Laser Systems, Part 2

281 Pages·2008·4.734 MB·English

by  R. Iffländer (auth.), W. Schulz, H. Weber, R. Poprawe (eds.)

Landolt-Börnstein
Numerical Data and Functional Relationships in Science and Technology
New Series / Editor in Chief: W. Martienssen
Group VIII: Advanced Materials and Technologies
Volume 1
Laser Physics
and Applications
Subvolume B: Laser Systems
Part 2
Editors: W. Schulz, H. Weber, R. Poprawe
Authors:
R. Beigang, A. Bruns, E. Gornik, H.-J. Hoffmann, R. Iffländer,
K.A. Janulewicz, M.J. Kelley, J. Limpert, G.R. Neil, P.V. Nickles,
W. Sandner, A. Tünnermann, H. Wenzel
ISSN 1619-4802 (Advanced Materials and Technologies)
ISBN 978-3-540-44380-3 Springer Berlin Heidelberg New York
Library of Congress Cataloging in Publication Data:
Landolt-Börnstein: Numerical Data and Functional Relationships in Science and Technology, New Series.
Editor in Chief: W. Martienssen.
Group VIII, Volume 1: Laser Physics and Applications. Subvolume B: Laser Systems. Part 2.
Edited by W. Schulz, H. Weber, R. Poprawe.
Springer-Verlag, Berlin, Heidelberg, New York 2008.
Includes bibliographies.
1. Physics - Tables. 2. Chemistry - Tables. 3. Engineering - Tables.
I. Börnstein, Richard (1852-1913). II. Landolt, Hans (1831-1910).
QC 61.23 502'.12 62-53136
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Editors
Schulz, Wolfgang
Fraunhofer-Institut fu¨r Lasertechnik (ILT), Aachen, Germany
Weber, Horst
Technische Universit¨at Berlin, Optisches Institut, Berlin, Germany
Poprawe, Reinhart
Fraunhofer-Institut fu¨r Lasertechnik (ILT), Aachen, Germany
Authors
Beigang, Ren´e
Technische Universit¨at Kaiserslautern, Fachbereich Physik, Kaiserslautern, Germany
Bruns, Adlin
Fraunhofer-Institut, Angewandte Optik und Feinmechanik, Jena, Germany
Gornik, Erich
Technische Universit¨at Wien, Institut fu¨r Festko¨rperelektronik, Wien, Austria
Hoffmann, Hans-Ju¨rgen
Technische Universit¨at Berlin, Institut fu¨r Werkstoffwissenschaften und -technologien, Fachgebiet
“Glaswerkstoffe”, Berlin, Germany
Iffl¨ander, Reinhard
TRUMPF Laser GmbH, Schramberg, Germany
Janulewicz, Karol Adam
Max-Born-Institut fu¨r Nichtlineare Optik und Kurzzeitspektroskopie (MBI), Berlin, Germany
Kelley, Michael J.
Thomas Jefferson National Accelerator Facility, Newport News, VA, USA
Limpert, Jens
Friedrich-Schiller-Universita¨t Jena, Institut fu¨r Angewandte Physik, Jena, Germany
Neil, George R.
Thomas Jefferson National Accelerator Facility, Newport News, VA, USA
Nickles, Peter V.
Max-Born-Institut fu¨r Nichtlineare Optik und Kurzzeitspektroskopie (MBI), Berlin, Germany
Sandner, Wolfgang
Max-Born-Institut fu¨r Nichtlineare Optik und Kurzzeitspektroskopie (MBI), Berlin, Germany
Tu¨nnermann, Andreas
Fraunhofer-Institut, Angewandte Optik und Feinmechanik, Jena, Germany
Wenzel, Hans
Ferdinand-Braun-Institut fu¨r Ho¨chstfrequenztechnik (FBH), Berlin, Germany
VI Authors
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Preface
The three volumes VIII/1A, B, C document the state of the art of “Laser Physics and Applica-
tions”. Scientific trends and related technological aspects are considered by compiling results and
conclusions from phenomenology, observation and experiments. Reliable data, physical fundamen-
tals and detailed references are presented.
