The century of the photon

The century of the photon

Most likely, the word photonics is not part of yourusual vocabulary, but the technologies developed in this field are increasignly used in the daily course of our lives.

If we pay attention to the definition of photonics given by dictionaries such as Merriam-Webster´ s:

“A branch of physics that deals with the properties and applications of photons especially as a medium for transmitting information”, perhaps this means nothing to you, unless you know research works such as those of the great pysicist Albert Einstein. Specifically, his explanation of the photoelectric effect discovered by Hertz in 1887 and for which, curiosities of life, Einstein received exactly 100 years ago (1921), the Nobel Prize and not for his famous theory of relativity.

Albert Einstein

Photonic is better understood if we use other definitions, such as the one described by the French scientist Pierre Aigrain in 1967:

“Photonics is the science of the harnessing of light. Photonics encompasses the generation of light, the detection of light, the management of light through guidance, manipulation, and amplification, and, most importantly, its utilization for the benefit of mankind.”

Therefore, light is the center of photonics, a physical phenomenon whose explanation has needed hundreds of years and great geniuses for its understanding, at least to a high degree. From the Greek schools with Aristotle and Euclid as outstanding exmples, numerous scientists, such as Al Haytham, Newton, Young, Maxwell or Einstein himself dedicated part of their lives to answering the question What is light?.

If we summarize some of the conclusions of these parents of photonics, we can say that light is defined by both a wave and a particle, which has been called the wave-particle duality of light. This duality was the source of fierce discussions like the one carried out between Huygens and Newton in the 17th century, Huygens defended the wave nature of light, while Newton only understood light as a set of luminous corpuscles. In the 19th century, it was Young with his famous double slit experiment and Maxwell with his treatise on electromagnetism who confirmed the wave nature of light, while in the early 20th century, Plank and Einstein demosntrated the need to quantify light in form of discrete packets of energy to be able to explain the radiation of a black body and the aforementioned photoelectric effect. In 1926, Gilbert Lewis called this “quantum” of energy a photon.

Wave-particle duality of light Source:

On the other hand, light is not only the radiation that we can see with our eyes, namely, the visible spectrum, but it is also associated with infrared, ultraviolet, microwaves, radio waves, X-ray and gamma radiation, since these ones are of the same nature as demonstrated by Maxwell. In fact, the International Society of Photonics and Optics (SPIE) in its 2020 annual report states that photonics covers the entire range of the electromagnetic spectrum, from gamma rays to radio waves.

photonics - electromagnetic spectrum
Electromagnetic spectrum

We could say, in a simplified way that:

“Light is made up of a set of particles, called photons, propagating in ther form of electromagnetic waves with a wide range of frequencies.”

Photons interact with matter at the subatomic level. If these particles have the right energy value, defined by the frequency of the wave, they will cause the electrons of the atoms to absorbb their energy and position themselves at higher energy levels. In the same way, these particles of light are released when electrons returns spontaneously or stimulated to lower or more stable energy levels.

photonics- interaction of photons with matter
The interaction of photons with the matter.

Well, these phenomena that occur at the suabtomic level are tha basis for the velopment of devices such as LEDs or LASERs, without which we could not, among other uses, improve the energy efficiency of our homes or have better bandwidth in fiber optic communications. These are a small part of the applications of photonics, but it gives an idea of the magnitude of its importance since it is present in a myriad of application sectors.

So when you turn on the lights, hear the news on the radio or watch them on television, connect to the internet via fiber optics or via wireles with yout tablet or smartphone to watch your favorite series, activate your home alarm sensors, take pictures, heat your breakfast in the microwave and other countless daily actions, think about how photonics has changed our lives. It is not surprising that the 21st century was the century of the electron and that photonics is one of the key technologies for humanity to continue its development and overcome many of thec omplicated challenges that has to face today and in the future.

Since 2020 CARTIF is part of PhotonHub Europe, a platform made up of more than 30 reference centers in photonics from 15 European countries in which more than 500 experts in photonics offer their support to companies (mainly SMEs) to help them to improve their productionprocesses and products through the use of photonics. With this objective, training, project development and technical and financial advisory actions have been organized until 2024.

