A Short A Short HHistory of Laseristory of Laser

H. R. KhalesifardH. R. KhalesifardInstitute for Advanced Studies in Institute for Advanced Studies in

Basic SciencesBasic SciencesEmail: khalesi@iasbs.ac.irEmail: khalesi@iasbs.ac.ir

Stimulated emission, The Stimulated emission, The MASER and The LASERMASER and The LASER

(1916) The concept (1916) The concept of stimulated of stimulated emission emission Albert Albert EinsteinEinstein

h

E1

E2

AbsorptionE1

E2h

Spontaneous Emission

E1

E2hh h

Stimulated Emission

hEE 12

(1928) Observation of negative absorption or (1928) Observation of negative absorption or stimulated emission near to resonant stimulated emission near to resonant wavelengths, wavelengths, Rudolf Walther LadenburgRudolf Walther Ladenburg

E1

E2hh h

Stimulated Emission(negative absorption)

(1930s) If a physical system be in thermodynamic (1930s) If a physical system be in thermodynamic equilibrium the population inversion and so the equilibrium the population inversion and so the stimulated emission is impossiblestimulated emission is impossible

E1, N1

E2, N2hh h

Stimulated Emission

h

E1, N1

E2, N2

Absorption

LASER(MASER)

Light (Microwave) Amplification by

Stimulated Emission of Radiation

The MaserThe Maser

Left to right: Prokhorov, Townes and Basov at the Lebedev institute (1964 Nobel prize in Physics for developing the (1964 Nobel prize in Physics for developing the “Maser-Laser principle”) “Maser-Laser principle”)

Townes (left) and Gordon (right) and the ammonia maser they had built at Colombia University

The LASERThe LASER

(1951) (1951) V. A. FabrikantV. A. Fabrikant ““A method for the amplification of A method for the amplification of electromagnetic radiation (ultraviolet, visible, infrared, and electromagnetic radiation (ultraviolet, visible, infrared, and radio waves)radio waves)” patented in Soviet Union.” patented in Soviet Union.

(1958) (1958) Townes Townes andand Arthur L. Schawlow Arthur L. Schawlow, “, “Infrared and Infrared and Optical Masers,Optical Masers,” Physical Review” Physical Review

(1958) (1958) Gordon GouldGordon Gould definition of “ definition of “LaserLaser” as “” as “Light Light Amplification by Stimulated Emission of RadiationAmplification by Stimulated Emission of Radiation””

(1960) (1960) Schawlow Schawlow andand Townes Townes U. S. Patent No. 2,929,922 U. S. Patent No. 2,929,922

(1960) (1960) Theodore MaimanTheodore Maiman Invention of the first Invention of the first Ruby LaserRuby Laser (1960) (1960) Ali JavanAli Javan The first The first He-Ne LaserHe-Ne Laser

Arthur Schawlow adjusting a ruby laser that he made at the Bell Labs in 1960

Arthur Schawlow adjusting a ruby laser that he made at the Bell Labs in 1960

Maiman Maiman and the and the first ruby first ruby laserlaser

Ali Javan and Ali Javan and the first He-the first He-Ne LaserNe Laser

The laser cavity length should be multiple of light wavelength

The laser cavity length should be multiple of light wavelength

The laser StructureThe laser Structure

Front Mirror

End Mirror

Lasing MediumLasing Medium

PumpPump

Properties of Laser BeamProperties of Laser Beam

A laser beam A laser beam Is monochromeIs monochrome Can be focused in a very small point Can be focused in a very small point Is intenseIs intense Is CoherentIs Coherent Has a very low divergenceHas a very low divergence Can be compressed in time up to few Can be compressed in time up to few

femto second femto second

Applications of Laser Applications of Laser

(1960s) (1960s) “A solution looking for a problem”“A solution looking for a problem”

(Present time) (Present time) Medicine, Research, Medicine, Research, Supermarkets, Entertainment, Industry, Military, Supermarkets, Entertainment, Industry, Military, Communication, Art, Information technology, …Communication, Art, Information technology, …