The future of solid state lasers Martin Richardson Townes Laser Institute, College of Optics & Photonics University of Central Florida, Orlando, Florida [email protected] June 21, 2011 The first laser – a ruby laser May 17, 1960 Q-switching – the invention that nearly killed it all! Vernueil Process Czochralski process The age of glass lasers Flashlamp-pumped pulsed crystalline lasers eventually limited by laser material size and damage threshold. Crystal size limited by boule diameters. Dopant ~ 1% Maximum Nd:YAG rod diameter ~ 1 cm. Damage thresholds ~ 20 J/cms Repetition rates 1- 10 Hz. Limited by heat deposition. Nd- doped glass Amplifiers use 3,072 42-kg neodymium- doped phosphate glass slabs, measuring 3.4 by 46 by 81 cms Solid state lasers at the end of the 80’s Flashlamp pumping kept commercial solid state systems to low powers. Largely pulsed regime. Low repetition-rates, ~ 100’s Hz – heating, flashlamp recycling time, Low efficiencies (<1%), poor pump- light coupling Low powers (< 100W av), limited by thermal loading, costs Enter the ‘90’s – the age of diode pumping 808 nm pumping for Nd:YAG LLNL 50 kW diode array …..940 nm pumping for Yb:YAG even better 10.5% for Yb:YAG Renewed interest in crystalline lasers - 100 x higher thermal shock resistance - higher thermal conductivity Average powers jump from 100’Ws to KW Efficiencies increase 100’s fold to 20-30% Diodes enable new pump architectures Rod type architecture Thin disc architecture Trumpf JHPSL Northrop Grumman 100 kW SSDPL To be deployed at HELSTF summer 2011 Trumpf markets 16 kW thin disc DP SSL Trumpf High power fiber lasers Rapid development of commercial systems (IPG, SPI, Nufern, ) Single mode powers of ~ 1 kW. IPG Nufern BEAM COMBINING SPI Multiple beam tiling Coherent Beam Combining 25 kW Spectral Beam Combining Diode pumping also enabled SS ultrafast Newport -Spectra CW – DPSL (2ω) pumped Ti:Sapphire Regenerative and multi-pass Coherent Ti:Sapphire amplifiers pumped by DP or flashlamp pumped SSl’s Pulse durations 50 -500 fs Pulse energies < 10 mJ Amplitude Repetition rates 1 kHz – 100 kHz The limits of today’s technologies High power SS lasers Created a near-$B market in high power lasers for manufacturing. Reaching limitations in high power architecture imposed by thermal loading and single crystal host. Beam quality and thermal loading primary constraints. Yb:YAG the most efficient SS laser material. Cryogenic Yb:YAG offering improvements in thermal dissipation. High power fiber lasers Rapid rise in high power fiber laser market ( $100M’s/year). Efficiency and cost important drivers. Mode size limiting maximum power. Component development (couplers, isolators..). Ultrafast lasers Ti:Sapphire based systems – limited market penetration. Power (rep.rate), cost, complexity and efficiency. Lack of identified single large market. Tomorrow – New transformative technologies New Laser Materials Polycrystalline materials – transparent ceramics New laser host materials. New SSL architectures New infra-red laser materials. High powers in the Mid IR New Pump Sources Currently limited to near IR high power diodes Visible and UV diode sources high power 15XX nm and 19XX nm diode sources New Fiber Architectures LMA fiber designs. Holey fiber and HOM designs New fiber preform and fabrications techniques Next generation of ultrafast lasers Fiber-based systems. Increased reliability, efficiency Reductions in cost, complexity, footprint. Manufacturing market-leverage development Tomorrow – New transformative technologies New Laser Materials Polycrystalline materials – transparent ceramics New laser host materials. New SSL architectures New infra-red laser materials. High powers in the Mid IR New Pump Sources Currently limited to near IR high power diodes Visible and UV diode sources high power 15XX nm and 19XX nm diode sources New Fiber Architectures LMA fiber designs. Holey fiber and HOM designs New fiber preform and fabrications techniques Next generation of ultrafast lasers Fiber-based systems. Increased reliability, efficiency Reductions in cost, complexity, footprint. Manufacturing market-leverage development General trend to monolithic integrated functionality – light engines of the future Single Crystal Growth Ceramic Process High Temperature Growth from Melt Low Temperature Powder Processing Sinter/Densify (Add sintering aid) Gas Grains containing rare earth ions RE doped powder Hot Press HIP Transparent Polycrystalline Ceramic Goal: Single crystal Many small grains • One large grain Grain boundaries • No grain boundaries • Low temperature (<70% T ) processing avoids high crack m temp issues (eg phase transitions) • Grain boundaries more accommodating to additional Split lattice strain: • Potential for higher RE doping and uniformity • Scalability