Exploring Adaptive Optics based Spectroscopy using a Spatial Light Modulator

Chandra, Amar Deo (2023) Exploring Adaptive Optics based Spectroscopy using a Spatial Light Modulator. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Amar Deo Chandra (15RS019)) 15RS019.pdf - Submitted Version Restricted to Repository staff only Download (13MB)

Abstract

The Universe has a variety of cosmic objects which radiate at different wavelengths. The emitted electromagnetic emission is primarily dependent on the chemical composition, temperature and the local environs of the radiating object. The light emanating from these objects carry information on all these aspects encoded in photons which can be studied as a function of time, intensity, wavelength and polarization using remote observations to probe the underlying radiative mechanism of stellar objects and study their evolution on different time scales. The tools available at an astronomer’s disposal are categorized as photometry, spectroscopy and polarimetry. In our work, we develop innovative methods in laboratory settings to carry out spectroscopy and imaging of a given target using adaptive optics. Our innovative approach employs a Spatial Light Modulator (SLM) in an interferometric setup without having any moving components and requires a modest power budget of a few volts of DC power, such that it can find useful applications in a variety of settings including space astronomy. We first provide a recipe of phase calibration of the SLM using novel multi-level phase masks which facilitate threefold faster phase measurements over conventional methods without altering the experimental setup. Subsequently, we generate optimised phase masks by using an Iterative Fourier Transform Algorithm for splitting the incident beam into an array of beams (known as beam multiplexing) which can find useful applications for wavefront sensing and optical trapping. We then move on to applications-wherein we focus on the challenging problem of capturing the spectral evolution of a given target whose spectra changes on short time scales, as is the case for solar dynamic activity. We address this issue by developing a novel SLM-based hyperspectral imaging setup employing a Michelson interferometer to record simultaneous multi-wavelength spectral information of a broadband optical source in near real-time. The biggest advantage offered by SLMs is their near real-time tunability, which facilitates configuring the desired spectral channels as per requirements unlike fixed spectral filters, thus reducing the cost, size, and weight of the instruments without involving any movable components. Towards imaging applications, we demonstrate an SLM-based wavefront sensor using structured light, which can be used to measure distorted wavefronts and improve the system’s imaging capability. Our work explores new territory in SLM-based imaging and spectrometry, and would hopefully lead to new and fascinating research in this promising area of science and technology.

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