颜色不稳定黄色蓝宝石的谱学特征与颜色成因

颜色不稳定黄色蓝宝石广泛存在市场中,如何有效鉴别颜色不稳定黄色蓝宝石的特征是当前宝石学研究的热点。利用改色实验、紫外-可见光谱（UV-Vis）、三维荧光光谱对颜色不稳定黄色蓝宝石进行深入的谱学特征研究。改色实验表明斯里兰卡黄色蓝宝石中部分存在光致变色的现象,短波紫外光会导致样品着色,而太阳光会导致样品褪色。紫外光照后黄色蓝宝石的颜色由稳定部分和不稳定部分共同组成。颜色不稳定蓝宝石的“着色态”和“褪色态”紫外-可见光谱可见明显的蓝紫区吸收,这可能与蓝宝石中O2--Fe3+的电荷转移有关,导致了蓝宝石稳定的黄色调。蓝宝石的紫外-可见光谱在“着色态”相比“褪色态”可见明显的蓝紫区吸收增强,可能由于紫外光照射增强了O2--Fe3+之间的电荷转移。紫外-可见光谱测试表明样品中具有弱的与Fe有关的吸收峰,这与样品含有较低的Fe含量一致,不足以产生稳定黄色调。三维荧光光谱分析结果表明颜色不稳定黄色蓝宝石的“着色态”和“褪色态”具有一致的激发光波长Ex=325～335 nm、发射光波长Em=560～570 nm的特征荧光中心,在“着色态”时的荧光强度明显高于“褪色态”。含铁黄色蓝宝石具有荧光效应且特征的荧光中心可作为识别这种颜色不稳定黄色蓝宝石的潜在鉴定手段。综合报道了颜色不稳定黄色蓝宝石的谱学特征与可能的颜色成因,为识别颜色不稳定的蓝宝石提供了鉴定依据,同时为后续改色处理的工艺提供了理论基础。     

变色磷灰石的可见光光谱特征研究

磷灰石是珠宝市场上常见的宝石品种,因颜色丰富而广受欢迎。变色磷灰石是稀有品种且价格高昂,该品种在D65光源（色温6 500 K）下呈黄绿色,A光源（色温2 856 K）下呈粉红色,其可见光光谱的谱学特征与变色成因未被详细研究。基于此,将一颗变色磷灰石晶体,沿其平行c轴和垂直c轴方向各切下一个薄片并双面平行抛光,分别测试其可见光光谱与微量元素。结果发现,其可见光光谱中谱峰较多：位于583和578 nm处的吸收双峰强度最强,位于748和738 nm处的吸收双峰强度中等,分别位于688和526 nm处的吸收峰,强度较弱。还有一些非常微弱的吸收峰,分别位于514,483,473和443 nm处。位于748和738 nm处的吸收双峰与583和578 nm处的吸收双峰共同造成了红橙光区的透射窗,583和578 nm处的吸收双峰与526 nm处的吸收峰共同造成了黄绿光区的透射窗。D65光源和A光源由于相对光谱功率分布不同,在不同透射窗的透过有所不同,导致变色磷灰石在不同光源下呈现出不同颜色。D65光源中黄绿光成分较多,透过黄绿光区透射窗的成分较多,D65光源下磷灰石呈黄绿色,A光源中红光成分较多,通过红橙光区透射窗的成分较多,A光源下磷灰石呈粉红色。因此,磷灰石的变色效应与位于748和738 nm处的吸收双峰,位于583和578 nm处的吸收双峰以及位于526 nm处的吸收峰相关。根据微量元素数据与稀土元素的晶体场理论,这些吸收峰是由稀土元素钕（Nd）导致。根据不同晶体方向样品的可见光光谱特征,平行c轴方向变色效果更好,建议加工变色磷灰石晶体时宝石台面应尽量平行c轴。该研究结合微量元素与可见光光谱分析了变色磷灰石的变色成因,并为其加工切割方向提供了指导。     

