FLUORIDE GLASSES – MATERIALS FOR BULK LASERS AND FIBRE OPTICAL AMLIFIERS

1. FLUORIDE GLASSES – MATERIALS FOR BULK LASERS AND FIBRE OPTICAL AMLIFIERS Michał Żelechower, Silesian University of Technology, Katowice, Poland

2. What are fluoride glasses? • The role of rare earth elelments • Interaction of electromagnetic radiation with matter • a. Scattering, absorption, spontaneous and stimulated emission • b. Reconstruction of electron energy structure • c. Radiative and non-radiative transitions • Real structure of fluoride glasses • Applications – advantages and disadvantages (drawbacks)

3. What is it? Fluoride glasses can be formed by total replacement of oxygen atoms in oxide glasses by fluorine atoms They are manufactured by melting of high purity single element fluorides mixture

4. ENERGY HEISENBERG’S UNCERTAINTY PRINCIPLE FREE ATOM  SOLID E~2·10-19 eV  t~1h E~10 eV  t~10-15s

5. Energy diagram showing two atoms encountering and resulting in a new molecule

6. DIELECTRICS EMPTY CONDUCTION BAND ENERGY FORBIDDEN BAND (ENERGY GAP) Eg > 2 eV EF VALENCE BAND FULL

7. CONDUCTION BAND(EMPTY) DOPED IONS LEVELS USED IN LASER ACTION FOR INSTANCE RARE EARTH ELEMENTS IN GLASSES VALENCE BAND DOPED DIELECTRICS

8. RARE EARTH IONS IN CRYSTALS AND GLASSES http://www.gel.ulaval.ca/~copgel/conferences/edfa1/tsld001.htm

9. RARE EARTH IONS IN CRYSTALS AND GLASSES

10. RARE EARTH IONS IN CRYSTALS AND GLASSES

11. RARE EARTH IONS IN CRYSTALS AND GLASSES

12. TABLE 1. CONVERSION FACTORS FOR ENERGY UNITS Unit joule electron volt cm–1 joule 1 6.24 × 1018 5.034 × 1022 electron volt 1.602 × 10–19 1 8065.73 cm–1 1.9864 × 10–23 1.24 × 10–4 1

13. EXAMPLE : CONVERSIONOF ENERGY IN JOULES TO CM-1 Given: A HeNe laser photon has a wavelength of 632.8 nanometers Find: (a) Photon energy in joules(b) Photon energy in cm–1 Solution:

14. X-rays Scattering Energy Phototionisation Ionisation energy Electronic level changes Ultraviolet Large no. of states -strongly absorbed Visible Infrared Vibration Small no. of states -almost transparent Microwaves Rotation THE INTERACTION OF RADIATION WITH MATTER

15. ATOM MUST RETURN FROM EXCITED STATE TO GROUND STATE. HOW?

16. SEVERAL WAYS TO RETURN TO GROUND STATE

17. QUANTUM YIELD OF LUMINESCENCE

18. SEVERAL WAYS TO RETURN TO GROUND STATE. LIFETIMES

19. FLUORESCENCE VERSUS PHOSPHORESCENCE

20. SYMBOLS USED IN ATOMIC PHYSICS Spin multiplicity A state can be specified by itsspinmultiplicity(2S+1). No. unpaired electronsSMultiplicityState 0 S= 0 2S+ 1 = 1 singlet 1  S= 1/2 2S+ 1 = 2 doublet 2  S= 1 2S+ 1 = 3 triplet 3  S= 3/2 2S+ 1 = 4 quartet S0 ground state singlet S1, S2……excited state singlets T1, T2….…excited state triplets

