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 by analyzing the speckle pattern with the help of intensity measurement and introducing spatial averaging. In order to suppress the coherent noise and perform complete characterization of the source, we introduce four shot intensity correlation measurements. Utilizing this feature, experimental reconstruction of the PPs obscured by the diffuser is presented for different cases. The effects of the spatial averaging window on the coherent noise suppression and reconstruction of the PPs are also evaluated.
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 scattering layer. The Stokes holography plays an important role in such situations and makes use of the Fourier transform relation between the Stokes parameters (SPs) at the scattering plane and the generalized Stokes parameters (GSPs) of the random field. In this paper, we propose and experimentally demonstrate the Stokes holography with the Hanbury Brown-Twiss (HBT) interferometer. We also propose and implement a lensless Fourier configuration for the Stokes holography. This permits us to reconstruct the wavefront from the GSPs at any arbitrary distance from the scattering plane. The application of the proposed technique is experimentally demonstrated for the 3D imaging of two different objects lying behind the random scattering medium. Depth information of the 3D objects is obtained by digitally propagating the generalized Stokes parameters to a different longitudinal distance. The quality of the reconstruction is assessed by measuring the overall visibility, efficiency, and PSNR of the reconstruction parameters.
The visible emission line coronagraph (VELC) on board the Aditya-L1 mission is an internally occulted reflective coronagraph. It is capable of simultaneous observations of the solar corona in imaging, spectroscopic, and spectropolarimetric modes very close to the solar limb, to 1.05 R ⊙ (R ⊙solar radius). Primary mirror (M1) of the VELC receives the light from both the solar disk and the corona up to 3 R ⊙ . In the VELC, occultation happens at the focus of the M1. Secondary mirror (M2) with a central hole size equal to 1.05 R ⊙ is mounted at the focal plane of M1 and serves the purpose of an internal occulter. To meet the proposed science goals of the payload, M1 surface should be super polished with good imaging characteristics. This results in stringent requirements of the surface figure and microroughness on the mirror surface. M1 is an off-axis parabola, so achieving the demanding requirements is quite challenging. At the same time, testing of M1 after development is crucial for evaluating its performance. This paper provides the details of the optical metrology tests carried out on M1 along with the results obtained and their implications on the performance of the VELC.
With the advent of the environmentally conscious decision-making period, the carbon footprint of any engineering project becomes an important consideration. Despite this, the carbon footprint associated with water resource projects is often overlooked. Water production, its supply and treatment processes involve significant energy consumption and thus, are source of emissions of greenhouse gases (GHGs) such as carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) which contribute to global warming. The emissions are not direct but come as a by-product of burning of fossil fuels to produce electricity to carry out these processes. Since water demand is continuous and keeps on rising, the quantification of carbon footprint associated with the water industry is vital. This paper studies and attempts to quantify the carbon footprint of one such urban water system, that is the Haiderpur Water Treatment Plant in Delhi, capital region of India by using the Life Cycle Assessment methodology and evaluate its performance from the point of view of energy consumption and make suggestions.
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