Automatically tunable second-harmonic generation of dye lasers

A new technique which realizes the phase-matching of second harmonic generation (SHG) over a wide spectral range without mechanical or temperature tuning of the SHG crystal is developed. The phase-matching is achieved by changing the angle of the laser beam incident on the SHG crystal using dispersive components such as gratings or prisms. Over the entire spectral range of a Rhodamine-6G dye laser, the phase-matching is realized with a KDP crystal using this technique. This system is capable of producing tunable coherent ultraviolet light from 2300 Å to 3500 Å with an extremely fast scanning rate, if the dispersion of the prism and the SHG crystal is carefully matched.     

Design and analysis of multilayered structures with metal-dielectric gratings for reflection resonance and color generation

A multilayered structure incorporating a metal-dielectric subwavelength grating, with the characteristic of polarization separation for visible light and the capability of creating reflection resonance and distinctive polarization-dependent color effects, is proposed. Its reflection resonance and color for TE and TM polarizations are discussed, as well as the influence of its structural parameters on them. Moreover, a reflection filter with characteristics of red for TE-polarized light, green for TM-polarized light, and yellow for daylight is designed and fabricated by replacing its grating region with a sinusoidal grating, and its related characteristics also are verified. The structure and its properties can achieve practical applications in various fields, such as color security, image reproduction, color filtering, and polarization-based information hiding.     

A possible method of exciting continuous lasers

Formulas convenient for estimating thereshold powers of continuous lasers with end face excitation are presented. Data on the spectral emission of Soviet high-intensity continuous light sources are cited and the absolute powers attainable in various spectral intervals through the use of the OKL-3a motion picture projector illuminator are indicated. It is shown that the OKL-3a system can be used in the design of continuous lasers.The authors are grateful to A. K. Shevchenko for his valuable comments, to A. S. Kovalev for his generous assistance in the conduct of the experiments, and to L. D. Kolpakov for the basic components of the experimental apparatus, which he built so well.     

Second order optical susceptibilities in alkali halide crystals due to FA color centers

This paper presents the first calculation of the second order optical nonlinearity of the F_A color center for second harmonic generation (SHG) in KCl:Li crystals. The real and imaginary components of the nonlinear susceptibility evaluated over a wide spectral range enclosing the resonance region of the center show interesting feature. Second harmonics generation and three wave mixing processes are nonlinear optical effects based on the second order susceptibility of materials and are very effective in providing laser radiation over a wide range of wavelengths. The density matrix formalism is employed and the equation of motion is solved by second order perturbation to evaluate the nonlinear susceptibility for SHG. It is found that the system shows large resonance-enhanced second order susceptibilities for color center concentration of 10²³ m⁻³. A scheme of phase matching in terms of anomalous dispersion of the centers is discussed.     

Laser intracavity absorption spectroscopy

Emission spectra of multimode lasers are very sensitive to spectrally selective extinction in their cavity. This phenomenon allows the quantitative measurement of absorption. The sensitivity of measurements of intracavity absorption grows with the laser pulse duration. The ultimate sensitivity obtained with a cw laser is set by various perturbations of the light coherence, such as quantum noise, Rayleigh scattering, four-wave mixing by population pulsations, and stimulated Brillouin scattering. It depends on the particular laser type used, and on its operative parameters, for example pump power, cavity loss, cavity length, and length of the gain medium. Nonlinear mode-coupling dominates the dynamics of lasers that feature a thin gain medium, such as dye lasers, whereas Rayleigh scattering is more important in lasers with a long gain medium, such as doped fibre lasers, or the Ti:sapphire laser. The highest sensitivity so far has been obtained with a cw dye laser. It corresponds to 70000 km effective length of the absorption path. The ultimate spectral resolution is determined by the spectral width of mode emission, which is 0.7 Hz in this dye laser. High sensitivity and high temporal and spectral resolution allow various practical applications of laser intracavity spectroscopy, such as measurements and simulations of atmospheric absorption, molecular and atomic spectroscopy, process control, isotope separation, study of free radicals and chemical reactions, combustion diagnostics, spectroscopy of excited states and nonlinear processes, measurements of gain and of spectrally narrow light emission. Intracavity absorption in single-mode lasers shows enhanced sensitivity as well, although not as high as in multimode lasers. Received: 10 May 1999 / Published online: 29 July 1999     

