Raman Research Institute and ISRO join hands to study the early Universe

MoU_RRI_SACIt’s official! The Raman Research Institute (RRI) and ISRO Space Applications Center (SAC) are teaming up! With the signing of an MoU, RRI and SAC will work together to further our understanding of the evolution of Universe by looking for wiggles in the first light from the very first stars born in the universe. The two institutions will partner to design and develop extremely sensitive radio receivers to detect this light, deploy them in locations free from man-made radio interference, ranging from remote sites on ground all the way to space in lunar orbit. These radiometers will be custom designed to detect signals from the formation of first atoms (Epoch of Recombination) to the formation of first stars (Cosmic Dawn and Epoch of Reionization). The collaboration also aims to design and develop astronomical observatories to look directly at the birth places of stars in our local Universe by studying radiation from molecules. From studying the formation of planetary systems, to molecules that are essential to life, these observatories have exciting science goals. RRI will focus on the science, proof of concept, ground based observing systems, and SAC will apply its expertise towards the space qualification of the experiments for deployment in high-altitude and space, away from the clutter of terrestrial radio frequency interference. Watch out for future updates of this partnership as it takes flight!

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Throwing light on dark Matter

All the matter that we see around us is ultimately made up of atoms, which in turn is made up of protons and neutrons. Surprisingly, such ordinary matter constitutes less than 15% of the total matter in the Universe. Most of the Universe is made up of dark matter – matter that does not emit any light but interacts with other objects only through gravity. Although we know dark matter exists, we do not know what exactly it is. Now, a study by researchers from Bengaluru has tried to understand the dark matter better.

Dark matter has never been directly observed or created in a lab. Its existence and properties are inferred from its gravitational effects on objects that we can see. In this study, published in the Journal of Cosmology and Astroparticle Physics, researchers from the Raman Research Institute (RRI), Indian Institute of Science (IISc), and the Indian Institute of Astrophysics (IIA), have examined what future experiments can reveal about the nature of dark matter.

“The first partial evidence for dark matter was seen long ago, in the 1930s. But the main evidence came in the 1970s. It was observed that galaxies are rotating too fast to be held together by the gravity of the visible matter alone. Hence the existence of additional invisible, dark matter was postulated. By the late 1980s, additional lines of evidence had emerged from observations of clusters of galaxies, and from even larger cosmological scales”, says Prof. Shiv Sethi from RRI, who is also an author of the study, talking about our quest to understand dark matter.

Although the exact nature of dark matter is unknown, there are several different models of what the dark matter particle could be, most of them motivated by different particle physics models. The most popular model is “cold dark matter”, where cold refers to the velocity of the dark matter particles in the early Universe. If dark matter particles were ‘hot’, travelling at high speeds, they would rush from high density to low-density regions in the early Universe, thereby wiping out these density differences. In contrast, ‘cold’ dark matter, which moves slowly, would allow density differences in the early Universe to grow into galaxies. Since we can observe galaxies in the present Universe, hot dark matter model is now ruled out.

Scientists probe the nature of dark matter in several ways, including experiments that hope to detect dark matter particles directly. But in this study, the researchers focus on observations of the cosmic microwave background (CMB) — relic radiation left over from the Big Bang. “CMB is the most precise measurement in almost all of astrophysics. Moreover, the physics that goes into it is extremely clean. So when we want to look for something in an experiment, we want to manage these two aspects,” explains Prof. Sethi.

The cosmic microwave background is nearly uniform, but there are small differences in temperature and density. The pattern of variations in temperature and density depends on what particles are present in the early Universe, and their properties. Hence each type of particle leaves behind a distinct signature in the spectrum of temperature and density fluctuations in the CMB.

In this study, the researchers calculate the effects of different dark matter particle models on the CMB spectrum. “We have considered a whole range of models that exhaust nearly all possibilities that are still consistent with current experimental constraints,” says Prof. Sethi. The researchers have tried to answer the question — ‘If dark matter changes its nature below a certain scale, how well can we probe it with future experiments? What kind of constraints can we put on these models?’

