Related Experiment Video
Updated: Oct 18, 2025
09:23
Harmonic Nanoparticles for Regenerative Research
Published on: May 1, 2014
11.9K
SHG in a centrosymmetric crystal - can it be possible?
1UCSI University, Cheras, Kuala Lumpur, Malaysia.
Acta Crystallographica. Section C, Structural Chemistry
|October 5, 2021
Summary
This study examines centrosymmetric compounds exhibiting second harmonic generation (SHG). It explains that apparent contradictions arise from twinned, noncentrosymmetric crystals, suggesting authors clarify space groups for SHG-active materials.
Area of Science:
- Solid-state physics
- Crystallography
- Materials science
Background:
- Second harmonic generation (SHG) is a nonlinear optical phenomenon.
- Centrosymmetric compounds theoretically should not exhibit SHG.
- Publications report SHG responses in compounds with centrosymmetric crystal structures.
Purpose of the Study:
- To review literature on SHG in centrosymmetric compounds.
- To address the discrepancy between inversion symmetry and observed SHG.
- To propose a resolution for conflicting experimental outcomes.
Main Methods:
- Literature review of selected publications on SHG.
- Analysis of studies reporting contradictory results.
- Examination of explanations for apparent symmetry violations.
Main Results:
- Selected publications report SHG in centrosymmetric compounds.
- Some studies dispute these laser outcomes.
- Two studies explain the contradiction: crystals are noncentrosymmetric and twinned by inversion.
Conclusions:
- The apparent contradiction between SHG and centrosymmetry is resolved by crystal twinning.
- Noncentrosymmetric and inversion-twinned crystals can exhibit SHG.
- Authors should consider specifying noncentrosymmetric space groups for SHG-active compounds.
Related Concept Videos
01:03Modes of Standing Waves - I
3.2K
A close look at earthquakes provides evidence for the conditions appropriate for resonance, standing waves, and constructive and destructive interference. A building may vibrate for several seconds with a driving frequency matching the building's natural frequency of vibration; this produces a resonance that results in one building collapsing while the neighboring buildings do not. Often, buildings of a certain height are devastated, while other taller buildings remain intact. This...
3.2K
01:192D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)
1.0K
Heteronuclear single-quantum correlation spectroscopy (HSQC) is a 2D NMR technique that reveals one-bond correlations between hydrogen and a heteronucleus. The HSQC experiment is similar to the heteronuclear correlation experiment (HETCOR) but is more sensitive. In the HSQC spectrum, the proton chemical shift is plotted on the horizontal F2 axis, while the 13C chemical shift is plotted on the vertical F1 axis. The corresponding proton and 13C spectra are also shown. The HSQC contour plot does...
1.0K
02:25Centrosome Duplication
4.2K
The primary microtubule organizing center (MTOC) in animal cells is the centrosome. A centrosome has two cylindrical centrioles at its core. Each centriole consists of nine sets of three microtubules held together by proteins. The centrioles are positioned at right angles to each other and surrounded by a shapeless protein cloud called the pericentriolar matrix, or pericentriolar material (PCM).
To ensure that each daughter cell receives a centrosome after cell division, centrosome duplication...
To ensure that each daughter cell receives a centrosome after cell division, centrosome duplication...
4.2K
02:33Lattice Centering and Coordination Number
10.3K
The structure of a crystalline solid, whether a metal or not, is best described by considering its simplest repeating unit, which is referred to as its unit cell. The unit cell consists of lattice points that represent the locations of atoms or ions. The entire structure then consists of this unit cell repeating in three dimensions. The three different types of unit cells present in the cubic lattice are illustrated in Figure 1.
Types of Unit Cells
Imagine taking a large number of identical...
Types of Unit Cells
Imagine taking a large number of identical...
10.3K
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
1.2K
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
1.2K
02:18X-ray Crystallography
24.5K
The size of the unit cell and the arrangement of atoms in a crystal may be determined from measurements of the diffraction of X-rays by the crystal, termed X-ray crystallography.
Diffraction
Diffraction is the change in the direction of travel experienced by an electromagnetic wave when it encounters a physical barrier whose dimensions are comparable to those of the wavelength of the light. X-rays are electromagnetic radiation with wavelengths about as long as the distance between neighboring...
Diffraction
Diffraction is the change in the direction of travel experienced by an electromagnetic wave when it encounters a physical barrier whose dimensions are comparable to those of the wavelength of the light. X-rays are electromagnetic radiation with wavelengths about as long as the distance between neighboring...
24.5K