Rakesh kumar Singh

Indian Institute of Technology (Banaras Hindu University) Varanasi | BHU · Department of Physics

The orbital angular momentum (OAM) of the vortex or helical beam, connected with the topological charge (TC) of the beam, has been used as an alternative degree of freedom to encode and decode the information in the optical signals. Many detection schemes have been established to determine the TC configurations and decode the information at the rec...

We have demonstrated using higher-order Stokes correlations that the retrieved amplitude and phase information of the optical vortex (OV) beam and its orbital angular momentum (OAM) spectrum when it is propagating through a scattering medium are insensitive to the external aberration in the propagation channel. A theoretical framework of the propos...

A digital holographic (DH) imaging system design is based on a Wollaston prism to recover the complex information (i.e. amplitude and phase) of the object using the Fourier fringe analysis algorithm on the digitally recorded hologram. To make the experimental setup simple, a common path configuration based on a Wollaston prism is implemented. The p...

Imaging through random scatterer is a challenging problem due to spatial scrambling of the light wavefront and formation of the speckle pattern. Here, we present a new experimental configuration in holography with a two-point intensity correlation to reconstruct the orthogonal polarization modes from a single shot measurement of the speckle pattern...

The fascinating domain of ghost imaging has been a subject of interest in the fundamental and applied research for the last two decades with its promising applications in various imaging and characterization scenarios. In this chapter, we discuss the recently developed ghost diffraction holography (GDH) system with due emphasis on the capability of...

We present a ghost diffraction scheme with spatially fluctuating fields. This is implemented by replacing ensemble average with spatial average rather than temporal average as used in conventional ghost diffraction schemes.

We propose and experimentally demonstrate an on-axis phase-shifting correlation holography technique with un-polarized light. The randomness of the un-polarized light is exploited to evaluate the higher-order polarization correlation and to consequently apply it in the reconstruction of the hologram from the randomness. A detailed theoretical analy...

We report a new method to reconstruct a two-dimensional object in Ghost diffraction scheme using a spatial statistical optics approach. This is implemented by using a static diffuser rather than a pseudo thermal light source generated with a rotating diffuser as used in conventional ghost imaging systems. The experimental implementation makes use o...

We present and experimentally demonstrate a holography technique with a higher-order Stokes correlation of the random light field. The proposed technique is capable to reconstruct the complex-valued object from the random light field, and overcome twin image issues in the higher-order correlation holography without angular shift, phase shifting, an...

The wavefront is scrambled when coherent light propagates through a random scattering medium and which makes direct use of the conventional optical methods ineffective. In this paper, we propose and demonstrate a structured light illumination for imaging through an opaque scattering layer. Proposed technique is reference free and capable to recover...

We report the reconstruction of a transparency image in Ghost diffraction scheme using a statistical optics approach. This is implemented by using a static diffuser rather than a pseudo thermal light source with a rotating diffuser. The experimental implementation makes use of spatial ergodicity and spatial stationarity for spatially distributed ra...

The orbital angular momentum (OAM) of the vortex or helical beam, connected with the topological charge (TC) of the beam, has been used as an alternative degree of freedom to encode and decode the information in the optical signals. Many detection schemes have been established to determine the TC configurations and decode the information at the rec...

A novel technique to measure the orbital angular momentum (OAM) spectrum of the beam obscured by a complex random media is proposed and experimentally demonstrated. This is realized by measuring the complex correlation polarization function (CPCF) with the help of a two-point Stokes fluctuations correlation of the random light. The OAM spectrum ana...

The coherence holography offers an unconventional way to reconstruct the hologram where an incoherent light illumination is used for reconstruction purposes, and object encoded into the hologram is reconstructed as the distribution of the complex coherence function. Measurement of the coherence function usually requires an interferometric setup and...

Vector vortex beams play an important role to tailor tightly focused fields by creating an additional longitudinal component at the focal plane. Till now, mainly focusing properties of fundamental, higher order vector fields and negative indexed ellipse fields have been investigated. In this paper we numerically analyze tight focusing behaviour of ell...

In recent years, rapid developments in imaging concepts and computational methods have given rise to a new generation of imaging technologies based on chaos. These chaos-inspired imaging technologies (CI2-Tech) consist of two directions: non-invasive and invasive. Non-invasive imaging, a much older research direction with a goal of imaging through...

Quantitative phase imaging (QPI) plays an essential role in exploring properties of objects exemplified by transparent and absorption-free samples. Within the realm of QPI, the holography that records both the amplitude and the phase of optical fields is widely used. However, when the object is obscured by a scattering medium, conventional holograp...

