Variable wavelength interferometry of birefringent retarders

A new interferometric procedure is proposed for testing birefringent retarders. The procedure uses monochromatic light with a continuously variable wavelength and two parallel pointer lines localized at a distance from each other in the fringe interference field of a double-refracting interferometer. The zero-order fringe of the empty interference field is brought into coincidence with one pointer line, and higher-order interference fringes displaced by an object under study are next brought into consecutive coincidence with the other pointer line as the wavelength of the monochromatic light is continuously varied.     

Film thickness measurement with white light fringes

A method is described of measuring the thickness of thin films by using white light fringes obtained in a double pass Michelson interferometer. The method is suitable for the determination of thickness ranging from 15 nm to 2500 nm.     

LINC-NIRVANA: MCAO toward Extremely Large Telescopes

LINC-NIRVANA is a Fizeau (imaging) interferometer exploiting the full spatial resolution of a 23 m class telescope in the combined beam of the Large Binocular Telescope supported through Multi-Conjugated Adaptive Optics (MCAO). By means of science cases, we show how LINC-NIRVANA takes advantage of the MCAO, increasing the sky coverage of the instrument and the field of view for the Fringe and Flexure tracker. We introduce the MCAO system of LINC-NIRVANA in detail, which in a first step will be installed with two deformable mirrors per arm and has the provision to be upgraded with a third mirror. The MCAO system implements several novel concepts proposed for extremely large telescopes, such as layer oriented MCAO, optical co-adding of guide stars, or Multiple Field of View sensing. LINC-NIRVANA will demonstrate some of the concepts for the first time on sky. To cite this article: W. Gaessler et. al., C. R. Physique 6 (2005).     

利用菲涅耳双镜测金属线膨胀系数

分析了菲涅耳双镜在干涉实验中 ,由金属受热膨胀引起的光源位置变化对干涉条纹的影响 ,导出金属受热时绝对伸长量与干涉条纹位置变化之间的关系 ,并通过它对黄铜棒的线膨胀系数进行测量。     

Experimental observation of a strange temporal oscillation of X‐ray Pendellösung fringes

As a strange property not explained by existing theories, it has been known from experiment that X‐ray moiré and Pendellösung interference fringes show a small spatial oscillation in the beam path in free space that the diffraction image carrying those fringes is propagated after emerging from the crystal. In connection with the investigation into this strange fringe oscillation, it has been found, by an experiment successively recording Pendellösung‐fringe topographs using an X‐ray CCD camera, that X‐ray Pendellösung fringes also show a small temporal oscillation. Characteristics of this temporal Pendellösung‐fringe oscillation, namely irregularities in the fringe profile, the manner of fringe oscillation and a reciprocal correlation between oscillation amplitude and fringe contrast, are shown to be very similar to those of the previously reported spatial oscillation of moiré and Pendellösung fringes. Therefore this temporal oscillation is supposed to have the same origin as the spatial oscillation, revealing another section of the same phenomenon. This discovery of the temporal oscillation advances a step nearer to the full understanding of this strange phenomenon, while disclosing a new property of Pendellösung fringes. As well as the above, a three‐dimensional profile representation (surface plot) is given of the image of Pendellösung fringes, to make it clear that unidentified fine intensity modulations, called subfringes in this paper, are produced superposed on the main fringe system. Overall inspection of the intensity profiles of the fringe‐imaged topographs suggests that temporal intensity oscillations also occur on a more global scale than the extension of individual fringes, as an unidentified action of the wavefield.     

Automatic fringe analysis of the induced anisotropy of bent optical fibres

A new theoretical model considering the refraction of the incident light beam by the fibre is suggested to determine the refractive index profile of bent optical fibres. This new model (slabs model) considering the cross section of the bent optical fibre consists of large number of slabs. The slabs model bases on the refraction of the incident beam by the fibre. The refractive index profile of the optical fibre cladding before bending obtained using the automated Fizeau interferometer with the aid of suggested model is compared with other models such as, the homogenous model and the multilayer model to verify the ability of this slab model. The refractive index profile of the bent optical fibre cladding is investigated using this suggested model. In addition, the new model is used to obtain the induced birefringence and the guiding parameters. The bending radius is recommended to be greater than 7.1 mm for the used optical fibre. The consideration of the refraction increases the accuracy of the results.     

检测大口径光学平面镜时干涉条纹的子孔径拼接方法

提出了用Ritchey_Common法检测大口径光学平面镜时干涉条纹的子孔径拼接方法。通过确立基准点将多幅子孔径检测数据统一到全口径归一化坐标系下进行拼接,解决了在检验光路中因Ritchey角所引起的投影变形问题和如何消去因被检平面的大曲率所造成的像散。通过Zernike多项式拟合重建连续波面,可恢复全口径波面图像。     

一种干涉条纹细化算法的改进

针对经典Hilditch细化算法处理干涉条纹有过多的毛刺和断点的不足的问题,提出了改进的Hilditch细化算法。该算法借鉴了OPTA算法中的8个模板,在每次扫描图像之前,调用这8个模板。改进的细化算法可对干涉条纹进行细化处理,细化结果相对光滑,无毛刺分叉,有利于干涉条纹的精确判读。     

干涉测量系统中杂散条纹影响的抑制

 为了抑制杂散条纹的影响，提出了一种简单实用的单幅三表面干涉条纹傅里叶分析法，它根据三表面干涉时各个表面干涉的条纹调制度不同，从三表面干涉图的频谱中提取测试面的频谱，从而准确地恢复测试面的面形。模拟结果证明了该方法的有效性，准确度可以达到l/1 000。实验表明：单幅三表面干涉条纹傅里叶分析法得到的面形形状与波长调谐时域傅里叶变化法和涂消光漆法得到的结果基本一致，PV值和RMS值与波长调谐时域傅里叶变化法相差分别为0.001l和0.004l，与涂消光漆法相差分别为0.042l和0.019l。通过7次单幅三表面干涉条纹傅里叶分析法测量，得到PV和RMS值的重复性分别为0.007 8l和0.002 6l。     

多光束非定域干涉反射光强分布

研究了多光束非定域干涉现象,得到了多光束非定域干涉的反射光强分布函数.数值计算结果表明:随着镜面反射系数的增加,多光束非定域干涉条纹半值宽度降低,条纹变得更加锐细,光谱分辨率提高;当镜面反射率较高时,除了暗条纹外,在低干涉级次处紧邻暗条纹还有很窄的亮条纹存在;亮条纹振幅逐渐衰减至背景光强度,干涉级次越低亮条纹振荡越明显;第一束反射光提供了一个均匀的背景,第二束反射光的加入产生了双光束干涉,干涉条纹较粗,对比度较低,更多光束的加入使干涉暗条纹变得锐细,在相邻暗条纹间出现了明暗相间的低强度明暗条纹;足够多光束的加入使相邻暗条纹间低强度变化的明暗条纹消失,同时在紧邻暗条纹处出现了振幅振荡衰减的亮条纹.最后,将多光束非定域干涉理论应用于光学滤波器的研究,结果表明:提高镜面反射率,可以显著降低多光束非定域干涉的滤波带宽;改变镜面间距,可以灵活调整多光束干涉仪滤波波长和相消波长间距.