1. A Short History of Laser H. R. Khalesifard Institute for Advanced Studies in Basic Sciences Email: khalesi@iasbs.ac.ir

2. Stimulated emission, The MASER and The LASER (1916) The concept of stimulated emission Albert Einstein (1916) The concept of stimulated emission Albert Einstein

3. E1E1 E2E2 Absorption E1E1 E2E2 Spontaneous Emission E1E1 E2E2 Stimulated Emission

4. (1928) Observation of negative absorption or stimulated emission near to resonant wavelengths, Rudolf Walther Ladenburg (1928) Observation of negative absorption or stimulated emission near to resonant wavelengths, Rudolf Walther Ladenburg E1E1 E2E2 Stimulated Emission (negative absorption)

5. (1930s) If a physical system be in thermodynamic equilibrium the population inversion and so the stimulated emission is impossible (1930s) If a physical system be in thermodynamic equilibrium the population inversion and so the stimulated emission is impossible E1, N1E1, N1 E 2, N 2 Stimulated Emission E 1, N 1 E 2, N 2 Absorption

6. LASER (MASER) Light (Microwave) Amplification by Stimulated Emission of Radiation

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

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

9. The LASER (1951) V. A. Fabrikant “A method for the amplification of electromagnetic radiation (ultraviolet, visible, infrared, and radio waves)” patented in Soviet Union. (1951) V. A. Fabrikant “A method for the amplification of electromagnetic radiation (ultraviolet, visible, infrared, and radio waves)” patented in Soviet Union. (1958) Townes and Arthur L. Schawlow, “Infrared and Optical Masers,” Physical Review (1958) Townes and Arthur L. Schawlow, “Infrared and Optical Masers,” Physical Review (1958) Gordon Gould definition of “Laser” as “Light Amplification by Stimulated Emission of Radiation” (1958) Gordon Gould definition of “Laser” as “Light Amplification by Stimulated Emission of Radiation” (1960) Schawlow and Townes U. S. Patent No. 2,929,922 (1960) Schawlow and Townes U. S. Patent No. 2,929,922 (1960) Theodore Maiman Invention of the first Ruby Laser (1960) Theodore Maiman Invention of the first Ruby Laser (1960) Ali Javan The first He-Ne Laser (1960) Ali Javan The first He-Ne Laser

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

11. Maiman and the first ruby laser Maiman and the first ruby laser

12. Ali Javan and the first He-Ne Laser Ali Javan and the first He-Ne Laser

13. The laser cavity length should be multiple of light wavelength

14. The laser Structure Front Mirror End Mirror Lasing Medium Pump

15. Properties of Laser Beam A laser beam Is monochrome Is monochrome Can be focused in a very small point Can be focused in a very small point Is intense Is intense Is Coherent Is Coherent Has a very low divergence Has a very low divergence Can be compressed in time up to few femto second Can be compressed in time up to few femto second

16. Applications of Laser (1960s) “A solution looking for a problem” (1960s) “A solution looking for a problem” (Present time) Medicine, Research, Supermarkets, Entertainment, Industry, Military, Communication, Art, Information technology, … (Present time) Medicine, Research, Supermarkets, Entertainment, Industry, Military, Communication, Art, Information technology, …