21. Wavenumber [cm-1] Absorbance Wavelength [nm] REE ABSORPTION SPECTRA IN FLUORIDE GLASSES Pr Eu Ho Er Tm

22. EACH ABSORPTION LINE CORRESPONDS TO THE RESPECTIVE ELECTRON TRANSITION BETWEEN TWO ENERGY LEVELS (GROUND STATE AND EXCITED STATE) WE ARE ABLE TO RECONSTRUCT THE ELECTRON ENERGY STRUCTURE ON THE BASE OF ABSORPTION SPECTRA

23. RECONSTRUCTED ELECTRON ENERGY LEVELS IN FLUOROINDATE GLASSES Energy [cm-1] Pr Eu Ho Er Tm

24. SPONTANEOUS EMISSION

25. THREE-LEVEL LASER (TRANSITION PROBABILITIES AND LIFETIMES) E3 E2 E1 Pij = Pji P23 > P13 >> P12 2 >> 3 INVERSION N2 >> N1

26. STIMULATED EMISSION

27. U U h h 2h L L Emission of Radiation Stimulated Emission Stimulated emission is the exact analogue of absorption. An excited species interacts with the oscillating electric field and gives up its energy to the incident radiation. Stimulated emission is an essential part oflaser action.

28. LIFETIMES OF EXCITED STATES

29. FOUR-LEVEL LASER (Cr3+ doped ruby)

30. THREE-LEVEL LASER (quantum amplifier) E3 10-8 s E2 10-3 s E = h· = E2 – E1 E1 OPTICAL PUMPING

31. Time-schedule of laser action

32. To amplify number of photons going through the atoms we need more atoms in upper energy level than in lower. Amplification or loss is just Nupper-Nlower. Nupper > Nlower, more out than in Nupper < Nlower, fewer out than in

33. PRINCIPLE OF LASER ACTION

34. PRINCIPLE OF LASER ACTION NUMBER OF PHOTONS ~ 2N (N – ACTIVE ELEMENT CONTENT)

35. LASER RESONANCE SYSTEM

36. HISTORY 1974 - Marcel & Michel Poulain and Jacques Lucas discovered first fluoride glass (Univ. Rennes, France) Accidentally !!! First commercial fluoride glass – about 1990 FLUOROZIRCONATE GLASS ZrF4-BaF2-LaF3-AlF3-NaF Acronym - ZBLAN FLUOROINDATE GLASS InF3-ZnF2-BaF2-SrF2-GaF3-NaF Acronym - IZBSGN

37. ADVANTAGES • Low phonon energy • Low absorption in IR range • Wide transmission band • High refraction index

38. Comparison of various glasses properties to those of silica glasses

39. A PIECE OF PHYSICS Acoustic branch-wide frequency band Phonons in a lattice Optical branch - almost constant frequency THIS FREQUENCY IS MUCH LOWER IN FLUORIDE GLASSES THAN IN SILICA GLASSES IR light absorbtion in fluoride glasses is much lower than in silica glasses

40. VIBRATIONS OF DIATOMIC CHAIN – OPTICAL PHONONS

41. Equation of motion (Newton’s second principle) Disperssion relations

44. Wavelength TRANSMISSION BAND FLUOROINDATE GLASSES FLUOROZIRCONATE GLASSES SILICA GLASSES

45. TRANSMISSION BAND – FLUOROINDATE GLASS Wavenumber [cm-1] 100 Transmission[%] 0 Wavelength [m]

46. Energy [cm-1] ELECTRON ENERGY LEVELS Pr Eu Ho Er Tm

47. LUMINESCENCE (IZBSGN) Ho 0.5 % mol. 6 % mol. EMISSION E [cm-1] E [cm-1] Wavelength [nm] 0.5 % mol. Luminescence intensity [a.u.] 6 % mol. Wavenumber [cm-1]

48. EMISSION (IZBSGN) E [cm-1] 0.5 % mol Ho

49. LUMINESCENCE (IZBSGN) Pr EMISSION Wavelength [nm] Luminescence intensity [a.u.] Wavenumber [cm-1]

50. EMISSION (IZBSGN) E [cm-1] Pr