基于色差分析的不同光源下颜色稳定性研究

产品颜色是衡量产品质量的重要指标,由于产品流通环境中光源的变化无法避免,产品颜色必然受到光源变化的影响,因此研究不同光源下颜色的稳定性具有现实意义。以D65光源为标准光源,以A光源、F2光源为试验光源,选择大量色块作为样品,用不同光源下样品色差大小来衡量不同光源下样品颜色稳定性。通过对不同兴奋纯度的样品的分析,发现样品色差与其兴奋纯度是正相关的;通过对不同主波长/补色波长的样品进行分析,发现样品色差与其主波长/补色波长密切相关。样品主波长在479 nm时,色差较大,ΔE_ab*（D65/A）、ΔE_ab*（D65/F2）分别为14.50、13.81;样品主波长在561 nm时,色差较小,ΔE_ab*（D65/A）、ΔE_ab*（D65/F2）分别为5.17、2.78。将主波长/补色波长与色相对应后,发现紫、黄、黄绿等色相的样品在不同光源下色差较小,而红、青、浅蓝等色相的样品在不同光源下色差较大。结果表明,不同光源下颜色稳定性与其兴奋纯度以及主波长/补色波长有关。在实际生产与应用中,可以通过以下2种方式提高不同光源下产品颜色的稳定性:一是选择兴奋纯度较低的颜色;二是选择特定色相如紫、黄、黄绿等色相的颜色。     

Plasmon-Assisted Phase-Matched Second- and Third-Harmonic Generation in Single-Negative Heterostructures

Dispersion relations of surface plasmon polaritons （SPPs） in sandwiched optical systems are studied. The system is actually a kind of SPP waveguides, with two kinds of single negative material （SNG） as core and cladding layers, respectively. Since both TM and TE polarized SPPs can be excited in the structure, the dispersion of SPPs becomes more abundant and leads to colorful nonlinear opticM properties. The authors demonstrate the effective phase-matched second and third-harmonic generation （SHG, THG） assisted by the coupled SPPs. A cascaded second-order nonlinear process can Mso be achieved in the structure when the thickness of the core layer is properly selected, leading to the simultaneous SHG and THG. Further investigations show that much easier phase-matching can be fulfilled in the SNG waveguide array. Our results would be of potential use for surface-enhanced frequency conversion device such as light emitters or lasers.     

High Resolution Linear Laser Absorption Spectroscopy-Review

Throughout the optical spectral region from the visible to the far infrared, lasers have in recent years become increasingly important for high resolution spectroscopy in both laboratory measurements and practical applications. In general, laser sources can be classified into broadly tunable and discretely tunable types with the gas laser belonging to the latter. While gas lasers oscillate in narrow lines scattered throughout the optical spectral region, broadly tunable laser emissions cover a range of wide spectral region depending on the lasing media and operating characteristics. For example, the Pb-salt diode laser covers the spectral region from about 2.6 to 30 μm, the dye laser from 400 to 700 nm, the color center laser from 0.8 to 3.3 μm, the difference frequency spectrometer from 2.2 to 4.2 μm and the spin-flip Raman laser from 5.2 to 6.0 μm. The very limited tunability of the gas laser can sometimes be extended to many times the Doppler width by Zeeman tuning the gain medium or pressure broadening the gain profile or electrooptically modulating the laser output frequency with a tunable microwave source.     

