Photons emitted via stimulated emission have identical characteristics

Stimulating electrons to emit identical photons produces lasers

This effect was predicted by Albert Einstein in 1917, and requires all excited electrons in a material to exist in the same excited metastable state within their atoms. Pumping all atoms through the same mechanism, such as electricity or flash lamps, can create this environment.

Lasers are classified based on their gain medium and mode of emission

All lasers possess a material whose atoms must be energized by a power source, such as electricity or chemical reactions. Different media will produce different colors of light through a cascade of emissions resulting from an initial stimulated emission.

Electron accelerators are used to create X-ray lasers

In an X-ray free-electron laser, electromagnetic fields are used to accelerate and move electrons in wiggling patterns, causing them to emit synchronized, high-energy X-rays. This resulting light beam can strike targets up to 120 times per second to create movies of changing molecular structures and phenomena.

Light can be used to slow the motion of atoms

While photons possess energy, they also have momentum, which allows them to collide with other particles, much like billiard balls, thereby slowing them down and reducing their kinetic energy, or temperature. Using multiple lasers from different directions, particles can be cooled to within one degree of absolute zero.

Photons are both particles of light and messengers of the electromagnetic force

Einstein's model of light as a wave and a massless particle of energy revolutionized physics, and scientists' application of the model led to groundbreaking technologies, including medical imaging and treatments, telecommunication signals, and probes of the quantum and cosmological realms.

Random lasers can be created from biomaterials, such as peanuts and birch leaves

Rather than creating a narrow beam of light via amplification in an optical cavity, the random laser produces a red glow by scattering photons created in the natural pores of a peanut kernel after it has been injected with a solution of light-generating carbon dots derived from birch leaves.

Concentrated sound waves can collapse microscopic bubbles, creating light

The phenomenon, known as sonoluminescence, can generate extremely short, high-intensity flashes from the sudden focusing of sound energy, which can drive the temperature within the bubbles to values over twice that of the sun's surface.

Lasers, semiconductors, medical imaging, and atomic clocks rely on quantum mechanics

Semiconductors, crucial in electronics, operate based on quantum superposition. Lasers use stimulated emission, a quantum process, and MRI machines leverage the quantum spin of hydrogen atoms for imaging. Atomic clocks measure time with unprecedented precision using quantum transitions.

Light echoes are expanding shells of reflected starlight

Just as sound waves reveal the location of obstacles by reflecting off them, pulses of light emitted by stars illuminate rings of interstellar dust, giving the appearance of ejected material as the light travels outward.

Solid neon mirrors help trap single electrons to create stable quantum bits

Researchers created this new unit of information for a quantum computer by trapping a single electron near the surface of solid neon. The electron was held in its quantum state by attraction to its mirror image.

The different energy levels of each element result in unique colors when burned

When heated, electrons absorb energy and move to excited states within an atom. They promptly drop back down and release light energy corresponding to the size of the drop, which is unique to each element.

A nuclear reactor's characteristic blue light is produced from superluminal particles

When light travels through water, its effective speed is 25% lower than its speed in a vacuum. Just as sound waves bunch up and produce a sonic boom when objects move faster than the speed of sound, particles moving faster than this reduced speed generate a shock wave of light, visible as a blue hue.

Bioluminescence produces new light while biofluorescence re-emits absorbed light

A chemical reaction between luciferin and oxygen—catalyzed by luciferase—produces light within bioluminescent organisms. Biofluorescence, on the other hand, involves special proteins that absorb light of one wavelength and re-emit the light at a different, typically longer, wavelength.

As of 2023, the world's smallest particle accelerator is smaller than a penny

The prototype is an example of a photonic accelerator, which utilizes tiny lasers to accelerate electrons rather than relying on oscillating electromagnetic fields to move them. It can deliver about 1 electron per second with energies equivalent to those found in cathode-ray tube televisions.

Solar sails use light as a means of propulsion

Photons possess momentum and can transfer it to objects they strike or bounce off, imparting radiative pressure, or a light-based force over a small surface area. Lasers fired at observational equipment with specially designed sails can theoretically use this mechanism to accelerate up to 20% the speed of light.

Holograms are produced by shining light through recordings of interference patterns

When one half of a split laser beam that was reflected off the surface of an object recombines with its other, unreflected half, the two produce an interference pattern that becomes etched onto holographic film. When light shines through the back of the film, it reacts with the pattern to create the reflected light, projecting the original object.

How helium greatly improves the efficiency of barcode-scanning lasers

Rather than directly energizing neon atoms, electrical discharge at lower, more practical power levels can excite helium atoms to energy levels nearly equal to those in neon atoms. Within a helium-neon laser, these gases are present in a 10-to-1 ratio, enabling helium to efficiently transfer energy to neon, which is then discharged as red light.

Cathode-ray tube televisions are examples of electron accelerators

CRT TVs work by converting electricity into heat, which causes electrons to be emitted from the rear of the device in three beams responsible for the colors red, green, and blue. Electromagnets direct electrons to phosphor molecules on the screen, which emit light and illuminate the pixels.