to large sizes & complex shapes • Difficult to grow crystals from high temperature melt: • High ruggedness and toughness • Compositional variations • Crucible interactions • Phase transitions (strain cracking) • Poor RE solubility and uniformity • Traditional limitations are overcome • Size limitations with Polycrystalline Ceramic • Low yield Cannot grow large crystals or complex shapes from best crystalline materials Ish Aggarwal NRL Fabrication of transparent laser ceramics Nano-powder synthesis (wet-chemistry, spray pyrolysis) Powder handling CRITICAL STEPS (de-agglomeration, blending) Powder shaping (cold pressing, slip casting) Binder burn-out, pre-sintering Pressureless Sintering Field Assisted Sintering Hot-uniaxial pressing Sinter-HIP Hot-Isostatic Pressing (Ar, >150 MPa) Post-sintering heat-treatments spinel (annealing, re-crystallization) Milestones on the ceramic laser road 100 kW 67 kW 2006 2011 Ceramic Nd:YAG – large sizes - bonded materials Konoshima LLNL Improvements in Nd:YAG ceramic laser power 102 106 5 101 10 ) Maximum Laser (W) Power Maximum -1 104 100 103 10-1 2 10 10-2 101 10-3 100 Attenuation coefficient (cm -4 10 10-1 10-5 10-2 1980 1985 1990 1995 2000 2005 2010 Develop of ceramic laser materials will be driven also by other applications. Next generation Large IR-transmitting nuclear scintillators windows Preliminary diffusion bonded SPINEL samples Medical imaging (3” x 3” x ½”) showing excellent bonding Homeland Security Sangera, NRL Scintillator Ceramics Scintillator Applications Bruno Viana Property Comparison with Other Materials Property Measurements Fused Silica OFG Glass SPINEL Optical Absorption Coefficient (ppm cm-1 at 12 75 6 1.06 µm) Refractive Index (at 1.06 µm) 1.45 1.45 1.707 dn/dT (/K) at 633 nm 1.2x10-5 -9.2x10-6 2.3 x10-5 Stress Optic Coefficient (/Pa) 3.4x10-13 4.1x10-13 3x10-13 Mechanical Density (g/cm3) 2.2 3.75 3.58 Poisson’s Ratio 0.17 0.31 0.27 Hardness (kg/mm2) 600 500 (est) 1645 Fracture Strength (MPa) 50 102 350 Young’s Modulus (GPa) 74.5 69.6 271 Thermal Thermal Expansion Coeff. (/K) 0.5x10-6 14.9x10-6 5.9 x 10-6 Heat Capacity Cp (J/g/K) 0.74 0.67 0.604 Thermal Conductivity (W/(m.K) 1.38 0.7 13.4 Aggawal & Sanghera SPINEL compared to Fused Silica: SPINEL compared to OFG glass: • 2x lower absorption coefficient • >10x lower absorption coefficient • > 2.5x harder and 7x stronger • 3x stronger and > 3x harder • 10x higher thermal conductivity • 3x lower CTE • 20x higher thermal conductivity Engineered Laser Ceramics Example of a non-uniform doping Transverse doping profile geometry scalable to multiple kW R. Gaume Stanford Engineered Laser Ceramics Fabrication of dopant-engineered ceramics • Non-reactive sintering: Cold-pressing, Slip-casting, Tape-casting • Reactive sintering: Cold-pressing, Slip-casting, Tape-casting • Bonding of bulk materials: Ceramic – ceramic bonding Ceramic – single crystal bonding Courtesy of A. Ikesue Anisotropic Ceramic Materials - A new class of ceramics Magnetic orientation of rare Interaction between spin-orbit momentum of earth-doped diamagnetic material f-electrons and host material under an RE: Ca10(PO4)6F2 (RE:Nd, Yb) FAP applied magnetic field. Crystal orientation of ceramics For Yb:FAP (002) and (004) planes corresponded to c-plane: (003) plane corresponded to a-plane B For Nd:FAP (003) plane corresponded to c-plane: 2 T Absorption and Emission spectra applied during Strongly axis-dependent slip casting c-axis/a-axis absorption coefft 1.3 C-axis/a-axis emission ~ 1.43 Akayama, Sato & Tiara, Adv. Solid State Lasers, Denver 2009 New fiber laser technologies New fiber designs New IR fiber lasers Rod-type PCF fibers NKT Photonics High power tunable, ‘all-fiber’ 2μm Tm fiber laser. C-R 790 nm pumping 200 pm linewidth Nufern LPL, Townes Institute New LMA fiber designs For the future: 100 kW class fiber lasers? High power mid- IR fiber laser? Polycrystalline (ceramic) fiber lasers? Single crystal fiber lasers? New ultra-fast lasers New Geometries OPCPA systems. Hybrid amplifier technologies Quasi- single cycle, CEP. IMRA Amplitude New compact high power fiber lasers Rugged low cost systems Initial niche market applications Many new start-up companies Raydiance New laser component technologies New high power dispersive optics Optics for phase control fractive optical elements beam engineering Direction of translation Focusing element DOE Glass sample Volume Bragg gratings Glebov, Optigrate Input writing beam Diffractive Array of Guided-mode Holes Resonant Waveguide Layer Filters 5 mm Johnson, UNCC 5 mm Summary A new era in SS laser technology Light engines of the future Approaching light-bulb efficiencies Monolithic integrated architectures New laser sources and materials ceramic lasers New infra-red materials Diode pump sources in