Stuff You Should Know

How Lasers Work

February 12, 2026

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  • The acronym LASER stands for Light Amplification by Stimulated Emission of Radiation, and laser light is fundamentally different from regular light because it is monochromatic (single wavelength), coherent (photons are perfectly in phase), and collimated (traveling in the same direction). 
  • The theoretical foundation for lasers was established by Albert Einstein in 1917, who theorized stimulated emission, but the first functional laser, which used a ruby crystal, was built by Theodore Maiman in 1960. 
  • Lasers are categorized into types like Solid State, Gas, Fiber, Liquid (Dye), and Diode, with applications ranging from common uses like barcode scanning and fiber optics to advanced uses like nuclear fusion research and laser cooling for atomic clocks. 

Segments

LASER Acronym and Light Comparison
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(00:02:08)
  • Key Takeaway: LASER stands for Light Amplification by Stimulated Emission of Radiation, and laser light differs from white light by being monochromatic, coherent, and collimated.
  • Summary: The acronym LASER stands for Light Amplification by Stimulated Emission of Radiation. Regular white light contains many different wavelengths, but laser light is highly concentrated at a single, specific wavelength. Laser light is also coherent, meaning its photons are perfectly in phase, and collimated, meaning all photons travel in the exact same direction.
Einstein’s Theoretical Foundation
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(00:09:14)
  • Key Takeaway: Einstein theorized stimulated emission, where a photon can create an identical second photon without losing the first, which is crucial for laser operation.
  • Summary: Einstein laid the theoretical groundwork for lasers by proposing that light is made of discrete packets called photons (E=hf). He theorized stimulated emission, where an incoming photon can cause an excited atom to release an identical photon without the original photon being absorbed. This cascading effect allows for the creation of many identical, non-interfering photons traveling in the same direction.
Maser and First Laser Construction
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(00:15:58)
  • Key Takeaway: Charles Towns built the first functional device, a maser (microwave laser), before Theodore Maiman built the first optical laser using a ruby crystal in 1960.
  • Summary: In the 1950s, Charles Towns created a maser, which used microwave beams instead of light, based on Einstein’s theories. Theodore Maiman built the first functional laser in 1960 using a pink ruby crystal as the gain medium, surrounded by a flash bulb and reflective silver ends. This initial ruby laser produced light at the precise wavelength of 694 nanometers (Ruby Red).
Types of Lasers Explained
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(00:21:00)
  • Key Takeaway: Lasers are classified by their gain medium, including solid-state crystals (like those used in tattoo removal), gases (like CO2 for welding), and fiber optics (highly efficient for telecommunications).
  • Summary: Solid-state lasers use doped crystals or glass as the gain medium, following the tradition of Maiman’s original device. Gas lasers, excited by electrical current, include powerful carbon dioxide lasers used for welding and excimer lasers that use UV light to break molecular bonds without heat. Fiber lasers are highly efficient, converting over 50% of input electricity into light, often used in fiber optic internet.
Diode Lasers and Pulsed Energy
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(00:29:31)
  • Key Takeaway: Weak diode lasers power pointers using semiconductor junctions, while pulsed lasers achieve extreme power by releasing built-up energy in ultra-short bursts.
  • Summary: Laser pointers use diode (semiconductor) lasers powered by electron exchange between two materials, making them cheap but weak, causing their beam to spread over distance. Pulsed lasers release energy in bursts lasting billionths or trillionths of a second, allowing them to achieve power levels thousands of times greater than a continuous beam.
High-Power Laser Applications
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(00:34:36)
  • Key Takeaway: Extremely powerful lasers, like the Zeus system, are being built to recreate conditions inside stars and black holes, and high-energy lasers achieved net energy gain in nuclear fusion experiments in 2022.
  • Summary: Physicists are building ultra-powerful lasers, such as the Zeus system, to study extreme cosmic phenomena. In 2022, Lawrence Livermore Lab used 192 lasers to achieve the first nuclear fusion reaction with a net energy gain, a moment likened to the Wright brothers’ first flight. These high-energy lasers are key to unlocking the potential of fusion power.
Medical and Military Uses
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(00:37:43)
  • Key Takeaway: Lasers offer precise, less invasive surgical options, exemplified by brain tumor removal through tiny skull openings and the reshaping of the cornea during LASIK surgery.
  • Summary: In medicine, lasers are preferred over scalpels for surgery because they are more precise, cause less tissue damage, and self-cauterize, leading to quicker healing. LASIK, approved in 1999, uses lasers to reshape the cornea, significantly improving vision for many recipients. Military applications include directed energy systems used by the Navy to destroy drones, and laser cooling is used to trap atoms for next-generation atomic clocks.
Listener Mail on Color Psychology
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(00:45:33)
  • Key Takeaway: In some 21st-century African-American church traditions, attendees wear the deceased person’s favorite color, and purple specifically often signifies royalty associated with Jesus Christ.
  • Summary: A listener provided insight into color traditions at African-American churches, noting that attendees sometimes wear the favorite color of the deceased. Purple is typically associated with royalty in Jesus Christ. Therefore, seeing purple at a service may recognize the deceased returning to God or simply reflect that person’s favorite color.