16.7 Lasers

16.7 Lasers

When light at the frequencies corresponding to the transition between two energy levels of atoms is passed through a collection of these atoms, photons are absorbed from the light beam by atoms in the lower energy level raising them to the higher excited level.

The photon can return to the lower state by emitting at the resonance frequencies.

In an excited state, atoms can emit light.

Albert Einstein used quantum mechanics and equilibrium considerations to analyze the interaction of radi ation with matter in 1916.

While light interacts with atoms in a lower energy state, there is a parallel interaction of light with atoms in the excited energy state.

The excited atoms are stimulated by the light at the resonance frequency to return to the lower energy state.
Each stimulated atom emits a photon at the resonance frequencies and in phase with the stimulating light.

More atoms are in a lower energy state than in a higher one under equilibrium conditions.

When a beam of light at resonance Frequency passes through a collection of atoms in equilibrium, more photons are taken out of the beam by absorption than are added to it by stimulated emission.
It is possible to cause more atoms to occupy a higher energy state through a variety of techniques.
When light passes through atoms with inverted population distribution, more light is added to the beam by stimulated emission than by absorption.

The light is amplified.

There are some unique properties of the light emitted by a laser.

It can be formed into a beam that can be focused into a small area on the order of the wavelength of light.
A large amount of energy can be delivered into a small region with high degree of precision.
The wavelength of the light is determined by the medium used to amplify it.

In 1960, the first laser was built.

There are many different types of laser that operate over a wide range of energies and wavelength.

Some of the lasers at www.nationallaser.com operate in a continuous mode.

Lasers are increasingly used in medicine.

The development of the first laser indicated that it would be useful as a surgical tool.

Laser light focused on a small area could burn off and destroy selected tissue.
Nerve endings are sealed and blood vessels are cauterized to make the procedure less painful.
The cutting tool is not in contact with the tissue.

Before lasers could be used in surgical procedures, a wide range of studies had to be conducted to understand the effect of intense light on various types of tissue.

Technology had to be developed for precise control of light intensity and duration and for accurate positioning of the focal point.
While the surgical use of lasers is growing in many areas of medicine and dentistry, the positional accuracy of laser tissue-removal is particularly important in neurosurgery and eye surgery where a fraction of a millimeter offset can make the difference between success and failure.

Lasers were used for a wide range of procedures.

One such application is the repair of retinal tears.
The back of the eye can be damaged as a result of trauma or disease.
This condition leads to a loss of vision.
Laser procedures have been very successful in restoring normal vision.

A doctor is performing eye surgery.

The tissue is burned and then the retina is "welded" to the underlying tissue.

In an ophthalmological application, lasers are used.

Diabetes can cause disorders in blood circulation.
It can cause serious damage to the eyes.
A laser light focused on the damaged blood vessel stops the leak.
The course of the disease is not halted and new leaks need to be treated.

Laser-assisted in Situ Keratomileusis, also known as the LASIK technique, is a relatively recent application of lasers in ophthal mology.

The aim of this procedure is to correct focusing problems associated with myopia, hyperopia and astigmatism.
The amount and location of the tissue to be removed are programmed by the computer that controls the laser.