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Related Concept Videos

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

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Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
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Spin–Spin Coupling Constant: Overview01:08

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In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
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Nuclear Overhauser Enhancement (NOE)01:07

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Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically bonded or involved in J-coupling.  This phenomenon, called the Nuclear Overhauser Enhancement (NOE), results from through-space interactions between the nuclear spins. The NOE effect decreases with increasing internuclear distance and is generally not observed beyond 4 angstroms. In NOE, dipole-dipole interactions between neighboring...
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Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
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Double Resonance Techniques: Overview01:12

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Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
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Electromagnetic waves are consistent with Ampere's law. Assuming there is no conduction current Ampere's law is given as:
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Spin injection enhancement in CW VECSEL at room temperature using push-pull optical pumping.

Alexandre Joly, Ghaya Baili, Jean-Marie George

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    This study enhances spin injection efficiency in vertical-cavity surface-emitting lasers (VCSELs) using a novel double pumping technique. This method improves spin polarization for more efficient laser operation.

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    Area of Science:

    • Optoelectronics
    • Spintronics
    • Semiconductor Lasers

    Background:

    • Vertical-cavity surface-emitting lasers (VCSELs) are crucial optoelectronic devices.
    • Efficient spin injection is key for advanced spintronic applications.
    • Current methods for spin polarization in VCSELs have limitations.

    Purpose of the Study:

    • To enhance spin injection efficiency in external-cavity VCSELs.
    • To investigate a novel double pumping scheme for improved spin control.
    • To analyze the impact of polarized optical resonant illumination on spin polarization.

    Main Methods:

    • Utilizing a non-resonant pumping method.
    • Coupling non-resonant pumping with polarized optical resonant illumination.
    • Experimentally measuring laser polarization states and ellipticity.

    Main Results:

    • Achieved enhanced spin injection efficiency through a double pumping scheme.
    • Demonstrated control over spin orientation for electron/hole recombination.
    • Observed a significant increase in laser ellipticity (approx. 50%) compared to non-resonant pumping alone.
    • Experimentally confirmed polarization state flips with specific ellipticities (+31° for spin down, -33° for spin up).

    Conclusions:

    • The proposed double pumping scheme effectively enhances spin injection efficiency in VCSELs.
    • This technique offers precise control over spin polarization for laser processes.
    • The findings pave the way for more efficient spintronic devices based on VCSELs.