The study finds that previous and current observations of the CMB are not sensitive enough to distinguish between these dark matter particle models. However, many experiments are being proposed in the next decade to observe the CMB, such as the space-based PIXIE (Primordial Inflation Explorer) mission by NASA and the ground-based CMB S-4 (Stage 4) experiment at the South Pole. Based on the expected sensitivity of PIXIE, the researchers expect these experiments to be able to distinguish between at least some of the dark matter particle models, thereby shedding light on the enduring mystery of what dark matter is.img_20180222_152835

What’s cooking in the ‘LMC X-4’ binary star system?

In a new study, researchers from the Raman Research Institute (RRI), Bengaluru, present observations about the binary star system ‘LMC X-4′ in the neighbouring Large Magellanic Cloud satellite galaxy. Their findings, published in the New Astronomy Journal, uses data from receivers aboard spacecraft XMM-Newton launched by the European Space Agency, and the Rossi X-ray Timing Explorer satellite from NASA. The findings hold important clues in the mechanics behind X-ray emissions seen from this binary system of stars.

The Large Magellanic Cloud (LMC) is a satellite galaxy that orbits our own, much larger, Milky Way. LMC X-4 is a two-star system consisting of a pulsar – a highly magnetised neutron star beaming X-rays – and a companion star. Scientists believe that such pulsars are formed after a supernova explosion, when a dying star spectacularly shoots material and expanding shockwaves into space, before being reborn as a compact star. The neutron stars are so dense that their mass could be twice that of the Sun, with a radius of only 10 kilometres. Its high density makes its magnetic field a trillion times stronger than Earth’s.

In this study, Dr. Aru Beri and Dr. Biswajit Paul from RRI examined characteristics of the X-ray signals emitted from LMC X-4, using signal processing techniques and analysis. The scientists observed three states in the intensity of X-ray emitted by the pulsar: ‘flaring’, ‘persistent emission’, and ‘eclipse’.

Neutron stars evolve through ‘accretion’ – the continuous addition of usually gaseous particles by gravitational attraction. Due to very strong gravitational attraction, the neutron stars accumulate gas in streams from its orbiting companion onto ‘hotspots’ on the surface of the neutron star, which briefly flare with X-rays when the accretion abruptly increases. The ‘flaring state’ of LMC X-4, which happens when there is a sudden increase in the amount of material accreting onto the surface of the neutron star resulting in larger X-ray radiation, showed four distinct flares. These flares exhibit a pattern of pulsation that, when plotted, is broad and sinusoidal in shape. This is followed by a non-flaring or ‘persistent emission state’ where a low signal of X-rays is recorded. The third state of ‘eclipse’ is identified by an absence of X-rays when our view of the neutron star is blocked by its much larger companion.

The researchers focused on the complex structure of the X-ray pulses during the persistent emission state, defined as the region with no flares and no eclipse. They observed ‘dips’ in the pulses during the period of steady, low X-rays, identified by sharp drops in the intensity of radiation. They attribute this to the hotspots becoming obscured by optically dense bands of accreting gas that falls from the companion star into the neutron pulsar star.

The study estimates the timescales involved in the formation of the flares, and the subsequent formation of the accretion column that causes dips, stating that “observed differences in the pulse profiles during and after the flares suggest that significant change in the accretion stream happens during the transition between flares and the persistent state”.

This study takes us a step closer to confirming theories on the nature of light, magnetism, gravity and general relativity. Observing and analysing cosmic phenomena such as pulsars, enables a deeper understanding of some extreme conditions in the cosmos that cannot be created in laboratories. This study gives insight into the behaviour of plasma in extremely high magnetic field and very strong gravity.

The researchers of the study have plans to further their research on X-rays emitted from other stars. “We are currently making an X-ray polarimeter named POLIX, which is the main scientific instrument onboard XPoSat, a satellite mission of ISRO to be launched in 2019, dedicated for investigation of polarisation properties of cosmic X-ray sources”, shares Dr. Paul, about his future plans. Observations with POLIX will allow scientists to determine the magnetic field structure of neutron stars, the key element in the formation of the flares and dips in LMC X-4 that have been discovered with the current investigation.Untitled

Hermit photons coaxed to interact via one-dimensional confinement!

Photons, the particles of light, do not contain any charge and hence typically do not interact with each other. In fact, they are so aloof that when you shine a beam of light from a torch onto one from another, they cross each other’s path and move on as if the other beam does not exist.

While this property makes them excellent candidates for long distance communication, it also serves as a hindrance for applications in optical information processing and realization of all-optical circuits, where photon-photon interaction at the level of individual photons (for example, controlling the motion of a single photon with another photon) is highly desired. The question now is this: How do we achieve photon-photon interactions at the level of individual photons?