Digital holography is an emerging method with a coherence light. Here, we discuss holography with a stochastic light and highlight the role of coherence optics in steering new trends in the DH.

We demonstrate a double-shot technique by superposing two uncorrelated speckle patterns to retrieve any arbitrary polarization of a light beam behind a scattering layer using intensity correlation. The theoretical details and the results are presented.

Orbital angular momentum (OAM) of optical vortex beams has been regarded as an independent physical dimension of light with predominant information-carrying potential. However, the presence of scattering environment and turbulent atmosphere scrambles the helical wavefront and destroys the orthogonality of modes in vortex beam propagation. Here, we...

We present a spatial light modulator (SLM) assisted compact holographic method and illustrate its application by imaging through a random scattering medium. The merit of the proposed method is wavefront division multiplexing, i.e. the dual wavefront modulations over a single SLM. Two different wavefront shapes: a reference-light shape and a phase o...

In this Letter, we propose and experimentally demonstrate a new, to the best of our knowledge, non-interferometric and highly stable technique to unscramble the incident orbital angular momentum (OAM) state and quantitatively measure the phase structure from the non-imaged random light. A new theoretical basis is developed and also verified by nume...

We present a method to unscramble the orbital angular momentum (OAM) mode from the scrambled light. This is implemented by evaluating two-point Stokes fluctuations correlation of the scrambled light which helps to recover complex polarization correlation function (CPCF). The complex field of the CPCF is projected onto spiral harmonics to quantitati...

The coherence holography offers an unconventional way to reconstruct the hologram where an incoherent light illumination is used for reconstruction purposes, and object encoded into the hologram is reconstructed as the distribution of the complex coherence function. Measurement of the coherence function usually requires an interferometric setup and...

Phase of an object plays a crucial role in retrieving the complete information. Digital in-line holography is a simple and effective technique to retrieve the phase information and 3D features of object. However the twin image formation limits the total information that can be obtained using in-line holography. Here in this paper, we show how deep...

A novel technique to measure the orbital angular momentum (OAM) spectrum of the beam obscured by a complex random media is proposed and experimentally demonstrated. This is realized by measuring the complex correlation polarization function (CPCF) with the help of a two-point Stokes fluctuations correlation of the random light. The OAM spectrum ana...

We propose and experimentally demonstrate a noninterferometric method to quantitatively determine the topological charge and complete phase structure of a vortex beam scrambled by a random scattering medium. In the proposed technique, the vortex beam with an arbitrary topological charge coaxially enters into the scattering medium with another nonvo...

The correlation holography uses incoherent light for the reconstruction of the hologram and the object is reconstructed as a distribution of the two-point coherence function rather than as the optical field as in the conventional holography. The basic principle of this technique is derived from the van Cittert-Zernike theorem and relies on the simi...

The correlation holography uses incoherent light for the reconstruction of the hologram and the object is reconstructed as a distribution of the two-point coherence function rather than as the optical field as in the conventional holography. The basic principle of this technique is derived from the van Cittert-Zernike theorem and relies on the simi...

Field based polarization measurement is essential to understand and quantify the optical response of any target sample. The method discussed here is digital holography microscopy (Yang et al. in Opt. Express 24:25, 2016, [1]) that enables us to quantify spatially the Jones Matrix of a transparent anisotropic sample. Our method provides precise info...

Coherence function is a complex quantity and follows wave equation similar to the optical field. Utilizing this analogy, wepropose a new method to craft the correlation structure of the light. This is realized by considering the interference of coherence waves due specially positioned incoherent sources in the Fourier space. Basic principle of the...

We extend the wide-sense spatial stationarity concept of coherence holography in the regime of phase-space using the wigner distribution function. We focus mainly on the incoherent light source and the Fourier and Fresnel propagation kernels for the optical-field transformation rule (inputoutput relation) and derive the same analogy in WDF. We furt...

Encoding information using the topological charge of vortex beams has been proposed for optical communications. The conservation of the topological charge on propagation and the detection of the topological charge by a receiver are significant in these applications and have been well established in free-space. However, when vortex beams enter a dif...

Propagation of light through random scattering medium scrambles information and generates randomness. This paper covers some of our works towards measuring incident light modes from the random pattern.

