ir solid laser

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Slide1: 

Solid State Lasers 1.Activator and Host 2.Operatiion mode and efficiency 3.Neodymium doped Lasers 199921186 Yoo HyunSeung Division of Natural Science 4.Titanium Sapphire Laser 5.Color Center Laser

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Solid State (SS) Laser A solid crystalline material as the lasing medium usually optically pumped entertainment materials processing Application semiconductor fabrication medical and surgical graphic arts scientific research Most solid state lasers operate in near-IR ! Green laser pointer is a Diode Pumped Solid State (DPSS) laser ! The largest lasers in the World are solid state lasers !

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Lasing Media 1 - General Laser Media an Active Species + a Host Active Species (Activator) - Usually Ions Color centers occasionally Rare earth : Nd3+ Er3+ Yb3+ Host - Solid Crystal : Oxides Fluoride Glass : Silicate Phosphate Transition metal : Cr3+ Ti3+ Polymer occasionally Usually Low concentration of activator in dissolved host ! (Lower doping High thermal conductivity) (Higher doping Low thermal conductivity)

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Lasing Media 2 – Activator Laser Media Examples Ruby - Chromium doped aluminum oxide Nd:Glass Nd:YAG Nd:YVO4 lasing wavelength : 694.3 nm Much lower lasing threshold than ruby Strongest output wavelength of neodymium doped lasers : 1064 nm Lasing lines depends on the actual host material Neodymium (Nd) doped materials (majority of modern solid state lasers) Nd:LSB Nd:YLF Ruby

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Lasing Media 3 – Activator Laser Media Examples - continued Tm:YAG, Tm:LuAG, Tm,Ho:YLF (2000 to 2030 nm) Alexandrite chromium doped chrysoberyl (655 to 815 nm ) Titanium Sapphire (840 to 1100 nm) Ytterbium doped (Yb) doped materials Yb:KGW (1025 to 1045 nm) Thulium doped (Tm) doped materials Holmium (Ho) doped materials Ho:YAG, Ho:YLF, Ho:Glass (2000 to 2100 nm) Er:YAG (2940 nm) Er:Glass (1540 nm) optical repeaters and amplifiers Erbium doped (Er) doped materials

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Lasing Media 3 – Host Properties of good host Heat dissipation Spectroscopically suitable Grown in high quality (homogeneous, low loss) With appropriate concentration of dopant High thermal conductivity Good mechanical properties Easy to fabricate ( polishing , fracture ) Local field : Stark effect Ion-ion interaction Phonon spectrum Line broadening , lifetime Limit use at high concentration

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Power Output Pulsed Solid State Laser xenon or krypton arc lamps or other sources various versions of xenon flashlamps CW Solid State Laser Quasi-CW Solid State Laser pulsed lasers but operating with a Pulse Repetition Rate (PRR) Q-switching arrays of high power laser diodes (lower power consumption, heat dissipation, much more compact size) 10s or 100s of kHz if electro-optically Q-switched

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Efficiency of Solid State Laser Ranges more for those pumped with laser diode pumped vary from well under 1 percent for flashlamp resonator and pump assembly design dependent ! Nd:YAG Laser a net 18% of efficiency from electrical power to the diodes arc lamp pumped SS lasers to 25 percent diode pumped Nd:YAG may have a 40% efficiency pump diodes themselves have about a 45% efficiency thermal issues may cause the efficiency to decrease !

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Properties of Some Common Laser Media

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Neodymium Lasers Neodymium doped Yttrium Aluminum Garnet (Nd:YAG) Main absorption : 570 to 600 nm, 730 to 760 nm, 790 to 820 nm, 860 to 890 nm Main emission : 1,064.17 nm (strong line) and 1,064.4 (week line) 4 Level system Low pumping threshold Relatively long upper level lifetime Q-switching mode or an Amplifier High thermal conductivity Limited crystal size Nd ion doping : 1.0 – 1.5 % High repetition rate (Pulsed laser) Limiting power and energy output Higher doping -> reduction of lifetime Attractive for pumping with efficient diode lasers Ex) GaAs diode

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Neodymium Lasers Neodymium doped Yttrium Lithium Fluoride (Nd:YLF) long fluorescence lifetime (twice that of Nd:YAG) two distinct output lines depending upon polarization 1047 nm for the extraordinary 1053 nm for the ordinary large thermal conductivity Diode pumping high-power diode-pumped system rather expensive

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Neodymium Lasers Neodymium doped Yttrium orthoVanadate (Nd:YVO4) The most efficient laser crystal for diode laser-pumped solid-state lasers Large stimulated emission cross-sections Short fluorescence lifetime ( 2.4 times shorter than that of Nd:YAG) ( 4 times that of the Nd:YAG ) much lower laser threshold compared to a similar size Nd:YAG high-pump quantum efficiency Emission wavelength : precisely 1064.3 nm (strong) 1342 nm (weak)

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Neodymium Lasers Neodymium doped Glass (Nd:Glass) Very large size of laser material Broader absorption bands High power Longer fluorescence decay times Depending on Types of glass used Emission wavelength : 1054nm – 1062nm more heavily and more homogeneously doped than crystals Susceptibility to solarization Significantly lower thermal conductivity Broad fluorescence line widths limit the use of glass laser rod for CW and high-repetition rate lasers

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Titanium Sapphire Laser Titanium doped Sapphire ( Ti:Al2O3 ) Relatively large stimulated emission cross section Titanium doping : 0.1% by weight Pumping source : argon ion laser (CW) or Nd:YAG, Nd:YLF (pulsed) Short upper laser level lifetime (3.8㎲) The most widely used tunable solid state laser Emission wavelength : 660 nm – 1180 nm High thermal conductivity, good mechanical rigidity, good chemical inertness Absorption band : 400 nm – 630 nm peaks around 490 nm Effectively 4 level system

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Color Center Laser Optically pumped by other lasers Color center materials : producing point defects in an alkali-halide lattice defects Operate in the near IR : 800 – 4000 nm Tuning : several different color center crystals Random locations within crystal & how long the crystal is irradiated How to make point defects : Irradiating an alkali-halide crystal with X-rays halide ion vacancies & doped alkali ion impurities Color center duration : from days to years 4 level system : absorption band 500 – 1300 nm Upper level life time : 100s nm F - center FA - center F2 - center F2+ - center

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References William T. Silfvast , ‘Laser Fundamentals’ , 146p – 155p William T. Silfvast , ‘Laser Fundamentals’ , 447p – 469p http://www.stanford.edu/class/ee231/LectureNotes/ Lecture 26-TiSapphire.pdf Lecture 24-SSL1.pdf Lecture 25-SSL2.pdf http://www.repairfaq.org/sam/laserssl.htm