our knowledge, were found to be 652,389,757.16(34) MHz and 652,386,593.2(5) MHz, respectively. The hyperfine coefficients for the$6s6p(1P∘<#comment/>)8P9/2$state were found to be$A(151)=−<#comment/>228.84(2)MHz$,$B(151)=226.9(5)MHz$and$A(153)=−<#comment/>101.87(6)MHz$,$B(153)=575.4(1.5)MHz$, which all agree with previously published results except for A(153), which shows a small discrepancy. The isotope shift is found to be 3163.8(6) MHz, which also has a discrepancy with previously published results.
2. Electro-optic quantum coherent interfaces map the amplitude and phase of a quantum signal directly to the phase or intensity of a probe beam. At terahertz frequencies, a fundamental challenge is not only to sense such weak signals (due to a weak coupling with a probe in the near-infrared) but also to resolve them in the time domain. Cavity confinement of both light fields can increase the interaction and achieve strong coupling. Using this approach, current realizations are limited to low microwave frequencies. Alternatively, in bulk crystals, electro-optic sampling was shown to reach quantum-level sensitivity of terahertz waves. Yet, the coupling strength was extremely weak. Here, we propose an on-chip architecture that concomitantly provides subcycle temporal resolution and an extreme sensitivity to sense terahertz intracavity fields below 20 V/m. We use guided femtosecond pulses in the near-infrared and a confinement of the terahertz wave to a volume of$VTHz∼<#comment/>10−<#comment/>9(λ<#comment/>THz/2)3$in combination with ultraperformant organic molecules ($r33=170pm/V$) and accomplish a record-high single-photon electro-optic coupling rate of, 10,000 times higher than in recent reports of sensing vacuum field fluctuations in bulk media. Via homodyne detection implemented directly on chip, the interaction results into an intensity modulation of the femtosecond pulses. The single-photon cooperativity is$C0=1.6×<#comment/>10−<#comment/>8$, and the multiphoton cooperativity is$C=0.002$at room temperature. We show$><#comment/>70dB$dynamic range in intensity at 500 ms integration under irradiation with a weak coherent terahertz field. Similar devices could be employed in future measurements of quantum states in the terahertz at the standard quantum limit, or for entanglement of subsystems on subcycle temporal scales, such as terahertz and near-infrared quantum bits.
3. We experimentally demonstrate simultaneous turbulence mitigation and channel demultiplexing in a 200 Gbit/s orbital-angular-momentum (OAM) multiplexed link by adaptive wavefront shaping and diffusing (WSD) the light beams. Different realizations of two emulated turbulence strengths (the Fried parameter$r0=0.4,1.0mm$) are mitigated. The experimental results show the following. (1) Crosstalk between OAM$l=+1$and$l=−<#comment/>1$modes can be reduced by$><#comment/>10.0$and$><#comment/>5.8dB$, respectively, under the weaker turbulence ($r0=1.0mm$); crosstalk is further improved by$><#comment/>17.7$and$><#comment/>19.4dB$, respectively, under most realizations in the stronger turbulence ($r0=0.4mm$). (2) The optical signal-to-noise ratio penalties for the bit error rate performance are measured to be$∼<#comment/>0.7$and$∼<#comment/>1.6dB$under weaker turbulence, while measured to be$∼<#comment/>3.2$and$∼<#comment/>1.8dB$under stronger turbulence for OAM$l=+1$and$l=−<#comment/>1$mode, respectively.
4. We experimentally demonstrate the utilization of adaptive optics (AO) to mitigate intra-group power coupling among linearly polarized (LP) modes in a graded-index few-mode fiber (GI FMF). Generally, in this fiber, the coupling between degenerate modes inside a modal group tends to be stronger than between modes belonging to different groups. In our approach, the coupling inside the$LP11$group can be represented by a combination of orbital-angular-momentum (OAM) modes, such that reducing power coupling in OAM set tends to indicate the capability to reduce the coupling inside the$LP11$group. We employ two output OAM modes$l=+1$and$l=−<#comment/>1$as resultant linear combinations of degenerate$LP11a$and$LP11b$modes inside the$LP11$group of a$∼<#comment/>0.6-km$GI FMF. The power coupling is mitigated by shaping the amplitude and phase of the distorted OAM modes. Each OAM mode carries an independent 20-, 40-, or 100-Gbit/s quadrature-phase-shift-keying data stream. We measure the transmission matrix (TM) in the OAM basis within$LP11$group, which is a subset of the full LP TMmore »
5. The optical phase$ϕ<#comment/>$is a key quantity in the physics of light propagating through a turbulent medium. In certain respects, however, the statistics of the phasefactor,$ψ<#comment/>=exp⁡<#comment/>(iϕ<#comment/>)$, are more relevant than the statistics of the phase itself. Here, we present a theoretical analysis of the 2D phase-factor spectrum$Fψ<#comment/>(κ<#comment/>)$of a random phase screen. We apply the theory to four types of phase screens, each characterized by a power-law phase structure function,$Dϕ<#comment/>(r)=(r/rc)γ<#comment/>$(where$rc$is the phase coherence length defined by$Dϕ<#comment/>(rc)=1rad2$), and a probability density function$pα<#comment/>(α<#comment/>)$of the phase increments for a given spatial lag. We analyze phase screens with turbulent ($γ<#comment/>=5/3$) and quadratic ($γ<#comment/>=2$) phase structure functions and with normally distributed (i.e., Gaussian) versus Laplacian phase increments. We find that there is a pronounced bump in each of the four phase-factor spectra$Fψ<#comment/>(κ<#comment/>)$. The precise location and shape of the bump are different for the four phase-screen types, but in each case it occurs at$κ<#comment/>∼<#comment/>1/rc$. The bump is unrelated to the well-knownmore »