《晶体光学》课程中矿片45°位置分析的教学方法研究

《晶体光学》是地质学、地球化学、资源勘查工程等专业的主干课程之一,利用偏光显微镜鉴定法鉴定透明矿物和岩石是地质专业所必须掌握的技能。文章分别利用光振幅矢量分解、偏振光的干涉以及半波片的特性等方法详细分析了矿片在45°位置时视域最亮的原因,以便学生更好的理解偏光显微镜下矿片的光学现象。

《晶体光学》课程的教学改革与实践

晶体光学主要是研究可见光通过透明晶体所产生的一些光学现象(颜色、折射、双折射、干涉等)及其规律的一门学科,是地质学、地球化学、资源勘查等专业的基础课程之一,目标是培养学生掌握在偏光显微镜下研究、鉴定透明矿物的基本原理和基本方法,熟悉一些常见造岩矿物的光学性质.根据不同的晶体其光学性质不同的特点来鉴定透明矿物,可以对相关矿物进行定量和半定量分析.秉承"加强基础、强化应用、激励创新、体现特色"的教学指导思想,为加强地质科学研究、矿产资源勘查的基本能力打下坚实的基础.

Crystal Growth and Structure of Novel Tolane Nonlinear Optical Materials

A novel tolane 4-methoxy-4'-nitro-diphenyl-acetylene (MONA) has been prepared quantitatively by reacting cuprous p-methoxy phenyl-acetylene with p-iodonitrobenzene. A single crystal of the Moan was grown by solution growth method. The crystal was then characterized by X-ray diffraction structure analysis and second-harmonic generation(SHG)investigation. Polymorphous crystal forms of the MONA were grown from different solvents having different nonlinear optical properties depending on their different crystal structures. The relationship between the crystal growth and crystal structure is discusse.

Measurement of Optic Axis Direction Based on Interference Fringe Method

In order to conquer the defect in low precision and small range for measuring optic axial angle based on conoscopic interference method, interference fringe method is proposed. It is not the distance deviating from melatope but fringe numbers to decide optic axial angle. Fringe numbers are divided into integer portion and decimal fraction portion, the decimal fraction portion is calculated by non-linear interpolation method and integer portion is determined by the relative placement of interference fringes in the principal section. Extremum arithmetic of digit image is proposed and can be used to determine the interference fringes conveniently and precisely. After different niobate crystals were measured, the result shows that measurement range of optic axial angle is increased efficiently and measurement error is reduced to 0.1°.

Enhancement effect of phase-conjugate waves of third order nonlinear medium in the Bragg microcavity

The enhancement effect of the phase-conjugate wave produced by a third order nonlinear optical medium in a （AB）^N （D）^2 （BA）^N Bragg microcavity made of one-dimensional photonic crystals is studied. The gain factor of the phase-conjugate wave is derived when the resonance condition is satisfied by the incident optical wave and the Bragg microcavity mode. Because of stronger resonance enhancement to incident pump beam given by the Bragg microcavity, the enhancement effect of the phase-conjugate wave produced by a third order nonlinear optical medium inside Bragg microcavity is more outstanding than that caused by the naked third order nonlinear optical medium. The theoretical analysis and the numerical calculation show the Bragg microcavity with larger number N of periods is identical with a Fabry-Perot cavity when the resonance condition is satisfied by the incident optical wave and the Bragg microcavity mode.

Characteristic analysis of photonic crystal resonant cavity in the terahertz region

In this letter, a kind of two-dimensional photonic crystal structure applicable to THz devices is designed, and how to form a microcavity in this structure is discussed. The primary properties of the resonant cavity are analyzed, in which plane wave expansion method is used to make the calculation and the simulation. We've studied the variation of the bandgap structure and resonant frequency in THz region by changing the parameters, such as lattice constant, dielectric constant contrast and filling factor. The research results provided theoretical support for manufacturing the THz devices and the application of THz system.

Fabrication of holographic 3-D polymeric photonic crystals in near-Infrared band and study of Its optical property

A three-sidewalls-prism holographic method has been provided for the fabrication of 3-D fcc-type polymeric photonic crystal using negative photoresist. Special fabrication treatment has been introduced to ensure the stability of the fabricated nanostructures. The scanning electronic microscopy (SEM) and the diffraction results testified the good dependability of the fabricated structures. The simulation of the partial band structure is in good agreement with the transmission and reflection spectra obtained by Fourier transform infrared spectroscopy.

