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 pointer incorporating nonlinear optics

Combination of rare-earth materials and Engineered nonlinear crystals in DPSSL Pump diode Gain media PPKTP Frequency Mixing of two DPSSLs in PPKTP Energy diagram for Neodymium Pump green 532=1064+1064 blue 473=946+946 Turquoise 491=1064+914 yellow 593=1064+1342 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).

Moulded version (plastic) The Silicon micro-bench laser concept Laser crystal Lens Fiber Pump 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 Optical Material Period, L Thickness, d Strength, n1 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 Conventional input coupler Bragg grating input coupler

Laser with low quantum defect 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) Spatial Pump: M2 = 35×5 Laser: M2 < 1.1 997 nm Pump: Dl = 2 nm Laser: Dl = 0.033 nm (10GHz) J. Hellström, B. Jacobsson, V. Pasiskevicius & F. Laurell Opt. Express, 15, 13930 (2007)

Oblique incidence – change of grating period = wavelength tuning Beam steering when tuning No beam steering with retroreflector Grating at oblique incidence - rotate l=l0cosq

Widely tunable narrow linewidth Yb:KYW laser using volume Bragg gratings incidence angle wavelength Reflectivity 0° 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 Difficult to write gratings in doped fibers Low-loss splicing problematic Narrow bandwidth can be a problem 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)

High power VBG Er:Yb-fiber laser Slope eff. ~44 % Slope eff. ~24 % Slope eff. ~27 % 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)