Phase recovery in the ghost imaging and other correlation based methods

Unconventional systems that adopt the concept of ghost schemes have led to advancements in some imaging applications. However, their application in quantitative phase imaging remains a challenge. Here, we introduce a basis for quantitative phase imaging with ghost diffraction and demonstrate ghost diffraction holographic microscopy for complex-valu...

Unconventional systems that adopt the concept of ghost schemes have led to advancements in some imaging applications. However, their application in quantitative phase imaging remains a challenge. Here, we introduce a basis for quantitative phase imaging with ghost diffraction and demonstrate ghost diffraction holographic microscopy for complex-valu...

A technique based on the superposition of two uncorrelated speckle patterns and speckle contrast measurement is proposed and demonstrated to track the polarization rotation of an optical beam behind a scattering layer. One of the superposed speckle patterns is considered as reference, and it is shown that with the help of the reference speckle patt...

A phase-retrieval algorithm can reconstruct the phase of an object from an intensity image of a diffraction pattern recorded at the Fourier plane, provided one makes a right initial guess. For the algorithms that are based on an initial random guess, at times, the output either becomes nondeterministic, becomes nonconvergent, or develops a twin ima...

This project is undertaken to study and analyse about how machine learning algorithms can be applied to problems in optics and quantum information.Firstly, worked on the Inverse scattering problem. The goal is to test and analyse the performance of machine learning algorithms with the increasing complexity of the speckle patterns.Also scope of mach...

This paper presents a review on the application of off-axis speckle holography for looking through an optical barrier. In off-axis speckle holography technique, a titled reference speckle pattern is superposed with an object speckle pattern to retrieve the phase information of the Fourier spectrum of the object embedded into the speckles. The two-p...

The Wigner Distribution Function is a local frequency spectrum function that can provide information in phase-space simultaneously. The propagation of wave in weakly homogeneous and dispersive medium can also be studied via Transport equation which has a resemblance to the ray optics based description.

We propose a new scheme for the recovery of complex-valued objects in a single-pixel hybrid correlation holography. The idea is to generate an intensity correlation hologram from the correlation of intensity fluctuations obtained over two channels, namely an optical channel equipped with a single pixel detector and a digital channel. The scheme has...

Light propagating through a scattering medium generates a random field, which is also known as a speckle. The scattering process hinders the direct retrieval of the information encoded in the light based on the randomly fluctuating field. In this study, we propose and experimentally demonstrate a method for the imaging of polarimetric-phase objects...

We show a digital holographic approach for polarimetric characterization of a twisted nematic liquid crystal spatial light modulator (TNLC-SLM). An experimental scheme is designed to perform polarization analysis of the SLM with gray levels. This is realized by simultaneous detection of the polarization states of the light from the SLM for a given...

Light propagating through a scattering medium generates a random field, which is also known as a speckle. The scattering process hinders the direct retrieval of the information encoded in the light based on the randomly fluctuating field. In this study, we propose and experimentally demonstrate a method for the imaging of polarimetric-phase objects...

We show a digital holographic approach for polarimetric characterization of a twisted nematic liquid crystal spatial light modulator (TNLC-SLM). An experimental scheme is designed to perform polarization analysis of the SLM with gray levels. This is realized by simultaneous detection of the polarization states of the light from the SLM for a given...

We report a phase shifting holography for coherence waves in the Hanbury Brown and Twiss approach. This technique relies on the wave nature and interference of the coherence waves in the two-point intensity correlation. Experimentation is carried out by recovery of the complex coherence using phase shifting in the intensity correlation. As an appli...

Wepresent a new polarization holographic microscopy technique based on speckle-field illumination with enhanced spatial resolution and controlled coherent noise reduction. The proposed technique employs a spatial light modulator for the generation of a sequential speckle pattern for the illumination of the sample. The developed microscope is capabl...

We discuss various new aspects of the Hanbury Brown-Twiss (HBT) approach. A possible extension of the HBT to the vectorial light is discussed and few imaging applications are highlighted.

Inhomogeneous and random scattering in a static-scattering medium diffuses an incident light field into a complex speckle pattern. This phenomenon leads to uncontrolled and unpredictable changes in the spectrum as incident polychromatic light is scattered by the static-scattering medium. In this paper, we propose and demonstrate a novel technique f...

Optical transmittance measurements of MoS2 nanostructures with varying film thickness are reported here. Optical transmittance value of the films containing assorted MoS2 nanostructures (revealed by SEM studies) was obtained from optical microscope images taken under white light with 100× magnification and also from the images acquired under an ord...

