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Lithium niobate (LiNbO3) is a non-naturally-occurring salt consisting of niobium, lithium, and oxygen. Its single crystals are an important material for optical waveguides, mobile phones, piezoelectric sensors, optical modulators and various other linear and non-linear optical applications. Lithium niobate is sometimes referred to by the brand name linobate.
After a crystal is grown, it is sliced into wafers of different orientation. Common orientations are Z-cut, X-cut, Y-cut, and cuts with rotated angles of the previous axes.
Thin-film lithium niobate (eg. for optical wave guides) can be grown on sapphire and other substrates, using the MOCVD process. The technology is known as Lithium Niobate-On-Insulator (LNOI).
Nanoparticles of lithium niobate and niobium pentoxide can be produced at low temperature. The complete protocol implies a LiH induced reduction of NbCl5 followed by in situ spontaneous oxidation into low-valence niobium nano-oxides. These niobium oxides are exposed to air atmosphere resulting in pure Nb2O5. Finally, the stable Nb2O5 is converted into lithium niobate LiNbO3 nanoparticles during the controlled hydrolysis of the LiH excess. Spherical nanoparticles of lithium niobate with a diameter of approximately 10 nm can be prepared by impregnating a mesoporous silica matrix with a mixture of an aqueous solution of LiNO3 and NH4NbO(C2O4)2 followed by 10 min heating in an infrared furnace.
In the past few years lithium niobate is finding applications as a kind of electrostatic tweezers, an approach known as optoelectronic tweezers as the effect requires light excitation to take place. This effect allows for fine manipulation of micrometer-scale particles with high flexibility since the tweezing action is constrained to the illuminated area. The effect is based on the very high electric fields generated during light exposure (1-100 kV/cm) within the illuminated spot. These intense fields are also finding applications in biophysics and biotechnology, as they can influence living organisms in a variety of ways. For example, iron-doped lithium niobate excited with visible light has been shown to produce cell death in tumoral cell cultures.
However, due to its low photorefractive damage threshold, PPLN only finds limited applications: at very low power levels. MgO-doped lithium niobate is fabricated by periodically-poled method. Periodically-poled MgO-doped lithium niobate (PPMgOLN) therefore expands the application to medium power level.
The Sellmeier equations for the extraordinary index are used to find the poling period and approximate temperature for quasi-phase matching. Jundt gives
valid from 20 to 250 °C for wavelengths from 0.4 to 5 micrometers, whereas for longer wavelength,
which is valid for T = 25 to 180 °C, for wavelengths ? between 2.8 and 4.8 micrometers.
In these equations f = (T - 24.5)(T + 570.82), ? is in micrometers, and T is in °C.
More generally for ordinary and extraordinary index for MgO-doped LiNbO3:
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