Empirical Characterization of Wood Surfaces by Means of Iterative Autocorrelation of Laser Speckle Patterns.

Rojas, Juan Antonio Martínez; Alpuente, J.; Bolivar, Estefania; LÃ3pez-EspÃ­, Pablo; Vignote, S.; Rojas, Martinez

doi:10.2528/pier07112706

Cited by 4 publications

(3 citation statements)

References 24 publications

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“…As shown in Figure 6, field distributions by applying the four Hadamard phase patterns are similar with typical features like granular noise, which is quite similar to optical speckles [20]. But they are not the detected images, which are not only decided by the field distributions, but also by the power coupling mechanism of the field to the detectors.…”

Section: Reflected Waves Imaging Sub-systemmentioning

confidence: 69%

Discussion on Validity of Hadamard Speckle Contrast Reduction in Coherent Imaging Systems

Feng¹,

Tavakol²,

Schreurs³

et al. 2010

PIER

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Abstract-Hadamard speckle contrast reduction (SCR) is considered to be an effective approach to deal with speckle problems in coherent imaging systems. A Hadamard SCR system is divided into two subsystems, which implement phase patterns projection and reflected waves imaging respectively. The performances of both sub-systems are discussed with numerical simulations and linked to certain parameters so as to give more insights of this approach. For generality, both optical and millimeter wave imaging systems are discussed. To distinguish from former literature based on Fourier optics, the simulation is implemented via wave optics, which is more physical and more accurate. Moreover, considering the fact that the Hadamard method originates from statistics, the effectiveness of Hadamard SCR is in the first place linked to the texture of the object's surface. Statistical optics is also adopted during qualitative analysis of the results. It is shown that the ratio between the dimension of a resolution cell and the granular size of the object's randomly rough surface is closely linked to the performance of Hadamard SCR. Differences in the roughness model in imaging cases of optical and millimeter waves are discussed, which would help to evaluate the validity of the Hadamard SCR approach in practice. The purpose of this paper is to clarify the misunderstandings of Hadamard SCR in previous literature and to give a guideline to apply this approach.

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Section: Reflected Waves Imaging Sub-systemmentioning

confidence: 69%

Discussion on Validity of Hadamard Speckle Contrast Reduction in Coherent Imaging Systems

Feng¹,

Tavakol²,

Schreurs³

et al. 2010

PIER

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“…The fluctuation characteristics of the amplitude and phase of an optical wave propagating through a turbulent medium have been a source of theoretical and experimental investigations for many years [1][2][3][4][5][6][7][8][9]. There are also many other correlative researches [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Ishimaru [1] used spectral analysis techniques to obtain expressions for the covariance and structure functions of log-amplitude and phase in locally homogeneous and isotropic turbulence.…”

Section: Introductionmentioning

confidence: 99%

Log-Amplitude Variance of Laser Beam Propagation on the Slant Path Through the Turbulent Atmosphere

Wei¹,

Wu²,

Ma³

2010

PIER

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Abstract-Based on the altitude-dependent model of ITU-R slant atmospheric turbulence structure constant, the log-amplitude variance of laser beam propagation on the slant path through turbulent atmosphere is obtained with transmitter and receiver parameters and can be degenerated to the result of the horizontal path with atmospheric structure constant as a fixed value. These expressions are convenient tools for beam-wave analysis. Finally, we apply the ITU-R turbulence structure constant model to calculate collimated, divergent and convergent beam log-amplitude variance. The numerical conclusions indicate the log-amplitude variance of laser beam propagation on slant path is generally smaller than those on horizontal path.

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“…However, the presence of speckles, a random granular appearance in images resulting from the interference of the coherent waves scattered from a rough object, degrades the image quality and leaves fine details irresolvable [1][2][3]. Although the speckles in the patterns have been successfully applied to identify fine features of objects [3,4], suppression of speckles has been a critical issue and has been widely studied in coherent imaging. Numerous methods have been proposed to reduce speckle noise: using a source of multiple wavelengths, inserting a moving (vibrating or rotating) diffuser or ground glass, coupling with a vibrating multimode fiber, moving an optical aperture in the Fourier plane, and spatial averaging in the detection plane (Readers may refer to references [3] and [5] for critical reviews and categorization of the speckle suppression methods).…”

Section: Introductionmentioning

confidence: 99%

Speckle Suppression by Integrated Sum of Fully Developed Negatively Correlated Patterns in Coherent Imaging

Hsu¹,

Chu²

2011

PIER B

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Abstract-A coherent imaging system images a frame or an object onto a changing diffuser and projects the resulting pattern which generally contains speckles. Using a spatial light modulator (SLM) as the changing diffuser, the speckles in the pattern are suppressed without the need for any other mechanisms. With M random phasor arrays being displayed in the SLM during the integration time of a detector, a suppression factor (C f ) of speckles, 1/ √ M , is achievable in the projected pattern, which is the sum of the intensity of M uncorrelated patterns. This paper shows both theoretically and in simulations that the C f of the sum pattern was considerably reduced when two elementary patterns with fully developed speckles were negatively correlated. With the correlation coefficients of the elementary patterns found at [−0.3, −0.25], the C f of the sum of 10 negatively-correlated speckle patterns was 48% lower than the C f of the sum of 10 uncorrelated speckle patterns. The negatively correlated patterns can be implemented using spatial light modulators or diffractive optical elements, and are used to suppress speckle noise in digital holography, laser projection display, and holographic display projections with relatively high efficiency.

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Empirical Characterization of Wood Surfaces by Means of Iterative Autocorrelation of Laser Speckle Patterns.

Cited by 4 publications

References 24 publications

Discussion on Validity of Hadamard Speckle Contrast Reduction in Coherent Imaging Systems

Discussion on Validity of Hadamard Speckle Contrast Reduction in Coherent Imaging Systems

Log-Amplitude Variance of Laser Beam Propagation on the Slant Path Through the Turbulent Atmosphere

Speckle Suppression by Integrated Sum of Fully Developed Negatively Correlated Patterns in Coherent Imaging

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