Good morning. It's Tuesday, Oct. 14, and we're bringing you the latest Science & Technology newsletter. Every week, we provide fascinating deep dives into the worlds of physics, chemistry, biology, geoscience, computer science, and more.
This week, we're covering lasers. The diverse range of use cases for these devices, from hair removal and timekeeping to fiber-optic communication and vision repair, made us curious about how they work and what makes their properties so varied.
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— Marco Machado, 1440 Science and Technology Editor |
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Background
Lasers are tools that emit concentrated beams of visible light by pushing electrons into emitting photons. The term is an acronym for light amplification by stimulated emission of radiation.
Lasers are the successors to the maser, a microwave beam device invented in the 1950s (explore lasers’ history). They are designed to emit monochromatic (single-color) light in one direction rather than the blackbody spectrum of colors emitted in all directions by a light bulb, star, or other source.
These properties have made lasers ubiquitous in manufacturing, medical treatment, military use, and communications technology (learn more).
Population Inversion
Atoms can be modeled as positively charged nuclei surrounded by negatively charged electrons at discrete levels that vary in distance from the nuclei (atomic models, explained).
Like moving through a ladder's rungs, electrons can move up to a higher energy level upon absorbing energy. Typically, this excited state does not last long—negative charges are attracted to positive ones—and electrons drop to a lower energy level, emitting light in the process (atomic spectra, explained).
However, some levels are considered metastable. Just as glow-in-the-dark toys slowly emit light after short exposure to energy, electrons can be quickly energized into metastable states, where they can linger for minutes before dropping.
If more atoms in a material have their electrons pumped up to these states than atoms with electrons in their natural, lower states, the material exhibits population inversion. Electricity, flash lamps, chemical reactions, and other pumping methods ensure a steady reservoir of these excited electrons while the laser operates.
Stimulated Emission
Over 40 years before the invention of the laser, Albert Einstein proposed that electrons could be stimulated to drop from their energy levels and emit light.
Much like vibrating vocal cords can produce a musical note to cause glass to vibrate with the same note and shatter (resonance, visualized), Einstein surmised that a passing photon—a particle of light—could cause an excited electron to emit an identical particle. This is only possible if the difference in the electron’s levels matches the energy of the passing photon.
Within a laser, a photon with an energy corresponding to the material’s metastable state passes through the population-inverted material. This triggers electrons to drop and produce identical photons that travel in the same direction. These photons bounce between mirrors on either end of the material, stimulating additional emissions of identical photons (watch visualization).
The emerging laser beam consists of a small percentage of these photons that pass through a cavity or a semitransparent portion of one of the mirrors. So long as the laser is “on,” the population inversion mechanism continues to pump electrons, maintaining the reservoir of metastable electrons for stimulated emission.
Lasers can be made from crystals, gases, fiber optics, and other materials with unique metastable states, producing various colors and beam durations (types of lasers).
Applications
Surgical lasers can burn and seal wounds, destroy cancer cells, kidney stones, and gallstones, reshape the eye's cornea (LASIK, explained), and seal tears in the retina to prevent further detachment.
Dermatologists use lasers to remove hair, tattoos, and blemishes (learn more), while dentists use them to remove tooth decay and diseased gums during root canals and accelerate teeth-whitening procedures.
Lasers allow for precise marking, welding, cutting, drilling, and surface treatments of materials in industrial settings, including when manufacturing integrated circuits. They are also the backbone of CD, DVD, and Blu-ray systems, which use lasers to write and read digital data (watch explainer).
Counterintuitively, lasers can cool objects to observe quantum phenomena at temperatures near absolute zero and to ensure the accuracy of clocks for GPS systems. |
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Tweezers made out of lasers won the 2018 Nobel Prize in physics |
At 96, Arthur Ashkin became the oldest person to win a Nobel Prize for showing how light can hold and measure objects. The award was also given to Gérard Mourou and Donna Strickland for developing a method of creating optical pulses. Watch how these tools work and their applications in microbiological environments here. |
Gravitational waves are detected by measuring shifts in interfering lasers |
The Laser Interferometer Gravitational-Wave Observatory splits a laser and sends the two beams down 4-kilometer-long perpendicular tunnels, where they reflect off two mirrors. Passing gravitational waves warp space, causing the reflections to be out of sync when they meet. Explore a LIGO replica and learn how it works here. |
Optical clocks track time using electron transitions involving visible light |
Since the frequency of visible light is significantly greater than that of microwaves used in cesium atomic clocks, optical clocks are about 100 times more accurate, losing about one second across the entire age of the universe. Read about how this technology will change the definition of a second for the first time in 50 years here. |
Fiber lasers used for metal engravings can’t burn your skin |
These devices use diodes and mirrors to create pulses of light that can vaporize metal in billionths of a second, though at wavelengths that cannot react with organic material. Pulse width, power, and speed adjustments can produce white, black, and even colored patterns via controlled heat reactions. Learn more about them here. |
Laser-etched electric charges guide toner during laser printing |
When sending a print job, a laser uses file data to map an image of positively charged regions onto a drum separately for each color toner. Once the negatively charged toner is applied where it was electrically attracted, heat and pressure fuse it onto the paper. Read more about lasers and toner chemistry here. |
Space probes propelled by lasers may one day visit distant solar systems |
Launched in 2016, Breakthrough Starshot is a project to send gram-sized spacecraft to the nearest stars and their planets at 10%-20% the speed of light after being accelerated by ground-based laser systems. The project requires orders of magnitude advancements to current technology, which you can read about here. |
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Like all great scientists, we love spending time researching the latest scientific breakthroughs, tech releases, engaging explainers, and the connections between science and society that are making headlines. Here's what we found this week.
> Renewable energy surpasses coal electricity generation for the first time
NPR | Alana Wise. In the first half of 2025, renewable energy—including solar, wind, and hydropower—contributed 34.3% of all electricity generated worldwide, compared with 33.1% from coal, led by growth in countries like China and India. (Read)
> Researchers develop biodegradable bamboo plastic
Earth.com | Sanjana Gajbhiye. A team at Northeast Forestry University developed the material by breaking bamboo down into a gel, which can form dense, flexible structures with temperature and pressure resistance of commercial plastics. (Read)
> Financial institutions express concern about a possible AI bubble
The Associated Press | Kelvin Chan & Matt O'Brien. With tech stock prices surging for years amid the expected productivity improvements AI may bring, analysts warn markets may suffer severe collapses if the potential proves to be unmet. (Read)
> Phase 1 human trials for Salmonella vaccine show promising results
Gizmodo | Ed Cara. The University of Maryland's trial involved 22 healthy adults, with those who received the vaccine developing immune responses to three types of Salmonella—the leading cause of food poisoning. (Read)
> What a psychological analysis of 38,245,928 obituaries revealed about legacy
ZME Science | Tibi Puiu. Tradition and benevolence were identified as two key values in how individuals are remembered, where the former was most prominent in older males and the latter in younger females, highlighting potential biases. (Read)
> Lasers: How these devices help the immune system remove tattoos (Watch) |
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New in 1440 Science & Technology |
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During a pulse lasting 25 quintillionths of a second, the most powerful laser in the US produces over 100 times the global output of electrical power. |
Learn more about the Zettawatt-Equivalent Ultrashort Pulse Laser System here. |
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