Laser = Light Amplification by the Stimulated Emission of Radiation
26/12/2010 § Leave a comment
photo source: wikipedia.org
LASER is an acronym for Light Amplification by the Stimulated Emission of Radiation. In 1917, Albert Einstein first theorized about the process which makes lasers possible called "Stimulated Emission."
Before the Laser there was the Maser
In 1954, Charles Townes and Arthur Schawlow invented the maser (microwave amplification by stimulated emission of radiation), using ammonia gas and microwave radiation – the maser was invented before the (optical) laser. The technology is very close but does not use a visible light.
On March 24, 1959, Charles Townes and Arthur Schawlow were granted a patent for the maser. The maser was used to amplify radio signals and as an ultrasensitive detector for space research.
In 1958, Charles Townes and Arthur Schawlow theorized and published papers about a visible laser, an invention that would use infrared and/or visible spectrum light, however, they did not proceed with any research at the time.
Many different materials can be used as lasers. Some, like the ruby laser, emit short pulses of laser light. Others, like helium-neon gas lasers or liquid dye lasers emit a continuous beam of light.
In 1960, Theodore Maiman invented the ruby laser considered to be the first successful optical or light laser.
Many historians claim that Theodore Maiman invented the first optical laser, however, there is some controversy that Gordon Gould was the first.
Gordon Gould – Laser
Gordon Gould was the first person to use the word "laser". There is good reason to believe that Gordon Gould made the first light laser. Gould was a doctoral student at Columbia University under Charles Townes, the inventor of the maser. Gordon Gould was inspired to build his optical laser starting in 1958. He failed to file for a patent his invention until 1959. As a result, Gordon Gould’s patent was refused and his technology was exploited by others. It took until 1977 for Gordon Gould to finally win his patent war and receive his first patent for the laser.
The first gas laser (helium neon) was invented by Ali Javan in 1960. The gas laser was the first continuous-light laser and the first to operate "on the principle of converting electrical energy to a laser light output." It has been used in many practical applications.
Robert Hall – Semiconductor Injection Laser
In 1962, Robert Hall created a revolutionary type of laser that is still used in many of the electronic appliances and communications systems that we use every day.
Kumar Patel – Carbon Dioxide Laser
The carbon dioxide laser was invented by Kumar Patel in 1964.
Hildreth "Hal" Walker – Laser Telemetry
Hildreth Walker invented laser telemetry and targeting systems.
Doctor Steven Trokel patented the Excimer laser for vision correction. The Excimer laser was originally used for etching silicone computer chips in the 1970s. Working in the IBM research laboratories in 1982, Rangaswamy Srinivasin, James Wynne, and Samuel Blum saw the potential of the Excimer laser in interacting with biological tissue. Srinivasin and the IBM team realized that you could remove tissue with a laser without causing any heat damage to the neighboring material.
New York City ophthalmologist, Steven Trokel made the connection to the cornea and performed the first laser surgery on a patient’s eyes in 1987. The next ten years were spent perfecting the equipment and the techniques used in laser eye surgery. In 1996, the first Excimer laser for ophthalmic refractive use was approved in the United States.
Note: It took the observations of Dr. Fyodorov in a case of eye trauma in the 1970’s to bring about the practical application of refractive surgery through radial keratotomy.
How a Laser Works
Lasers are possible because of the way light interacts with electrons. Electrons exist at specific energy levels or states characteristic of that particular atom or molecule. The energy levels can be imagined as rings or orbits around a nucleus. Electrons in outer rings are at higher energy levels than those in inner rings. Electrons can be bumped up to higher energy levels by the injection of energy-for example, by a flash of light. When an electron drops from an outer to an inner level, "excess" energy is given off as light. The wavelength or color of the emitted light is precisely related to the amount of energy released. Depending on the particular lasing material being used, specific wavelengths of light are absorbed (to energize or excite the electrons) and specific wavelengths are emitted (when the electrons fall back to their initial level).
For a ruby laser, a crystal of ruby is formed into a cylinder. A fully reflecting mirror is placed on one end and a partially reflecting mirror on the other. A high-intensity lamp is spiraled around the ruby cylinder to provide a flash of white light that triggers the laser action. The green and blue wavelengths in the flash excite electrons in the chromium atoms to a higher energy level. Upon returning to their normal state, the electrons emit their characteristic ruby-red light. The mirrors reflect some of this light back and forth inside the ruby crystal, stimulating other excited chromium atoms to produce more red light, until the light pulse builds up to high power and drains the energy stored in the crystal.
High-voltage electricity causes the quartz flash tube to emit an intense burst of light, exciting some of the atoms in the ruby crystal to higher energy levels.
At a specific energy level, some atoms emit particles of light called photons. At first the photons are emitted in all directions. Photons from one atom stimulate emission of photons from other atoms and the light intensity is rapidly amplified.
Mirrors at each end reflect the photons back and forth, continuing this process of stimulated emission and amplification.
The photons leave through the partially silvered mirror at one end. This is laser light.