One way would be to tap into what is known as nonlinear optical behavior, which is exhibited by certain materials that change their refractive index as a function of the intensity of incident light. As a consequence, the propagation of light in the interior of such materials can be controlled by another beam. This gives rise to effective interaction between otherwise noninteracting light beams. Intensity-dependent refractive index is routinely employed in many nonlinear optical devices in laboratory optics and in technology. Could this feature of nonlinear optics be used to make individual or at most a few photons interact?

Unfortunately, the electric fields (and hence the intensity) associated with individual photons is tiny; therefore a vast number of photons are required to realize optical nonlinearity in the interior of any known nonlinear optical material. Let us take a minute here to ponder this question: why do we need a large number of photons to generate nonlinear behavior in a material? Answering this question could point one in the right direction towards achieving nonlinearity with a few photons. Let us consider a cylindrical light beam of diameter ‘d’ incident upon a material made up of atoms. The chance that one photon will “see” one atom in the material is given by the ratio of the effective size of the atom as seen by a photon and the transverse area of the beam. The word, “see” is in inverted quotes because of the following: how well a photon sees an atom is dependent on how well the energy of the photon matches the energy levels of the atom; the closer they are more the chance of interaction. When the energy of the photons matches the energy levels of the atom, the effective size of the atom is approximately the square of the wavelength of the incident photon. The beam diameter is usually much greater than the photon wavelength, and hence the chance of one photon interacting with an atom in bulk materials is very very small. Right away, we see that to improve the chances of interaction and hence nonlinearity we need a lot of photons (which we do not want, since we are aiming for nonlinearity with a few photons) or—here is our aha moment—reduce the diameter of the light beam ‘d’ to such a small value, in fact far below the wavelength of photons, and couple it to an artificial atom whose effective size is far greater than any existing real atom.

Enhanced atom-photon coupling with just a few photons, leading to strong optical nonlinearity, is achieved by confining the photons into tiny spaces with dimensions much smaller than the wavelength of the photons. This has been experimentally realized by squeezing the photons along with individual atoms in confined geometries such as waveguides. One-dimensional waveguides such as superconducting transmission lines can confine microwave photons to deeply sub-wavelength sizes in their transverse dimensions. When we couple an atom (a superconducting qubit here) with a large transition dipole (equivalent to a large effective size) to such confined photons, strong optical nonlinearity may be manifested with a just few photons. In such a case, photons are transversely focused to an area comparable with the scattering cross-section of the atom, and their electric field at the atom becomes large enough to excite the atom (which means that atom absorbs energy from the incident photon and goes to a higher energy state) with very high probability.

In a recent colloquium, Dr. Dibyendu Roy from the Raman Research Institute along with international collaborators has discussed the topic of photons interacting strongly when confined to a one-dimensional geometry from experimental and theoretical perspectives.

To know more about this new exciting research field, please visit

https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.89.021001

Colloquim_1Dphotons

Figure caption: A superconducting qubit (indicated in orange) embedded in a one dimensional transmission line waveguide. The waveguide confines light to deeply sub-wavelength dimensions in the transverse direction.

‘Organic’ material set to make solar energy truly ‘green’

IGs - Part 9 (1)_0Illustrations: Purabi Deshpande

Scientists believe that inorganic semiconductors used in making solar cells may have hit the efficiency ceiling besides being environment hazard.

In my opinion, silicon technology has reached a sort of limit regarding efficiency. It is around 20% efficient right now, but it hasn’t seen a huge leap in efficiency in a long time. Production of electronic grade silicon pollutes the environment significantly and manufacturing silicon wafers indigenously on a large scale is still a challenge,” says Prof. Sandeep Kumar, of the Raman Research Institute (RRI), Bangalore, who specializes in Soft Condensed Matter. 

Going ‘organic’ is the alternative, says Prof. Kumar, who along with his team of researchers, is studying the use of organic materials like polymers or carbon fullerenes in solar cells. “Organic photovoltaic (OPV) research has received a good momentum in the past decade as promising sources of alternative energy due to their low cost, ease of fabrication, roll-to-roll processing, flexibility, and lightweight, he says.

