History of Ti:sapphire and Ce-doped UV Lasers. Peter F. Moulton Q-Peak, Inc. ISLNOM-3 July 21, 2003 Keystone, CO

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1 History of Ti:sapphire and Ce-doped UV Lasers Peter F. Moulton Q-Peak, Inc. ISLNOM-3 July 21, 2003 Keystone, CO

2 Outline Background of laser development Ce-doped lasers Ti:sapphire laser

3 Stimulated polaritons no: stimulated emission: yes? (1972)

4 First brush with crystal growth (1973) (A.J. Strauss, R. MacLean)

5 Isoelectronic traps in Te-doped CdS

6 Divalent Ni in MgF2 :Properties at 77 K pump

7 Vertical gradient freeze furnace (T.B. Reed, R.E. Fahey)

8 Me, a crystal grower?

9 Energy levels of transition metals

10 pump Divalent Co in MgF2 :at 77 K (1977)

11 Co:MgF2 boule and assorted TM-doped crystals

12 Inspiration for Ce-doped lasers

13 Fundamentals of Ce 3+ Trivalent cerium (Ce) has one electron in outer shell Ground state of electron is 4f, with two levels split 2300 cm-1 by spin-orbit coupling Next state is 5d, with energy and state splitting strongly influenced by host crystal Large difference between 5d and 4f states leads to a large lattice shift and resulant broad. Stokes-shited absorption and emission 5d 20,000-40,000 cm-1 2 F 7/2 5/2

14 Results with Ce:YAG were discouraging JAP 49, 6109 (1978) APL 33, 410 (1978)

15 Things that go wrong Conduction band e - e - e - e - e - e - ESA Dielectric breakdown Pump Laser Induced color center N-photon absorption Valence band Direct lasers Harmonic generation

16 D. Gabbe and A.L. Harmon, Scheelite structure fluorides: The growth of pure and rare earth doped LiYF4, J. Cryst. Growth 3, 544 (1968) YLF (LiYF 4 ) was being developed at MIT

17 Ce:YLF absorption/emission (1979) (with Dan Ehrlich, Rick Osgood)

18 First Ce:YLF laser setup

19 One reviewer was skeptical

20 We did publish, and later made another laser

21 Later we found Ce:YLF had high gain and high (3 mj) output

22 ASSL 93 Ce:LiCAF revived interest in Ce doping

23 Highest-energy Ce-doped laser (ASSL 2002)

24 Color-center laser levels inspired search for systems without ESA

25 Periodic table H Li Be B C N Na Mg Transition metals Al Si P K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb

26 Levels of single d electron in octahedral site

27 Early work on Ti in sapphire (1962)

28 Crystal growers studied Ti:sapphire as well

29 MIT efforts studied defect diffusion using Ti J. Am Ceramic Soc. 52, 331 (1969)

30 J. Chem Phys 60, 2003 (1974) First data on fluorescence (1974)

31 Ti:sapphire absorption/emission (1982) 1 FLUORESCENCE INTESITY (arb. units) Fluorescence lifetime 3.2 usec ,000 WAVELENGTH (nm) 0 ABSORPTION COEFFICIENT (arb. units)

32 First Ti:sapphire laser operation

33 Ti:sapphire - early photos in

34 MIT couldn t afford (!) to patent Ti:sapphire

35 Parasitic absorption was a party spoiler 7E-20 CROSS SECTION (cm^2) 6E-20 5E-20 4E-20 3E-20 2E-20 1E-20 PI SIGMA ABS. COEFFICIENT (arb. units) ,000 1,200 WAVELENGTH (nm)

36 Work at LL examined Ti 3+ -Ti 4+ as culprit

37 Predictions that were right MIT LL Solid State Research 1982:3

38 Predictions that were (mostly) wrong

39 Technology genealogy Livermore V:MgF2 FUSION DRIVER ESA-crippled Understand ESA Try again COLOR-CENTER LASERS Bell Simple energy levels Crystal engineering? Livermore Cr:LiSAF LASER Aha! Ti:SAPPHIRE LASER Lincoln Not a good fusion driver, but...

40 Ti:sapphire HEM crystal growth by Chandra Khattak at Crystal Systems

41 Ti:sapphire Czochralski growth by Milan Kokta at Union Carbide (now Saint-Gobain)

42 A new player Shanghai Institute of Optics and Fine Mechanics Titanium Doped Sapphire Crystal and Laser Using New Temperature Gradient Technique Titanium Doped Sapphire is a unique material revolutioninzing the laser and photonics industry. This material is the most widely used crystal for wavelength tunable lasers. It is also an excellent medium capable of generating ultra-shortpulsed high gain and high power lasers. Our scientists have successfully developed Ti : Sapphire crystals based on the new Temperature Gradient Technique (TGT) and induction thermal Field Up-shift Method (IFUM).

43 My own group s work on Ti:sapphire

44 200-W average power from Ti:sapphire

45 Counting optical cycles

46 Ti:sapphire laser - highlights Broadly tunable ( nm) output used widely for scientific and applied linear and nonlinear spectroscopy of gases and condensed media, atmospheric research Mode-locked output <10 fs has probed ultrafast dynamics of media (Zewail awarded Nobel Prize in Chemistry for work on molecules) Mode-locked systems also can generate new optical frequency standards and allow measurement accuracies of a part in Amplified mode-locked lasers (with CPA) have approached Petawatt (10 15 W) of output (30 J in 30 fs) to study laser-matter interactions at extremely high intensities, generate x-rays Commercial laser sales are on the order of 6000 systems, about $500 million.