Laser Uses

1. Eye surgeons can use laser beams to "weld" detached retinas back onto the eyeball without cutting into the eye. The laser beam is directed onto the retina through the pupil of the eye. Scar tissue forms at the impact site of the laser beam and at that point fastens the retina to the inner surface of the eye.

2. Laser beams have been used for industrial purposes. The diamond dies through which extremely thin wire filaments are drawn can be drilled with a laser beam. The already narrow beam of light can be further reduced to a diameter of less than 0.001 inch. The energy concentrated in this tiny beam is known to be sufficient to cut through diamond.

3. Laser beams are sometimes used as reference points* in building construction. They accurately mark straight lines along the course of large buildings. A laser beam is used by scientists to detect whether portions of a two-mile-long particle accelerator in Stanford, California, move out of alignment.

4. Three-dimensional images can be produced by laser beams. Holography, or laser photography, relies on the coherent beam of laser light to produce a hologram, a three-dimensional information record of an object on photographic film. A portion of a laser beam is reflected off the object and into the path of a reference beam of unreflected laser light. The interaction of the two beams produces a unique interference pattern in the film. When another laser beam is aimed through the hologram's interference "picture," a three-dimensional image of the original object is reconstructed. The image looks like a picture or a slide.

5. The distance between the Earth and the Moon has been measured accurately by means of a laser beam. Scientists recorded the time taken for a laser beam to bounce off a reflector placed by astronauts on the moon. Knowing the speed of light in a given period of time, scientists were able to compute the distance with accuracy.

Exercise 1. Answer the questions.

1. What are main applications of lasers?

2. What can you tell about measuring distances by means of a laser beam?

3. What do you know about medical uses of lasers?

TASK 9

Read and entitle the text.

To produce laser light it is necessary to have a pair of mirrors at either end of the lasing medium. These mirrors are often known as an optical oscillator due to the process of oscillating photons between the two mirrored surfaces. The mirror positioned at one end of the optical oscillator is half-silvered, therefore it reflects some light and lets some light through. The light that is allowed to pass through is the light that is emitted from the laser. During this process photons are constantly stimulating other electrons to make the downward energy jump, hence causing the emission of more and more photons and an avalanche effect*, leading to a large number of photons being emitted of the same wavelength and phase.

Below is a graphical illustration of what has been detailed above. The graphics illustrate how laser light is created using a ruby laser, the first folly functioning laser. (Theodore Maiman invented the ruby laser on May 16th 1960 at the Hughes Research Laboratories.)

Fig.1. Schematic of Laser in Non-Lasing State.

Fig.2. Schematic Illustrating the Excitation of Atoms Using Light Source.

Fig.3. Schematic Showing Photon Emission.

Fig.4. Schematic Showing the Stimulated Emission of Further Photons.

Fig.5. Schematic Showing Column of Laser Light Leaving Optical Osculate.

*avalanche effect – лавинообразный эффект

Exercise 1. Say what you have learnt about:

1. a ground-state energy level and an excited level.

2. the properties of laser light.

3. the stimulated emission.