Collimation technique and testing applied to finite size polychromatic sources

Torcal-Milla, Francisco José; Sanchez‐Brea, Luis Miguel

doi:10.1364/ao.56.003628

Cited by 8 publications

(3 citation statements)

References 27 publications

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“…Numerous applications involving moiré fringes have evolved over the years. Moiré fringes based on Talbot effect are employed to generate collimated beams [28,29]. The technique of sampling moiré finds applications in displacement measurements in material science as it provides better resolution at high-speed [30].…”

Section: Sampling Moiré Effectsmentioning

confidence: 99%

Sampling moiré method: a tool for sensing quadratic phase distortion and its correction for accurate quantitative phase microscopy

Jayakumar¹,

Ahmad²,

Mehta³

et al. 2020

Opt. Express

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The advantages of quantitative phase microscopy (QPM) such as label-free imaging with high spatial sensitivity, live cell compatibility and high-speed imaging makes it viable for various biological applications. The measurement accuracy of QPM strongly relies on the shape of the recorded interferograms, whether straight or curved fringes are recorded during the data acquisition. Moreover, for a single shot phase recovery high fringe density is required. The wavefront curvature for the high-density fringes over the entire field of view is difficult to be discerned with the naked eye. As a consequence, there is a quadratic phase aberration in the recovered phase images due to curvature mismatch. In the present work, we have implemented sampling moiré method for real-time sensing of the wavefront curvature mismatch between the object and the reference wavefronts and further for its correction. By zooming out the interferogram, moiré fringes are generated which helps to easily identify the curvature of the fringes. The wavefront curvature mismatch correction accuracy of the method is tested with the help of low temporal coherent light source such as a white light (temporal coherence ∼ 1.6 µm). The proposed scheme is successfully demonstrated to remove the quadratic phase aberration caused due to wavefront mismatch from an USAF resolution target and the biological tissue samples. The phase recovery accuracy of the current scheme is further compared with and found to better than the standard method called principle component analysis. The proposed method enables recording of the corrected wavefront interferogram without needing any additional optical components or modification and also does not need any post-processing correction algorithms. The proposed method of curvature compensation paves the path for a high-throughput and accurate quantitative phase imaging.

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Section: Sampling Moiré Effectsmentioning

confidence: 99%

Sampling moiré method: a tool for sensing quadratic phase distortion and its correction for accurate quantitative phase microscopy

Jayakumar¹,

Ahmad²,

Mehta³

et al. 2020

Opt. Express

View full text Add to dashboard Cite

show abstract

“…To circumvent the above limitations, other techniques for beam collimation have also been investigated [12,13]. Sanchez-Brea et al developed techniques for collimation testing based on Lissajous figures, period comparison and achieved improved measurement characteristics [14][15][16][17]. However, these techniques require a precise estimate of period of the grating and the self-image to determine the collimation position.…”

Section: Introductionmentioning

confidence: 99%

Histogram error based algorithm for efficient collimation testing

Dhanotia

Bande

Bhatia

et al. 2019

J. Opt.

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This communication reports an investigation undertaken towards setting collimation of an optical beam using a self-imaging technique and histogram error (HE) based approach. The beam under test illuminates an amplitude type Ronchi grating. After the grating, a beam splitter is placed such that the grating’s self-images are formed in two perpendicular directions, at the different Talbot planes. The images are then recorded using two identical CCD cameras. Towards implementing a HE based algorithm, first, element-by-element subtraction of the normalized histogram of both self-images is computed. Next, the sum of the elements of the resultant image matrix is determined. Finally, the square of the sum yields the HE. HE provides an estimate of the collimation errors in the beam. For an incident collimated beam, the self-images recorded at different Talbot planes have identical unit magnification with respect to the grating; however, when the beam diverges or converges, the size and fringe width of self-images are differentially magnified or demagnified. Hence, when the beam is collimated, the HE is minimum. For the decollimated beam, the value of HE is higher, and increases as the decollimation errors increase. Using the proposed method, we could set the collimation position to a resolution of 1 μm, which relates to ±0.22 μ radians in terms of collimation angle (for a lens of focal length 300 mm and diameter 40 mm). Experimental results conclusively establish the viability of the technique. Good accuracy and precision in the measurement have been achieved.

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“…Alternative approaches for testing of beam collimation are being explored worldwide. These approaches are mainly based on use of Moiré [9,10], Talbot [11][12][13][14] and interferometers [15][16][17], as well as other optical techniques [18][19][20][21]. Few of these systems are cost effective, as generally only two gratings are required but physical separation and alignment accuracy play important roles in such configurations.…”

Section: Introductionmentioning

confidence: 99%

High contrast laser beam collimation testing using two proximately placed holographic optical elements

Rajkumar

Dubey

Debnath

et al. 2018

J. Opt.

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Accuracy in laser beam collimation is very important in systems used for precision measurements. The present work reports a technique for collimation testing of laser beams using two proximately placed holographic optical elements (HOEs). The required HOEs are designed and fabricated such that upon illumination with the test beam, they release two laterally sheared wavefronts, at desired angles from the directly transmitted beam, that superimpose each other to generate straight interference fringes. Deviation from the collimation of the test beam results in orientation of these otherwise horizontal fringes. The novelty of this setup comes from the fact that HOEs are lightweight, as well as easy to fabricate as compared to conventional wedge plates used for collimation testing, and generate high contrast fringes compared to other interferometry, holography, Talbot and Moiré based techniques in a compact manner. The proposed technique is experimentally validated by measuring the orientation of fringes by an angle of 16.4° when a collimating lens of focal length 200 mm is defocused by 600 μm. The accuracy in the setting of this collimation position is obtained to be 10 μm.

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Collimation technique and testing applied to finite size polychromatic sources

Cited by 8 publications

References 27 publications

Sampling moiré method: a tool for sensing quadratic phase distortion and its correction for accurate quantitative phase microscopy

Sampling moiré method: a tool for sensing quadratic phase distortion and its correction for accurate quantitative phase microscopy

Histogram error based algorithm for efficient collimation testing

High contrast laser beam collimation testing using two proximately placed holographic optical elements

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