Intherecentdecadesthelasersourcematuredtoanuniversaltoolcommontoscientificresearch
as well as to industrial use. Today the technical goal is the generation of optical power towards
shorter wavelengths, shorter pulses, higher efficiency and higher power for applications in science
and industry. Tailoring the optical energy in wavelength, space and time is a requirement for the
investigation of laser-induced processes, i.e. excitation, non-linear amplification, storage of optical
energy, etc. According to the actual trends in laser research and development, Vol. VIII/1 is split
into three parts: Vol. VIII/1A with its two subvolumes 1A1 and 1A2 covers laser fundamentals,
Vol.VIII/1Bwithitsthreesubvolumes1B1,1B2and1B3dealswithlasersystemsandVol.VIII/1C
gives an overview on laser applications.
In Vol. VIII/1B2 the following topics are treated in detail:
Part 4: Solid-state lasers
In four sections, the physical and engineering aspects of different solid-state lasers and laser active
materials are presented. Solid-state lasers matured to versatile instruments applied for high-power
industrial applications, enabling display technique providing the basic colors, becoming tools in
medical surgery and dentistry, as well as entering scientific approaches for diagnosis of chemical
reactions on the femto-second time scale. Glasses showing a strong inhomogeneous broadening
and therefore facilitating laser excitation and tuning the wavelength are discussed in comparison
with crystals. Promising alternatives to early concepts using bulk solid-state laser systems are
rare-earth-doped fibers. Decades after the advent of low-loss fused silica fibers by Corning in
1970 an impressive development of beam power and quality happened. In 2004 kilowatt powers
at diffraction-limited beam quality were demonstrated and actually multiple kilowatt high-power
applications are in the focus of scientific research and industrial development of the corresponding
applications.
Part 5: Diode lasers
Diodelasersrepresenttheextremewithrespecttocompactness,efficiencyandlowlaserthreshold.
Enablingphysicalproperties,successfulapplicationsandpromisingperspectivesarepresented.The
small spatial size below 500 μm allows their use for entertainment, data storage and printing as
well as high-performance fiber-based communication systems. The impact of diode lasers spans
fromdemonstratingsingle-frequencylaseremissiontogivingperspectivesforscreeningdiagnostics
in life-science. Flash lamps are substituted by high-power diode arrays to pump high performance
solid-state lasers and enabling basically new laser design. Tuning the gain spectra with quantum-
well structures laser diodes operate at wavelength not attainable with bulk material. Light from
diodelasersinthevisiblespectralregionentersourdailylife.Historyandadvancesaboutmultiple
VIII Preface
hetero-structures having a thickness between 2 and 20 nm, made out of unstrained and strained,
single or multiple quantum wells, emitting light in the visible spectral region are presented.
Part 6: Free-electron lasers
Free Electron Lasers (FEL’s) are moving from an exotic tool of a few specialists to something
broadly available. FEL’s provide photon characteristics unobtainable from more conventional
sources. Radiation comes directly from an oscillating bunch of electrons with relativistic proper-
ties instead of an inverted extra active medium. Physical principles and properties of ready-to-use
machines with high average power from the InfraRed (IR) through Extreme Ultra-Violet (EUV)
to X-ray are presented.
Part 7: X-ray lasers
Thehistoryandactualadvancesofconceptsforpopulationinversiondeeplyinsidetheatomiccore
are presented. Laser systems in the Extreme Ultra-Violet (EUV) spectral region, also called X-ray
lasers, are taking up the challenge to control coherence of light where the emission wavelength
matches the spatial dimensions of micro- and nano-scaled objects. With a wavelength between 2
and 60 nm these lasers approach the future needs of nano- and life-sciences, materials research as
well as structuring.
