Intensity fluctuation light-scattering spectroscopy using a conventional light source

Using a mercury arc lamp as light source we have studied intensity fluctuations in light scattered by a liquid crystal sample, thus confirming that laser sources are not in principle essential in such studies. The experimental problems, particularly the relevant parameters of temporal and spatial coherence, are outlined and discussed.     

光源编码的白光散斑剪切干涉计量术

本文提出了一种用非相干光源照明进行剪切干涉计量的方法—光源编码的白光散斑剪切干涉计量术.它采用光栅对光源进行编码以提高空间相干性,使物体的两个剪切像的波面部分相干叠加,以实现剪切干涉.     

Coherent backscattering spectroscopy

Coherent backscattering (CBS) of light in random media has been previously investigated by use of coherent light sources. Here we report a novel method of CBS measurement that combines low spatial coherence, broadband illumination, and spectrally resolved detection. We show that low spatial coherence illumination leads to an anomalously broad CBS peak and a dramatic speckle reduction; the latter is further facilitated by low temporal coherence detection. Thus CBS can be observed in biological tissue and other media that previously were beyond the reach of conventional CBS measurements. We also demonstrate, for the first time to our knowledge, spectroscopic analysis of CBS. CBS spectroscopy may find important applications in probing random media such as biological tissue in which depth-selective measurements are crucial.     

Full-field and single-shot quantitative phase microscopy using dynamic speckle illumination

We developed an off-axis quantitative phase microscopy that works for a light source with an extremely short spatial coherence length in order to reduce the diffraction noise and enhance the spatial resolution. A dynamic speckle wave whose coherence length is 440 nm was used as an illumination source. To implement an off-axis interferometry for a source of low spatial coherence, a diffraction grating was inserted in the reference beam path. In doing so, an oblique illumination was generated without rotation of the wavefront, which leads to a full-field and single-shot phase recording with improved phase sensitivity of more than a factor of 10 in comparison with coherent illumination. The spatial resolution, both laterally and axially, and the depth selectivity are significantly enhanced due to the wide angular spectrum of the speckle wave. We applied our method to image the dynamics of small intracellular particles in live biological cells. With enhanced phase sensitivity and speed, the proposed method will serve as a useful tool to study the dynamics of biological specimens.     

Suppressed speckle contrast of blue light emission out of white lamp with phosphors excited by blue laser diodes for high-brightness lighting applications

The speckle contrast of blue light emission out of high-brightness white lamps using phosphors excited by InGaN/GaN blue laser diodes is evaluated as a measure of coherence. As a result, speckle contrast of as low as 1.7%, the same level as a blue light emitting diode, is obtained. This implies that the original blue laser light can be converted into incoherent light through lamp structures without any dynamic mechanisms. This unique speckle-free performance is considered to be realized by multiple scattering inside the lamp structure, the multi-longitudinal mode operation of the blue laser diodes, and the use of multiple laser diodes. Such almost-incoherent white lamps can be applied for general lighting without any nuisance of speckle noise and should be categorized as lamps rather than lasers in terms of laser safety regulation.     

Spatial structure of the degree of coherence for broadband dispersed laser beams

1D and 2D spatial distributions of a complex degree of coherence are obtained using numerical simulation for the broadband dispersed laser beams. The configuration of the spatial inhomogeneities (speck-les) of the degree of coherence is studied at various spectral widths and dispersions of the beam. It is shown that the speckle size increases with increasing distance from the initial plane where the light field is assumed to be spatially coherent. The small- and large-scale structures of the degree of coherence are shown for the transverse cross section of the beam. The results are compared with the analytically calculated correlation functions of the spatial coherence. The features of the speckle structure are interpreted using the concept of partial speckles.     

Holographic Image Denoising using Random Laser Illumination

In holographic applications, coherent lasers are indispensable source of illumination. Despite high intensity from coherent light sources, they fail in full-field image projection and illustrate speckle images due to high spatial coherence. This article demonstrates speckle-free high contrast computer-generated holographic image projection upon illumination with a perovskite–polystyrene 10 wt%-based random laser. Solvent-engineered efficient and durable perovskite and perovskite–polystyrene 10 wt%-based random lasers are fabricated. Optical characterizations are elucidated and controlled coherence random lasing operation is achieved under room temperature upon addition of polystyrene concentration 10 wt% on perovskite thin film. The addition of 10 wt% polystyrene concentration results in a low far-field divergence angle of ≈10⁰. The controlled coherence in random lasers is necessary to produce a stable interference pattern and to retain the depth of field in holograms. Additionally, the holographic image projection using random lasers reduces diffraction noise, and exhibits high spatial resolution with full-field imaging. Moreover, this study is clear evidence of an effective strategy to achieve high-performance, indigenous designed-controlled coherence in disordered random lasing media and its application to novel holographic image projection.     