1.55-μm supercontinuum based on dispersion-flattened photonic crystal fiber

A dispersion-flattened photonic crystal fiber with normal dispersion is designed for generating flat wideband supercontanuum, and the supercontinuum generation in this fiber is numerically analyzed. The results show that by appropriately designing the photonic crystal fiber, it can achieve flattened dispersion in the normal dispersion region. It is found that a fiber characterized by a flattened dispersion with a small normal dispersion is suitable for a flat wideband supercontinuum generation. In the process of spectral broadening, self-phase modulation effect plays a dominant role. By filtering the supercontinuum, pulses with different central wavelength over a wide spectral range can be obtained. The pulse width is determined by the bandwidth of the filter.

Supercontinuum Generationin Normal-dispersion Photonic Crystal Fiber Using Picosecond Pulse

Studied is the Super-continuum(SC) generation of a normal-dispersion photonic crystal fiber(PCF) using picosecond pulse excitation. In experimental analyses, a 237 nm broadband infrared continuum was generated pumped at 1 550 nm(normal dispersion regime) by 1.6 ps pulses from an erbium-doped fiber laser. In addition, we conduct the numerical analyses of SC based on generalized nonlinear Schr dionger equation. The results have been applied to investigate the dominant physical processes underlie the generation of SC. We conclude that dispersion, self-phase modulation(SPM),four-wave-mixing(FWM) and Raman scattering are determinants of SC generation rather than fission of soliton in normal-dispersion PCF.

High-quality single-crystal CdSe nanoribbons and their optical properties

Large-scale synthesis of single-crystal CdSe nanoribbons is achieved by a modified thermal evaporation method, in which two-step-thermal-evaporation is used to control CdSe sources＇ evaporation. The synthesized CdSe nanoribbons are usually several micrometers in width, 50 nm in thickness, and tens to several hundred micrometers in length. Studies have shown that high-quality CdSe nanoribbons with regular shapes can be obtained by this method. Room-temperature photolumines-cence indicates that the lasing emission at 710 nm has been observed under optical pumping （266 nm） at power densities of 25-153 kW/cm^2. The full width half maximum （FWHM） of the lasing mode is 0.67 nm

Second harmonic generation of a new nonlinear optical material:urea L-malic acid

Second harmonic generation （SHG） of a new organic optical crystal-urea L-malic acid （ULMA） was studied. A comparison of SHG efficiency of ULMA and KDP at a fundamental wavelength of 1064 nm using the Kurtz powder method demonstrated that the second order nonlinear coefficient of ULMA is 1 57 times of that of KDP,and the damage threshold of ULMA is relatively higher Finally,both Type Ⅰ and Type Ⅱ phase match angles of the biaxial crystal ULMA were calculated.

New High Nonlinear and Dispersion Flattened Photonic Crystal Fiber

A new high nonlinear dispersion flattened photonic crystal fiber is proposed. This fiber has three-fold symmetry core. The doped region in the core and the big air-holes in the 1-st ring can make high nonlinearity in the PCF. And the small air-holes in the 1-st ring and the radial increasing diameters air-holes rings in cladding can be used to turn the dispersion properties of the PCF. We can achieve the optimized optical properties by carefully selecting the PCF's structure parameters. A PCF with flattened dispersion is obtained. The dispersion is within ±0.8 ps·nm-1·km-1 from 1.50 μm to 1.62 μm. The nonlinear coefficient is about 12.645 6 W-1·km-1, the fundamental mode area is about 10.257 9 μm2 and the birefringence is about 3.086 96×10-5 at 1.55 μm. This work may be useful for effective design and fabrication of dispersion flattened photonic crystal with high nonlinearities.

Growth and Spectral Properties of Nd^(3+):NaLa(WO_4)_2 Crystals

Nd^3＋ ：NaLa（WO4）2 crystals with a dimension up to 7 mm were grown from a high temperature solution using a double-crucible method. Scanning electron microscopy observations of the crystals showed that there were no small cracks on the surface of the crystals although they underwent two phase transitions when cooling down from high temperatures. X-ray diffraction studies indicated that the as-obtained product is pure low- temperature tetragonal Nd^3＋ ：NaLa（WO4）2. The absorption and fluorescence spectra for Nd^3＋ ：NaLa（WO4）2 were measured at room temperature. The absorption band at 804 nm has a wide full-width half maximum of 23 nm whose origin is discussed. The absorption and emission cross sections were calculated to be 7.24×10^-20 cm^2 at 804 nm and 6.54×10 ^-20 cm^2 at 1057 nm, respectively.

Dispersion Properties in Total Internal Reflective Photonic Crystal Fiber

The dispersion properties in the short wavelength region of total internal reflective photonic crystal fiber have been studied by using the models of the equivalent twin waveguide soliton coupling,effective refractive index,effective normalized frequency and dispersion management solitons.It is shown that the dispersion in the cladding waveguide of the total internal reflective photonic crystal fiber is a positive dispersion,and the dispersion of its core waveguide is a negative dispersion.The method of the compensated probing laser diffraction by the phase hole induced by the stationary pumping laser in the cladding waveguide enables the average dispersion value of the total internal reflective photonic crystal fiber to be close to zero and the zero dispersion point to shift to the short wavelength region.

