basic principles of lasers

8/14/2019 Basic Principles of Lasers

1/21

1

Basic Principles of Lasers

Presentation By: Zack Hansel

Instructor: Dr. Cristian Bahrim

Presentation for an Honors Contract

Spring 2007 Modern Physics


2/21

2

Summary

Classification of light-atom interaction. Necessary conditions for a lasing transition.

Standard lasing systems:- three-level atom system,

- four-level atom system.

Properties of a laser.

Types and uses of lasers.


3/21

3

Classification of Light-atomInteraction

Stimulated absorption + h >

Spontaneous emission

> + h

Stimulated emission

+ h > + 2h


4/21

4

The Cascade of Photons


5/21

5

Energy Distribution For No atoms in thermal equilibrium at temperature T

the population of atoms Nj on thej-state isNj=Noexp(-Ej/kT) (Boltzman distribution)

where kTrepresents the mean energy of the atoms.

0

1

2

3

4

5

6

7

8

2 4 6 8 10 12 14 16 18 20

Energy

Populati

on

(N1; E1)

(N2; E2)

Ground state

(N2; E2)

(N1; E1)


6/21

6

Understanding the LasingProcess

LASER Light Amplification by

Stimulated Emission of Radiation

Necessary conditions for a lasing transition:

- population inversion,- metastable states.


7/21

7

Population Inversion

0

1

2

3

4

5

6

7

8

2 4 6 8 10 12 14 16 18 20

Energy

P

o

ulatio

n

(N1; E1)

(N2; E2)

Metastable States

Ground state

Long-lived state (~1 ms)

Short-lived state (~1 ns)

Laser beam

Spontaneous

(N2; E2)

(N1; E1)


8/21

8

Three-level Atom

Example: Ruby laser (uses Cr++

ions) Deficiency Photons may be re-absorbed

during the lasing process > it makes the

laser beam weaker.

E3

E2

E1

PUMPING


9/21

9

The build-up of a Laser

1) Pumping

(excitation of atoms)

2) Stimulated emission

of atoms

3) The lasing process

is enriched by multiple

reflections between mirrors

4) A laser beam exits.


10/21

10

Ruby Laser Developed by Theodore H. Maiman in 1960

Creates a beam at = 694 nm (deep red).

Metastable state of ~3ms

Has efficiency of less than 1% but creates a diameterranging from 1 mm to about 25 mm, so a large energy

density is achieved in the laser beam.


11/21

11

Four-level Atom Example: HeNe laser

PUMPING

PUMPING


12/21

12

Properties of a Laser

Monochromaticity same or frequency

Directivity

Highly correlated photons for long distances. High energy-density

Polarization

Modes


13/21

13

Resonant Cavity

HeNe


14/21

14

Modes of Lasers Mono-mode laser Gaussian profile

Multimode lasers


15/21

15

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)

Atomic laser Bose-Einstein condensate.


16/21

16

HeNe Laser


17/21

17

A Look at Laser

Sizes

Dye Laser

Wavelengths


18/21

18

YAG-Nd Laser

Electronic Laser


19/21

19

Comparisons of a Few Lasers

BothIR940-1440nmYAG:Nd

CWMicrowaves

-X-rays

1mm-1nmElectronic

Usually PulseIR-UV360-720nmDye

CWIR9.4-10.6mCO2

CWIR-Visible1.15m-633nmHeNe

Pulse or CWRangeTypical Laser


20/21

20

The 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


21/21

21

Resources

Modern Physics, Kenneth Krane, 2nd

ed., JohnWiley & Sons, Inc. (1996).

Introduction to Laser Physics, Koichi Shimoda,Springer-Verlag (1984).

Optics, Eugene Hecht, 4th ed., Addison Wesley(2002).

Sams Laser FAQ, Samuel Goldwasser,

http://www.repairfaq.org/sam/lasersam.htm.

Wikipedia, www.wikipedia.org

basic principles of lasers

Documents