In addition, to be aware of what is happening in the worl of photonics, we encourage you o be part of the community created in PhotoHub Europe. In this community you can be aware of the activities of the platform as well as news and events related to photonics.

Guiding dancing structures

Guiding dancing structures

Despite the title, this blog is not about ballroom dances, but about something related to movement and how to guide your dance partner.

Have you ever felt how a footbridge sways when you walk over it or how a stadium stand vibrates under your feet when you are jumping and cheering up your favorite football team? If not, I highly recommend you to see these videos: Millenium Bridge London, Commerzbank-Arena Frankfurt or Volga Bridge Volgograd.

Why do these structures sway if they are building with strong and rigid materials like concrete or steel? In general, all structures vibrate in response to external excitation like people, vehicles or wind gust, but some structures sway more perceptible than others.

Structures perform more or less amplitude oscillations depending on their stiffness, mass and damping parameters. As a rule of thumb, the more slender, the more sensitive to develop noticeable rocking motions and even ones annoying and dangerous for people.

The best way to understand these concepts is by testing. If you are at home, I encourage you to go to the kitchen and take some spaghetti noodles and strawberries. Also you can use small balls made with a putty-like modelling material like plasticine® instead of the fruit.  Now, hold tightly one end of a noddle and pierce a strawberry/plasticine® ball in the opposite end. Then, make small back and forth movement with your hand.

Changing the frequency of the movement you realize that the noddle performs big oscillations and even is broken at a particular rate. This frequency is called resonance frequency and is defined by the noddle flexibility or “stiffness” and the strawberry/plasticine® weight or “mass”. If now you try with two noodles instead of one and later you use a heavier or lighter strawberry, you will perceive how the resonance frequency changes, being lower as long as you have lower stiffness and/or bigger mass.

With regard to damping, this property is related to the material used and basically it opposes to the movement. In other words, the more damping, the lower oscillations will be developed at the resonance frequency and the vibration will stop sooner once the excitation is ceased. This can be checked using a steel wire instead of the spaghetti. You notice the spaghetti damping is higher however it is more fragile than steel.

Coming back to structures, these ones are designed and built using different materials and geometries. Therefore they have different mass, stiffness and damping values and consequently different resonance frequencies. What would happen if one of the footbridge resonance frequencies was closed or the same to the people pacing rate crossing over it? As we saw in the experiment, the footbridge would sway perceptibly with lower or bigger oscillations depending on the damping. With a very low damping value, the oscillations performed would be so big that the structure must be closed to be modified. This was what happened three days after the London Millenium Bridge opening day.

Basically, there are two solutions to avoid noticeable vibrations in a structure. The first one would be modifying its resonance frequency changing its stiffness and/or mass. The second one would be based on adding damping to the structures. The first solution is in general expensive and would modify the final structure design becoming less slender what usually dislike the structure designer/architect. The second solution would be more affordable and unnoticeable. It would consist on adding damping devices along the structure in order to increase the structure global damping. Some examples of these devices are oil dampers and viscoelastic dampers. To work properly, these devices need to link two points of the structure with relative movement.

Other damping systems in what CARTIF has been working for years are the “Tuned Mass Dampers” or TMD. These systems consist on a mass attached to the structure by means of coil springs or metallic cables (pendulum TMD) and passive damping devices like oil dampers and neodymium magnets or active ones like magnetorheological dampers.

These systems only need to be attached to one point of the structure, being generally the one with the biggest oscillations.  Its functioning principle is based on kinetic/inertial energy transference between the structure and the TMD. An example of these systems is the one recently installed in the second world tallest building, the Shanghai Tower, where a 1000 tons pendulum TMD drastically reduces the skyscraper oscillations in response to wind loads.

Summarizing, in spite of the fact that structures sway, it is always possible to “guide” them to gentle movements by means of damping system such as Tuned Mass Dampers.