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Einstein's Excited Atoms...and the Rest is History.

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The invention of lasers gave birth to a multi-billion dollar industry, with laser technology now being used to do everything from removing tattoos to corrective eye surgery, to scanning the price of your loaf of bread in the supermarket. Here at Needham Laser Tech, we think lasers are seriously cool. Okay, maybe we are a bit biased, but in the midst of every day, it's worth taking a pause to reflect on the journey laser technology has taken to reach the point we are at today. So, without further ado, let's take a dive!

 

What does LASER actually mean?


“Laser” is an acronym for Light Amplification by Stimulated Emission of Radiation. It describes any device that creates and amplifies a narrow, focused beam of light whose photons are coherent. In a laser, the atoms or molecules of the lasing medium–either a crystal-like ruby or garnet or a gas or liquid–are “pumped,” so that more of them are at higher energy levels than at the ground state. But, how was this all discovered? It was all thanks to a gentleman whose name we know well...


Einstein's Excited Atoms and Stimulated Emission


Albert Einstein first broached the possibility of stimulated emission in 1917. According to Albert Einstein, when more atoms occupy a higher energy state than a lower one under normal temperature equilibrium, it is possible to force atoms to return to an unexcited state by stimulating them with the same energy as would be emitted naturally. He further proposed that photons prefer to travel together in the same state and that if enough atoms release their photons together with the identical frequency and phase as the original atom, then a cascading effect ensues; as the crowd of identical photons moves through the rest of the atoms, ever more photons will be emitted from their atoms to join them.

In 1928, Einstein's theory of Stimulated Emission was proven by German Atomic Physicist Rudolf Ladenburg. Another decade passed and in 1939 Valentin Fabrikant predicted that stimulated emission will be used to amplify short waves. Then, in 1947, Lamb and Retherford, for the first time, demonstrated stimulated emission. 

Throughout the 1930s and 1940s, several scientists produced demonstrations of the existence of Einstein's Stimulated Emission. It wasn't until the 1950s, however, that scientists found a use for the concept.

 

Along comes the MASER (yes, you read that correctly)


29jpTOWNES1obit-superJumboIn 1953, Charles Hard Townes (pictured right) and graduate students James P. Gordon and Herbert J. Zeiger produced the first microwave amplifier, a device operating on similar principles to the laser, but amplifying microwave radiation rather than infrared or visible radiation. Unfortunately, their MASER was unable to produce a continuous output - the technique was limited by the wavelength of the light produced: in this case, the microwave.

The first continuously operating maser was produced in the Soviet Union by Basov and Prokhorov. They shared the 1964 Nobel Prize with Townes for their work on the maser-laser principle.

In April 1957, Japanese engineer Jun-ichi Nishizawa proposed the concept of a "semiconductor optical maser" in a patent application. That same year, Townes and Arthur Leonard Schawlow began studying infrared "optical masers". As ideas developed, they abandoned infrared radiation to instead concentrate on visible light. In 1958, they filed a patent application for their proposed optical maser alongside a manuscript of their theoretical calculations.

 

Light Amplification by Stimulated Emission of Radiation

 

gordongouldWhile Townes and Schawlow were publishing their findings on optical masers, a graduate student named Gordon Groud (pictured left) was working on a doctoral thesis about the energy levels of excited thallium. When Gould and Townes met, they spoke of radiation emission, as a general subject. Afterwards, in November 1957, Gould noted his ideas for a "laser", including using an open resonator (later an essential laser-device component). In 1959, Gordon Gould first published the acronym "LASER" in the paper The LASER, Light Amplification by Stimulated Emission of Radiation.

 

The first operational LASER!


On May 16, 1960, Theodore H. Maiman operated the first functioning laser at Hughes Research Laboratories, Malibu, California, ahead of several research teams, including those of Townes, Schawlow, and Gould. Later the same year the first gas laser was produced by Ali Javan and William R. Bennett, and Javan would go on to propose the laser diode concept which was operationalised by numerous scientists through the 1960s and early 1970s.


Since then, laser technology has made vast improvements and specialised applications utilised every day with a wider range of laser sources available. The rest really is history. We hope you found our history lesson in laser technology informative!