Pulse-width compression based on photonic crystal fiber

According to the characteristics of high-order solitons,compressed picosecond pulses are numerically simulated in the photonic crystal fiber (PCF),by means of split-step Fourier method. The results show that,PCF enables input pulse with lower peak power to form high-order solitons for the purpose of femtosecond pulse-width compression. For example,60- femtosecond pulse width was made for 1-ps initial pulse width only over the distance of 2.2 m.Besides,shorter optimum fiber length for compression and higher compression ratio could be obtained on the premise of pre-chirp technique.

Experimental investigation of hollow-core photonic crystal fibers with five photonic band-gaps

The hollow-core photonic crystal fibers （HC-PCFs） with integrity structure have been fabricated with an improved twice stack-and-draw technique. The transmission spectrum shows that five photonic band-gaps within 450-1100 nm have been obtained.And the green fight transmission in the HC-PCFs has been observed remarkably.

Interface-Optical-Phonon Modes in Quasi-one-dimensional Wurtzite Rectangular Quantum Wires

By employing the dielectric continuum model and Loudon＇s uniaxial crystal model, the interface optical （IO） phonon modes in a freestanding quasi-one-dimensional （Q1D） wurtzite rectangular quantum wire are derived and analyzed. Numerical calculation on a freestanding wurtzite GaN quantum wire is performed. The resulte reveal that the dispersion frequencies of IO modes sensitively depend on the geometric structures of the Q1D wurtzite rectangular quantum wires, the free wave-number kz in z-direction and the dielectric constant of the nonpolar matrix. The degenerating behavior of the IO modes in Q1D wurtzite rectangular quantum wire has been clearly observed in the case of small wave-number kz and Iarge ratio of length to width of the rectangular crossing profile. The limited frequency behaviors of IO modes have been analyzed deeply, and detailed comparisons with those in wurtzite planar quantum wells and cylindrical quantum wires are also done. The present theories can be looked on as a generalization of that in isotropic rectangular quantum wires, and it can naturally reduce to the case of Q1D isotropic quantum wires once the anisotropy of the wurtzite material is ignored.

ZnS0.8Se0.2 film for high resolution liquid crystal light valve

The structural characteristics and optical and electrical properties of molecular-beam-epitaxy (MBE) grown ZnS0.8Se0.2 thin films on indium-tin-oxide (ITO) glass substrates were investigated in this work. The X-ray diffraction (XRD) results indicated that high quality polycrystalline ZnS0.8Se0.2 thin film grown at the optimized temperature had a preferred orientation along the (111) planes. The transmission electron microscopy (TEM) cross-sectional micrograph of the sample showed a well defined columnar structure with lateral crystal dimension in the order of a few hundred angstroms. Ultraviolet(UV) photoresponsivity as high as 0.01 A/W had been demonstrated and for wavelengths longer than 450 nm, the response was down from the peak response by more than 3 orders of magnitude. The thin ZnS0.8Se0,2 photosensor layer, with a wide energy gap and anisotropic electrical property, makes a transmission UV liquid crystal light valve (LCLV) with high resolution feasible.

Properties of defect mode and optical enhancement of 1Dphotonic crystals with a defect layer of negative refractiveindex material

The band gap properties of one-dimensional photonic crystals with a defect layer of negative refractive index materials are studied.The defect mode width is bigger than that of conventional one-dimensional photonic crystals with a defect layer of positive refractive index materials.The defect mode of the former is different from that of the latter,shifts towards the direction of high frequency (short wavelength),and has a bigger shifting velocity.Furthermore the effects on the transmission properties of the former photonic crystals caused by change in the position of the defect layer of negative refractive index are investigated.Finally the optical enhancement of the former photonic crystals is also investigated.

Raman crystal lasers in the visible and near-infrared

Raman lasers based on potassium gadolinium tungstate and lead tungstate crystals pumped by a≈120 ps Nd: YAG laser at 1.064/μm were developed. High reflection mirrors for the Stokes wavelength have been used to generate near-infrared and eye safe spectral region of 1.15 - 1.32/μm. Second harmonic generation of the generated Raman lasers was observed. Eifficient multiple Stokes and anti-Stokes picosecond generation in 64 crystals have been shown to exhibit stimulated Raman scattering on about 700 lines covering the whole visible and near-infrared spectrum. All stimulated Raman scattering (SRS) wavelengths in the visible and near-infrared spectrum are identified and attributed to the SRS-active vibration modes of these crystals.