Light Beyond. Luz más allá de 2015

By Ana María Cetto and María Teresa Josefina Pérez de Celis Herrero

El Año Internacional de la Luz y las Tecnologías Basadas en Luz 2015 fue una iniciativa global adoptada por las Naciones Unidas. Numerosas organizaciones culturales, académicas, industriales y gubernamentales alrededor del mundo unieron fuerzas para celebrar la luz y crear conciencia sobre las muchas maneras en que la fotónica impacta nuestras vidas en áreas como la energía, educación, cambio climático, salud y bienestar social. De la iniciativa resultaron miles de actividades que involucraron a millones de personas en más de 100 países del mundo. Los temas de este volumen surgieron a lo largo de 2015 como los más relevantes y con mayor interés. Se espera que este libro se convierta en un documento de consulta básica y un legado imborrable.

• Language: English
• Publisher: UNAM, Dirección General de Publicaciones y Fomento Editorial
• Release date: May 26, 2020
• ISBN: 9786070298608

Book preview

Esta obra se realizó con el apoyo financiero de las siguientes instituciones:

COLECCIÓN HETERODOXOS

Dirección General de Publicaciones y Fomento Editorial

Ana María Cetto

María Teresa Josefina Pérez de Celis Herrero

EDITORAS

Universidad Nacional Autónoma de México

México 2017

Indice

Preface

Prefacio

Ana María Cetto, María Teresa Josefina Pérez de Celis Herrero

Introduction

Introdución

Enrique Graue Wiechers

Foreword

Prólogo

Irina Bokova

A better world with light

Un mundo mejor con luz

John Dudley

On IYL 2015: quotation

IYL 2015: mensaje

Ban Ki-moon

An Introduction

Una introducción

Rolando Zapata Bello

Research in optics and photonics Shaping human destiny

Investigación en óptica y fotónica: Moldear el destino humano

Tuan Vo-Dinh

Biophotonics: Light for life

Biofotónica: luz para la vida

Rainer A. Leitgeb, Peter E. Andersen (editors), Jürgen Popp, Katarina Svanberg, Nimmi Ramanujam

New sources of light for research and applications

Nuevas fuentes de luz para la investigación y aplicaciones

Luis E. Zapata, Caterina Biscari, Gastón García, Ana Belén Martínez, Salvador Ferrer, Inmaculada Ramos, Gihan Kamel, Sekazi K. Mtingwa

The invention of high-effi ciency blue LEDs and future solid-state lighting devices

La invención de un LED azul de alta eficiencia y la futura iluminación de estado sólido

Shuji Nakamura

The history of the universe from its beginning to its end: Where did we come from, and where can we go?

La historia del universo de principio a fin: ¿de dónde venimos y hacia dónde podemos ir?

John Mather

A plea for dark skies

En defensa de un cielo oscuro

Silvia Torres-Peimbert

Archeoastronomy: Recreating the sky of the past through its light

Arqueoastronomía: la recuperación del cielo del pasado a través de su luz

Jesús Galindo Trejo, Stanislaw Iwaniszewski

Ptolemy, Ibn al-Haytham, and Al-Fārisī: The beginnings of quantitative research in optics

Ptolomeo, Ibn al-Haytham y al-Fārisī: los comienzos de la investigación cuantitativa en óptica

Roshdi Rashed

Harvesting solar energy

La captación de energía solar

Jesús Antonio del Río Portilla

Light for all

Luz para todos

Beth Taylor, Jorge Ávila Treviño, Olivia Otieno, Rodrigo Limón Chávez

Global education in optics: A case of success

Educación mundial en óptica: un caso de éxito

Joe Niemela

Outreach through light: A major legacy of the International Year of Light

Divulgación por medio de la luz: un legado fundamental del Año Internacional de la Luz

Ana María Cetto, Jorge Rivero González, John M. Dudley, Hanan Dowidar, Ahmed Salim

Light and the city: Social experience in the collective imagination

Luz y ciudad: la experiencia social en el imaginario colectivo

Gustavo Avilés

Evanescence: Orchestration of light to mutate through time

Evanescencia: orquestación de la luz para que mute en el tiempo

Henry Plummer

In medias res: Light in fine arts

In media res: la luz en las bellas artes

Bettina Pelz

Light and cultural heritage

La luz y el patrimonio cultural

José Luis Ruvalcaba Sil

About the authors

Sobre los autores

Aviso legal

p. 10 | The Thin Blue Line. Image Credit: NASA (Photo courtesy of: IYL 015/Light beyond the bulb).

Preface

While celebrating the closing of the International Year of Light (IYL) 2015 in early 2016, it became clear that a year of intense and fruitful activities at the local, national, and international levels had not been sufficient to exhaust the subject of light. On the contrary, IYL 015 served to awaken public interest worldwide and highlight the many topical aspects that deserve to be addressed further. This motivated us to create a list of topics that we believe are worthy of a closer look and to invite a select group of authors to do so from the perspectives of their specialties. We are aware that this list is not exhaustive and that other topics could be identified that would lead to a different publication.

We are very grateful for our collaborators’ excellent response: their voluntary, timely, and generous contributions to this volume. The result of this collective effort can be summarized by listing the following messages, each of which is significant in itself but which have special strength together:

Light belongs to all and is for everyone,

yet there are millions of humans who cannot access it when they need it.

Light from the skies reveals the history of the universe to us, showingus our place within it and where we are headed,

yet light-pollution from cities no longer allows us to see our own galaxy.

Three and a half centuries after the discovery of cells using an optical microscope,

laser microscopes now allow us to see isolated molecules andto measure the forces between them.

One hundred and twenty five years after the first working incandescent lightbulb was lit,

light-emitting diode (led) lamps, which are 30 times more efficient, produce light with customized intensity and color.

The quantum theory of light revolutionized physics in the 20th century,

and it has changed how we conceive of and understand nature.

