The ruby
laser was the first laser to be made functional. Built by Theodore Maiman in
1960, the device was created out of the concept of an "optical
maser," a maser that could operate in the visual or infrared regions
of the spectrum.
In 1958,
after Charles Townes and Arthur Schawlow published an article in the Physical Review,
regarding the idea of optical masers, the race to build a working model began.
While attending a conference in 1959, Maiman listened to a speech given by
Schawlow, describing the use of ruby as a lasing medium. Schawlow stated that
pink ruby, having a lowest energy-state that was too close to the ground-state,
would require too much pumping energy for laser operation, suggesting red ruby as a
possible alternative. Maiman, having worked with ruby for many years, and
having written a paper on ruby fluorescence, felt that Schawlow was being
"too pessimistic." His measurements indicated that the lowest energy
level of pink ruby could at least be partially depleted by pumping with a very
intense light source, and, since ruby was readily available, he decided to try
it anyway.
Also attending the conference was Gordon Gould. Gould suggested that, by pulsing the laser, peak
outputs as high as a megawatt could be produced.
Maiman's
original ruby laser
Components
of original ruby laser
As time went
on, many scientists began to doubt the usefulness of ruby as a laser medium.
Maiman, too, felt his own doubts, but, being a very "single-minded
person," he kept working on his project in secret. He searched to find a
light source that would be intense enough to pump the rod, and an elliptical
pumping cavity of high reflectivity, to direct the energy into the rod. He
found his light source when a salesman from General Electric showed him a few
xenon flashtubes, claiming that the largest could ignite steel wool if
placed near the tube. Maiman realized that, with such intensity, he did not
need such a highly reflective pumping cavity, and, with the helical lamp, would
not need it to have an elliptical shape. Maiman constructed his ruby laser at Hughes
Research Laboratories, in Malibu, California.He used a pink ruby rod, measuring
1 cm by 1.5 cm, and, on May 16, 1960, fired the device, producing the
first beam of laser light.
Theodore
Maiman's original ruby laser is still operational.It was demonstrated on May 15, 2010
at a symposium co-hosted in Vancouver,
British Columbia by the Dr.
Theodore Maiman Memorial Foundation and Simon Fraser University, where Dr. Maiman was Adjunct
Professor at the School of Engineering Science. Maiman's original laser was
fired at a projector screen in a darkened room. In the center of a white flash
(leakage from the xenon flashtube), a red spot was briefly visible.
The ruby
lasers did not deliver a single pulse, but rather delivered a series of pulses,
consisting of a series of irregular spikes within the pulse duration. In 1961,
R.W. Hellwarth invented a method of q-switching, to concentrate the output into a single pulse.
In 1962, Willard Boyle, working at Bell Labs, produced the first continuous output from a ruby laser.
Unlike the usual side-pumping method, the light from a mercury arc lamp was
pumped into the end of a very small rod, to achieve the necessary population
inversion. The laser did not emit a continuous wave, but rather a continuous train of pulses, giving
scientists the opportunity to study the spiked output of ruby. The continuous ruby laser was the first laser to be
used in medicine. It was used by Leon Goldman, a pioneer in laser medicine, for treatments such as tattoo removal, scar
treatments, and to induce healing. Due to its limits in output power,
tunability, and complications in operating and cooling the units, the
continuous ruby laser was quickly replaced with more versatile dye, Nd:YAG, and argon lasers.
Ruby lasers have declined in use with the discovery of better lasing media. They are still used in a number of applications where short pulses of red light are required. Holographers around the world produce holographic portraits with ruby lasers, in sizes up to a meter square. Because of its high pulsed power and good coherence length, the red 694 nm laser light is preferred to the 532 nm green light of frequency-doubled Nd:YAG, which often requires multiple pulses for large holograms. Many non-destructive testing labs use ruby lasers to create holograms of large objects such as aircraft tires to look for weaknesses in the lining. Ruby lasers were used extensively in tattoo and hair removal, but are being replaced by alexandrite and Nd:YAG lasers in this application.
source : http://en.wikipedia.org/wiki/Ruby_laser
