Advances in High-Power Fiber and Diode Laser Engineering

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Contents
1 Diode laser: fundamentals and improving the brightness
1.1 A brief history of high-power semiconductor laser: the rise of a disruptive technology
1.1.1 The beginning of a semiconductor laser
1.1.2 Era of high-temperature operation—birth of quantum-well gain medium
1.1.3 Era of high-reliability operation
1.1.4 Race for super high efficiency for defense application
1.1.5 Era of high brightness—the rise of a disruptive technology
1.2 High power and high brightness broad area diode lasers
1.2.1 Fundamentals of diode lasers
1.2.2 Optical gain medium—quantum well
1.2.3 Optical waveguide
1.2.4 Optical feedback
1.2.5 Electrical-to-optical power conversion efficiency
1.3 Mitigation of slow-axis divergence blooming in broad area diode lasers
1.3.1 Why brightness degrades as BPP increases
1.3.2 The origin of slow-axis divergence blooming in high-power diode lasers
1.3.3 Mitigating slow-axis divergence blooming
1.3.3.1 Reducing junction temperature via thermal management
1.3.3.2 Reducing thermal gradient across the stripe-width
1.3.3.3 Reducing the divergence by suppressing higher-order modes
1.3.4 Fiber-coupled multi-single-emitter diode lasers
1.3.5 Reliability of fiber-coupled multi-single-emitter diodes
1.4 Diode laser applications
1.4.1 Diode-pumped solid-state lasers and fiber lasers
1.4.2 Markets and applications
1.4.2.1 1980s: optical storage and initial niche applications
1.4.2.2 1990s: optical networking boom
1.4.2.3 2000s: laser as a tool
1.5 The future prospects of diode lasers
1.5.1 Increasing power and efficiency
1.5.2 Reducing slow-axis BPP and increasing fast-axis brightness
1.5.3 Increasing submount thermal conductivity
1.5.4 Improving optical coupling scheme
Acknowledgments
References
2 Coherent beam combining architectures for high-power laser diodes
2.1 Introduction
2.2 High-power semiconductor lasers and amplifiers used for coherent beam combining
Arrays versus individual emitters
2.3 Principles of coherent beam combining architectures
2.3.1 Phase locking
2.3.2 Coherent superposition
2.3.2.1 Tiled aperture approach: far-field superposition
2.3.2.2 Filled aperture approach: near-field superposition
2.4 Master-oscillator power amplification architectures
2.4.1 Coherent beam combining of amplifier arrays
2.4.1.1 Ridge waveguide amplifiers
2.4.1.2 Tapered waveguide amplifiers
2.4.1.3 Limitations related to coherently combined arrays
2.4.2 Coherent combining of individual amplifiers
2.4.2.1 Coherent beam combining of three high power tapered amplifiers
2.4.2.2 Coherent beam combining module based on commercially available amplifiers
2.5 Extended-cavity architectures
2.5.1 Principles of operation
2.5.2 Cavity architectures based on beam superposition
2.5.2.1 General description
2.5.2.2 Self-organisation and spectral filtering
2.5.2.3 Multi-arm interferometric cavities: experimental results
2.5.2.4 Back-side resonator configurations
2.5.3 Parallel coupled cavities
2.5.3.1 Cavities using near-field spatial filtering: the Talbot cavity
2.5.3.2 Cavities using far-field angular filtering
2.6 Conclusion
References
3 High-power laser diodes for direct applications and laser pumping
3.1 Introduction
3.2 High power broad area lasers
3.2.1 Motivation
3.2.2 Device configurations and performance comparison
3.2.3 Challenge 1: efficiency and power
3.2.4 Challenge 2: beam quality
3.2.5 Challenge 3: external stabilization
3.3 High power laterally single mode lasers
3.4 High power lasers with monolithic grating stabilization
3.4.1 Overgrown gratings
3.4.2 Surface gratings
3.4.3 Comparison
3.5 Seed lasers
3.5.1 Gain switching
3.5.2 Q-switching
3.5.3 Mode locking and pulse picking
3.5.4 Pulse gating
3.6 Wavelength limits on GaAs-based high radiance quantum well lasers
3.6.1 Introduction
3.6.2 Short wavelength limit
3.6.3 Long wavelength limit
3.7 Conclusions and path forward
Acknowledgments
References
4 Quantum cascade lasers
4.1 Introduction
4.2 Governing equations for pulsed QCL operation
4.3 Laser core design
4.4 Waveguide design
4.5 CW power scaling
4.6 Beam combining
4.7 External cavity QCLs
4.8 Distributed feedback QCLs
4.9 Conclusion
References
5 Diode pumped high power lasers
5.1 Material selection
5.1.1 Laser properties
5.1.2 Thermal properties
5.1.3 Nonlinear properties
5.1.4 Gain bandwidth
5.1.5 Comparison
5.2 Laser amplifiers
5.2.1 Regenerative amplifiers
5.2.2 Multipass amplifiers
5.2.3 Chirped pulse amplification
5.3 Geometry of the active medium in high power amplifier
5.3.1 Rod-type amplifiers
5.3.2 Fiber amplifiers
5.3.3 Thin-disk and active mirror amplifiers (incl TRAM)
5.3.4 Slab (zig-zag, multislab, innoslab)
5.4 Thin-disk high power system
5.4.1 Yb: YAG active medium
5.4.2 Pump geometry for thin-disk lasers