Light has been central to the history of painting, from primitive artto the present day,

and now, light-based techniques allow us to better understandthis history.

Sunlight is the primary source of energy and life on our planet,

but we have not yet learned to use it sustainably.

The movement of the Sun and other celestial bodies has been followed by people since antiquity,

as evidenced by humanity’s rich archaeological and cultural heritage.

One hundred and twenty five years after the first wireless telegraphwas developed,

an extensive radio and fiber optic communications network envelopsthe planet.

One hundred and twenty-years after the discovery of X-rays,

increasingly powerful radiation sources are being developedto interrogate nature and create new materials.

Barely six decades after the invention of lasers,

the combination of optical and photonic techniques in medicinehas begun to revolutionize the processes of diagnosis, therapy,and surgery.

Light in the hands of talented architects expresses and enhancesthe quality of spaces,

connecting us to both the natural world and that of the built environment.

Explanations of light-based phenomena awaken the curiosity of young and old,

bringing them closer to the world of science.

Since ancient times, the phenomenon of light has puzzled humanity,

and thinkers and scientists from all periods and cultures have contributed to revealing its secrets.

Research and development in optics and photonics are occurring rapidly

and contribute to flourishing industries through their applications.

The 20th entury is known as the century of electronics becauseof the impact of electronics on our lives and the economy;

likewise, we now live in the century of photonics.

Light and its associated technologies can become powerful toolsfor sustainable development,

and thus, it is important that we all collaborate in their promotionand development.

It is a privilege to have this compendium of valuable specialist contributions be accompanied by introductory messages from selected personalities, and we extend special thanks to them for their collaboration: Ban Ki-moon, Irina Bokova, Rolando Zapata Bello, and Enrique Graue Wiechers. Likewise, we thank John Dudley not only for his introductory summary but also for his loyal support, always generous and timely.

For providing resources to finance the production and publication of this work, we are grateful to, Secretaría de Investigación, Innovación y Educación Superior de Yucatán; IYL 015 Global Secretariat; Consejo Nacional de Ciencia y Tecnología; Coordinación de la Investigación Científica, unam; Dirección General de Publicaciones y Fomento Editorial, unam, and finally, The International Society for Optics and Photonics (spie).

We also express sincere thanks to Taller de comunicación gráfica, for their fine work regarding the editorial design, typography, and printing of this work.

Lastly, we are pleased to mention the support received from the Instituto de Física de la unam, and that received from Dirección General de Divulgación de la Ciencia de la unam. This support made it possible for us to conduct our work.

Because of the support of all our collaborators and friends, the production of this volume was a rewarding enterprise for us. We hope that delving into its pages will be equally rewarding for you, dear reader.

Ana María Cetto

María Teresa Josefina Pérez de Celis Herrero

EDITORS

Mexico City, October 2016

Introduction

The United Nations named 2015 the International Year of Light (IYL 015) with the aim of spreading knowledge of the importance of light in everyday life, scientific progress, and society’s future and to promote sustainable development using light-based technologies; raise awareness of light pollution; enhance international cooperation; and highlight the relationship that exists among light, art, and culture. To this end, more than 13,000 scientific, educational, and cultural activities occurred in 147 different countries, reflecting the success of these 12 months of work and reflection.

Why make light the subject of a whole year? Why raise awareness of its importance internationally? The answer is simple: Light is origin and destination. Life as we know it would be impossible without the luminous activity of our Sun; without it, plant life and the animal kingdom would not exist. It is difficult to imagine the evolution of human beings without the ability to visualize our environment or the ability to exploit the opportunities that light provides for us. Indeed, the luminous phenomenon is present in almost all religious beliefs and, certainly, in all areas of knowledge.

The science of light and its applications has enabled the development of industry and civilization, and the electronics and telecommunications revolution was born in the last third of the 20th entury. Our destiny also lies in light: Clean energy is the promise of the new industrial revolution of the 21st entury. Light is a global tool, and therefore, the opportunities and problems that derive from it must be managed globally.

IYL 015 has been a powerful communication and education strategy that has chartered the way for knowledge to reach all countries, allowing all to reap the benefits of light-based technology through international cooperation.

IYL 015 has also been a reminder of the great inequalities that persist in our world: 1.1 billion people on the planet have no access to electricity, and most of them rely on kerosene to light their lives. Inhaling this smoke kills 1.5 million people a year. Furthermore, 56% of the world’s population has no access to the Internet¹. In other words, more than four billion people lack this necessary tool and, thus, are unable to access knowledge.

Although it is true that these indices have improved, the existence of such a large number of people without access to electricity and modern technologies is a very sobering reality that serves to further social inequality and isolate people from the global environment.

In addition, the important problem of light pollution requires our urgent attention. Light pollution is a recent phenomenon that has been increasing with industrialization, urban growth, and expanding public lighting. The negative effects of this type of environmental threat remain inadequately studied, but it is known with certainty that light pollution affects indigenous peoples’ cultures and harms nocturnal ecosystems and astronomical research.

Therefore, it is clear that efforts must be focused on developing new technologies and renewable energy. This type of energy is obtained from natural sources, such as sunlight, and is part of the solution for both reducing greenhouse gas emissions and ensuring universal access to affordable energy services that are safe and modern.

Science education must keep pace with these technological advances, as it is the key to integrating science into our culture and making it a way of life. This point emphasizes the importance of the book Light Beyond 2015. Its chapters are a reminder of the goals of IYL 015, the progress we have made, the challenges that remain, and the results that could be achieved if we continue to focus our efforts on light-based technologies. Indeed, if, after reading this book, the readers are enthused about the technological advances being developed and aware of the inalienable right that light and its impact and importance in all areas represents, then this book, and IYL 015, will have been successful.

Enrique Graue Wiechers

RECTOR OF THE UNAM

---

1 https://www.itu.int/en/ITU-D/Statistics/Documents/publications/misr2015/MISR2015-ES-S.pdf

pp. 16–17 | Noctilucent Clouds Santa Barbara, California. Image Credit: NASA (Photo courtesy of: IYL 015/Light beyond the bulb).

