Curvature measurement of optical surface using digital holography

In this paper, an optical surface curvature measurement technique based on digital holography is proposed. Unlike the previous digital holographic methods, which only involve a small part of the measured data for parameter estimation, the proposed method adopts more of them using least square method. Hence, the analyzed result is not affected by data extraction direction and less sensitive to imperfect phase compensation. The proposed method is demonstrated with a sample of reflection mirror in laser resonator, and verified by comparing the measurement result with that of the white light interferometer.     

Film thickness measurement and defect inspection using optical coherence tomography

An optical sensing technology based on optical coherence tomography is presented for film thickness measurement and defect inspection. In order to improve the imaging quality, a simple interference spectrum processing procedure is proposed to eliminate the DC and the autocorrelation noise. With the proposed method, we obtain high quality one-dimensional depth and two-dimensional cross-sectional images of the films. Then, the thickness and the defect information of the film can be obtained from the acquired images. The experiment result demonstrates that this nondestructive imaging technique is applicable for measuring film thickness and inspecting defects.     

Dynamic optical correlation using localized holography

A new technique for optical correlation using gated holographic recording is demonstrated. Several persistent holograms are localized within separate slices as close as 33 microm apart along the crystal. Individual holograms can be dynamically erased and rerecorded with no need to refresh all other recorded holograms. Experimental results showing the correlation capability, cross talk, shift invariance, and dynamicity of the localized holographic correlator demonstrate unique performance and capabilities for these correlators.     

Casimir force measurement using dynamic holography

The first holographic measurements are reported of the force between macroscopic objects mediated by zero-point electromagnetic fluctuations (Casimir force). A holographic interferometer is used to measure mirror oscillations with an amplitude of 1 pm. The objects under study are two thin metal films deposited on dielectric substrates. When one film is periodically oscillated, the first and second harmonics of the Casimir force acting on the other are detected. For the first time, an order-of-magnitude estimate is obtained for the Casimir force by using radiation pressure as a natural reference scale. The discrepancy between calculated and measured values of the Casimir force may be attributed to the small thickness and low conductivity of the metal films.     

用脉冲激光同轴全息技术测量微射流

 用脉冲激光同轴全息技术建立了全息照相系统和高精度同步时序系统，获得了采用爆轰加载产生高速运动的微射流全息图，并再现出微射流的全息像，得到粒子的大小和分布情况，从图像处理得到粒子尺寸的统计结果表明，最大尺寸在300μm左右，最小尺寸在30μm左右。证明了研制的全息系统和测试技术可以测量高速的微射流场。 .     

Precision measurement with visual feedback using binary phase diffractive optical elements

A novel method for obtaining precision measurements by using two binary diffractive optical elements is presented. The system provides visual feedback of the measurement without the use of electronics.     

Underwater hybrid near-field acoustical holography based on the measurement of vector hydrophone array

Hybrid near-field acoustical holography(NAH) is developed for reconstructing acoustic radiation from a cylindrical source in a complex underwater environment. In hybrid NAH,we combine statistically optimized near-field acoustical holography(SONAH) and broadband acoustical holography from intensity measurements(BAHIM) to reconstruct the underwater cylindrical source field. First,the BAHIM is utilized to regenerate as much acoustic pressures on the hologram surface as necessary,and then the acoustic pressures are taken as input to the formulation implemented numerically by SONAH. The main advantages of this technology are that the complex pressure on the hologram surface can be reconstructed without reference signal,and the measurement array can be smaller than the source,thus the practicability and efficiency of this technology are greatly enhanced. Numerical examples of a cylindrical source are demonstrated. Test results show that hybrid NAH can yield a more accurate reconstruction than conventional NAH. Then,an experiment has been carried out with a vector hydrophone array. The experimental results show the advantage of hybrid NAH in the reconstruction of an acoustic field and the feasibility of using a vector hydrophone array in an underwater NAH measurement,as well as the identification and localization of noise sources.     

用脉冲激光同轴全息技术测量微射流

用脉冲激光同轴全息技术建立了全息照相系统和高精度同步时序系统,获得了采用爆轰加载产生高速运动的微射流全息图,并再现出微射流的全息像,得到粒子的大小和分布情况,从图像处理得到粒子尺寸的统计结果表明,最大尺寸在300μm左右,最小尺寸在30μm左右。证明了研制的全息系统和测试技术可以测量高速的微射流场。.     

