Effect of the average number of reference speckles in speckle imaging using off-axis speckle holography

Abstract

The propagation of coherent light through a random scattering medium generates speckle pattern. Although the speckle is random in nature, the object information is scrambled into it. The scrambled object information can be retrieved using off-axis holographic technique where the retrieval is made from coherence hologram which is constructed from the interferogram formed by object speckle and a tilted reference speckle. It is shown that the SNR of the object retrieved from the coherence hologram, calculated from the far-field intensity correlation of the interferogram, depends on the average number of reference speckles. The effect of average number of reference speckles on the SNR of the retrieved object in off-axis holographic technique is investigated experimentally by changing the reference speckle while keeping the object speckle unchanged. The experimental observations are presented in this paper.

Spatial statistics of superposition of two uncorrelated speckle patterns with polarization diversity

“…In order to calculate the DoC of the superposed random field using Eq. ( 4), we exploit the established fact that in case of superposition of two mutually uncorrelated fields, the CP matrix of the superposed random field can be written as the sum of the CP matrices of the constituent random fields under the assumptions that both the random fields follow Gaussian statistics [3,15]. Hence, the CP matrix of the superposed random field,  S (𝐫 𝟏 , 𝐫 𝟐 ) can be written as…”

“…The manipulation and proper characterization of the spatial statistics of speckles, a random intensity distribution, have emerged as a major area of research in recent times due to the wide range of applications of the speckles. The speckles are useful in biomedical studies [1], nondestructive testing and measurement of surface roughness [2], looking through an optical barrier [3] etc. The characterization of the speckles has led to the discovery of the existence of memory effect of a speckle pattern, the implementation of which has made imaging through a scattering medium more convenient [4].…”

“…The characterization of the speckles has led to the discovery of the existence of memory effect of a speckle pattern, the implementation of which has made imaging through a scattering medium more convenient [4]. The randomness of spatial intensity distribution of a speckle pattern, which is another important characteristic, can be determined from the study of the Shannon entropy of the speckle pattern [3,5].…”

“…Several other techniques have been developed to measure various parameters, which are required to study different spatial properties of a speckle pattern. The measurement of the spatial degree of coherence (DoC) provides information about the spatial coherency of a speckle pattern and the size of a speckle grain, determined from the intensity correlation of the pattern, is considered as the coherence length of the speckles [3,6]. Besides, the spatial distribution of polarization can be estimated from the study of the degree of polarization (DoP) [6].…”

“…Another widely used technique based on the speckle interferometry is the off-axis speckle holography, where the speckle interferometry is combined with the two-point intensity correlation of the speckle pattern. The off-axis speckle holography based approach can be used for imaging of 2D objects through a random scattering medium [3]. In the off-axis speckle holography, speckle patterns from two different sources are interfered, and as the speckle patterns are generated from two different sources, they are mutually uncorrelated.…”