Sci-Advent – Mathematics and physics help protect the sight of patients with diabetics: Sabino Chávez-Cerda

This is a translation of the article by Antimio Cruz in Crónica. You can read the original in Spanish here. As a former student of Prof. Chávez-Cerda, I am very pleased to see that his research continues getting traction and the recognition it deserves.

Exotic Beam Theory was created by Sabino Chávez-Cerda, but for over four years it was rejected until it gained acceptance.

The Mexican scientist Sabino Chávez-Cerda has received numerous international awards over thirty years for his contributions to understanding one of the most complex phenomena in nature: light. This year, together with one of his graduates and other collaborators from Mexico and England, he presented a model that reproduces with great precision the operation of the flexible lens located behind the iris of the human eye: the crystalline lens. This work was recognised as one of the most important investigations in optics of the year 2020 by the magazine Optics and Photonics News.

Now, in conversation for the readers of Crónica, the researcher from the Instituto National de Asfrofísica, Óptica y Electrónica (INAOE) in Mexico says that we all should be made aware that science is much closer to our daily life than we imagine. For example, his studies are able to help care better for the eyes of patients with diabetes.

“My studies on how light travels have enabled me and my collaborators to make important contributions through the use of the physics and mathematics, the same that everyone is able to learn. I have made new interpretations that at first were rejected and with the availability of more evidence they have ended up being accepted”, says the man who created the Theory of Exotic Beams for which he was elected as Fellow member in 2013, one of the most important accolades in the field, by the Optical Society of America (OSA), one of the most prestigious organisations in the world.

“My recent work with the lenses of human eyes began in an interesting way. A few years ago some ophthalmologist surgeons from Puebla, Mexico, invited us to organise a seminar on how light propagates. This was because they had equipment to perform laser surgeries, but they had doubts on the subject aberrations. I then realised that what we were investigating about beams could be of great use in healthcare,” says Chávez-Cerda, who since childhood has lived in many cities in Mexico and abroad. He mentions that one of the things he most enjoys is watching the sunset on the shores of the Mexican Pacific.

“I was born in Celaya, Guanajuato, Mexico. My father was an agronomist and we had to move many times. So during my childhood and youth I lived in Nayarit, Veracruz, Guanajuato and Mexico City”, says the physicist and PhD who has also carried out research in England, China, Brazil and the United States.

COMPLEX QUESTIONS – Light is the part of electromagnetic radiation that can be perceived by the human eye and that may have a complex behaviour. It is made up of photons, which have the duality of being a wave and a massless particle. The field of science that studies light, optics, has become so diverse that today it can be compared to a tree with diverse branches: including the study of fibre optics, the use of laser light, non-linear optics and many more. 

“For example, physical optics tries to understand how light travels and how it changes when an obstruction or lens is put on its path. We have all seen when a CD generates a rainbow when placed in front of a light source. This is due to the physical phenomenon called diffraction, just like holograms. What happens there is that the light is ‘spread’ and that is one of the many phenomena that we study ”, details the INAOE researcher whose individual and team work averages around 4 thousand citations in four of the main databases of scientific articles: Web of Science (WoS), Scopus, Research Gate and Google Scholar.

His long academic career is based on his bachelor’s degree from the Escuela Superior de Física y Matemáticas (ESFM) of the Instituto Politécnico National (IPN) in Mexico. He later obtained an MSc at Centro the Investigaciones en Óptica (CIO) in León, Guanajuato, Mexico and his PhD in England, at the Imperial College London (IC).

The story of how he created the theory of exotic beams may require a larger, separate text. However, it is worth saying that it started from some reports made in the 1980s by the University of Rochester claiming that it was possible to create beams of light that were not ‘spread’ or did not show diffraction. That caused a stir because it violates the laws of physics and mathematics. When the Dr Chávez-Cerda showed interest in studying the subject his own English supervisors told him that they did not believe it was worth pursuing. He dedicated though several hours to study this and after performing many calculations and computer simulations he was able to find an answer that was not immediately understood by us all: the beams of light that did not ‘spread’ were not beams, but instead apparent beams, resulting from a phenomenon called interference.

“When I proposed this theory, it was rejected for four years. Over and over again they rejected my articles, but I improved and improved my ideas until there was no argument to reject them ”, says the professor who says that since he was young he has treasured two activities that he practiced for many years and that gave him love for discipline and freedom: martial arts and regional dance.