Imaging through a scattering medium or focusing light through a scattering layer using light in the visible region of the electromagnetic spectrum is a challenging task. When a beam of light enters into a non-absorbing opaque medium such as living tissue, white paint, fog, atmospheric turbulence etc., the constituent photons undergo scattering even...

We propose an approach where temporal as well as the spatial phase shifts are utilized simultaneously in order to reduce the number of shots and also the carrier frequency currently employed in digital shearography.

This talk covers fundamental and practical challenges of imaging from randomly scattered fields.

Fourier Transform Holography (FTH) encodes object information as the Fourier spectrum in an interference pattern with the help of a reference point source. Hence, a single Fourier transform (FT) operation is capable to provide a complete object from a digitally reconstructed FTH. However, high intensity values in the central region of the FTH deman...

A technique based on speckle contrast measurement is proposed and demonstrated to track the polarization rotation of an optical beam behind a scattering layer. It is shown that with the help of a reference speckle pattern with a known linear polarization, it is possible to track the polarization rotation behind a scattering layer in a non-invasive...

We propose and demonstrate a technique to tailor and analyze the vectorial coherence in three-dimension paraxial propagation. This is realized by proposing a new experimental scheme to simultaneously admit and modify the transverse polarization components of the light with a single spatial light modulator. Subsequently, these polarization component...

We propose a new scheme for recovery of complex valued object in a single- pixel hybrid correlation holography. Idea is to generate an intensity correlation hologram by correlation of the intensity of a single pixel detector and digitally propagated two dimensional intensity patterns. The proposed scheme with theoretical basis is described to recon...

Propagation of polarized monochromatic light through inhomogeneous media generates a noisy pattern known as a laser speckle. The speckle pattern obscures recovery of the polarimetric parameters (PPs) of the incident light. In this paper, we propose and demonstrate a technique to suppress the speckle and recover the desired PPs. This is implemented...

The recording and reconstruction of the Stokes parameter is of paramount importance for the description of the vectorial interference of light. Polarization holography provides a complete vectorial wavefront, however, direct recording and reconstruction of the hologram is not possible in a situation where the object is located behind the random sca...

Polarization is a fundamental property of light which makes direct impact on the image recording- reconstruction and can have significant and nontrivial effects on high-level visual perception, such as color vision, depth measurement etc. Polarization vision has special utility in seeing the otherwise obscured object, and some animals make use of p...

Lens-less digital holography for quantitative phase contrast imaging is established with a cyclic lateral shearing interferometer and non-collimated light beam. In a self-reference type configuration, the object and reference beams are generated from the same spherical wavefront after the light beam has passed through the sample plane. The experime...

We present our recent research studies on single-shot complex amplitude information retrieval through a visually opaque scattering layer realized using different architectures based on speckle interferometry, intensity correlation interferogram, phase-retrieval algorithm and digital holography.

We present a technique based on an interferometric approach to sense the polarization rotation through scattering media with the help of a known reference speckles, by studying the degree of coherence of the mixed speckles.

We experimentally demonstrate that the intensity correlation of speckled speckles before and after the lateral displacement of the concealed scatterer discloses the axial separation though speckle size, decorrelation length and speckle gearing. We expect to apply this technique into tracking objects hidden in the diffuse layer, measuring biological...

Amplitude Shifting Holography method for imaging complex value objects is based on the consideration that one point can be taken from the object as a reference and by shifting its amplitude to record the digital hologram.

We present a technique for polarization holographic imaging that employs the complex speckle pattern (rather than a uniform field) to illuminate the sample and utilizes the randomness of the speckle pattern for image enhancement. The vectorial wave front is recovered by developing a polarization holographic imaging system with the potential of simu...

Quantitative measurement of Jones matrix elements is crucial for the study of light polarization with the wide range of applications. Here, we propose and experimentally demonstrate a novel method of Fourier space sharing to determine spatially resolved all four elements of the Jones matrix from a single-intensity frame. This is achieved by applyin...

A new technique based on superposition of two speckle patterns is proposed and demonstrated for controlled modulation of the spatial polarization distribution of the resultant speckle. It is demonstrated both theoretically and experimentally that controlled modulation of the spatial polarization distribution of laser speckle can be achieved by prop...

Propagation of a coherent light through a random birefringent scatterer generates a speckle pattern with spatially varying polarization called polarization speckle. The spatial polarization distribution of the polarization speckle is random in nature making zero net polarization. In this paper, we experimentally characterize the memory effect of th...