LASERSLight Amplification by Stimulated Emission of Radiation

It is a device that emits light(Electromagnetic Radiation) Through the process called OPTICAL AMPLIFICATION based on the stimulated emission of photons

The laser light is notable for its high degree of spatial and temporal coherence

LOSER“Light Oscillation by Stimulated Emission of Radiation”the FIRST and more CORRECT term for LASER

MaserMicrowave Amplification by Stimulated Emission of

Radiation

 Charles H. Townes, James P. Gordon, and H. J. Zeiger built the first ammonia maser at Columbia University in 1953. This device used Stimulated Emission in a stream of energized ammonia molecules to produce amplification of microwaves at a frequency of about 24.0 GHertz.

Townes later worked with Arthur L. Schawlow to describe the principle of the optical maser, or LASER, which Theodore Maiman created the first working model of in 1960. For their research in the field of stimulated emission, Townes, Basov and Prokhorov were awarded the Nobel Prize in Physics in 1964.

How Laser Works?

Ruby Laser Developed by Theodore H. Maiman in 1960 Creates a beam at λ = 694 nm (deep red). Metastable state of ~3ms Has efficiency of less than 1% but creates a diameter ranging from 1 mm to about 25 mm, so a large energy density is achieved in the laser beam. Used by rangefinders in 1960, until the more efficient

Nd:YAG came a Decade later It is now used for drilling holes in diamonds It is the first laser made functional

Properties of a Laser • Monochromaticity – same λ or

frequency • Directivity • Highly correlated photons for long

distances. • High energy-density • Polarization • Modes

MODES of LASER

MONO-MODE LASER

MultiMode Lasers

Types of LASERS • Gaseous laser : - atomic gaseous lasers (e.g. HeNe) - molecular laser (e.g. CO2) • Dye laser (e.g. N2 - rhodamine) • Electronic laser (uses the acceleration of

electrons) • Solid laser – semiconductor (YAG-Nd laser Neodymium:Yttrium Aluminium Garnet) • Atomic laser – Bose-Einstein condensate.

Comparisons of a Few Lasers

Laser Typical λ Range Pulse or CW

HeNe 1.15µm-633nm IR-Visibile CW

CO2 9.4-10.6µm IR CW

Dye 360-720nm IR-UV Pulse

Electronic 1mm-1nm Microwaves - Xray

CW

YAG:Nd 940-1440nm IR BOTH

Use of Lasers

Science – precise measurements, spectroscopy

Medicine – laser scalpel, eye surgery Industry – cutting and welding, guidance

systems Arts – etching Telecommunications (fiber optics) Radars Precise measurement of long distances (e.g.

Moon) Consumer – CDs, DVDs, laser lights

Magnifying Glass

A magnifying glass (simple magnifier) is a converging lens. It allows us to focus on objects closer than the near point, so that they make a larger, and therefore clearer, image on the retina.

Telescope

A refracting telescope consists of two lenses at opposite ends of a long tube. The objective lens is closest to the object, and the eyepiece is closest to the eye.

Astronomical Telescopes

Astronomical telescopes need to gather as much light as possible, meaning that the objective must be as large as possible. Hence, mirrors are used instead of lenses, as they can be made much larger and with more precision.

Terrestrial Telescope

A terrestrial telescope, used for viewing objects on Earth, should produce an upright image. Here are two models, a Galilean type and a spyglass:

Compound Microscope

A compound microscope also has an objective and an eyepiece; it is different from a telescope in that the object is placed very close to the eyepiece.

Cameras

There is a certain range of distances over which objects will be in focus; this is called the depth of field of the lens. Objects closer or farther will be blurred