May 16th is the International Day of Light, a worldwide initiative sponsored by UNESCO to celebrate the role light plays in scientific innovation, culture, and art. This day is a special day in history because it marks the first successful operation of the laser in 1960 by Theodore Maiman. In the past century, we have learned ways to manipulate light far beyond anything previously. Hopefully, these facts help you get lit, for the International Day of Light.
1. Light can move superfast, superslow, and not at all
|Image credit: Chien Liu and Lene Hau, Harvard University|
The speed of light in a vacuum is equal to 3 x 10⁸ m/s, that’s over 1 billion km/hr! When light is injected into an odd form of matter called a Bose-Einstein Condensate however, it can travel as slow as 25 km per hour! Bose-Einstein Condensates are a strange state of matter consisting of supercool atoms with almost zero energy, where atoms behave in a quantum state. To slow light, traveling photons collide with atoms in the BEC to form a hybrid particle called a polariton, which moves slower than a photon.
Just as Bose-Einstein Condensates can be used to slow down light, they can also be used to temporarily store it. In the same experiment, a team of scientists stored light for 1.5 seconds, before releasing a pulse back to motion. This discovery could lead to developments in transmitting quantum information.
2. There’s such a thing as a random laser
|Image Credit: Diederik Wiersma/LENS/INFM|
Random lasers are like normal lasers in that they emit light of all the same frequency, but unlike lasers, they emit pulses of light into all directions. These look more like small orbs of light than a laser beam. So, why does this happen? Normal lasers use crystals to amplify and focus their light, but if that crystal were to be crushed into a powder, the laser would be reflected in all directions. Researchers are still looking for practical applications for random lasers, but new research could improve optical cables, biosensors, and more.
|Image Credit: NASA, ESA, and A. Feild (STScI).|
When light comes a little bit too close to a massive star, the star’s gravity warps it. This means if you were looking at a star in a telescope, its observed position may be different than its actual position. This concept is predicted by Einstein’s Theory of Relativity, because massive objects such as a star can curve spacetime. In 2017, scientists used this concept to study the light emitted from a nearby white dwarf star. By measuring shifts in the apparent versus actual position of the star (based on the light it emits), researchers were able to estimate the mass required to cause that shift. This method has proven to be far more accurate than previous mass calculations.
|Image Credit: CDC|
Malaria is a fast-acting sickness that can kill patients within hours, but current testing methods can take the same amount of time. Lasers can help provide a quick diagnosis. When a malaria-causing parasite infects a person, they alter the red blood cells, visually changing the structure of the cells. With this in mind, a team of scientists created a device that can microscopically identify malaria. By analyzing the pattern that a laser creates when interacting with the red blood cells, medical professionals can diagnose the infection within 30 minutes, with an 85% accuracy.
5. We can use light as tweezers
|Image Credit: I. Heller/VU Amsterdam|
This one you may have heard of because their pioneers won the Nobel Prize in Physics for its development in 2018. Optical tweezers work by using a laser beam to trap and isolate an object. Because light carries momentum proportional to its energy and direction of travel, the movement of the laser can alter its momentum, resulting in a force acting on the object trapped between the laser. Scientists have used optical tweezers to manipulate incredibly tiny objects, including unwinding tiny strands of DNA under a microscope, allowing them to study how chromosomes read genetic information.
6. Bubbles can turn sound into light
|Image Credit: UCLA Putterman Research Group|
When ultrasonic sound waves are created in a pool of water, tiny air bubbles are created, which emit a tiny burst of light, as shown above. The concept of sonoluminescence was first discovered in 1934, but researchers still aren’t sure how it exactly works. Here’s the leading hypothesis: high-intensity sound waves cause oscillation in bubbles, which expand and then crash with intense energy from the soundwave. Researchers wonder if this effect can be utilized to help reactors reach thermonuclear fusion.
|Image Credit: Getty|
8. Lasers can make things cold
|Image Credit: Kristian Helmerson, NIST|
In addition to heating atoms, lasers are also used to cool atoms down to incredibly low temperatures. When a laser hits an atom traveling in the opposite direction, it decreases its velocity, and thus cools the atom. A method developed in 1985 called “Doppler cooling” cools atoms by shooting a laser at a frequency slightly lower than the target atom, reducing the velocities for many atoms. This cooling method is usually used for experiments involving Bose-Einstein Condensates.
|Image Credit: Flickr|
Lasers differ than normal light in that they emit waves of all the same frequency, and they can focus on small areas. We know that normal lasers generate light by running a current through glasses or crystals, which then emit photons. In a recent study, researchers found they could make air behave like a laser. By shooting a pulse of infrared light at nitrogen and oxygen compounds, and hitting the broken up atoms with a UV light, the atoms themselves will give off light like a laser. Future work could help these lasers cover longer distances, and perhaps work in outer space.
Did you know that light has its own superhero? Spectra is a comic that follows an ordinary middle schooler, who also happens to have all of the functionalities of a laser beam. It was also created at APS, so you can read all of the Spectra comics free online.
Lasers have shed a light on many phenomena in our lives. Igniting curiosity for over 50 years, lasers have highlighted the ways we interact in the world on a scale unobserved by the naked eye. Gathering data at lightning-fast speeds has been a product of laser advancement as well. Having this resource has brightened the lives of so many people around the world. Today, we hope that you take a moment to reflect on how light affects your life.
–Lissie Connors and Phoebe Sharp