Watt-level red-emitting diode lasers and modules for display applications

Red-emitting lasers for display applications require high output powers and a high visibility. We demonstrate diode lasers and modules in the red spectral range based on AlGaInP with optical output powers up to 1 W and a nearly diffraction limited beam. These high-luminance light sources based on tapered lasers are well suited for laser TVs and projectors for virtual reality simulators based on the flying spot technology. Additionally, we developed diode lasers with internal distributed Bragg reflector (DBR) surface gratings. These DBR tapered lasers and master-oscillator power-amplifiers based on DBR ridge-waveguide lasers and tapered amplifiers feature high power, single mode emission with coherence lengths up to several meters, which are suitable for the next-generation 3D displays based on holography.     

铌酸锂晶体中多畴层带区倍频光的研究

本文研究用声光调Q-YAG激光器作为基波光源,测量了LiNbO₃及BNN晶体中倍频光强-温度曲线。在生长层区,倍频曲线上往往出现双峰,同时有一一对应的NPM双光环出现。LiNbO₃的双峰之一在极化处理后消失,本文对此峰的产生进行了分析。LiNbO₃多畴层带区倍频光强比单畴区大10倍左右,实验表明此乃层带区180°畴的形成导致应力松弛的结果。 关键词：     

Efficient generation of tunable VUV laser radiation below 205 nm by SFM in BBO

Design and performance characteristics of a tunable dye laser system for sum frequency mixing (SFM) in a BBO crystal are presented. The system is composed of two tunable pulsed dye lasers pumped synchronously by the second harmonic of a commercial Nd:YAG laser. The radiation produced by the first dye laser is frequency doubled by second-harmonic generation (SHG) in KDP and subsequently mixed by SFM in BBO with the light of the second dye laser. The interest was focussed on generation of tunable laser radiation below 205 nm with high output power and long-time wavelength stability. High conversion efficiencies enable output energies of 100 J (20 kW) at 196 nm using only moderate Nd:YAG pump energies of 67 mJ. Altogether, a laser system with very good specifications for analytical application in the near VUV spectral region is reported.     

Miniaturized highly brilliant diode laser modules for future display applications

We demonstrate diode laser modules with high spectral radiance larger than 1 GW/cm²/sr/nm in the visible spectral range. These highly brilliant laser light sources enable the development of next-generation 3D displays. About 1W output power from small-sized modules was achieved at 635 nm by direct diode laser emission and at 530 nm using single pass second harmonic generation (SHG) of a highly brilliant near-infrared laser diode.     

白光LED荧光粉涂敷工艺及光学性质

在20mA电流下,对自行设计的白光LED进行测试,发现荧光粉远离芯片封装方法与传统封装方法相比,流明效率提高了20.3%。效率的提高主要是因为减小了LED芯片对荧光粉散射的吸收。同时测得随着正向电流的增加,色坐标x,y的值逐渐减小,色温升高,而光通量呈非线性增加,流明效率逐渐下降。     

半导体激光船舶号灯颜色属性的设计与仿真

为了提高现行船舶号灯在复杂光环境中的可识别性,更好地保障船舶夜航安全,运用色度学及半导体激光器的发光原理,设计了一种新型船舶号灯。选取长度大于等于50 m的机动船的右舷灯和桅灯为实验对象,在三维实体建模软件（Lighttools）环境下建立右舷灯和桅灯的实体模型,并对这2种号灯的半导体激光器光谱区波长、光谱权重、功率、光线数量、光线追迹阈值等参数进行设置,模拟了不同接收距离处灯光的颜色属性。模拟结果表明:半导体激光号灯右舷灯颜色刺激纯度为1;半导体激光号灯中桅灯光色的色品坐标与参考白光（色品坐标为（1/3,1/3））接近,二者均符合《国际海上避碰规则》对号灯颜色属性的要求。     