Foreword

Because of its role in photosynthesis, light is at the origin of life itself. By means of ground-breaking discoveries in the applied sciences, light has continuously revolutionized human society through the ages. The International Year of Light and Light-based Technologies 2015 (IYL 015) was proclaimed by the United Nations General Assembly to recognize the centrality of light to humanity. Guided by the United Nations Educational, Scientific and Cultural Organization (UNESCO), this International Year was a special opportunity to highlight the power of optical technologies for positive change.

This spirit underpins this book, Light Beyond 2015, resonating with the objectives set forth in the 2030 Agenda for Sustainable Development and the Paris Agreement for Climate Change. Light and light-based technologies are essential to crafting new paths to sustainable development, deepening inclusion, and promoting equality and human rights. From food security and water purification to the fight against diseases and light pollution, light-based technologies offer cost-effective solutions and new perspectives on a better future for all. The vast potential of light industries opens wide horizons for eradicating poverty, combatting illiteracy, and advancing quality education.

Light Beyond 2015 emonstrates that light could be an essential generator of clean and renewable energy. Light-emitting diodes, for instance, will play a vital role in decreasing energy consumption. Additionally, their industrial application will reduce environmental pollution and enable some 1.5 billion people who currently use kerosene lamps or candles after sunset to enjoy prolonged time for reading and studying.

The power of light is woven into the fabric of all cultures. Light enhances quality of life and provides a source of inspiration, nourishing cultural diversity. Examples abound from all regions of the world. In pre-Columbian cultures, light from the sun was associated with life and rebirth. Koreans light thousands of lanterns annually to celebrate the birth of Buddha. The aesthetics of Kente cloth are imbued with color symbolism from the Ashanti culture. In this new era, technology is creating vast opportunities for artists to explore the potential of light in visual arts.

The Chinese philosopher Confucius once said, It is better to light one small candle than to curse the darkness. Through our combined efforts to share the power of light, I am confident that we can deepen sustainability for the benefit of all and lay the foundations for more inclusive, knowledge-based societies. This was the message of IYL 015, and this is our message today.

Irina Bokova

DIRECTOR-GENERAL OF UNESCO

A better world with light

People throughout the world and across history have always attached great importance to light. We see this in universal symbolism, myths and legends, and the many practical applications that have shaped society. It was in recognition of the importance of light in so many areas of life that the United Nations (UN) proclaimed the year 2015 as the International Year of Light and Light-based Technologies (IYL 015), and the last 12 months have seen unparalleled international cooperation to promote activities in outreach and education around the theme of light in its broadest sense.

The year kicked off with Ban Ki-moon’s proclamation Let there be a Year of Light at the Opening Ceremony in Paris in January 2015, and when reviewing the events that have taken place since, we can be immensely proud of what we have achieved together. IYL 015 involved a total of 13,168 activities of various types reaching 147 countries on all continents, including Antarctica. Specific events (e.g., outreach and conferences) were conducted in 129 countries, and a further 18 countries issued commemorative stamps or coins or provided support in other ways (e.g., through political support at the UN Educational, Scientific, and Cultural Organization [UNESCO] or UN).

Activities took diverse forms, including multiday scientific conferences; light-themed exhibitions and festivals; one-day conferences and special events; events linking light, art, and music; activities in schools; citizen science; and open days. Events were targeted at all levels, from preschool children learning science for the first time to politicians and diplomats attending high-level meetings on the importance of technology for the future.

It is extremely difficult to accurately estimate the audience reached by an International Year, but if we include participants in specific activities and those potentially reached by media and television, then estimates are well into the hundreds of millions. In addition, searching media databases in multiple languages returned over 23,000 media mentions of the Year of Light, reflecting the efforts by the IYL 015 community to publicize widely the importance of light and its applications to the public at large.

A particular feature of IYL 015 was the extremely broad support it received from all sectors, including, in some countries, high-level endorsement or patronage from royalty or the government. The partnerships were very diverse, including academic and industry organizations, nongovernmental organizations (NGOs), and the relatively new category of very effective social entrepreneurs. Twenty-six countries issued commemorative stamps or coins, over 100 videos were produced to promote various aspects of light and its applications, and the cultural dimension of light inspired more than five original musical compositions.

Part of the reason for the broad appeal of this particular international year was the fact that light and lighting impact our lives in ways that are important and topical from societal and political perspectives. The world shared many shocking moments during 2015, with concerns being dominated by extremist violence, growing inequality and poverty, natural disasters, epidemics, and climate change. However, 2015 also saw signs of real optimism, with the adoption of the UN Sustainable Development Goals, and the agreement reached at the Paris Climate Conference COP21, which showed that the nations of the world can come together to address critical issues that affect us all. We also observed many examples of the symbolic power of light. From the celebration of the UN’s 70th nniversary by illuminating 300 monuments around the world to the Night of Heritage Light organized by SLL that illuminated UNESCO World Heritage Sites across the UK, light and lighting have been used to unite people worldwide.

IYL 015 forged many new links and collaborations between decision makers, industry leaders, scientists, artists, social businesses, NGOs, and the public at large. After the success of our work in 2015, our challenge now is to ensure that the partnerships established for IYL 015 will continue to develop. To this end, one important aspect of the IYL 015 official Closing Ceremony in Mexico on February 4–6, 2016, was the consideration of concrete legacy actions for the future. Some examples are already firmly on the table: improved coordination in outreach and science education through expanded regional hubs, such as the European Centres for Outreach in Photonics; continued support for initiatives promoting the economic importance of light-based technologies, such as Photonics 21 (Europe), the Photonics Initiative of South Africa, and the National Photonics Initiative (US); increased awareness-­raising regarding the scientific heritage of Ibn al-Haytham through a wide range of educational materials developed for IYL 2015 and the creation of an Ibn al-Haytham International Society; the expansion of UNESCO’s Active Learning in Optics and Photonics programme; and the promotion of solar energy solutions and light poverty issues in the multi-partner Power for All initiative.