Traditionally, inorganic semiconductors like silicon and its alloys have been used in making solar cells due to their appropriate electrical properties and wide availability. In addition to being an environmental hazard, some scientists believe that silicon-based solar cells may have also hit the efficiency ceiling. The power conversion efficiency (PCE) of OPV’s has crossed the 10% mark and is increasing day by day”, he explains.

In a recently published study, Prof. Kumar of the Raman Research Institute in collaboration with researchers at the Center of Material Sciences, University of Allahabad, and National Physical Laboratory, New Delhi, have used indigenously developed Discotic Liquid Crystals (DLC) to build effective organic solar cells that could become an eco-friendly alternative to conventional solar cells. This study was funded by the Department of Electronics and Information Technology (DEITY) and published in the Liquid Crystals Journal.

“DLCs were discovered at the Raman Research Institute in 1977. They are of fundamental importance not only as models for the study of energy and charge migration in self-organized systems but also as functional materials for device applications such as one-dimensional conductors, photoconductors, light emitting diodes, photovoltaic solar cells, field-effect transistors and gas sensors”, remarks Prof. Kumar.

DLCs are made of stacks of disc-like molecules in a state of matter that lies between those of a liquid and a solid crystal, like powdered sugar, which is made of solid crystals, but collectively behaves like a liquid taking the shape of the vessel in which it is stored.  Earlier studies have shown that DLCs efficiently conduct electricity along their length with very little loss, effectively making them molecular wires.   In this study, the researchers have used DLCs in solar cells to increase their efficiency.

The world is witnessing a shift in its primary energy sources, with fossil fuels giving way to renewable sources like solar and wind. India is well along this line of transformation with 10GW of electricity currently produced from solar energy, compared to just 2.6 GW in 2014. This shift to solar energy across the world has revived the solar cell (also known as the photovoltaic cell) industries, and now increased investments pour into this sector.

A solar cell, in principle, converts the energy of light falling on it, into electricity. The light conversion in OPV cells is based on charge generation at the interface between two different organic semiconductors, followed by their separation and migration toward opposite electrodes. The researchers of the study sandwiched a layer of DLC between an active layer (PCDTBT and PCBM) and a molybdenum trioxide buffer layer.

“We have explored the use of DLC as an additive in classical organic photovoltaic cells and observed significant improvement in conversion efficiency from 1.24% to 5.14%. The enhancement is attributed to the better charge mobility in the ordered system due to the presence of columnar phase of the DLC”, exclaims Prof. Kumar.

Although solar is hailed as a ‘green’ energy source, the mining and the manufacturing process associated with silicon based solar cells releases large amounts of pollutants, overshadowing the eco-friendly status of solar power. Organic solar cells, on the other hand, overcome these shortcomings and with studies like this, they may soon surpass the efficiency of silicon-based cells, finally providing us a true ‘green’ source of power.

RRI at the India International Science Festival, IISF 2017

The third edition of the India International Science Festival (IISF, 2017), jointly organized by the Ministry of science and technology, Ministry of Earth sciences and Vijnana Bharati was held between 13-16 October at Anna University, IIT and CSIR-CLRI campus in Chennai. IISF is one of the largest outreach events of its kind and showcases achievements in Indian science to the general public. One of the many events at IISF 2017 was a “Mega Science and Technology Expo: theme based pavilions in Engineering, Water, Healthcare, Agriculture, Environment, Strategic Sectors, etc”.

Raman Research Institute participated in this expo with an eye catching pavilion that had the shape of the antenna element that forms the International MWA Radio Telescope array in Western Australia, in which RRI has been a partner for the last decade and for which RRI built the digital receivers. For the benefit of visitors we had an explanatory “Why does the RRI stall have this weird shape?” at the entrance to our pavilion.

Our pavilion included posters highlighting the research achievements at our Institute this past year as well as models of a radio telescope, antenna and detectors. We also had a screen that constantly replayed images of the Milky way galaxy and distant universe at a range of frequencies from Gamma rays down to radio frequencies. Incidentally the image of the radio sky that was part of the slide show resulted from the sky survey using the MWA telescope.

