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Topic Name: Bath physicists' discovery about harnessing light makes new sub-branch of photonics
Category: Photonics
Research persons: Dr Fetah Benabid
Location: University of Bath, United Kingdom
Details
A discovery of a new way to manipulate light a million times more efficiently than before is announced in the journal Science this week.
Using a special hollow-core photonic crystal fibre, a team at the University of Bath,
UK, has opened the door to what could prove to be a new sub-branch of photonics, the science of light guidance and trapping.
The team, led by Dr Fetah Benabid, reports on the discovery, which relates to the emerging attotechnology, the ability to send out pulses of light that last only an attosecond, a billion billionth of a second.
These pulses are so brief that they allow researchers to more accurately measure the movement of sub-atomic particles such as the electron, the tiny negatively-charged entity which moves outside the nucleus of an atom. Attosecond technology may throw light, literally, upon the strange quantum world where such particles have no definite position,only probable locations.
To make attosecond pulses, researchers create a broad spectrum of light from visible wavelengths to x-rays through an inert gas. This normally requires a gigawatt of power, which puts the technique beyond any commercial or industrial use.
But Dr Benabid’s team used a photonic crystal fibre (pcf), the width of a human hair, which traps light and the gas together in an efficient way. Until now the spectrum produced by photonic crystal fibre has been too narrow for use in attosecond technology, but the team have now produced a broad spectrum, using what is called a Kagomé lattice, using about a millionth of the power used by non-pcf methods.
“This new way of using photonic crystal fibre has meant that the goal of attosecond technology is much closer," said Dr Benabid, of the University of Bath’s Department of Physics, who worked with students Mr Francois Couny and Mr Phil Light, and with Dr John Roberts of the Technical
University of Denmark and Dr Michael Raymer of the
University of Oregon, USA.
“The greatly reduced cost and size of producing these phenomenally short and powerful pulses makes exploring matter at an even smaller detail a realistic prospect.”
Dr Benabid’s team has not only made an important step in applied physics, but has contributed to the theory of photonics too. The effectiveness of photonic crystal fibre has lain so far in its exploitation of what is called photonic band gap, which stops photons of light from “existing” in the fibre cladding and enabled them to be trapped in the inside core of the fibre.
Instead, the team makes use of the fact that light can exist in different ‘modes’ without strongly interacting. This creates a situation whereby light can be trapped inside the fibre core without the need of photonic bandgap. Physicists call these modes bound states within a continuum.
The existence of these bound states between photons was predicted at the beginning of quantum mechanics in the 1930s, but this is the first time it has been noted in reality, and marks a theoretical breakthrough.
Note For Photonic-crystal fiber
Photonic-crystal fiber (PCF), also spelled fibre, is a new class of optical fiber based on the properties of photonic crystals. Because of its ability to confine light in hollow cores or with confinement characteristics not possible in conventional optical fiber, PCF is now finding applications in fiber-optic communications, fiber lasers, nonlinear devices, high-power transmission, highly sensitive gas sensors, and other areas. The term "photonic-crystal fiber" was coined by Philip Russell in 1995-1997 (he states (2003) that the idea dates to unpublished work in 1991), although other terms such as microstructured fiber are also used and the nomenclature in the field is not entirely consistent. More specific categories of PCF include photonic-bandgap fiber (PCFs that confine light by band gap effects), holey fiber (PCFs using air holes in their cross-sections), hole-assisted fiber (PCFs guiding light by a conventional higher-index core modified by the presence of air holes), and Bragg fiber (photonic-bandgap fiber formed by concentric rings of multilayer film).
In general, such fibers have a cross-section (normally uniform along the fiber length) microstructured from two or more materials, most commonly arranged periodically over much of the cross-section, usually as a "cladding" surrounding a core (or several cores) where light is confined.
Note for Inert gas
An inert gas is any gas that is not reactive under normal circumstances. Unlike the noble gases an inert gas is not necessarily elemental and are often molecular gases. Like the noble gases the tendency for non-reactivity is due to the valence, the outermost electron shell, being complete in all the inert gases. This is a tendency, not a rule, as noble gases and other "inert" gases can react to form compounds.
Although the term "rare gases" is sometimes used as a synonym for the elemental inert gases, i.e. noble gases—they are only rare relative to other gases found in Earth's atmosphere (i.e. air) with the exception of argon which makes up a significant portion of air, around %0.934; hardly rare at all. Because of their unreactivity, and perhaps their relative scarcity, the inert gases were not discovered until helium was discovered to exist in the Sun, where it is abundant, before it was discovered to exist in Earth's atmosphere. This is possible through the analysis of spectral lines.
Helium and neon are the only true elemental inert gases, because they do not form any (known) true chemical compounds, unlike the heavier noble gases (argon, krypton, xenon and radon).
In marine applications, inert gas refers to gases with a low content of oxygen that are used to fill void spaces in and around tanks for explosion protection. There are two types of inert gas which are either based on nitrogen or on flue gas.
About Researcher
Dr. Fetah Benabid
Telephone
+44 (0)1225 38 6307
Email
pysab@bath.ac.uk
Research Interests
Gas-Laser Devices
Fetah Benabid is an EPSRC Advanced Fellow and Lecturer. He did his PhD at the University of Western Australia on high precision optical metrology of sapphire-based components for interferometric gravitational wave detectors. He has been at the University of Bath since 2001. He has developed new fabrication techniques for hollow core photonic crystal fibre (HC-PCF), enabling the production of HC-PCF with a very high air-filling fraction whilst keeping its structural integrity.
He has been a pioneer in incorporating these fibres into scientific and technological applications, which includes the demonstration of stimulated Raman scattering (SRS) in hydrogen filled HC-PCF with pump powers one million times lower than those required using conventional techniques. He was at the forefront in demonstrating electromagnetically-induced transparency (EIT) in molecular gases such as acetylene. More recently he has developed a novel technology capable of fabricating compact and all-fibre integrable HC-PCF based gas cells, with which he has demonstrated a number of quantum and nonlinear effects.
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