February 2008 The Editors
Contents
Part 4 Solid-state lasers
4.1 Solid-state laser systems
R. Iffla¨nder .......................................................... 3
4.1.1 Solid-state laser systems.................................................. 3
4.1.1.1 Introduction ............................................................ 3
4.1.1.2 Energy-level diagram and rate equations ................................... 3
4.1.1.2.1 Rate equations for a 4-level system ........................................ 4
4.1.1.3 Amplifiers .............................................................. 5
4.1.1.3.1 Stationary case for low intensities (J (cid:2)Js) ................................. 6
4.1.1.3.2 Stationary case (or T (cid:3)τ) and J ≥Js ..................................... 6
4.1.1.3.3 Pulse operation for short pulses (T (cid:2)τ) ................................... 7
4.1.1.4 Oscillator .............................................................. 8
4.1.1.4.1 Oscillator condition...................................................... 10
4.1.1.4.2 Output power........................................................... 10
4.1.1.4.3 Optimal reflection coefficient.............................................. 11
4.1.1.5 Influence of the temperature .............................................. 12
4.1.1.6 Oscillator in pulsed operation ............................................. 14
4.1.1.6.1 Threshold .............................................................. 14
4.1.1.6.2 High pump power Pp (cid:3)Pth .............................................. 14
4.1.1.6.3 Relaxation oscillation .................................................... 15
4.1.1.6.4 Spiking ................................................................ 16
4.1.1.6.5 Long-pulse regime ....................................................... 16
4.1.1.7 Q-switch operation ...................................................... 16
4.1.1.7.1 Single Q-switch pulse .................................................... 17
4.1.1.7.2 Periodical Q-switch for high pulse repetition rate (rτ (cid:3)1) ................... 19
4.1.1.8 The 3-level system....................................................... 21
4.1.1.8.1 Stationary case with dN/dt=0 and dJ/dt=0.............................. 22
4.1.1.9 Efficiency and optimization ............................................... 24
4.1.1.10 Stable resonators........................................................ 26
4.1.1.10.1 Eigenvalues for TEM-00 mode ............................................ 26
4.1.1.10.2 Introducing a virtual reference plane....................................... 28
4.1.1.10.3 Beam parameter product................................................. 29
4.1.1.11 Thermal effects ......................................................... 29
4.1.1.11.1 Steady-state temperature profile........................................... 30
4.1.1.11.2 Thermal load ........................................................... 31
4.1.1.11.3 Thermal lensing......................................................... 33
4.1.1.11.4 Experimental determination of the refracting power.......................... 34
4.1.1.12 Solid-state laser concepts................................................. 35
4.1.1.12.1 Multicavity resonators ................................................... 35
4.1.1.12.2 Two external mirrors and two rods ........................................ 35
X Contents
4.1.1.12.3 Multiple cavities with flat mirrors ......................................... 36
4.1.1.12.4 Thermally invariant resonators............................................ 37
4.1.1.13 Excitation by diodes..................................................... 38
4.1.1.13.1 Rod ................................................................... 38
4.1.1.13.1.1 Longitudinally pumped rod............................................... 38
4.1.1.13.1.2 Transversally pumped rod ................................................ 39
4.1.1.13.2 Disk ................................................................... 40
4.1.1.13.2.1 Longitudinal disk........................................................ 40
4.1.1.13.2.2 Transversally pumped disk ............................................... 40
4.1.1.13.3 Fiber .................................................................. 40
4.1.1.13.3.1 Longitudinally pumped fiber.............................................. 40
4.1.1.13.3.2 Transversally pumped fiber ............................................... 41
4.1.1.13.4 Slab ................................................................... 41
4.1.1.13.4.1 Transversally pumped slab ............................................... 42
4.1.1.13.4.2 Longitudinal slab........................................................ 42
4.1.1.13.5 Diode-pumped solid-state lasers in research and development ................. 42
4.1.1.14 Solid-state laser products................................................. 43
4.1.2 Laser material parameter................................................. 45
4.1.2.1 Parameter specification .................................................. 45
4.1.2.1.1 Laser data.............................................................. 45
4.1.2.1.2 Optical properties ....................................................... 46
4.1.2.1.3 Thermal parameters ..................................................... 48
4.1.2.1.4 Mechanical properties.................................................... 49
4.1.2.1.5 Crystal properties ....................................................... 49
4.1.2.1.6 Derived data............................................................ 52
4.1.2.1.7 Supplier data ........................................................... 53
4.1.2.1.8 Measured values......................................................... 53
