Collimation testing with linear dual-field, spiral, and evolute gratings: a comparative study

A comparative study of the performance of linear dual-field, spiral, and evolute gratings for collimation testing with Talbot interferometry is reported.     

Collimation testing with optically active materials

A novel method to test the collimation of laser beams with optically active mediums and a pair of crossed polarizers is presented. Optically active materials rotate the plane of polarization of incident plane-polarized light. A decollimated laser beam passing through such a material will experience a greater effective thickness than a collimated laser beam, resulting in greater outputs. In this method the output intensity variation is related to the amount of decollimation of the incident beam, and the method does not require any referencing or fringe analysis and is easy to implement.     

Stacked subwavelength gratings as circular polarization filters

We have stacked subwavelength gratings (SWGs) on a single substrate to create a compact, integrated circular polarization filter. The SWGs consist of a wire grid polarizer and a broadband form-birefringent quarter-wave plate (QWP). Rigorous coupled-wave analysis was used to design the QWP for operation over the 3.5-5.0-mum wavelength range. The fabricated silicon broadband QWP exhibited a phase retardance of 82-97 degrees across this wavelength range. Two stacked structures are presented, each with a different wire grid polarizer fabricated on an organic planarization layer (SU-8) that is deposited on a QWP grating. Transmittance measurements of the first structure when illuminated with nominally right- and left-circularly polarized light indicate a circular extinction ratio (CER) limited by the low linear extinction ratio of the polarizer. Use of a wire grid polarizer with a higher extinct ratio led to a stacked SWG structure that demonstrated CERs of 10-45 across the 3.5-5.0-mum wavelength range.     

Design of circular Dammann gratings by employing the circular spot rotation method

A new concept based on the theory of Dammann gratings is proposed for the generation of circular optical beams. This grating shows that it can achieve equal intensity and equal spacing with acceptable efficiency that is controlled by set of transition points. A numerical solution is also presented together with the fabrication of 4-order circular Dammann grating by e-beam lithography. Experimental results agree well with the scalar diffraction theory. This grating has the potential to be further developed into practical applications.     

Polarization holographic gratings in side-chain azobenzene polyesters with linear and circular photoanisotropy

We investigate thin phase polarization holographic gratings recorded with two waves with orthogonal linear polarizations in materials in which illumination with linearly/circularly polarized light gives rise to linear/circular birefringence. The theoretical analysis shows that the presence of circular photoanisot-ropy changes significantly the diffraction characteristics of the gratings. The intensities of the waves diffracted in the +1 and -1 orders of diffraction and their ratio depend substantially on the reconstructing-wave polarization. Experiments with films of side-chain liquid-crystalline azobenzene polyester that is a photoanisotropic material of the considered type confirm the unusual polarization properties. It is shown that polarization holography may be used for real-time simultaneous measurement of photoinduced linear and circular birefringence.     

Talbot interferometer with circular gratings for the measurement of temperature in axisymmetric gaseous flames

A detailed study for measuring the temperature distribution in axisymmetric flames by using a Talbot interferometer with circular gratings is presented. We increased the sensitivity of the interferometer by optimizing the pitch of the grating and the Talbot plane. We compare the experimental results with the values that were measured with a thermocouple to an accuracy of ±0.2% of full scale ±4 digits. Good agreement is seen between the temperatures measured by use of a thermocouple and those measured by use of Talbot interferometry.     

一种新型带有自标定的数字准直瞄准测量系统

设计了一种新型带有自标定的数字准直瞄准测量系统。系统采用测微准直望远镜与CCD视觉系统相结合的方式,将测微准直望远镜的目视测量视场转换成数字测量视场,进而实现在整个数字视场范围内取样测量。通过对CCD相机的角度当量和位移当量进行标定,可直接计算出线位移和角位移,实现了数字化测量。通过实验验证,该系统的定位测量不确定度优于激光跟踪仪,定向测量不确定度优于经纬仪,可用于工业大尺寸测量。     

Properties of high-gradient magnetogravimetric systems--I. Single rods and gratings with oval and circular cross sections

The properties of two-dimensional rod systems are examined, use being made of the complex potential in conjunction with the conformal-transformation technique. The concept of prescribed trajectories whereby stronger, effective, levitational forces can be obtained is introduced. It is shown that the high-gradient magnetogravimetric-separation system is amenable to scale-up since sufficient levitational force, in terms of the equivalent specific gravity, is generated. Examples of gratings with circular and different oval cross sections, which are subject to the magnetizing field in two alternative directions, are discussed.     

Measurement of temperature profile of a gaseous flame with a Lau phase interferometer that has circular gratings

We have investigated the utility of a Lau phase interferometer with circular gratings and a white-light source to measure the temperature and temperature profile of an axisymmetric flame. The temperature measured with a Lau phase interferometer is in good agreement with the temperature measured with a thermocouple and multilogger. Detailed theoretical analysis and experimental investigation are presented.     

瞄准指示器光路设计

介绍了瞄准指示器的光路设计原理，着重讲述分光镜的设计原理，并对干涉场光强分希进行了简单推导，给出了瞄准测量的判断依据。     

Dynamic holographic gratings with photoresist

The theoretical development of dynamic holographic gratings with piezoelectric crystals is presented. A thin layer of photoresist is applied over the surface of the piezoelectric crystal. A holographic grating was recorded over the photoresist-piezo device in such a way that when it is activated the changes in its dimensions produce a geometrical change in the grooves of the grating. Hence the initial diffraction pattern created may be dynamically modified.     

Microspectrometer with slab-waveguide transmission gratings

An integrated transmission diffraction grating in a planar optical waveguide is presented for broadband spectroscopic analysis of liquids and gases. Silicon oxynitride slab waveguides on silicon substrates with low optical loss in the visible range are combined with a phase transmission grating exhibiting a blaze effect at 500 nm to achieve high-efficiency diffraction and high spectral dispersion. Collimated white light propagates through the waveguide and couples into air at a stepped formed planar grating. The beams of each adjacent step interfere constructively at the focal line of a cylindrical lens, its focal line positioned perpendicular to the waveguide plane. We used a common silicon photodiode array to detect the spectral data. Our approach is to develop a compact and economic spectrometer without moving parts that can be applied for UV-visible analysis and near-infrared industrial process control as well.     

Wave-front analysis method of circular aperture sampling for collimation testing

A new type of wave-front analysis method for the collimation testing of laser beams is proposed. A concept of wave-front height is defined, and, on this basis, the wave-front analysis method of circular aperture sampling is introduced. The wave-front height of the tested noncollimated wave can be estimated from the distance between two identical fiducial diffraction planes of the sampled wave, and then the divergence is determined. The design is detailed, and the experiment is demonstrated. The principle and experiment results of the method are presented. Owing to the simplicity of the method and its low cost, it is a promising method for checking the collimation of a laser beam with a large divergence.