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Laser: the story on HearLore | HearLore
Laser
On the 16th of May 1960, Theodore Maiman stood in a laboratory in Malibu, California, and turned on a device that would change the course of modern physics. He did not use a complex array of mirrors or a gas mixture, but a synthetic ruby crystal pumped by a high-intensity flash lamp. This machine produced a pulse of red light at 694 nanometers, the first functional laser ever built. Before this moment, the concept of light amplification by stimulated emission of radiation existed only in the theoretical papers of Albert Einstein and the laboratory notes of Charles Townes. Maiman's achievement was so unexpected that it caught the scientific community off guard, as major research teams at Columbia University and Bell Labs had been racing to build one but had been stymied by technical hurdles. The device was capable of only pulsed operation, yet it proved that a coherent beam of light could be generated artificially. This single event marked the transition from quantum theory to practical application, creating a tool that would eventually become ubiquitous in every sector of human society.
The War Over the Word Laser
While Maiman built the first working machine, a bitter legal and intellectual battle was already brewing over who deserved credit for the invention. Gordon Gould, a graduate student at Columbia University, had sketched the design of an optical resonator and coined the acronym LASER in his notebook on the 11th of November 1957. He envisioned a future where different parts of the spectrum would have their own names, such as XASER for X-rays and RASER for radio waves. However, the United States Patent and Trademark Office denied his application, awarding the patent instead to Charles Townes and Arthur Schawlow of Bell Labs. This decision sparked a twenty-eight-year legal fight that would drag on until 1987, when Gould finally won his first significant patent infringement claim. The dispute was not merely about money but about the fundamental definition of the technology. Gould had proposed using an open resonator, a critical component that allowed the laser to function as an oscillator rather than just an amplifier. The history of the laser is thus a story of competing egos, where the theoretical foundations laid by Townes and Schawlow clashed with the practical ingenuity of Gould. The term laser itself, originally an acronym for light amplification by stimulated emission of radiation, eventually became an anacronym, used as a noun so widely that it is no longer considered an abbreviation. The back-formed verb to lase entered the lexicon, describing the act of emitting coherent light, a linguistic evolution that mirrors the rapid adoption of the technology itself.
The Physics of the Chain Reaction
Common questions
When did Theodore Maiman build the first functional laser?
Theodore Maiman built the first functional laser on the 16th of May 1960. He used a synthetic ruby crystal pumped by a high-intensity flash lamp to produce a pulse of red light at 694 nanometers.
Who coined the acronym LASER and when did he sketch the design?
Gordon Gould coined the acronym LASER and sketched the design of an optical resonator on the 11th of November 1957. He envisioned future names for different parts of the spectrum such as XASER for X-rays and RASER for radio waves.
What is the difference between a laser and thermal radiation?
A laser produces a beam that is spatially and temporally coherent with a very narrow frequency spectrum. Thermal radiation emits photons randomly with varying energies and directions without coherence.
When was the first gas laser constructed and what did it use?
Ali Javan and his colleagues at Bell Labs constructed the first gas laser later in 1960. They used a mixture of helium and neon to produce continuous infrared light at 633 nanometers.
Who invented the semiconductor laser and when did it happen?
Robert N. Hall invented the semiconductor laser in 1962. His device was made of gallium arsenide and emitted near-infrared light at 850 nanometers.
What is the power output of the ELI-NP facility laser as of 2019?
The ELI-NP facility in Romania houses the world's most powerful laser as of 2019. It is capable of delivering 10 petawatts of power.
The operation of a laser relies on a quantum mechanical phenomenon known as stimulated emission, a process where an incoming photon triggers an excited atom to release a second photon that is identical in wavelength, phase, and direction. This creates a chain reaction, but it requires a specific condition called population inversion, where more atoms are in an excited state than in a lower energy state. In a standard two-level system, this is impossible to maintain because the probability of stimulated emission increases as the upper level is populated, eventually balancing the absorption rate. To overcome this, laser designers utilize three-level or four-level systems, allowing electrons to relax quickly to a metastable state where they can accumulate. The gain medium, which can be a gas, liquid, solid, or plasma, absorbs energy from a pump source, such as an electric current or another light source. This energy raises electrons to higher energy levels, and when they drop back down, they emit photons. These photons bounce back and forth between two mirrors, one of which is partially transparent, amplifying the light with each pass. The result is a beam that is spatially coherent, meaning it can be focused to a tiny spot, and temporally coherent, meaning it has a very narrow frequency spectrum. This coherence distinguishes the laser from thermal radiation, where photons are emitted randomly with varying energies and directions. The laser is essentially an optical oscillator, a device that sustains a wave of light through positive feedback, much like the screech of a microphone placed too close to a speaker in a public address system.