The many different sectors involved in light science and its applications have demonstrated what they can achieve when working together, and the foundations are now in place for continued development that will build a better world for us all tomorrow.

John Dudley

PROFESSOR AT THE UNVERSITÉ DE FRANCHE-COMTÉ

PRESIDENT OF THE STEERING COMMITTEE OF THE IYL 2015

On IYL 2015: quotation

From the dawn of our history, humanity has been fascinated by light. Its magic and beauty have inspired poems, music, and art. And with this International Year, we have celebrated our global efforts to understand light and harness its potential. Light is the driver of photosynthesis and the main source of energy for most living creatures. It holds the key to major advances in medicine, engineering, and communications. By celebrating light, this International Year has celebrated life.

This Year has shown how the science of light, photonics, and related technologies can promote sustainable development in many fields, including climate change and energy, agriculture, health, and education. Light, in all its applications, will be essential to advance the 2030 Agenda for Sustainable Development, as well as the objectives of the Paris Agreement on climate change.

The International Year has catalyzed and strengthened partnerships between the public and private sectors and among civil society and academic institutions. I thank UNESCO and all its partners, as well as the Steering Committee, for their commitment to this International Year. The efforts under this initiative to foster education and communication on this theme have lit a beacon to illuminate our future.

Ban Ki-moon

SECRETARY-GENERAL OF THE UNITED NATIONS

pp. 22–23 | Sunrise From Space. Image Credit: NASA/JSC (Photo courtesy of: IYL 2015/Light beyond the bulb).

An Introduction

Light is a universal language. Thanks to light, we can perceive our surroundings and those who inhabit them. Light, then, has been and will continue to be a decisive factor in our development as both individuals and a society that is broad, multisectoral, and multifaceted.

Health sciences, exact sciences, arts, and all other branches of human knowledge advance on a daily basis, and with these advances, our knowledge and awareness of light grows and transforms. Today, we live in a world of unprecedented knowledge, in which technology is one of the primary foundations of human welfare. In this technological context, light has been both a symbol and a tool: a symbol, because it has always represented knowledge, mental clarity, and scientific certainty, and a tool, because its contributions to improving the quality of life for all and its potential to grow, are myriad and very clear. Therefore, we must continue to build this society of knowledge and this path of science and research.

In this sense, I believe that all who participated in the International Year of Light can walk away satisfied. Its message reached millions of people, and the contributions made to raising awareness and disseminating knowledge were undeniably impactful. Thus, we all have the privilege of reaping what we have sown. Academic institutions, international organizations, government agencies, scientific societies, and private organizations: The call to bring light, its benefits, and awareness of its use to all corners of the world is for us all.

The year 2015 was named the International Year of Light and Light-based Tech­nologies by the United Nations (UN) General Assembly and will be remembered as the year in which the international community worked to disseminate and promote progress on the subject of light.

In this book, you will find thought spoken by the most prestigious voices on the subject. Here, specialists and researchers address how light impacts not only science but also art, culture, and technology. This book will bear witness to our advances and our joint commitment to continue the progress achieved by all involved in the International Year of Light.

Finally, I would like to conclude this introduction with a personal reflection. Choosing Yucatan to host the Closing Ceremonies of the Year of Light was an honor: first, because we are a state where innovation and research are major players in the economic and social development and innovation necessary for our future, and second, because we are a land where our past remains alive and present and where the cultural and scientific influence of our past has exerted significant impacts.

The Maya were great astronomers, remarkable mathematicians, and possessed traditions that still amaze us today. They taught us that culture, arts, and science always go hand in hand and are all necessary for development. Indeed, the Maya evoke in us and all who know their achievements a feeling of deep admiration. Let us allow that admiration to become inspiration. Let us make the most of our surroundings, care for our environment, and reach our full potential. And just as we look back to the Maya today, to the researchers and scientists of past centuries, so let us fight so that our children, youth, and future generations may look back and admire what we achieved. Let 2015 have been the Year of Light for us and for the future.

Sincere thanks are due to the UN; the UN Educational, Scientific and Cultural Orga­nization (UNESCO); the Universidad Nacional Autónoma de México (National Auto­nomous University of Mexico [UNAM]), to everyone involved in creating this work, and to you, dear reader. I hope that the knowledge that this book imparts will be useful to you and those around you.

Rolando Zapata Bello

governor of yucatán

pp. 26–27 |

Introduction

Because of the exponential growth of research in optics and photonics, light-based technologies will continue to develop into one of the most vital industries in the future, making the 21st century the century of the photon. The significance and impact of photonic technologies in the 20th century have been emphasized in various reports identifying the technological and economic opportunities enabled by photonics, evaluating important trends in market needs, and discussing areas where progress in photonics innovation has translated into economic benefits¹, ². This chapter aims at providing an overview of the current status and future potential of research in optics and photonics. Specific photonic research topics and technologies are not discussed in great detail here because other sections in this monograph address these topics in depth. Instead, this chapter highlights the equal importance of basic and applied research and key photonic areas ranging from biophotonics, nanophotonics, and quantum optics to advanced materials. A glimpse is provided of the vital role of photonic research for society in areas including information technology, health, environment, security, cultural heritage, and sustainability. Finally, this chapter discusses how the inquiry into the nature of light and color perception has entered many Humanities fields and how the dual wave-particle nature of light and its basis in quantum theory have profoundly affected many fields beyond science, such as philosophy and art.

Basic research: The fundamental route

Basic scientific research, i.e., the quest for pure knowledge without a specifically foreseen practical application, is sometimes perceived as an unnecessary luxury. However, as illustrated in the following example, fundamental research in photonics led to many technologies that have changed the world. Indeed, major technological innovations with important practical uses are very often based on fundamental knowledge obtained through painstaking basic research performed many decades ago.

