2. Stimulated emission Spontaneous emission L ight A mplification by S timulated E mission of R adiation

5. T he operation of the Laser

6. T he operation of the Laser (Pumping the Laser)

7. T he operation of the Laser absorption

8. T he operation of the Laser Spontaneous emission

10. T he operation of the Laser

11. T he operation of the Laser Stimulated emission

12. T he operation of the Laser Light: Coherent, polarized The stimulating and emitted photons have the same: frequency phase direction

13. Two level system absorption Spontaneous emission Stimulated emission h  h  h  E 1 E 2 E 1 E 2 h  =E 2 -E 1

15. Einstein’s coefficients Probability of stimulated absorption R 1-2 R 1-2 =  (  ) B 1-2 Probability of stimulated and spontaneous emission : R 2-1 =  (  ) B 2-1 + A 2-1 assumption: n 1 atoms of energy  1 and n 2 atoms of energy  2 are in thermal equilibrium at temperature T with the radiation of spectral density  (  ): n 1 R 1-2 = n 2 R 2-1 n 1  (  ) B 1-2 = n 2 (  (  ) B 2-1 + A 2-1 ) E 1 E 2

19. How to realize the population inversion? Thermal excitation: Optically, electrically . impossible. The system has to be „pumped” E 1 E 2

20. Measurement disturbes the system The Uncertainty Principle

24. E 1 E 3 E 2 szybkie przejścia akcja laserowa - optical pumping - occupation of E3 of a short life time, 10-8s. It is a band, the metastable and ground states are narrow : - electrons are collected on E2: population inversion - stimulated emission (one photon emitted spontaneously starts the stimulated radiation ) - Beam of photons moves normally to the mirrors – standing wave. The laser operation

28. Ruby laser First laser: Ted Maiman Hughes Research Labs 1960