From Ruby Crystals to Gas Discharges
The early history of lasers was defined by the search for materials that could sustain population inversion. The first laser, built by Maiman, used a ruby crystal doped with chromium, which emitted red light at 694 nanometers. Later that same year, Ali Javan and his colleagues at Bell Labs constructed the first gas laser, using a mixture of helium and neon to produce continuous infrared light. This breakthrough allowed for continuous-wave operation, a significant improvement over the pulsed ruby laser. The helium-neon laser became a staple of optical research and educational laboratories, operating at 633 nanometers with high coherence. The development of the carbon dioxide laser by C. Kumar N. Patel in 1964 marked another turning point, as it became the first high-power continuous-wave gas laser. With an efficiency of over 30 percent, the CO2 laser found widespread use in industry for cutting and welding. Gas lasers continued to evolve, with argon-ion lasers providing multiple lasing transitions between 351 and 528.7 nanometers, and metal ion lasers generating deep ultraviolet wavelengths. The diversity of gas lasers expanded to include nitrogen transverse electrical discharge lasers, which produced incoherent ultraviolet light at 337.1 nanometers. These devices demonstrated that the choice of gain medium determined the wavelength and application of the laser, from the visible spectrum used in spectroscopy to the infrared used in industrial processing. The evolution from solid-state ruby to gas mixtures laid the groundwork for the specialized lasers that would follow, each tailored to specific needs in science and industry.
The Semiconductor Revolution
The invention of the semiconductor laser, or laser diode, in 1962 by Robert N. Hall marked the beginning of the modern era of compact and efficient light sources. Hall's device, made of gallium arsenide, emitted near-infrared light at 850 nanometers and could only operate in pulsed mode. By the end of that year, Nick Holonyak Jr. demonstrated the first semiconductor laser with visible emission, though it required cooling to liquid nitrogen temperatures. The development of room-temperature, continuous-operation diode lasers by Zhores Alferov in the Soviet Union and Izuo Hayashi and Morton Panish of Bell Labs in 1970 revolutionized the field. These devices, based on heterojunction structures, became the backbone of optical communication and consumer electronics. Commercial laser diodes now emit wavelengths ranging from 375 to 3500 nanometers, powering everything from laser pointers to high-power industrial cutting systems. Vertical cavity surface-emitting lasers, or VCSELs, offer a circular output beam and have become essential for data transmission and sensing applications. The pursuit of a silicon laser remains a holy grail for optical computing, as silicon is the material of choice for integrated circuits. Teams have developed hybrid silicon lasers and monolithically integrated nanowire lasers to overcome the material's natural resistance to lasing. These advancements have enabled on-chip optical signal processing with repetition frequencies up to 200 GHz. The semiconductor laser has transformed the laser from a bulky laboratory instrument into a ubiquitous component of modern life, embedded in CD players, barcode scanners, and fiber-optic networks.
The Pulse of Ultrafast Science
The ability to generate pulses of light lasting only femtoseconds, or quadrillionths of a second, has opened a new frontier in physics and chemistry. Mode-locked lasers, such as those using titanium-doped sapphire, can produce pulses as short as a few femtoseconds, allowing scientists to observe processes that were previously too fast to see. These pulses repeat at the round-trip time of the laser cavity, creating a frequency comb that is invaluable for precision metrology. The optical bandwidth of such a pulse is spread over a considerable range, contrary to the narrow bandwidth of continuous-wave lasers. This capability has led to the field of femtosecond physics, where researchers study the dynamics of chemical reactions and electron movements in real time. Q-switching techniques allow for the storage of energy in the gain medium and its rapid release, creating giant pulses with peak powers that can reach petawatts. The National Ignition Facility, with its 192-beam, 1.8-megajoule laser system, represents the pinnacle of this technology, designed to ignite nuclear fusion reactions. The ELI-NP facility in Romania houses the world's most powerful laser as of 2019, capable of delivering 10 petawatts of power. These ultrafast lasers are not just tools for research; they are essential for applications ranging from laser ablation to the creation of optical parametric oscillators. The ability to control the duration and intensity of laser pulses has made them indispensable for studying the fundamental laws of nature.
The Weapon and The Healer
Lasers have found their way into the most unexpected places, from the operating room to the battlefield. In medicine, lasers are used to treat cancer by shrinking or destroying tumors, to perform eye surgery, and to remove kidney stones. The precision of laser therapy allows surgeons to cause less damage, pain, and scarring than traditional methods. However, the same properties that make lasers useful for healing also make them dangerous weapons. Laser weapons, such as the Laser Weapon System or LaWS tested by the United States Navy, can shoot down small unmanned aerial vehicles and rocket-propelled grenades. The Protocol on Blinding Laser Weapons bans the use of weapons designed to cause permanent blindness, yet dazzlers are still used by military and law enforcement organizations to temporarily incapacitate targets. The moral controversy surrounding laser-induced blindness remains a significant issue, as even low-power lasers can cause immediate and permanent vision loss. The safety of lasers is classified into different categories, with Class 4 lasers capable of burning skin and causing severe eye damage. Despite these dangers, lasers continue to be used in a wide range of applications, from laser lighting displays to laser-based traffic enforcement. The dual nature of the laser, as both a tool for healing and a weapon of war, underscores its profound impact on human society.