A simple and comprehensive electromagnetic theory uncovering complete picture of light transport in birefringent crystals

Birefringence production of light by natural birefringent crystal has long been studied and well understood.Here,we develop a simple and comprehensive rigorous electromagnetic theory that allows one to build up the complete picture about the optics of crystals in a friendly way.This theory not only yields the well-known refraction angle and index of ellipse for birefringence crystal,but also discloses many relevant physical and optical quantities that are rarely studied and less understood.We obtain the reflection and transmission coefficient for amplitude and intensity of light at the crystal surface under a given incident angle and show the electromagnetic field distribution within the crystal.We derive the wavefront and energy flux refraction angle of light and the corresponding phase and ray refractive index.We find big difference between them,where the phase refractive index satisfies the classical index of ellipse and Snell’s law,while the ray refractive index does not.Moreover,we disclose the explicit expressions for the zero-reflection Brewster angle and the critical angle for total internal reflection.For better concept demonstration,we take a weak birefringent crystal of lithium niobate and a strong birefringent crystal tellurium as examples and perform simple theoretical calculations.In addition,we perform experimental measurement upon z-cut lithium niobate plate and find excellent agreement between theory and experiment in regard to the Brewster angle.Our theoretical and experimental results can help to construct a clear and complete picture about light transport characteristics in birefringent crystals,and may greatly facilitate people to find rigorous solution to many light-matter interaction processes happening within birefringent crystals,e.g.,nonlinear optical interactions,with electromagnetic theory.

The optimum scheme of a static Fourier-transform spectrometer based on birefringent crystal

An optimum design of static Fourier-transform spectrometer based on Savert prisms is presented in this paper. A new method of increasing path difference and resolution of spectrometer is given. When the angle between the crystal optical axis of the first Savert prism and the incident interface is 58° and the angle between the crystal optical axis of the second Savert prism and the incident interface is 28°, the maximum path difference will be 0.63 mm, the maximum resolution will be 15.8 cm-1, and the whole field-of-view will reach 6°.

Polarisation-sensitive four-wave mixing and soliton self-frequency shift effect in the highly birefringent photonic crystal fibre

By adjusting the polarisation state of the pump at 805 nm parallel to slow （x） and fast （y） axes of the highly birefringent photonic crystal fibre with zero dispersion wavelengths 790 nm and 750 nm, this paper demonstrates the efficient polarisation-sensitive four wave mixing involved in pump, anti-Stokes and Stokes signals and soliton self- frequency shift effects induced by the phase-matching between red-shifted solitons and blue-shifted dispersive waves. If the reduction of coupling efficiency to the circular pump laser mode or other circular fibres due to asymmetry of the core is neglected, more than 98% of the total input power is kept in a single linear polarisation. Controlled dispersion characteristic of the doublet of fundamental guided-modes results in achieving light field strongly confined in principal axes of photonic crystal fibre, and enhancing the corresponding nonlinear-optical process through the remarkable nonlinear birefringence.

Efficient frequency upshift of 10 fs laser pulses propagating in a 5-cm length birefringent photonic crystal fibre

This paper reports that a 5-cm length birefringent photonic crystal fibre is used to tune the output frequency of unamplified 10-fs Ti：sapphire pulses. The zero dispersion of the fibre is at 823 nm and 800 nm for slow and fast fundamental modes, respectively. It is demonstrated that efficient upshift of the output frequency can be achieved when the pumped radiation is polarized along the slow axis of the fibre. When the average input power reaches 320 mW, about 60% of the output energy is located in one peak at 600 nm and is accompanied by depletion of the pulse inside the anomalous dispersion region.

Electro-optical properties of high birefringence liquid crystal compounds with isothiocyanate and naphthyl group

Liquid crystal（LC） compound with isothiocyanate and naphthyl group is an attractive high birefringence LC material,and can be used in optical devices. In this paper, the electro-optical properties of a series of this type of LC compounds were investigated. The melting points and enthalpy values of these LC compounds were higher than those of corresponding compounds with the phenyl group. These compounds exhibited high birefringence with a maximum value of 0.66. Fluorine substitution in the molecular almost does not affect the birefringence value. When these LC compounds with the naphthyl group were dissolved in a commercial LC mixture, the electro-optical properties depending on temperature were investigated. In the low-temperature region, LC mixtures with the naphthyl-group LC compounds exhibited higher viscosity than pure commercial LCs. In the high-temperature region, viscosity values very closely approached each other. When response performance was investigated, figure-of-merit（FoM） values were measured. The Fo M values of LC mixtures containing LC compounds with naphthyl group were lower than those of reference benzene LCs in the low-temperature region. However, in the high-temperature region, the results were reversed. These isothiocyanate LC compounds with naphthyl group can be applied in special fast-response LC device, particularly the ones used under high-temperature conditions.