5.4.3 Zero-phonon-line pumping
5.4.4 Thin-disk module manufacturing
5.4.5 High power regenerative amplifiers
5.4.6 Thin-disk-based multipass amplifier
5.5 Multislab high power system
5.5.1 Modeling [ 103,104]
5.5.2 System layout
5.5.2.1 Front-end
5.5.2.2 10 J main preamplifier
5.5.2.3 100 J power amplifier
5.5.3 Output parameters
References
6 High average power large mode area (LMA) fiber amplifiers
6.1 A brief history of fiber lasers
6.2 Advantages of fiber lasers
6.3 Rare-earth-doped fibers
6.3.1 Fundamentals of optical fibers
6.3.2 Design of fiber amplifiers
6.4 Limitations of high average power Yb-doped fiber amplifiers
6.5 Overcoming the limitations of power scaling in combinable LMA fibers
6.5.1 Mitigating SBS
6.5.2 Mitigating TMI
6.5.3 Chirally coupled core fiber technology
6.5.4 Conclusions
Acknowledgments
References
7 Optical fibers for high-power operation
7.1 A brief historical overview
7.2 High-power fiber laser systems: performance against the odds
7.2.1 Stimulated Brillouin scattering
7.2.2 Stimulated Raman scattering
7.2.3 Self-phase modulation
7.2.4 Self-focusing
7.2.5 Mode shrinking
7.2.6 Transverse mode instabilities
7.3 Optical fibers for high-power operation
7.3.1 The fiber core: guiding mechanisms
7.3.1.1 Step-index fibers
7.3.1.2 Photonic-crystal fibers
7.3.1.3 General considerations
7.3.2 The fiber cladding: added functionality
7.3.2.1 Single-clad fibers
7.3.2.2 Double-clad fibers
7.3.2.3 Triple-clad fibers
7.3.3 The fiber material: laser properties
7.3.3.1 Laser active ions
7.3.3.2 General considerations
7.4 Outlook: multicore fibers
References
8 High power fiber lasers
8.1 Introduction
8.1.1 Diode-laser pumped solid-state laser media
8.2 High power Yb fiber lasers
8.2.1 Yb: silica spectroscopy
8.2.2 1 micron fiber lasers
8.2.3 Fiber laser architectures and fiber design
8.2.3.1 High power fiber designs
8.2.3.2 High power fiber laser architectures
8.2.4 Nonlinear optical loss mechanisms
8.2.4.1 Stimulated Raman scattering
8.2.4.2 Stimulated Brillouin scattering
8.2.4.3 Transverse mode instability
8.3 High power TM fiber lasers
8.3.1 Spectroscopic properties
8.3.2 Cross-relaxation pumping with 790 nm diodes
8.3.3 In-band pumping with 1,550—1,950 nm sources
8.4 Other fiber laser media
8.4.1 Er-fiber lasers
8.4.1.1 Concentration quenching
8.4.1.2 Er: Yb codoped fibers
8.4.1.3 Yb-free Er-doped fiber
8.5 High power Raman lasers
8.5.1 Raman fiber lasers for wavelength conversion
8.5.2 Raman fiber lasers for brightness enhancement
8.6 Conclusions
References
9 Beam combinable, kilowatt all-fiber amplifiers for directed energy
9.1 Introduction
9.2 Time-dependent nonlinear SBS theory and model
9.3 Phase modulation in kW class all-fiber amplifiers
9.3.1 WNS and PRBS SBS suppression comparison
9.3.2 WNS and PRBS coherent beam combining analysis
9.3.3 Filtered PRBS phase modulation
9.3.3.1 Filtered PRBS: coherent combining
9.3.3.2 Filtered PRBS: SBS suppression
9.3.4 PRBS re-coherence
9.4 Multi-kW coherent beam combining of PRBS modulated fiber amplifiers
9.5 Laser gain competition of all-fiber amplifiers
9.5.1 Laser gain competition (two-tone): power scaling
9.5.2 Laser gain competition (two-tone): beam combining
9.6 Conclusion
Acknowledgments
References
10 Applications of high-power 2 μm thulium fiber lasers in materials processing
10.1 Introduction
10.2 Interaction of 2-μm laser light with materials
10.2.1 Polymers
10.2.2 Semiconductors
10.2.2.1 Absorption in semiconductors in the infrared
10.2.2.2 Nonlinear material response in semiconductors
10.2.2.3 Alternative material modification mechanisms
10.2.2.4 Temperature dependence of absorption processes
10.2.3 Infrared optical materials
10.3 Joining of polymers
10.3.1 Experimental details
10.3.2 Butt-welding experiments
10.3.3 Transmission welding experiments
10.4 Processing of semiconductors
10.4.1 Experimental details
10.4.2 Processing of uncoated semiconductor surfaces
10.4.3 Processing of coated semiconductor surfaces
10.5 Processing of chalcogenide glasses
10.5.1 Experimental conditions
10.5.2 Characterization of the film composition and morphology
10.5.3 Refractive index changes
References
11 High-power GHz linewidth diode lasers and their applications
11.1 GHz linewidth high-power diode laser sources
11.1.1 Introduction
11.1.2 Volume Bragg gratings in PTR glass [9]
11.1.2.1 Volume Bragg gratings—description and properties
11.1.2.2 Holographic recording materials
11.1.3 100 W 20 GHz spectral width laser diode system operating at 1,550 nm
11.1.4 250 W 10 GHz laser diode system operating at 780 nm
11.2 Applications of narrow-line high-power diode laser systems
11.2.1 Spin-exchange optical pumping (SEOP)
11.2.2 Diode-pumped alkali laser
11.2.3 Rare gas lasers applications
11.3 Conclusion remarks
References
Index
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