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

2. 1.What are fluoride glasses? 2.The role of rare earth elelments 3.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 4.Real structure of fluoride glasses 5.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. HEISENBERG’S UNCERTAINTY PRINCIPLE  E~2·10 -19 eV   t~1h  E~10 eV   t~10 -15 s FREE ATOM  SOLID ENERGY

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

6. DIELECTRICS VALENCE BAND FORBIDDEN BAND (ENERGY GAP) CONDUCTION BAND ENERGY E g > 2 eV EMPTY FULL EFEF

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

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

12. TABLE 1. CONVERSION FACTORS FOR ENERGY UNITS Unitjoule electron voltcm –1 joule1 6.24 × 10 18 5.034 × 10 22 electron volt 1.602 × 10 –19 18065.73 cm –1 1.9864 × 10 –23 1.24 × 10 –4 1

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

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. Spin multiplicity A state can be specified by its spin multiplicity (2S+1). No. unpaired electrons SMultiplicityState 0 S = 0 2S + 1 = 1singlet 1  S = 1/22S + 1 = 2doublet 2  S = 12S + 1 = 3triplet 3  S = 3/22S + 1 = 4quartet S 0 ground state singlet S 1, S 2 ……excited state singlets T 1, T 2 ….…excited state triplets SYMBOLS USED IN ATOMIC PHYSICS

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

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

24. SPONTANEOUS EMISSION

25. E3E3 E2E2 E1E1 P ij = P ji P 23 > P 13 >> P 12 INVERSION N 2 >> N 1  2 >>  3 THREE-LEVEL LASER (TRANSITION PROBABILITIES AND LIFETIMES)

26. STIMULATED EMISSION

27. 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. Emission of Radiation Stimulated emission is an essential part of laser action. UU LL h LL h UU 2h

28. LIFETIMES OF EXCITED STATES

29. FOUR-LEVEL LASER (Cr 3+ doped ruby)

30. E3E3 E2E2 E1E1 E = h· = E 2 – E 1 THREE-LEVEL LASER (quantum amplifier) OPTICAL PUMPING 10 -8 s 10 -3 s

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 N upper -N lower. N upper > N lower, more out than in N upper < N lower, fewer out than in

33. PRINCIPLE OF LASER ACTION

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

35. LASER RESONANCE SYSTEM

36. First commercial fluoride glass – about 1990 FLUOROZIRCONATE GLASS ZrF 4 -BaF 2 -LaF 3 -AlF 3 -NaF Acronym - ZBLAN FLUOROINDATE GLASS InF 3 -ZnF 2 -BaF 2 -SrF 2 -GaF 3 -NaF Acronym - IZBSGN 1974 - Marcel & Michel Poulain and Jacques Lucas discovered first fluoride glass (Univ. Rennes, France) HISTORY Accidentally !!!

37. ADVANTAGES 1.Low phonon energy 2.Low absorption in IR range 3.Wide transmission band 4.High refraction index

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

39. A PIECE OF PHYSICS Phonons in a lattice Acoustic branch-wide frequency band 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 FLUOROZIRCONATE GLASSES SILICA GLASSES FLUOROINDATE GLASSES

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

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

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

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

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

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

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

52. E [cm -1 ] Er EMISSION (IZBSGN)

53. Wavenumber [cm -1 ] Luminescence intensity [a.u.] Intensywność luminescencji [j.wzgl.] LUMINESCENCE (IZBSGN) Tm Tm + Tb EMISSION

54. EMISSION (IZBSGN) Tm E [cm -1 ]

55. EMISSION (IZBSGN) Tm - Tb

57. useless

58. Lifetime [ms] Dopant Level Concentr. [%mol] Experimental  m Computed  rad Quantum efficiency  =  m /  rad [%] 0.5 0.012 36.4 LIFETIMES & QUANTUM YIELDS OF DOPED FLUOROINDATE GLASSES

59. DISADVANTAGES (DRAWBACKS) 1.Substrates are hygroscopic (built-in OH groups result in additional absorption band in IR range) 2.Difference of T X and T g is low (  100 0 C) 3.Crystallization susceptibility is high

60. T g – glass transformation temperature T X – crystallization temperature (beginning) T P - crystallization temperature (peak)  T = T x – T g  HRUBY PARAMETER H = (T X – T G ) / T G  SAAD PARAMETER : S = [(T X – T G ) (T P – T X )] / T G PARAMETERS OF STABILITY

61. Various dopants in fluoride glass CHARACTERISTIC TEMPERATURES OF FLUORINDATE GLASSES

62. GLOVE DRY PREPARATION BOX

63. GLOVE DRY MELTING BOX

64. Pr 3+ doped fluoroindate glass

65. REVERSE MONTE CARLO MODELLING (RMC) RIETVELD MODELLING STRUCTURE OF FLUORIDE GLASSES

66. VARIATION OF GIBBS FREE ENERGY DURING VITRIFICATION AND CRYSTALLIZATION liquid Overcooled liquid glass Single crystal Stable glass Range of structural order

67. STRUCTURE OF FLUOROZIRCONATE GLASS (ZBLAN) POULAIN & LUCAS 1974

68. PROJECTION OF THE RMC CUBIC BOX SHOWING THE 300 [MF 6 ] POLYHEDRA NETWORK. EXAMPLE OF RMC MODELLING (NaPbM 2 F 9 )

69. NaPbFe 2 F 9 [MF 6 ] octahedra are in blue; Na atoms in green and Pb atoms in red

70. Five [MF 6 ] polyhedra linked by edges as found in the RMC model NaPbM 2 F 9

71. EXPERIMENTAL VERIFICATION BY NEUTRON DIFFRACTION OR LOW ANGLE X-RAY SCATTERING

72. SiO 2 - crystalline I coordination zone – 3 at II coordination zone – 3 at III coordination zone – 6 at SiO 2 - amorphous I coordination zone – 3 at II coordination zone – 4 at III coordination zone – 4 at EXAMPLE

73. LEAST SQUARES FIT TO EXPERIMENTAL RESULTS (NEUTRON DIFFRACTION AND X-RAY SCATTERING) NaPbM 2 F 9 : neutron data for M = Fe

74. neutron data for M = V LEAST SQUARES FIT TO EXPERIMENTAL RESULTS (NEUTRON DIFFRACTION AND X-RAY SCATTERING) NaPbM 2 F 9 (M = Fe, V)

75. X-ray data for M = Fe LEAST SQUARES FIT TO EXPERIMENTAL RESULTS (NEUTRON DIFFRACTION AND X-RAY SCATTERING) NaPbM 2 F 9 (M = Fe, V)

76. REFERENCES http://www.studsvik.uu.se/Software/RMC/mcgr.htm http://tigger.phy.bris.ac.uk/~liqwww/links.html http://www.cristal.org/glasses/glassvir.html http://www.cis.tugraz.at/ptc/specmag/struct/s.htm http://www.materials.leeds.ac.uk/Groups/Photonics/photonic.htm http://www.gel.ulaval.ca/~copgel/conferences/edfa1/sld001.htm http://irfibers.rutgers.edu/ir_rev_intro.html http://www.mete.metu.edu.tr/PEOPLE/FACULTY/aydinol/gfa/sld001.htm