The posters discussed (i) Cold Atoms – A chill cocktail of atoms and ions at near absolute zero temperatures (ii) Theoretical Physics – “Understanding the Universe – One equation at a time” (iii) Two posters on Theoretical Astrophysics – “Understanding the Dynamic Universe” (iv) Two posters on Radio Astronomy – “Seeing the Unseen” (v) Quantum Key Distribution – “A new security paradigm” (vi) POLIX: X-ray vision – “India’s own eye in the sky” (vii) Liquid crystals – “The fourth state of matter”. Apart from the above we also had posters that gave an overview of our Institute along with posters on the Knowledge Communication we do – PhD, postdoc, visiting student and research assistants programmes.

Over the course of the four days more than five thousand people from all walks of life – high-school students, undergraduates, graduates, PhD students, academics from the scientific fraternity, Ministry officials and also the general public visited our pavilion. A few elderly visitors were very interested in the shape of the pavilion as well as the science and with childlike enthusiasm bombarded us with questions and gently asked us if we could give our answers in the local vernacular. The same was the request from many school students who had made the trip to Chennai from remote locations in this vast country of ours. For many it was their first experience to any event of this kind and we hope they returned with positive memories and a good appreciation for science in general and our Institute’s research in particular. It is worth noting that a few alumni of our institute also visited us and appreciated our efforts.

The pavilion was ably managed by our PhD students Rishab Chatterjee (LAMP), Sagar Suthradhar (LAMP) and our visiting student Urvashi Nakul (AA). The interactions were not limited to questions and answers but to in depth scientific discussions with PhD students from other institutes. Needless to say, there was never a dull moment and everyone involved came back richer from the experience. We hope to continue such public engagements in the years to come.

International Science School at University of Sydney (Australia) for senior school students

ISS2017photoFor the sixth time in a row Indian senior high school students had a chance to participate in the Professor Harry Messel International Science School (ISS for short) at the University of Sydney in Australia. Talented science students from eight countries (that included Australia, China, India, Japan, New Zealand, Thailand, United Kingdom and United States, each of whom won a University of Sydney Physics Foundation scholarship) attended the 2-week lectures and activities event at the ISS2017, as it is popularly referred to. The awarded scholarship completely covers the entire 2 weeks of the Science School for each of the students.

“Future Power” was the theme this time, covering a wide array of fields that included Fusion, Fission, solar power, wave power, power from biogas, electricity grids and storage devices apart from most current research efforts and out-of-the-box thinking in fields of materials science tackling energy-related problems being faced today. The one word that comes to mind when describing the ISS is “quality”. Whether it is do with the lectures, the hands-on activities, the engineering challenges, the design and planning of the entire 2-weeks of the science school or the local arrangements, there is satisfaction all round, with any mishaps or problems that arise each day (of which there are several!) handled in a sensitive and satisfying manner. Experts in the particular fields from around the world give the lectures. Pitched at 1st or 2nd year undergraduate level the students are drawn into the beauty and intricacies of the subject areas, which this time (given the ISS theme of Future Power) also included a multi-disciplinary fare of policy and social as well as environmental considerations.

To give a background to India’s participation in this, one of the oldest of international science schools (since 1962), the journey began in 2007 when Indian students participated in the Sydney International Science School for the first time. Raman Research Institute, upon request from the University of Sydney School of Physics, agreed to facilitate the selection.

This year, the sixth year of participation for Indian students, was a particularly memorable one with one of the students, Poorvi Hebbar, having been chosen for the top and coveted Len Basser award for Science Leadership at the science school (as did Nruthya Madappa, the very first time that Indian students participated in 2007).

The Australian Minister for Industry, Innovation and Science lauded the Indian participant saying:“Poorvi Hebbar, attending from India, was selected from the 132 high-performing senior science students at the school. The students, including five Indigenous students, come from schools from all states and territories who have been joined by 46 from China, India, Japan, New Zealand, Thailand, the UK and the USA. She has been described as being a quiet achiever, who is diligent and very innovative in her ideas, always showing great interest in the lectures and activities and easily and openly sharing her knowledge and enthusiasm, inspiring her peers and drawing their respect.”

As many as 30 talented Indian students have been to the Sydney International Science School over the years, facilitated by the Raman Research Institute. The themes of the past six ISS that were attended by Indian students have covered topics such as Ecoscience, Light and Matter, From Genes to Galaxies, Nanoscience, BIG: Big ideas, big experiments, big challenges — big science.

No doubt the next ISS to be held in 2019 will be eagerly awaited.  It is going to cover humanity’s adventures in space and promises to once again thrill and fire the imagination of the those lucky few who will be there!