Photonic integrated circuits use light instead of electrons within circuit components

Instead of processing electric signals, photons in the visible and near-infrared serve as optical signals between chips made of electro-optical crystals. PICs can enable lower power consumption and heat generation by eliminating the friction from electrons moving along wires.

Light waves can interfere and cancel each other out

When light waves travel past one another, their peaks and valleys combine, just as overlapping ripples in water can combine to form a larger ripple. When the peak of a light wave meets the valley of another of the same wavelength and brightness, the waves combine to produce no light.

Synchrotron radiation has revealed the fur color of creatures millions of years old

When electrons are accelerated in the loop, they produce intense X-rays that can reveal properties of a sample struck by them, just as X-rays can be used to show bone structure in humans. Studying the reflected light from fossils can uncover the presence of known pigmentation compounds.

Black-body radiation is emitted by everything in predictable ways

All objects above absolute zero emit electromagnetic radiation, with the amount and distribution determined by temperature alone. The shape and intensity of this radiation follow Planck's law, while Wien's law governs the peak wavelength.

Stars appear to twinkle because turbulence in the motion of molecules in Earth's atmosphere causes light to bend and wiggle rapidly on its way to the surface—a phenomenon called scintillation.

The reflection of light within a material is the basis for fiber optics

As light travels from one material to another, it can be absorbed, reflected, or transmitted through, depending on the properties of the two materials. Fiber optic cables are designed to reflect light internally, minimizing data loss as information is sent at high speeds through flashes that represent zeros and ones.

Particle detection has evolved from cloud and bubble chambers to digital 3D displays

As invisible particles passed through cloud and bubble chambers, they disrupted supersaturated vapor and superheated liquid, respectively, creating trails that served as proxies for cosmic rays. The transition from photographed events to digital sensors enhanced data collection and accuracy.

While atoms are normally made of protons, neutrons, and electrons, exotic ones have been built with antimatter—alternate versions of normal matter that live for fractions of a second and are about a billion times as rare.

The Hubble Space Telescope uses curved mirrors to collect and focus light

Classified as a Cassegrain reflector, the observatory bounces incoming visible light and some infrared and ultraviolet light off a primary mirror with a diameter of 2.4 meters. The reflected light is directed to a secondary mirror, which reflects it through a tiny hole in the primary mirror and onto detectors.

Massive blooms of microscopic plankton called dinoflagellates produce the neon blue light seen in glowing tides.

How fusion—which releases energy when two lighter atoms combine to form a heavier atom—differs from fission

Learn how your body is, scientifically, like a firework with its own slow, controlled burn.

Radioactive elements can introduce software errors because the ionizing radiation they produce can detach electrons from atoms, and computer code relies on the distribution of electrons.

When caught in the mouths of cardinal fish, seed shrimp release glowing, bioluminescent chemicals, which alert predators of the cardinal fish, prompting the shrimp's ejection.

The first image of a black hole was captured by creating an Earth-sized virtual observatory from a network of eight radio telescopes.

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

The Mona Lisa's celebrity status and repeated restorations have obscured what made the painting so revolutionary for its time

When a Paris department store hesitated to sell Estée Lauder's perfume, she 'accidentally' broke a bottle, causing the smell to spread throughout the store and shoppers to start asking to buy the scent.

Objects can be 3D printed with light by projecting 2D computerized tomography (CT) scans onto rotating cylinders of resin, which solidify upon exposure.

Explore chaos in this simulation of two double pendulums, where small differences in the release angles produce wildly different outcomes.

The name 'Silicon Valley' arose from the founding of Shockley Semiconductor Laboratory in Fairchild Semiconductor in 1956-57, founded near Stanford University in Palo Alto

As of 2025, the most cited papers in science include a review of graphene, methods to improve image recognition, streamlining electron density calculations, and optimizing protein studies.

The first horror movie is believed to be George Méliès' 1986 short 'The Haunted Castle,' which pioneered the use of special effects

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

Some Pokémon have been named after real and fictional organisms, while some real-world species have been named after Pokémon, such as Chilicola charizard and Binburrum zapdos.

Sony set the standard for cylinder-shaped batteries when it repurposed manufacturing equipment used to make rolls of magnetic recording tape.

Budweiser stores yeast derived from the original 1800s strain in a secret bunker, which only the Head of Yeast Management can access—not even the CEO

Salvador Dalí believed he was his own dead brother, who had died nine months before he was born

An initial public offering or 'IPO' is the process of a private company becoming public by putting shares of the company on the stock market for purchase.

American short story writer Flannery O'Connor raised 40 peacocks, which became potent symbols for her fiction's elegant violence

Ebola is a filovirus, meaning it resembles a thread under a microscope, though it sometimes twists and can resemble a bowl of spaghetti.

Clever Hans was a 1900s horse that was believed to be able to solve math equations, tell time, and read and comprehend German, until a psychology student discovered how he got his answers.