The enduring value of basic research

From the quantum theory of the photon to magnetic resonance imaging (MRI). Who could have foreseen that the seemingly far-fetched fundamental research in quantum theory conducted during the 20th entury would be critical to the development of a myriad of life-saving photonics technologies a century later? Indeed, with the advent of quantum theory, research in molecular spectroscopy and the development of photonic technologies (such as lasers, optical biopsy, optical tweezers, and near-field probes) have provided powerful tools for understanding the fundamental causes of illnesses, interrogating the cell at the molecular level, and fighting diseases at the genetic level. Quantum theory is one of the most important discoveries of the 20th entury and brought about a monumental paradigm shift in the scientific worldview. A series of discoveries concerning the nature of light itself brought into question the underlying reality of the Newtonian world view and set the stage for the 20th entury revolution in quantum physics launched by Albert Einstein. Einstein called these particles of light quanta after the Latin quantus or how much?), the origin of the term quantum theory. Einstein showed that light consists of neither continuous waves nor small, hard particles. Instead, it exists as bundles of wave energy called photons. Each photon has an energy that corresponds to the frequency of the waves in the bundle. In quantum theory, atoms and, indeed, all matter are not seen as physically defined entities in the physical world but rather as fuzzy clouds with a wave-particle dual nature. According to quantum theory, all objects, including subatomic particles (i.e., electrons, protons, and neutrons in the nucleus), are entities having a dual aspect and are seen sometimes as waves and sometimes as particles. The quantum theory of molecular phenomena provides a fundamental framework for molecular biology and genetics because of its unique understanding of electrons, atoms and molecules, and light itself. This scientific framework led to the discovery of the structure of deoxyribonucleic acid (

DNA

) molecules, the molecular natures of cellular machinery, and the genetic causes of diseases, all of which form the basis of molecular medicine.

Basic research in quantum theory revolutionized an important field of photonics: molecular spectroscopy. Molecular spectroscopy, a research area in which the interaction of molecules with light is studied, has been a cornerstone of the renaissance in biomedical photonics since the mid-1950s. Spectroscopy, which refers to measurements of the light intensity emitted or absorbed by molecules analyzed as a function of the wavelength (i.e., color), provides information that facilitates a deep understanding of the structures and functions of biological molecules and systems. How do we learn about the molecules that constitute cells, tissues, and organs when most of them are too small to be seen even with the most powerful microscopes? There is no simple answer to this question. However, a large amount of information related to cells, tissues, and organs has been provided by various molecular spectroscopy theories and techniques.

Today, when a patient enters a hospital for cancer screening or checks into an emergency room with chest pains or severe headaches, a diagnostic test using x-ray computed tomography (

CT

) or

MRI

ill be performed to detect possible tumors, heart attacks, or strokes. The science underlying

CT

X-ray photons) and

MRI

radio-frequency photons) is based on quantum theory. The discovery of quantum theory not only gave birth to the field of molecular spectroscopy but also led to the development of a powerful set of photonics tools for investigating the natures and understanding the causes of disease at a fundamental level. Indeed, basic research over decades has facilitated many groundbreaking medical achievements today.

Polarized Photomicrograph. Image Credit: Marek Mis (Photo courtesy of: IYL 2015/Light beyond the bulb).

The quest for ultra-brightness with hot spots and lightning rods

Plasmonics refers to the study of the enhanced electromagnetic properties of metallic structures with nanoscale dimensions. This term is derived from plasmons, the quanta (energy bundles) associated with longitudinal waves propagating in matter through the collective motion of the conduction electrons in metals. When a light beam (e.g., a laser) irradiates a metallic nanostructured surface, the electrons on the surface oscillate; these oscillations are called surface plasmons and result in large secondary local electromagnetic fields on the surface³. The surfaces of metals, such as gold and silver, sustain electron density oscillations, much like waves in the ocean. For the last few years, interest in developing and using the plasmonics-related properties of metallic nanostructures for sensing has increased. Surface plasmons have been involved in important practical sensing applications, including surface plasmon resonance (

SPR

, metal-enhanced fluorescence, and surface-enhanced Raman scattering (

SERS

). The

SPR

ethod measures minute changes in the refractive index resulting from specific biochemical activity. It can detect these changes in very small volumes near the metal surface⁴ nd, since the 1990s, has found many commercial applications in biochemical sensing devices. The use of metallic nanostructures to favorably modify fluorophores’ spectral properties has been referred to as metal-enhanced fluorescence⁵. Analogous to a lightning rod effect, secondary fields can become concentrated at high-curvature points on the roughened metal surface that act as harvesting antennas for incident light. This is the basis of the

SERS

ffect, in which the intense field concentrations greatly increase the Raman signals from adsorbed molecules, sometimes by as much as 10^¹⁵ at hot spots, which are tiny interstitial crevices in metal structures that exhibit intense local field enhancement. The

SERS

ffect provides specific fingerprints for molecular identification⁶, thereby offering some distinct advantages for rapid chemical analysis.

SERS

anoplatforms have been the subject of increasing interest in the last three decades and are now used for a myriad of applications spanning chemical analysis, environmental sensing, food safety monitoring, and medical diagnostics⁷, ⁸, ⁹. Nanohole arrays, i.e., platforms consisting of sub-wavelength holes in metals, have been used for the sensitive detection of chemical species¹⁰. In other applications, plasmonic metallic nanostructures facilitate the precise concentration of light to very small, sub-wavelength volumes and the guiding light in sub-wavelength circuits¹¹.