Now, he has received awards such as the annual award from the European Optical Society and the recognition of “Visiting Foreign Researcher of Excellence” by the Government of China. He is also able to boast his graduate students; today scientists who have membership in the National System of Researchers (SNI) in Mexico. [Translator note: and a few of us that are abroad too!!! — Thanks Sabino!]

“The human virtue that I value the most is honesty,” says the teacher, husband and father of two adult sons, and two 13-year-old twins. “Throughout my life and my professional experience I have met people who, due to lack of honesty, prevent me from moving in the right direction. That is why I know that when there is honesty, one can advance and everyone can grow a lot,” says the man who remembers the day his mother took him to a new elementary school in Tepic, Mexico where they were rude to both of them”. She told me, ‘Be the best you can,’ and that’s when I became good at maths,” he shared with Crónica’s readers.

A new Bose-Einstein condensate

Originally published here.

A new Bose-Einstein condensate


Although Bose-Einstein condensation has been observed in several systems, the limits of the phenomenon need to be pushed further: to faster timescales, higher temperatures, and smaller sizes. The easier creating these condensates gets, the more exciting routes open for new technological applications. New light sources, for example, could be extremely small in size and allow fast information processing.

In experiments by Aalto researchers, the condensed particles were mixtures of light and electrons in motion in gold nanorods arranged into a periodic array. Unlike most previous Bose-Einstein condensates created experimentally, the new condensate does not need to be cooled down to temperatures near absolute zero. Because the particles are mostly light, the condensation could be induced in room temperature.

‘The gold nanoparticle array is easy to create with modern nanofabrication methods. Near the nanorods, light can be focused into tiny volumes, even below the wavelength of light in vacuum. These features offer interesting prospects for fundamental studies and applications of the new condensate,’ says Academy Professor Päivi Törmä.

The main hurdle in acquiring proof of the new kind of condensate is that it comes into being extremely quickly.’According to our theoretical calculations, the condensate forms in only a picosecond,’ says doctoral student Antti Moilanen. ‘How could we ever verify the existence of something that only lasts one trillionth of a second?’

Turning distance into time

A key idea was to initiate the condensation process with a kick so that the particles forming the condensate would start to move.

‘As the condensate takes form, it will emit light throughout the gold nanorod array. By observing the light, we can monitor how the condensation proceeds in time. This is how we can turn distance into time,’ explains staff scientist Tommi Hakala.

The light that the condensate emits is similar to laser light. ‘We can alter the distance between each nanorod to control whether Bose-Einstein condensation or the formation of ordinary laser light occurs. The two are closely related phenomena, and being able to distinguish between them is crucial for fundamental research. They also promise different kinds of technological applications,’ explains Professor Törmä.

Both lasing and Bose-Einstein condensation provide bright beams, but the coherences of the light they offer have different properties. These, in turn, affect the ways the light can be tuned to meet the requirements of a specific application. The new condensate can produce light pulses that are extremely short and may offer faster speeds for information processing and imaging applications. Academy Professor Törmä has already obtained a Proof of Concept grant from the European Research Council to explore such prospects.

Materials provided by Aalto University. Note: Content may be edited for style and length.

Journal Reference:

1 Tommi K. Hakala, Antti J. Moilanen, Aaro I. Väkeväinen, Rui Guo, Jani-Petri Martikainen, Konstantinos S. Daskalakis, Heikki T. Rekola, Aleksi Julku, Päivi Törmä. Bose–Einstein condensation in a plasmonic lattice. Nature Physics, 2018; DOI: 10.1038/s41567-018-0109-9

2015 – International Year of Light

2015 has been declared the International Year of Light (IYL 2015) and with me being an optics geek, well, it was difficult to resist to enter a post about it. The IYL 2015 is a global initiative adopted by the United Nations to raise awareness of how optical technologies promote sustainable development and provide solutions to worldwide challenges in areas such as energy, education, communications, health, and sustainability.

There will be a number of event and programs run throughout the year and the aim of many of them is to promote public and political understanding of the central role of light in the modern world while also celebrating noteworthy anniversaries in 2015 – from the first studies of optics 1000 years ago to discoveries in optical communications that power the Internet today.

You can find further information from the well-known OSA here and check out the International Year of Light Blog.

Here are some pictures I took a couple of years ago during CLEO Europe in relationship to the International Year of Light.