Musical quality assessment of clarinet reeds using optical holography

Vibrational modes of 24 clarinet reeds have been observed in both dry and wet conditions using holographic interferometry. Results have been compared with the "musical quality" of the reeds as judged by two professional clarinet players. An excellent correspondence has been demonstrated between specific vibrational behavior and musical quality. The results suggest that the presence and symmetry of a strong first torsional mode are indicative of good or very good musical quality. A second, but less stringent quality criterion is the proximity of frequencies corresponding to the second torsional and the second flexural mode. This proximity leads to the creation of mixed vibrational modes for the very best of the investigated clarinet reeds.     

Size measurement of Daphnia pulex using low-coherence Gabor digital holography

Optical Review - We measured the size of Daphnia pulex (D. pulex), which is an indicator organism used for examining toxicity, under freely-swimming and stress-free conditions, made possible by the...     

Simultaneous coherent imaging and strain measurement using coupled photorefractive holography and shearography

By coupling photorefractive holography with speckle shearography, it is possible to simultaneously perform both coherent imaging and strain measurement. Use of the photorefractive effect, which is insensitive to incoherently scattered light, is a significant advantage in coherent imaging as described. Experimental results obtained from a centrally loaded steel plate are presented.     

Dynamic holography and optical image processing

Possible applications of dynamic holograms for image amplification and image processing are discussed. The principal physical processes of holographic amplification of coherent light are analysed.Amplification of grey scale images during recording of dynamic holograms in pure reduced and Fe-doped crystals of LiNbO₃ is demonstrated. One-exposure technique of image subtraction or addition is proposed and realised in Fe-doped crystals of LiNbO₃.     

Associative mappings by optical holography

Algebra-based content addressable memories have been constructed recently using optical methods. We show here that holography can accomplish the same tasks on much larger vectors.     

Examination of the upper measurement limit in displacement measurement using fringe compensation in digital holography

Digital holography is a widely used method for displacement measurement in coherent optical metrology. An obvious limit of the method is that too large displacements result in dense fringes, so the fringes are practically invisible. The maximum number of contour fringes in displacement measurement is limited, because the cameras are discrete devices and sampling theory plays an important role. Because of the limited measurement range, compensation methods are promising tools for practical measurements. It can be shown that the practical measurement range can be extended above the Nyquist sampling limit. Compensation methods can be digital, because digital holographic interferometry operates with images recorded with a digital camera. In our research work the upper measurement range of fringe compensation method was examined. Our goal was to perform automatic compensation even if the displacement is higher than the measurement range of the basic method. The operation of the automatic fringe compensation method was based on the combination of two types of out-of-plane displacement measurements with different sensitivities.     

雾化场光学全息与数字全息联合测量

针对雾化场光学全息测量存在干板湿化学处理繁琐、再现像采集耗时的问题,提出光学全息与数字全息联合测量的方法,建立由同轴光学全息、同轴数字全息以及数字延迟信号发生器组成的测量系统,并以双孔直射式喷嘴产生的雾化场为测量对象,利用该测量系统在一次测量中同时获得雾化场的光学全息和数字全息的再现图像,两者具有很好的一致性。光学和数字再现图像相对应的视场范围分别为27.87 mm4.77 mm和27.59 mm6.67 mm,数字方式获得视场范围内单一层面再现像的时间仅为8 s,而光学方式将近1 h。结果表明,光学全息与数字全息联合测量时,通过数字全息的雾化再现图像能够对实验总体效果进行实时评估,提高了雾化场全息测量的实验效率。     

Effects of finite aperture on linewidth measurement using in- line Fraunhofer holography

Irradiance distributions in the reconstructed image plane are computed taking into consideration both finite and infinite hologram apertures. The influence on image quality of a finite aperture due to low-contrast response is discussed taking into account the average exposure level of holograms.     

光学扫描全息术的推广

给出了光学扫描全息术的基本原理。记录时用实时 FZP与物体强度透射率发生卷积从而产生扫描全息图 ;再现时用与记录时相对应的 FZP与全息图信号发生卷积即可再现出物体的信息。推广了光学扫描全息术 ,提出只要某一实时的光场强度分布函数具有如下性质 :(l)该函数中含有 x,y,z参量且相对于 z参量具有圆对称性 ;(2 )对于某一确定的 z参量 ,该函数的自相关是δ函数 ,就可以把该光场作为光学扫描全息术中的照明光场对物体进行扫描记录以得到扫描全息图。     

Twin-image elimination in optical scanning holography

We propose a novel multiplexing technique to solve the twin image problem in optical scanning holography without the use of a spatial carrier, as commonly used in conventional off-axis holography. The technique involves simultaneously acquiring sine and cosine Fresnel zone-lens plate coded images by optical scanning. A complex addition of the two coded images will then be performed and decoded to give a twin-image rejection reconstruction. Computer simulations will be presented to demonstrate the validity of the idea.