Using their astute sensory lens, the human eye, our ancestors mapped the stars by collecting light being scattered through the earth's atmosphere beholding stories of our universe's past. That's long before Galileo improvised his own version of the refraction telescope to stare at the moons of Jupiter and even longer before Hertz's experiments in the late 1800s in which he ricocheted radio waves off metallic objects. Manipulating light is a skill that scientists and others alike continuously aim to improve. The immense task of controlling electromagnetic (EM) waves in the macroscopic or sub nano world is key to fields ranging from biomedical imaging to quantum physics to astronomy. Then and today, the quality of an image, whether it depicts the outer appearance, an inner process, or the composition of an object, relies on the accuracy of the information gathered which is to say the efficacy of its collection.

Presently, material scientists are able to produce and manufacture optical devices such as lenses, filters, or mirrors which can control, amongst other properties, the frequency of light that is reflected, transmitted, and focused by the composite medium. These properties are explicitly dependent not only on the lens's shape and size but their physical makeup; often characterized for each material by its index of refraction. This index governs a material's ability to absorb, scatter, and amplify light as it travels within an object. These materials are frequently implemented monolithically within technology such as transistors and lasers in order to choose which frequency is processed in the device at hand. Having low absorption or gain in these structures is extremely important for effective collection of the light for eventual image processing.

Promising materials with a negative index of refraction have shown that you could provide an optical device that supplies a perfectly resolved image as light travels through it. This means that all the light will be collected and focused. This is done by simply aligning 2 identical materials of equal yet opposite signs of refractive index which thus yields an optical path length of zero[1]. The process includes the focusing of so-called evanescent waves which would normally rapidly decay after passing the intersection between two positively indexed mediums. In the past, the biggest obstacle in realizing such a device was the ability to reduce the absorption. Systems demonstrating low to zero absorption along with a negative index of refraction are now feasible and available in abundance within the infrared frequency range. More recently metamaterials such as the well-studied fishnet structures[2] or even dense atomic gases[3,4] have shown the potential to amplify the propagating EM field in order to create an enhanced image by using, for example, the chiral properties of materials in which the magnetic component of a propagating wave could manipulate the electric component or vice versa in order to subtly adjust the index of refraction.

So why is this useful? Let's consider for instance a doctor is performing extraction surgery on cancer cells in part of the body. In principle, the imaging device will be able to illuminate the particular frequency of light scattered from the harmful cancer cells while dulling those from healthy normal cells[5]. This is indeed being done today in the operating room, but imagine a medium which could be tuned in order to amplify, reflect, or transmit those scattered frequencies while producing a perfectly resolved image from the light collected. This would greatly increase the efficiency of the surgery not only by removing the cancer but reducing the time for which the patient is under anesthesia. The ability to tune a lens with a negative index of refraction in the optical range of wavelengths is being foreseen in the near future. Advancements in various chiral, metamaterial structures such as the aforementioned fishnet, dense gas or even U-shaped resonators[6] allow us to now manipulate light between positive and negative indices of refraction as well as the active (gain) or passive (absorbing) regimes. This added control will hopefully soon bring us fuller images with more detailed information of the object we aim to view from the inside or out.

[1] V. M. Shalaev, Nature Photonics 1, 41-48 (2007)

[2] S. Wuestner, A. Pusch, K. L. Tsakmakidis, J. M. Hamm, and O. Hess, Physical Review Letters 105, 127401 (2010)

[3] P. P. Orth, R. Henning, C. H. Keital, and J. Evers, New J. Phys. 15 013027 (2013).

[4] F. Bello, Physical Review A 84, 013803 (2011)

[5] M. Fink and M. Tanter, Physics Today, 28-33, (February 2010)

[6] D. R. Smith, W. J. Padilla, D. C. Vier, S. C. Nemat-Nasser, and S. Schultz, Physical Review Letters 84, 4184 (2000)