Dr. Vishwa Pal joined Department of Physics, Indian Institute of Technology Ropar, India, as an Assistant Professor in May 2018. His research expertise includes the phase locking of large arrays of coupled lasers and their potential applications for both applied and basic research. He received his PhD degree in 2014 from School of Physical Sciences, Jawaharlal Nehru University, New Delhi, India. He has done part of his PhD at CNRS Laboratoire Aimé Cotton, Orsay, France in the framework of Indo-French collaborations. During his Ph.D. program, he investigated semiconductor laser systems by probing noise correlations and dynamical control with delayed optical feedbacks. After Ph.D., he received PBC fellowship for outstanding postdoctoral researcher by the Council for Higher Education of Israel, and joined laser group of Prof. Nir Davidson and Prof. Asher A. Friesem at Weizmann Institute of Science, Israel. His postdocotral research focused on exploting coupled lasers for investigating topological effects, simulating spins and solving computationally hard problems. He also worked on laser beam shaping with industries in Israel, under magnet project on Advanced Laser Technologies for Industrial Applications. In 2018, he joined CREOL, The College of Optics and Photonics, Florida, USA, as a research scientist and worked on synthesizing non-diffracting optical beams in free space by exploiting space-time correlations. In 2018, he received Marie Sklodowska-Curie Actions Individual Fellowship By European Commission. Â
Lasers, Structured light, Optical computing, Topological photonics
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My research focuses on the following areas:
1)Â Phase locking of lasers (generating high powers):
Lasers are the key components for many branches of science and technology and also serve as fundamental tools for studying other systems. Particularly, lasers with very high power and ideal beam quality have a large potential in scientific research, material processing, communication, medical, industrial and defense applications, and research in this direction has been in progress ever since the invention of lasers. High-power lasers often have beam quality, stability, and heat dissipation inferior to those of lower-power lasers. The phase locking of several lasers is a promising approach to synthesize high-power optical sources with ideal beam quality. However, the phase locking of many lasers is a challenging task, since it requires, at the very least, a common lasing frequency to all the lasers, a prospect that vanishes exponentially with the number of lasers. Our group activities are focused on to find solutions to overcome such limitations, and thereby to push the upper limit on the number of lasers that can be phase locked, and hence to increase the output powers while maintaining the ideal beam quality.
2)Â Coherent computing with coupled lasers:
Optimization plays a crucial role in making decisions and in analyzing systems. Specifically, it deals with finding the best solution from among many feasible solutions (for example, traveling salesman problem). Such problems are ubiquitous across social science, biology, chemistry, physics, engineering, computer science, big data and artificial intelligence. Many such problems are classified as computationally hard problems (belong to non-deterministic polynomial time (NP)-hard or NP-complete complexity classes), and solving them efficiently has been beyond the reach of modern computers. Solving them efficiently and rapidly with physical systems has become an emrging field of research. Physical optimization relies on finding the ground state of a complex system as a physical analogy to the optimization problem.Â
There has been significant interest in building efficient solvers that are based on physical systems, and recently some of have realized. These include solvers that invlove coupled lasers, Bose-Einstein condenstae (BEC) polaritons and optical parametric oscillators. Particularly, our activities are focused on to build a rapid and efficient solver based on coupled lasers to solve these class of problems.
3)Â Laser beam shaping:
Generation of optical fields with complex spatial and temporal distribution has attracted considerable interest due to numerous applications, both in fundamental science as well as engineering applications, in various fields. Typically, the output from a laser source consists of a Gaussian distribution, which is undesirable for many applications. However, in recent years, it has become possible to control the distribution of light in the spatial and temporal domain, which allows to produce spatially variant polarization states, exotic phase structures and tailored intensity patterns. The structured light with a daisy-petal-like intensity pattern was used to probe planer and non-planner surface displacements at picometer scale resolution. This has opened a route to measure weak radiation pressure and optical manipulation of liquid/solid interface that possess the potentials for applications in opto-fluidics, microfluidics, and gravitational waves detection. A synthetic chiral structured light was shown to efficiently control chiral light-matter interaction, and provides the possibility for drug development. The optical vortices were exploited to probe magnetism in materials. The well- known Rayleigh limit was sown to overcome by structured illumination, and thus allowed to achieve super- resolution in the imaging techniques. Very recently, compressive three-dimensional super-resolution microscopy with speckle-saturated fluorescence excitation was demonstrated. Further, polarization based speckle-field digital holograpic microscopy was also shown to probe features in the biological tissues with enhanced spatial resolution and controlled coherent noise reduction. Moreover, structured light is also deployed in many other fields, such as optical metrology, optical communications, optical trapping and manipulations, and atomtronic devices.
Our group activities are focused on controlled laser beam shaping involving intra- and extra- laser cavity configurations. The main focus is to acheive the high quality structured light with high powers, extended depth of focus, and applicable to a wide spectral range.
4) Topological photonics:
The topological photonics has emerged a new exciting field of research, where the application of topology is creating a range of new opportunities throughout the photonics. The topology has emerged as another degree of freedom, which opens a new door for the discovery of fundamentally new states of light and possible revolutionary applications. For example, potential practical applications of topological photonics include photonic circuitry that is less dependent on isolators and slow light that is insensitive to disorder. Few more demonstrations of topological effects were realized in photonic crystals, coupled resonators, waveguides, metamaterials and quasicrystals. Our group activities are focused on to investigate topological effects in a non-Hermitian system of coupled lasers.
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