Unveiling and exploiting the secrets of quantum entanglement

Quantum entanglement, one of the last mysteries of quantum physics, is a physical phenomenon that occurs when pairs or groups of particles are induced to interact such that their quantum state must be described as a whole and not independently. In other words, the particles behave as if they were one entity, despite being separated by large distances. In this intimately linked (entangled) pair system, one particle somehow seems to know what measurement has been performed on the other and with what outcome, even though there is no known means of communication between the two particles. Albert Einstein, Boris Podolsky, and Nathan Rosen first debated the possibility (or impossibility) of this strange phenomenon, which is known as the

EPR

aradox¹². Nowadays, interest in fundamental research relating to quantum entanglement is increasing, and the effects of this phenomenon have been demonstrated experimentally with photons¹³, ¹⁴, electrons, and even molecules¹⁵. Light beams can be created to produce paired photons that maintain quantum entanglement over long separating distances¹⁶, ¹⁷, ¹⁸. These unique photonic quantum states of light have led to many important applications. For example, the use of entangled photons can allow remote users to communicate and exchange proprietary, private, or secret information¹⁹. Research on technologies such as quantum processors and quantum repeaters should accelerate the development of quantum computers, which use quantum-mechanical phenomena, such as superposition and entanglement, to perform operations on data²⁰, ²¹. Quantum computers are not limited to the 1s and 0s of the binary code bits used in the traditional computers but instead use qubits, which can essentially take the state of 0, 1, or a superposition of the two, enabling many simultaneous calculations and, thus, unprecedented processing power. For example, a quantum computer was used to perform a full simulation of a high-energy physics experiment: the creation of pairs of particles and their antiparticles²².

Photons traveling through a vacuum usually do not interact with each other. However, interactions can be made possible by nonlinear optical processes, which are phenomena that explain the nonlinear responses of various properties, such as the frequency, polarization, phase, or path of incident light, that usually occur in high-flux photon beams. Quantum nonlinear optics, even in low-flux regimes, can improve the performance of classical nonlinear devices, enabling fast energy-efficient optical transistors and nonlinear switches activated by single photons for optical quantum information processing and communication²³, ²⁴. Quantum information transfer using photons, often dubbed flying qubits, is an emergent technology²⁵. In this technique, the remote distribution of information can preserve the underlying quantum states, leading to applications such as quantum cryptography and the concept of the quantum Internet²⁶. Quantum information science remains an emerging field. As progress continues, developing robust and scalable systems with sufficient efficiency and fidelity of information transfer to implement error correction will be a challenge²⁷ Quantum teleportation, an idea that previously belonged to the realm of science fiction, refers to a method by which an unknown quantum state of a physical system is measured and subsequently reconstructed or reassembled at a remote location, while the physical constituents of the original system remain at the sending location²⁴, ²⁸, ²⁹. Via quantum teleportation, a quantum state can be transferred between remote physical systems through the use of quantum entanglement and classical communication techniques. Quantum teleportation is a fundamental part of quantum information science because of its critical role in important tasks, such as the long-distance transmission of quantum information using quantum repeaters, which create long-distance entanglement from shorter-distance entanglement²⁷. The combination of quantum teleportation with quantum memories can provide scalable schemes for quantum computation. The feasibility of the long-distance teleportation of single quanta of light onto a solid-state quantum memory has been demonstrated³⁰. By early 2008, the

US

had already recognized the importance of quantum science³¹, and American companies continue to actively invest in quantum computing³². More recently, the European Commission announced plans to launch a major project in quantum technology³³ to develop various technologies, such as atomic quantum clocks synchronized with the Global Positioning System for high levels of timing stability and traceability, quantum sensors capable of high sensitivity and resolution, and universal quantum computers with performance exceeding that of even the most powerful classical computers of the future³⁴. To minimize transmission path losses and noise in the detection system, researchers in South Africa have investigated advanced methods capable of recovering entanglement losses after propagation beyond an obstruction³⁵. New advances in quantum technology have been stimulated by the development of components for optical telecommunications and networking, such as highly efficient detectors, integrated photonic circuits, and waveguide- or nanostructure-based nonlinear optical devices³⁶.

Entanglement holds a central place in modern physical research, and most studies on the subject turn to its very extensive and important applications. However, beyond being a resource for revolutionary technological applications, entanglement—the quantum phenomenon par excellence—should also be regarded as a key resource in the search for a better understanding of our physical theories. In this sense, we must not forget that certain aspects of entanglement remain as elusive today as they were three quarters of a century ago to their pioneer researchers. This situation points toward the need to open a parenthesis in the rapidly increasing research focused on entanglement’s applications to delve into the very genesis of this phenomenon and elucidate the physical mechanism underlying its so-called spooky actions. Today, the understanding that quantum systems inevitably interact with environments that not only degrade entanglement but can generate it may facilitate finding a clue to some of this phenomenon’s secrets in these intricate system-surrounding interactions³⁷.

Light measurements in a split second

Over the past three decades, several techniques for studying the structure of matter have involved time-resolved spectroscopy, in which measurements are performed in defined temporal intervals on very fast timescales. For example, the ultrafast diffraction of molecules and condensed matter was measured using brief pulses of electrons. Additionally, femtosecond lasers have revolutionized the study of chemical dynamics of molecules³⁸. Currently, the new frontier in time-resolved spectroscopy is the attosecond domain. Whereas atomic motion in molecules occurs on femtosecond timescales (1 fs = 10⁻¹⁵ s), electronic motion in atoms takes place on attosecond time scales (1 as = 10⁻¹⁸ s). The duration of one attosecond is a billionth of a billionth of a second. To put this tiny duration in perspective, an attosecond is to a second what the second would be to 31 billion years. Attosecond experiments can shed light on the ultrafast electron dynamics in molecular systems. Furthermore, attosecond chemistry allows manipulation of the electronic degrees of freedom in molecular systems on attosecond timescales and can help reveal the role of electron correlation in molecules’ ultrafast responses to incident light³⁹. Molecular ionization with an attosecond pulse allows coherent electron dynamics to be investigated on the attosecond timescale and photoionization processes to be controlled⁴⁰. Attosecond transient absorption is a tool for the application of ultra-broadband pulses to the study of electron correlation in atoms and more complex targets⁴¹. Attosecond spectroscopic techniques have made it possible to measure differences in the times required to transport photoelectrons from localized core levels and delocalized valence bands in solids. The application of attosecond pulse trains has facilitated directly and unambiguously measuring the differences between the lifetimes of photoelectrons born into free-electron-like states and those excited into unoccupied excited states in a metal’s band structure⁴². Indeed, attosecond science is an emerging field that has great potential to improve our understanding of the ultrafast electronic processes in atoms, molecules, and condensed matter.