Quantum Tunnel Answers: Fresnel Lens

Hello everyone,

once again we have a question coming to the inbox of the Quantum Tunnel blog. If you are interested in asking a question, please feel free to get in touch using this page. We have once again a question by a very avid reader, let’s take a look:

Dear Quantum Tunnel,

Could you please explain how Fresnel lenses work? I am asking after listening to Dr Carlos Macías-Romero talking in one of the Quantum Tunnel podcasts. Thanks a lot.


Hello yet again Pablo, thanks a lot for your question. Well, I assume that you are familiar with the idea of a lens and that you may even wear a pair of spectacles or know someone who does and so you know that you can correct, among other things, the focal point and thus read your favourite blog (the Quantum Tunnel site of course!) with trouble.

Well, have you ever had a chance to go and see a lighthouse close enough? But not just the building, the actual place where the light is beamed out to see? If so you may have seen the lenses they use. If not, take a look the image here:

Lighthouse Lens
Lighthouse Lens (Photo credit: Wikipedia)

You can see how the lens is made out of various concentric layers of material and the design allows us to construct lenses that otherwise would be way to thick and therefore heavier. A lighthouse requires a light beam that uses a large aperture but a short focal length and a Fresnel lens offers exactly that without the need of a really thick lens. Fresnel lenses are named after the French physicist Augustin-Jean Fresnel.

Another example of Fresnel lenses are flat magnifying glasses such as the one shown below, you can see that they are effectively flat and no need to use one such as those used by Sherlock Holmes…

English: Creditcard-size Fresnel magnifier Ned...
English: Creditcard-size Fresnel magnifier Nederlands: Fresnelloep in creditcardformaat (Photo credit: Wikipedia)

The design of a Fresnel lens allows it to capture more oblique light from a light source. Remember that a lens works by refracting (bending) the light and the way in which the “layering” in the Fresnel lens helps with the refraction needed. See the diagram below:

Fresnel lens

A couple of other uses for these lenses are in overhead projectors and the headlights of cars. So next time you attend or give a lecture or drive at night, think of Monsieur Fresnel.

Mirror mirror, right and left, up and down

You are getting ready for the New Year’s party and cannot help to use a mirror to check that all is spot on. The tie is straight, the hair is tamed, the shoes are polished but wait… right is wrong, or rather right is left and left is right… but up is still up and down is down. Why, you ask, do mirrors reverse right and left but not up and down? Well, the answer is that they do not do either of them. They reverse front to back…

Madame Jeantaud in the Mirror

The image that you see in front of you has not been swapped, but inverted along the axis of the mirror. So the answer to this question can be understood with looking at how light gets reflected. If we consider a light source, its rays will bounce off various parts of your body, they will reflect off the mirror and will be caught by your eyes; plus we know consider that for all intents and purposes light travels in a straight line. And so, a mirror (not a fun fair mirror by the way) will simply reflect what is in front of it: the light bouncing of your right hand  will hit the mirror straight on and then will bounce into your eye. What you will perceive is that you see your right hand in the place of the left one. And notice that it is a matter of perception… Now, try the following: position yourself looking North and place the mirror in front of you. Now point at something East with your right hand, you will see that the hand in the mirror will also point East; the same happens if you point West with your left hand. So the directions are fine: East is East and West is West. But look at your nose, it points North, right? What about the nose in the image? Well, it points South! The image is reverted front to back.

Richard Feynman provides this explanation to the BBC TV Series “Fun to Imagine” in 1983.

Now, you have something to think about next time you are getting ready in front of the mirror.


Total Internal Reflection – Sci-advent – Day 18

Total Internal Reflection

We are well acquainted with some optical phenomena such as reflection an refraction; simply take a look at an object half-submerged in a glass of water. But light has other (many other) trick under its sleeve. One very useful trick is total internal reflection. As the name suggests, this phenomenon happens when a ray of light incides in a medium boundary at a very particular angle (known as the critical angle) with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary the light cannot pass through and instead it is all reflected, as if it had hit a perfect mirror.
Total internal reflection is widely used I the operation of optical fibres and devices such as endoscopes and in telecommunications, rain sensors in cars and some multi-touch displays.

Babinet-Soleil Compensator

The Babinet-Soleil Compensator is a variable waveplate which, for example, can convert circularly polarised light into linearly polarised light or vice versa. It comprises two opposed birefringent crystal wedges with a compensating crystal block in optical contact with the smaller wedge. Both wedges are cut with the optic axis parallel to their long edges, and the compensating block has its axis at right angles. In operation, the large wedge is translated across the smaller, thus presenting a variable path length difference to an optical beam passing through the instrument. The compensating block ensures that this difference is uniform across the aperture.