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Learn about rare-earth ions in shielded electron shells, suitable hosts for lasing, and high doping levels for powerful laser systems. Discover the benefits of passive Q-switching and advanced laser crystal technologies.
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Picking the laser ion and matrix for lasing • Rare–earth ions • Have shielded electron shells • - Long life times – store energy • Many hosts: • YAG, YLF, YVO4, glass ... • Double tungstates: (KYW ) • high rare–earth doping • high cross sections • short crystals can be used • suited for diode pumping
Passively Q-switched micro-chiplaser gunnars laser Typical data 1 kW, 5 ns, 10 kHz G. Karlsson, et al., Appl. Opt. 39, 6188 (2000).
Diode pumped solid-state laser – the green pointerincorporating nonlinear optics
Gain media Pump diode green 532=1064+1064 blue 473=946+946 Turquoise 491=1064+914 yellow 593=1064+1342 PPKTP Frequency Mixing of two DPSSLs in PPKTP Combination of rare-earth materials and Engineerednonlinearcrystalsin DPSSL Energy diagram for Neodymium Pump Wavelength Transition Stimulated emission cross-section 1064 nm R2 Y3 4 ·10-19 cm2 946 nm R1 Z5 5.1 ·10-20 cm2 938.5 nm R2 Z5 4.8 ·10-20 cm2
Kr-ion laser replacement Diode pumped Solid-state Lasers - DPSSL Intra-cavity SFG laser Yellow light 1064 + 1342 nm -> 593 nm 3 W +3 W gives 700 mW CW yellow light J. Janousek, S. Johansson, P. Tidemand-Lichtenberg, J. Mortensen, P. Buchhave and F. Laurell, Opt. Exp. 13, 1188-1192 (2005).
Combined diode and solid-state lasers for Ar-ion laser replacement An intra-cavity SFG laser locked by a transmission grating Turqoise laser 1064 + 916 nm 488 nm 30 mW with modulation for bio-application S. Johansson, S. Wang, V. Pasiskevicius, and F. Laurell, Opt. Exp., 13, 2590-2596 (2005).
Laser crystal Lens Pump Fiber The Silicon micro-bench laser concept A silicon chip structured by KOH etching with sub-micron resolution Si-chip Laser-chip mounted in Si-micro bench 6.5 W at 1064 nm 2 W Q-switched at 1064 nm with 1.4 ns pulses Nd:YVO4 chip cut from a 1 inch wafer for the Si-chip Moulded version (plastic) Q-switch bonded chip D. Evekull, S. Johansson, S. Bjurshagen, M. Olson, R. Koch and F. Laurell, Electron. Lett, 39, 1446-1448 (2004).
Er:micro-chip laser tunable with fiber-Bragg grating Acetylene G. Karlsson, N. Myrén, W. Margulis, S. Tacheo and F. Laurell, Appl. Opt.. 42, 4327, (2003)
Volume Bragg gratings • A grating permanently inscribed in a photothermal glass • Narrowband reflection peak • Tailored performance • Made in durable and cheap glass • Material • Period, L • Thickness, d • Strength, n1 Optical O.Efimov et al., Appl. Opt. 38, 619, (1999)
Why VBGs in lasers ? • Reduced linewidth • Stabilized output • Tunability • Spatial mode filtering • Low quantum defect • Increased efficiency? • The glass • Transparent: 350-2700 nm • High damage treshold: >10 J/cm2, >100kW/cm2 • Low absorption: < 0.2%/cm • Low scattering: < 2%/cm
External cavity Bulk Bragg grating locked Er-Yb laser Modes in internal cavity and external cavity Frequency tuning Linewidth < 90 kHz
Nd:GdVO4 laser Bandwidth < 40 MHz B. Jacobsson, et al. “Single-longitudinal-mode Nd-laser with a Bragg-grating Fabry-Perot cavity”, Opt. Express 14, 9284, (2006).
Yb:KYW laser with low quantum defect 3 mm, 5% Yb:KYW Bragg grating input coupler Conventional input coupler
Laser with low quantum defect Spatial Pump: M2 = 35×5 Laser: M2 < 1.1 997 nm Pump: Dl = 2 nm Laser: Dl = 0.033 nm (10GHz) • Quantum defect: (1.6%)energy difference between pump and laser photons Motivation • Reduced heat load -> improved performance at high power • Access to new laser wavelengths (near pump wavelength) J. Hellström, B. Jacobsson, V. Pasiskevicius & F. Laurell Opt. Express, 15, 13930 (2007)
Oblique incidence – change of grating period = wavelength tuning • No beam steering with retroreflector Grating at oblique incidence - rotate l=l0cosq Beam steering when tuning
Widely tunable narrow linewidth Yb:KYW laser using volume Bragg gratings Reflectivity wavelength 0° incidence angle retroreflector Δλ = 0.033 nm (10GHz) Very low quantum (1.6%) defect laser J. E. Hellström, IEEE J. Quantum Electron, 44, 81 (2008)
Why fiber lasers? • Fibers guide light efficiently with low losses • Double-clad fibers allows simple poor-pump-to-good-signal conversion, even at high power • Fibers can provide functionality for mode filtering, spectral filtering etc • Fibers have excellent thermal handling • Fiber lasers support a broad gain Poor quality pump light
Spectral control of fiber lasers Fiber Bragg gratings (FBGs) Gain fiber Narrow bandwidth can be a problem Difficult to write gratings in doped fibers Low-loss splicing problematic Diffraction gratings Large beam necessary for narrow linewidth Large complicated setups often necessary
VBG locked fiber lasers Nd-doped fiber - µ-structured design Core diameter = 18 µm, V-number ~18 (multimode) Similar slope efficiencies – mirrors vs. VBG Linewidth 0.07 nm (compared to 7 nm with mirror) Close to diffraction limited output Simple cavity design P. Jelger and F. Laurell, Opt. Express 15, 11336-11340, (2007)
Slope eff. ~27 % Slope eff. ~24 % Slope eff. ~44 % High power VBG Er:Yb-fiber laser Δλ = 0.4 nm M2~5.5 The role-off at 100 W is due to onset of strong ASE J. Kim, P. Jelger, J. Sahu, F. Laurell & W. Clarkson, Opt. Letts. 33, 1204 (2008)
