新しい拡大則の時代を迎えた世界の大型レーザー研究

新しい拡大則の時代を迎えた
世界の大型レーザー研究
固体レーザーは生き残れるか？
植田憲一
電通大レーザー研、浜松ホトニクス
将来展望を議論するシンポジウム
阪大レーザー研 ２０１３年３月１日
超高出力レーザー関係 国際会議 （この半年だけでも）
レーザー核融合だけ見ている時代は終わった。（少なくともレーザー技術については）
ICUIL 2012 @ Malibu, Rumania, Sep. 17-21, 2012 （高強度レーザー、レーザー加速）
ASILS 2012 @ Tokyo, Nov. 8-9, 2012
IZEST 2012 @ Glasgow Nov. 13-16, 2012
（レーザーと高エネルギー物理）
Russian ELI @ Nizhiny Novgorod, Russia, Dec. 3, 2012.
LCS 2012 @ Nizhiny Novgorod, Russia, Dec. 4-6, 2012
ICAN WS @ Southampton, UK, Jan. 21-22, 2013
（光コム増幅）
（セラミックレーザー）
（ファイバーレーザーアレイ）
DOE WS on Laser Technologies on Accelerators @ Napa Valley, US, Jan. 23-25, 2013
IZEST DLO WS @ Dusseldorf, Germany, Mar. 21-22, 2013.
Damage-Less Optics and C3 (Cascaded Compression Conversion)
将来構想：何年後？装置寿命？
２０年？３０年？５０年？
Lamp pump -> LD pump
Nd:glass -> ceramic
The path to LIFE is a four-step process:
1. NIF: Construction and operation of a laser facility at the scale required
for energy production (Achieved 2009)
2. Ignition: Demonstration of net energy gain from fusion fuel (In
progress)
3. LIFE demonstration: Integration of all the technologies required for a
power station (Planned for mid-2020s)
4. Commercial LIFE fleet: Rollout of LIFE plants onto the electric grid
(Late 2020s and beyond)
Laser Ceramic Symposium (Kaminskii, Strek, Ueda) 1st International Laser Ceramic Symposium, Warsaw, Poland, 2005
2nd International Laser Ceramic Symposium, Tokyo, Japan, 2006
3rd International Laser Ceramic Symposium, Paris, France, 2007
4th International Laser Ceramic Symposium, Shanghai, China, 2008
5th International Laser Ceramic Symposium, Biobao, Spain, 2009
6th International Laser Ceramic Symposium, Munster, Germany, 2010
7th International Laser Ceramic Symposium, Singapore, 2011
8th International Laser Ceramic Symposium, Nizhny Novgorod, Russia, 2012
5th Laser Ceramics Symposium:
International Symposium on Transparent Ceramics for Photonic
Applications
Bilbao, Spain, December 9-11, 2009
1064 nm Absorption
in YAG Ceramics and Single crystals
Absorption Coefficient (ppm/cm)
10000
Reactive
Sintered Ceramics
1000
Non-Reactive
Sintered Ceramics
Al2O3
100
single crystal
(Standard 1)
Ceramic
SC
10
YAG
Nd:YAG
Gd:YAG
Tm:YAG
Yb:YAG
Fused silica
(Standard 2)
Gaume, LCS 2010, Munster
Nature of Scattering Centers
Non-reactive sintering is essential from stoichiometry.
Effect of deviations from stoichiometry on the nature of scattering centers
Non‐reactive sintering is important for ceramics fabrication.: conclusion of Gaume and Ueda phase diagram issue
Vp(defect)
From Fit to Mie’s Model
V(Al2O3) calculated
Vp(Al2O3_calculated)
V(YAlO3) calculated
Vp(YAP_calculated)
Pore density (cm‐3)
Volume fraction of inclusions
Vp2defect
0.01
Stoichiometric
point
1E-3
Al2O3 rich
-1.0
-0.8
Al2O3 rich
Y2O3 rich
-0.6
-0.4
-0.2
0.0
0.2
0.4
stoichio(mol %)
Deviation from stoichiometry
(mol %)
0.6
0.8
Y2O3 rich
1.0
Deviation from stoichiometry (mol %)
The reason of 10 times smaller scattering in nano‐crystalline powder sintering is stoichiometric control of ceramics. It is very hard to keep stoichiometric condition in reactive sintering. : Our conclusion.
Importance for controlling the stoichiometry
Stoichiometry control during the whole
process!
Powder phase purity of YAG
YAG Phase formation
Densification
 Raw materials
 Processing: weighting errors,
concentration of the starting
solution (wet chemistry),
moisture and absorbing,
uniformity of the power, powder
mixing process…
Microstructure
Optical Quality!
Scattering loss @1064 nm: single pass
Scattering loss measurements setup
Nd:YAG-3 is a control sample: 0.6 at.%---Konoshima Chemicals
The fabricated ceramics owns pretty good optical quality
The single pass scattering loss is around 0.001~0.003 cm-1
TEXTRON: Nd:YAG
ceramics, ~100 kW
Northrop-Grumman’s high power
laser system: 105 kW, 85 min
中国、ロシアからの情報
Now ceramic lasers are
moving to 600 kW~1 MW
level!
