73 research outputs found
Assignment of the NV0 575 nm zero-phonon line in diamond to a 2E-2A2 transition
The time-averaged emission spectrum of single nitrogen-vacancy defects in
diamond gives zero-phonon lines of both the negative charge state at 637 nm
(1.945 eV) and the neutral charge state at 575 nm (2.156 eV). This occurs
through photo-conversion between the two charge states. Due to strain in the
diamond the zero-phonon lines are split and it is found that the splitting and
polarization of the two zero-phonon lines are the same. From this observation
and consideration of the electronic structure of the nitrogen-vacancy center it
is concluded that the excited state of the neutral center has A2 orbital
symmetry. The assignment of the 575 nm transition to a 2E - 2A2 transition has
not been established previously.Comment: 5 pages, 5 figure
Focused Deterrence and the Prevention of Violent Gun Injuries: Practice, Theoretical Principles, and Scientific Evidence
Focused deterrence strategies are a relatively new addition to a growing portfolio of evidence-based violent gun injury prevention practices available to policy makers and practitioners. These strategies seek to change offender behavior by understanding the underlying violence-producing dynamics and conditions that sustain recurring violent gun injury problems and by implementing a blended strategy of law enforcement, community mobilization, and social service actions. Consistent with documented public health practice, the focused deterrence approach identifies underlying risk factors and causes of recurring violent gun injury problems, develops tailored responses to these underlying conditions, and measures the impact of implemented interventions. This article reviews the practice, theoretical principles, and evaluation evidence on focused deterrence strategies. Although more rigorous randomized studies are needed, the available empirical evidence suggests that these strategies generate noteworthy gun violence reduction impacts and should be part of a broader portfolio of violence prevention strategies available to policy makers and practitioners
Searching for Exoplanets Using a Microresonator Astrocomb
Detection of weak radial velocity shifts of host stars induced by orbiting
planets is an important technique for discovering and characterizing planets
beyond our solar system. Optical frequency combs enable calibration of stellar
radial velocity shifts at levels required for detection of Earth analogs. A new
chip-based device, the Kerr soliton microcomb, has properties ideal for
ubiquitous application outside the lab and even in future space-borne
instruments. Moreover, microcomb spectra are ideally suited for astronomical
spectrograph calibration and eliminate filtering steps required by conventional
mode-locked-laser frequency combs. Here, for the calibration of astronomical
spectrographs, we demonstrate an atomic/molecular line-referenced,
near-infrared soliton microcomb. Efforts to search for the known exoplanet HD
187123b were conducted at the Keck-II telescope as a first in-the-field
demonstration of microcombs
Self-Injection Locking and Phase-Locked States in Microresonator-Based Optical Frequency Combs
Microresonator-based optical frequency combs have been a topic of extensive research during the last few years. Several theoretical models for the comb generation have been proposed; however, they do not comprehensively address experimental results that show a variety of independent comb generation mechanisms. Here, we present frequency-domain experiments that illuminate the transition of microcombs into phase-locked states, which show characteristics of injection locking between ensembles of comb modes. In addition, we demonstrate the existence of equidistant optical frequency combs that are phase stable but have nondeterministic phase relationships between individual comb modes
Charge switching dynamics and optimal excitation wavelength of single NV centers in ultrapure diamond
Photoluminescence excitation spectra of single NV centers in diamond are studied and an optimal wavelength for NV is found. The physics of bidirectional switching between NV0 and NV charge states of the defect is elucidated
Optimum photoluminescence excitation and recharging cycle of single nitrogen-vacancy centers in ultrapure diamond
Important features in the spectral and temporal photoluminescence excitation of single nitrogen-vacancy (NV) centers in diamond are reported at conditions relevant for quantum applications. Bidirectional switching occurs between the neutral (NV0) and negatively charged (NV -) states. Luminescence of NV - is most efficiently triggered at a wavelength of 575nm which ensures optimum excitation and recharging of NV0. The dark state of NV - is identified as NV0. A narrow resonance is observed in the excitation spectra at 521nm, which mediates efficient conversion to NV0
Electronic synthesis of light
We report on bidirectional frequency conversion between the microwave and optical domains using electro-optics. Advances in communications, time keeping, and quantum sensing have all come to depend upon the coherent interoperation of light wave and microwave signals. To connect these domains, which are separated by a factor of 10,000 in frequency, requires specialized technology that has until now only been achieved by ultrafast mode-locked lasers. In contrast, electro-optic modulation (EOM) combs arise deterministically by imposing microwave-rate oscillations on a continuous-wave laser. Here we demonstrate electro-optic generation of a 160 THz bandwidth super-continuum and realize f-2f self-referencing. Coherence of the supercontinuum is achieved through optical filtering of electronic noise on the seed EOM comb. The mode frequencies of the supercontinuum are derived from the electronic oscillator and they achieve < 5 x 10(-14) fractional accuracy and stability, which opens a novel regime for tunable combs with wide mode spacing apart from the requirements of mode locking
Charge switching dynamics and optimal excitation wavelength of single NV centers in ultrapure diamond
Photoluminescence excitation spectra of single NV centers in diamond are studied and an optimal wavelength for NV- is found. The physics of bidirectional switching between NV0 and NV- charge states of the defect is elucidated
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