Manipulating and bending light

Light does not propagate linearly in a medium because the rays’ geometric paths are dictated by the medium’s optical properties. This phenomenon reflects the mirage effect observed in hot deserts and explains the distortion of images viewed from across a campfire, which is caused by inhomogeneity of the refractive index of air resulting from the temperature gradient. Relatedly, transformation optics has been introduced⁴³, ⁴⁴ nd is utilized in various practical applications⁴⁵. Perhaps the most intriguing application was the design of invisibility cloaks that can wrap around microscopic objects and make them undetectable using specially designed negative-index metamaterials. These materials can guide light around the surface of the cloak, thereby preventing light from being reflected and, thus, making the object invisible. Metamaterials are man-made and have periodic, cellular structures that cause light to refract, or bend or propagate differently than in common materials, such as glass, which has a positive refractive index⁴⁵. These materials consist of cellular building blocks, called meta-atoms, arranged to form one-dimensional (1D) chains, two-dimensional (2D) metasurfaces, and three-dimensional (3D) metamaterials. The increasing research interest in metasystems is inspired by their ability to exhibit unique electromagnetic properties that are not exhibited by naturally occurring materials⁴⁶. Research in transformation optics has demonstrated that media containing gradients in their optical properties are equivalent to curved space-time geometries for the propagation of light. Conformal transformation optics, a particular variant of this field, can be used to design devices with novel functionalities from inhomogeneous, isotropic dielectric media⁴⁷.

p. 36 | Mouse Retina. Image Credit: National Institute of General Medical Sciences (NIGMS) (Photo courtesy of: IYL 2015/Light beyond the bulb).

Applied research: The cross-disciplinary age

From pure thought to empiricism

The vital importance of basic research in photonics was highlighted in the previous section. Equally important is applied research. Fundamental science and applied research have remained largely separate since the early times of Hellenic Greece. According to the Aristotelian tradition, the laws that govern the universe can be understood by pure thought, without the need for experimental observation. In the 17th entury, the boundary between theoretical science and experimental research blurred as basic science and applied research started to become interdependent. Italian astronomer and scientist Galileo Galilei, who studied the movement of bodies by rolling balls of different weights down a slope, underlined the important role of empirical inquiry. He also perfected an important optical instrument, the telescope, which led to revolutionary discoveries in astronomy. The development of the microscope exemplifies the interdependence between basic science and applied research. Indeed, the applied development of a practical optical device, such as the microscope, has resulted in many fundamental discoveries ranging from the germ theory of diseases to, centuries later, the elucidation of molecular processes in single cells. René Descartes, a French philosopher and scientist, who is perhaps best known for his philosophical statement "Cogito ergo sum (I think, therefore I am), advocated a rationalism based on pure thought and reason. In contrast, the British philosopher David Hume formulated his philosophy of empiricism, which regards empirical observation by the senses as the only reliable source of knowledge. Shortly thereafter, the bridge between pure thought and sensory perception was cemented by the German philosopher Immanuel Kant, who reconciled the philosophical divide between rationalists and empiricists (the so-called Battle of Descartes versus Hume")⁴⁸. The interdependence of basic science and applied research further increased in the 19th entury, culminating in the discoveries of electricity and electromagnetic induction by the English scientist Michael Faraday in 1831 and the creation of the incandescent light bulb in 1879 by the American inventor Thomas Edison in New Jersey and the British scientist Joseph Swan in England. The invention of the light bulb foreshadowed the next revolution in photonics. Today, the boundaries between basic science and applied research are often blurry. Typically, in the past, a discovery in basic science led to the development of new technology. In contrast, currently, a novel technology can be used to create new devices, and new instruments can drive fundamental scientific discoveries. Neither basic science nor applied research holds a privileged role in the quest for knowledge. Rather, both are expected to contribute equally to human development and societal progress as the Ying nd Yang of life, reflecting the ever-pervasive duality of being. The following sections discuss some important examples of technological developments that have greatly influenced the scientific progress of the 21st entury and will continue to do so.

Lighting up biological and biomedical research

Biophotonics is a field at the interface of optics, photonics, biology, and medicine and has the potential to revolutionize medicine as we know it. Lasers and optical imaging technologies have yielded powerful tools for studying disease on all scales: from single molecules to tissue materials and even whole organs. Many emerging techniques now find immediate applications in biological and medical research. For example, scanning laser microscopes permit spectroscopic and force measurements on single protein molecules. Indeed, almost six decades after their discovery by Charles Townes and Arthur Schawlow⁴⁹, lasers are critical tools for studying molecular dynamics and structures and have countless medical applications. Spectroscopic methods provide the fundamental information and experimental tools needed to understand the origin and progress of diseases from the organ and tissue levels down to the cellular or even molecular level. Indeed, all of our knowledge regarding how molecules bind together, how the building blocks of

DNA

control cellular growth, and how disease progresses on the molecular level has its basis in fundamental research in molecular spectroscopy. In molecular spectroscopic methods, light can be used in many different ways to analyze complex biological systems and understand nature at the molecular level. Today, a wide variety of molecular spectroscopic techniques, such as absorption, diffuse reflectance, fluorescence, Raman scattering, bioluminescence, photoacoustics, and optical coherence tomography (