High stability and low noise laser-diode end-pumped Nd:YAG ceramic passively Q-switched laser at 1123 nm based on a Ti_(3)C_(2)T_(x)-PVA saturable absorber

We report a high repetition frequency, high power stability and low laser noise laser-diode(LD) end-pumped Nd: YAG ceramic passively Q-switched laser at 1123 nm based on a Ti_(3)C_(2)T_(x)-polyvinyl alcohol(PVA) film as a saturable absorber(SA). A Brewster polarizer(BP) and a birefringent crystal(BC) are incorporated to enable frequency selection and filtering for the passively Q-switched 1123 nm pulsed laser to improve the power stability and reduce the noise. When the pump power is 5.1 W, an average output power of 457.9 m W is obtained, corresponding to a repetition frequency of 1.09 MHz,a pulse width of 56 ns, a spectral line width of 0.65 nm, a power instability of ±0.92%, and a laser noise of 0.89%.The successful implementation of the “Ti_(3)C_(2)T_(x)-PVA film passively Q-switching” combined with “frequency selection and filtering of BP + BC” technology path provides a valuable reference for developing pulsed laser with high repetition frequency, high stability and low noise.

Highly Birefringent Photonic Crystal Fibers B Using Asymmetric Core Design

We demonstrate a highly birefringent photonic crystal fiber by utilizing the asymmetric core design. Based on spectral measurements of the polarization mode interfering, we estimate that the fiber has a beat length of about 0.33 mm at 1545 nm.

ASb(SO_(4))_(2)(A=Rb,Cs):Two short-wave UV antimony sulfates exhibiting large birefringence

Herein,two antimony sulfates,named RbSb(SO_(4))_(2)(1)and CsSb(SO_(4))_(2)(2),have been successfully synthesized with the introduction of Sb^(3+)cation with stereochemically active lone pairs(SCALP)into sulfates by the conventional hydrothermal method.Both two compounds endow short ultraviolet(UV)absorption edges(281 nm and 278 nm,respectively)and large birefringence(0.171@546 nm and 0.174@546 nm,respectively),which means that they are promising short-wave UV optical materials.Interestingly,though both of the two compounds exhibit similar 1D chained structures,and possess the same functional moieties including SbO4 seesaws and SO4 tetrahedral groups,they exhibit significantly opposite macroscopic symmetries,i.e.,compound 1 crystallizes in a centrosymmetric(CS)manner(P2_(1)/n)and compound 2 in a noncentrosymmetric(NCS)manner(P2_(1)2_(1)2_(1)),due to the size of cations[r(Rb+)=1.56 A˚,r(Cs+)=1.67 A˚]affects the orientation of SCALP of the adjacent Sb^(3+).

Naphthylethyne based liquid crystals with high birefringence and characteristics of selective reflection

A series of high birefringence liquid crystalline molecules with cyano, isothiocyanato and trifluoromethyl terminal compounds based on naphthylethyne core was successfully synthesized and characterized. The molecular structures of the intermediates and resulting compounds were confirmed by Fourier transform infrared （FT-IR）, nuclear magnetic resonance （NMR）, mass spectrometry （MS）, and elemental analysis （EA）. Their thermal stability, transition temperatures, and phase sequences were investigated by simultaneous thermal analyzer polarized （STA）, optical microscopy （POM） and differential scanning calorimetry （DSC）. The birefringence was measured by using an Abbe refractometer. In addition, the selective reflection characteristics with naphthylethyne compounds were also studied.

"刚柔并济"构筑可"劈裂"光的高稳定性晶体材料

There is a pressing demand for the development of novel birefringent crystals tailored for compact optical components,especially for crystals exhibiting large birefringence across a range of temperatures.This has commonly been achieved by introducing various deformable groups with high polarizability anisotropy.In this study,we combined both rigid and deformable groups to synthesise a new birefringent crystal,Al_(2)Te_(2)MoO_(10),which demonstrates an exceptional birefringence value of 0.29@550 nm at room temperature.Not only is this higher birefringence than that of commercial crystals,but Al_(2)Te_(2)MoO_(10)exhibits excellent birefringence stability over a wide temperature range,from 123 to 503 K.In addition,the first-principles theory calculations and structural analyses suggest that although the rigid AlO_(6)groups do not make much contribution to the prominent birefringence,they nonetheless played a role in maintaining the structural anisotropy at elevated temperatures.Based on these findings,this paper proposes a novel structural design strategy to complement conventional approaches for developing optimal birefringent crystals under various environmental conditions.