基于紫外LED阵列光催化降解抗生素的研究

抗生素的大量使用对生态环境造成巨大的影响，光催化技术具有操作简单且无二次污染等特点被广泛应用于污染物的降解。在光催化降解抗生素过程中，光源对其降解效率至关重要，与传统的汞灯催化光源相比，紫外LED技术具有更高的能源效率及更低的功耗，使光催化工艺发生了巨大的变化。首先建立基于紫外LED阵列的光催化平台，采用光栅光谱仪和紫外照度计对LED阵列光源光谱特性及装置内光场分布进行测量分析。结果显示紫外LED光源波长介于265～295 nm之间，其主波长为275 nm，由于光场叠加效果，光照强度随着装置径向位置距离的增大而明显增大，装置轴向位置光照强度分布较为均匀；其次通过三维超景深显微镜、UV-Vis光谱测量技术对P25型光催化剂的粒子结构进行表征分析，同时使用半导体求导公式对TiO₂粉末进行禁带分析，结果显示TiO₂为球形，由于空气中相对湿度过大，水在TiO₂微粒表面的润湿性加强了微粒间的粘附力，因此有团聚现象产生，其禁带宽度为3.1 eV；最后以紫外LED阵列和高压汞灯为催化光源，P25型TiO₂为催化剂分别对甲基橙、磺胺类抗生素进行光催化降解，使用紫外-可见光分光光度计测量降解过程中的吸收光谱曲线，进而对抗生素降解率进行分析。结果表明，甲基橙和磺胺二甲嘧啶在紫外LED阵列为光源条件下均能够被降解，分别经过160和240 min的催化降解过程后，降解率分别达到70%和36%，符合一级动力学方程，经计算LED阵列光源与汞灯对甲基橙的降解动力学常数分别为-0.007 5和-0.113 5 min-1，对磺胺二甲嘧啶的降解动力学常数分别为-0.001 9和-0.019 4 min-1。因此对甲基橙和磺胺二甲嘧啶进行降解时，汞灯降解速率高于紫外LED阵列；由于紫外LED阵列和汞灯系统在催化降解污染物过程中功率和其与反应器中轴线距离不同，对两种光源的抗生素降解效率建立评价方法，即对紫外LED和汞灯以单位功率为标准进行距离降解效率分析，对于甲基橙，汞灯在单位功率下的距离降解效率高于紫外LED，但对于抗生素，紫外LED阵列的距离降解效率明显高于汞灯。依据以上各类光谱分析和应用结果，紫外LED阵列是一种有竞争力的光催化应用替代光源，此技术的广泛应用为抗生素的降解提供新途径。     

物光复合调制的数字全息散斑去噪方法

为了克服在数字全息术中激光源高相干度造成的散斑噪声降低成像质量问题,论文提出将石英退偏器与电控液晶散射片相结合用于数字全息术中。通过在物光路中加入一个石英退偏器,利用退偏器的退偏性能使物光光路中的线偏光变成随机偏振光,降低与参考光的相干程度,实现对散斑噪声的抑制;通过给液晶散射片外加电场可以引起液晶分子的运动和光轴取向改变,调整液晶驱动电压大小来改变入射光的不同散射效果,有效地降低了光源的相干性;分别将单独采用石英退偏器和电控液晶散射片的重建图像与组合装置的重建图像进行对比分析,通过实验验证了所提方法的有效性。实验结果表明：两种实验对象在组合装置下的重建像峰值信噪比分别达到16.91和18.30,结构相似度为0.47和0.43,等效视数较原始重建像提高了42%和30%,散斑指数为1.52和1.29。论文提出的方法可较好地去除散斑噪声,保留更多的图像细节部分。     

Analysis of non-ergodic behaviour in spatio-temporal coherence properties of speckle light

Spatio-temporal coherence properties of light scattered by rough surfaces that leads to speckle fluctuations are analysed. It is demonstrated that the scattered light is non-ergodic with the disorder due to the scattering process. Although the mutual coherence matrix vanishes with isotropic polarization fluctuations, it is shown that spatio-temporal coherence properties can be described with interference experiments that can be obtained between different speckles of the scattered light. For non-singular scattering processes, the maximal value of the modulus of the Wolf degree of coherence is analysed in the spatial time domain. This approach is also applied to totally unpolarized incident light with an isotropic and spatially independent scattering process. The mean value and the standard deviation of the Wolf degree of coherence are then determined from the coherence properties of the incident light.