OCT

, are being developed for applications in cancer diagnosis, disease monitoring, and drug discovery⁵⁰. Unlike traditional biopsy procedures, which are labor intensive, time consuming, and costly, optical measurements can be performed in vivo during a routine endoscopy and could lead to the development of rapid and cost-effective methods for cancer diagnosis. Advanced techniques, such as synchronous fluorescence and time-resolved detection, could further improve such optical diagnostic methods. When devices capable of detecting single photons are used, optical methods can be extremely sensitive. Coherent Raman imaging techniques, such as coherent anti-Stokes Raman scattering and stimulated Raman scattering, are sensitive to the same Raman-active molecular resonances but are capable of fast data acquisition speeds⁵¹. New optical techniques and fast data treatment methods are being developed to provide real-time images of tumor margins and, thus, allow rapid image-guided surgery. For example, miniaturized pill capsules containing cameras could be swallowed, pass through the body, and transmit images back to a doctor for real-time diagnosis. Photonic devices using OCT ⁵², ⁵³, ⁵⁴, a type of microscopic laser radar imaging that can probe beneath the tissue surface, are expected to be very useful in the diagnosis of age-related macular degeneration, one of the leading causes of blindness, particularly in older patients.

Bioluminescence methods using genetic promoters to drive the expression of luciferase, a type of oxidative enzyme that emits light, can generate molecular light switches, which serve as functional indicator lights reflecting cellular conditions and responses in living animals. These methods can also allow the rapid assessment of and responding to the effects of antitumor drugs, antibiotics, or antiviral drugs. Advanced imaging systems with the combined capability of high-resolution, high-throughput, and multi-spectral detection of fluorescent reporters have contributed to the dramatic growth of cell-based assays. Sensitive fluorescent reporters are critical elements in the development of live cell assays amenable to the in vivo sensing of individual biological responses across cell populations, tracking the transport of biological species within intracellular environments, and monitoring multiple responses from the same cell⁵⁵. One important advance in the fluorescent probes used for biological studies was the development of naturally fluorescent proteins that can serve as fluorescent probes, such as the green fluorescent protein (

GFP

) produced by the jellyfish Aequorea victori ⁵⁶, ⁵⁷. Research on the applications of

GFP

-based assays, which use the

GFP

gene as an expression reporter for the analysis of intracellular signaling pathways using libraries of cell lines engineered to report on key cellular processes, remains ongoing.

A new generation of nanoplatforms and nanomaterials has been developed for labeling cells and intracellular organelles with biocompatible optical materials using semiconductor quantum dots (QDs) and gold nanospheres, nanorods, nanoshells, and nanostars. Today, single-molecule detection techniques using various photonics modalities represent the ultimate tools for elucidating cellular processes at the molecular level. These new materials offer many advantages, including greatly improved resistance to photo-bleaching, very narrow spectral features for multiplex detection, and easy detection in the near-infrared (

IR

) tissue window in which tissue absorbs light the least.

Multiphoton microscopy (

MPM

) has enabled unprecedented dynamic explorations of living organisms. One example of

MPM

is two-photon excitation fluorescence, which involves the simultaneous absorption of two near-IR photons by a single molecule that then emits a single photon of fluorescence⁵⁸. Novel microscopic devices using near-field optics or that are capable of sub-diffraction optical resolution allow scientists to explore the biochemical processes and nanoscale structures of living cells at unparalleled resolutions. Near-field microscopy is a method that permits studying the complex electromagnetic fields that surround nanophotonic structures. At nanoscale dimensions, light-matter interactions are intimately linked to an object’s geometry and not just to the optical properties of its constituent materials, which allows the near-field mapping and imaging of nanosystems. This mapping facilitates better understanding of the physical processes underlying exciting phenomena, such as extraordinary optical transmission, light generation and propagation through photonic crystal waveguides and fibers⁵⁹, and optical responses of nanoantennas⁶⁰. The optical detection sensitivity and high resolution of near-field scanning optical microscopy (

NSOM

) have allowed the detection of the cellular localization and activity of the adenosine triphosphate-binding cassette proteins associated with multidrug resistance⁶¹. Super-resolution microscopy tools, such as photo-activated localization microscopy, stochastic optical reconstruction microscopy, and stimulated emission depletion microscopy, which can overcome the diffraction-limited resolution of traditional confocal microscopes, are emerging as useful tools for ultrahigh-resolution imaging and the investigation of materials and biological systems at the nanometer scale⁶², ⁶³, ⁶⁴  y ⁶⁵.

Fig 1.1. Image of the evolving universe. Astronomers usingthe Hubble Space Telescope have assembled a comprehensive picture of the evolving universe. This is among the most colorful deep space images ever captured by this telescope. This work, which utilized UV light, provides the missing linkin star formation. (Source: Hubble Space Telescope. http://hubblesite.org/newscenter/archive/releases/2014/27/).

Adaptive optics can also improve the detection accuracy of microscopes by reducing the optical aberrations in inhomogeneous media, such as biological samples and tissues (e.g., retinal imaging). Similarly, such aberrations resulting from atmospheric turbulence limit the performance of ground-based telescopes; in contrast, space telescopes, such as the Hubble telescope, which are not affected by atmospheric turbulence, can achieve exceptional resolution, highlighting the all-encompassing applications of photonics from imaging atoms and cells to exploring the universe (Figure 1.1). Research in wavefront-shaping techniques can achieve the diffraction-limited control of light in deep tissue by manipulating the spatial profile of an optical field before it enters a scattering medium and using feedback from within the biological sample⁶⁶.

Molecular nanoprobes allow the earliest signs of disease to be detected at the genetic, molecular, and cellular levels, leading to early and more effective therapies. Nanoparticles equipped with nucleic acid probes, such as molecular sentinel probes, are exceptional tools for gene disease diagnostics⁶⁷. The application of the

SERS

molecular sentinel nanoprobes could facilitate molecular genotyping with many advantages, such as spectral selectivity because of the sharp, narrow specific vibrational bands of Raman labels; this technique could be achieved single-laser excitation for multiple labels and, thereby, offer higher multiplexing capabilities than conventional optical detection methodologies. Exploiting the