顶发射白光OLED微型显示器的蓝光掺杂特性研究

白光OLED微型显示器在信息显示领域具有重要的应用。采用真空镀膜系统,依次蒸镀Ag/ITO复合薄膜作为阳极结构,共蒸制备Mg∶Ag复合膜作为半透明阴极结构,NPB作为空穴传输材料和黄光主体材料,rubrene作为黄光掺杂料,AND作为蓝光主体料,DSA-Ph作为蓝光掺杂料,Alq3作为电子传输材料,以结构和工艺简化的蓝、黄光互补色来实现白光,通过共蒸发形式制备了结构为Ag/ITO/NPB/NPB∶rubrene（1.5%）/ADN∶DSA-Ph（x%/x=2,5,8）/Alq3/Mg∶Ag的白光OLED微型显示器,利用由Photo Research PR655光谱仪、Keithley 2400程控电源组成的光谱测试系统对器件的光电性能进行表征,研究了蓝光掺杂比对白光OLED微型显器性能的影响。结果表明,随着蓝光掺杂比的增加,白光OLED微型显示器的亮度先增加后降低,蓝光、黄光峰位有所偏移,色坐标发生一定的漂移,蓝光色纯度增加,可通过调控发光材料掺杂比实现白光OLED微型显示器性能的可控制备。初步优化获得的蓝、黄混合白光OLED微型显示器的器件,当驱动电压为5.0 V时,器件亮度达到3 679 cd·m-2,CIE坐标为（0.263,0.355）。     

Blue‐green light generation using high brilliance edge emitting diode lasers

A review about second harmonic generation using edge emitting diode lasers and nonlinear crystals to obtain laser radiation in the blue‐green spectral range is presented. Therefore, pump laser radiation with high brightness and narrow bandwidth is necessary. Thus, this review gives an overview of the advances made with distributed feedback and Bragg reflector lasers, tapered lasers and amplifiers as well as external cavity diode lasers and master oscillator power amplifier schemes to achieve high brilliance emission. Since periodically poled materials have enabled high second harmonic conversion efficiencies with low and moderate pump powers, the review is focused on frequency doubling using those materials. The most commonly used materials, their properties and limitations are discussed briefly. Single pass and resonant SHG setups with waveguide and bulk nonlinear crystals are discussed and an emphasis on building compact and integrated devices is made.     

Chromatic-Spatial Vision of the Aging Eye

The human visual system undergoes continuous anatomical, physiological and functional changes throughout the life span. There is also continuous change in the spectral distribution and intensity of light reaching the retina from infancy through senescence, primarily due to changes in the absorption of short-wave light by the lens. Despite these changes in the retinal stimulus and the signals leaving the retina for perceptual analysis, color appearance is relatively stable during aging as measured by broadband reflective or self-luminous samples, the wavelengths of unique blue and yellow, and the achromatic locus. Measures of ocular media density for younger and older observers show, indeed, that color appearance is independent of ocular media density. This may be explained by a renormalization process that was demonstrated by measuring the chromaticity of the achromatic point before and after cataract surgery. There was a shift following cataract surgery (removal of a brunescent lens) that was initially toward yellow in color space, but over the course of months, drifted back in the direction of the achromatic point before surgery. The spatial characteristics of color mechanisms were quantified for younger and older observers in terms of chromatic perceptive fields and the chromatic contrast sensitivity functions. Younger and older observers differed with small spots or with chromatic spatial gratings near threshold, but there were no significant differences with larger spots or suprathreshold spatial gratings.     

简单MOPA结构窄线宽激光突破5 kW近单模输出

高功率窄线宽光纤激光器在非线性频率转换、光谱合成以及相干合成等领域有着重要的应用前景。本文基于自研的复合腔结构窄线宽振荡器作为种子,采用单级主振荡功率放大技术（MOPA）,实现了5 kW高效率的近单模窄谱激光输出。通过优化振荡器的时序特性和放大级结构,受激拉曼散射、光谱展宽和热致模式不稳定效应得到综合抑制。在最高功率时,信号光的3 dB和20 dB线宽分别为0.48 nm和2.1 nm,放大器的斜率效率约为86.1%,拉曼抑制比为28.3 dB,光束质量M2约1.35。本研究工作对于高功率窄线宽光纤激光的发展和研究具有重要的指导意义。