4.1.2.2 Active ions ............................................................. 54
4.1.2.2.1 Overview............................................................... 54
4.1.2.2.2 Most important ions ..................................................... 55
4.1.2.2.2.1 Chromium.............................................................. 55
4.1.2.2.2.2 Erbium Er3+ ........................................................... 57
4.1.2.2.2.3 Holmium Ho3+.......................................................... 59
4.1.2.2.2.4 Neodymium Nd3+ ....................................................... 60
4.1.2.2.2.5 Praseodymium Pr3+ ..................................................... 63
4.1.2.2.2.6 Titanium............................................................... 65
4.1.2.2.2.7 Thulium ............................................................... 65
4.1.2.2.2.8 Ytterbium.............................................................. 67
4.1.3 Laser crystals ........................................................... 69
4.1.3.1 Alexandrite............................................................. 69
4.1.3.2 BEL (lanthanum beryllate) ............................................... 70
4.1.3.3 Emerald................................................................ 70
4.1.3.4 GGG (gallium gadolinium garnet) ......................................... 71
4.1.3.5 GSAG (gadolinium scandium aluminum garnet)............................. 72
4.1.3.6 GSGG (gadolinium scandium gallium garnet) ............................... 73
4.1.3.7 GVO(4) (gadolinium (ortho)vanadate) ..................................... 74
4.1.3.8 KGW (potassium gadolinium tungstate) ................................... 75
4.1.3.9 LICAF (lithium calcium aluminum fluoride) ................................ 75
4.1.3.10 LNA (lanthanum neodymium hexa-aluminate),
LMA (lanthanum magnesium hexa-aluminate) .............................. 76
4.1.3.11 LSB (lanthanum scandium borate) ........................................ 77
Contents XI
4.1.3.12 NYAB (neodymium yttrium aluminum borate).............................. 77
4.1.3.13 Quartz................................................................. 78
4.1.3.14 Sapphire ............................................................... 79
4.1.3.15 YAG (yttrium aluminum garnet) .......................................... 80
4.1.3.16 YAP (yttrium aluminum perovskite),
YALO (yttrium aluminum oxide).......................................... 82
4.1.3.17 YLF (yttrium lithium fluoride)............................................ 83
4.1.3.18 YOS (yttrium ortho-silicate).............................................. 84
4.1.3.19 YSAG (yttrium scandium aluminum garnet)................................ 84
4.1.3.20 YSGG (yttrium scandium gallium garnet) .................................. 85
4.1.3.21 YVO(4) (yttrium (ortho)vanadate) ........................................ 86
References for 4.1 ....................................................... 87
4.2 Glasses
H.-J. Hoffmann ....................................................... 97
4.2.1 General properties of laser glasses ......................................... 97
4.2.1.1 Basic considerations ..................................................... 97
4.2.1.2 Lanthanides as active ions ................................................ 98
4.2.1.3 Glasses doped with Nd3+.................................................100
4.2.1.4 Radiative lifetime and concentration quenching..............................102
4.2.1.5 Glasses doped with other active ions, codoping..............................103
4.2.2 Temperature effects......................................................103
4.2.2.1 Thermal load of cylindrical rods...........................................103
4.2.2.2 Thermal lensing.........................................................104
4.2.2.3 Increasing the maximum laser power.......................................105
4.2.3 Quantities to characterize properties of laser glasses .........................107
4.2.3.1 Density of ions..........................................................107
4.2.3.2 Refractive index.........................................................107
4.2.3.3 The refractive index as a function of the temperature ........................108
4.2.3.4 Photoelastic coefficients ..................................................110
4.2.3.5 Nonlinear effects ........................................................110
4.2.4 Properties of commercial laser glasses doped with Nd3+ (Er3+) ions from
different manufacturers...................................................113
4.2.4.1 Meaning of the symbols ..................................................113
4.2.4.2 Manufacturer: Schott Glass Technologies ...................................114
4.2.4.3 Manufacturer: Hoya Optics ...............................................116
4.2.4.4 Manufacturer: Kigre .....................................................118
References for 4.2 .......................................................120
4.3 Diode-pumped fiber lasers
A. Tu¨nnermann, J. Limpert, A. Bruns.................................125
4.3.1 Introduction ............................................................125
4.3.2 Historical background of fiber lasers .......................................125
4.3.3 Basic principles of a fiber laser ............................................126
4.3.4 Fundamentals of fiber optics ..............................................127
4.3.5 Double-clad fiber lasers ..................................................128
4.3.6 Ytterbium-doped fiber lasers..............................................130
4.3.7 Fiber lasers versus bulk lasers.............................................131