Requirements for HiPER
Laser gain material
•1 kJ beamlet
•
•
~ 1 kJ beamlet
10 off 22 cm aperture slabs
5000 cm3 ceramic Yb:YAG
•10 kJ bundle
•
•
10 beamlets = 100 slabs
50,000 cm3 ceramic Yb:YAG
•IFE plant with 50 beamlines (0.5 MJ)
•
•
50 beamlines = 10,000 slabs
2.5 m3 ceramic Yb:YAG
Large aperture Faraday rotator
~ 10 kJ bundle
•Aperture 10 to 20 cm capable of handling 10 kW average power
•Ceramic TGG/GGG ?
2nd ICFA/ICUIL Joint WS in LBNL, US 9/20‐22/2011
High energy
Short pulse
High rep rate
Wall plug eff.
2 m is better
High power
30fs／30J module
Wavefront dividing interference generates satelite
lobes by diffraction theory.
Diffraction
pattern
波面分割型干渉によるビーム結合は、空間強度変調によるサテラ
イトピークの発生により、半分以上の光は集光できない光となる。
強度分割型干渉によるビーム結合が不可欠という（私の）結論
米国は T.Y. Fan (MIT, Lincoln Lab.)の Spectrum Beam Combining へ
Jenaグループのアイデア：高次回折光からのビーム結合
（同一波長ビーム ただし、強度比は大きい。）
高次回折光への分散
高次回折光からのビーム結合
透過型回折格子の場合
以下は、IZEST、DOE WSにおける私の提案
Ceramic Laser
Technology
and Thermal
Management
Ken-ichi
Ueda
Institute for Laser Science
Univ. of Electro-Communications
Chofu, Tokyo Japan
[email protected]
DOE WS in Napa Valley, CA, US
Jan. 24, 2013
Fiber laser array
DOE/DOD MOU for HPL
Solid state laser
FEL
We have MJ, PW, fs lasers today.
We need another scaling for our future.
NIF and LMJ are almost scaling limit in a conventional large aperture amplifier system. Multi‐stage amplifier & Aperture scaling
40 x 40 cm beam
Scaling limit
Beam number scaling:
Coherent addition in parallel: Phase matched beams
Small and thin
amplifiers
Coherent combining of small beams:
Scaling is unlimited.
Phase control feedback tech is
key.
Beam
combination
Aperture scaling:
Coherent addition in series: Laser Amplification
Scaling is limited
by ASE and heating.
Automatic phase locked by
stimulated emission process.
Osc
Pre-Amp
Main-Amp
Boost-Amp
We need paradigm shifting technology.
Another type of power scaling.
Aperture scaling
to Coherent beam combining
or These combination
Combination of Amplitude Dividing Beam
Combining and Aperture Scaling
We need
high quality and
large aperture amplifiers.
0.5
5
1.0
0.5
1
0
5
50
5
x10
amplifiers
100 50
5
500
50
1000
x10 amplifiers
Constant Fluence
amplification concept
50
500
x10 amplifiers
Thin Disk Laser:
1. Reflection geometry of thin disks (Active mirror concept)
2. Transmission geometry of thin disks
透過型Thin Disk 増幅器の提案
My proposal: Transmitting thin disk laser
透過光学系であるべきだ。
Transmission optics is better than reflection optics for monochromatic light.
Wavefront distortion is always small in transmission optics.
波面歪みは透過光学系の方が“必ず”よい。
冷却と熱問題の解決が最も重要
How to solve the problem on wavefront distortion?
• Propagation mode control  fiber laser
• Beam cleaning tech in OPCPA, SRS, SBS including phase conjugating optics.
• Efficient cooling geometry  thin disk laser
• Efficient cooling tech  high speed He cooling & multi‐disk geometry
• What is next?
Efficient cooling system for solid state lasers
LLNL Mercury laser
1 mm gap He cooling
50 psi 0.1 Mach flow velocity
1-3 W/cm2 cooling
50 psi = 3.4 atm
100 m/s flow
DiPOLE Amplifier Concept
~175K
• Diode-pumped multi-slab amplifier
•
•
Ceramic Yb:YAG gain medium
Co-sintered absorber cladding for ASE suppression
• Distributed face-cooling by stream of cold He gas
•
Low overall aspect ratio & high surface area
• Operation at cryogenic temperatures
•
•
•
Higher o-o efficiency – reduction of re-absorption
Increased gain cross-section
Better thermo-optical & thermo-mechanical properties
• Graded doping profile
•
•
Equalised heat load in each slab
Reduces overall thickness (up to factor of ~2)
• Scalable design
•
10 J, 100 J & 1 kJ
Schematic of 1 kJ
head design
Circulation cooling is available for liquid lasers (My Work in Osaka Univ.)
600 J output modular-type
amplifier
500 kV, 4x100 kA
ASE limited amplifier
600J from 30x20x100 cm3 @
10%/cm gain, 1MJ/cc pump
600 kJ from 3x2x10 m3 @ 1%/cm
gain, 100 kW/cc pump
Electra 30 cm x 30 cm Amplifier stage
Electra title page
730 J Plano-Parallel Oscillator ~100 ns FWHM, 5 Hz operation
E-Beam KrF Pump Source
500 kV, 110 kA
140 ns pulse
Laser gas recirculates
(provides cooling
and quiescent flow)
Discharging through the
1:12 step-up transformer
Charging of the
PFL to 1 MV
(3-4 s)
30x30
x100 cm
Capacitor charging to +/- 43 kV
(>160 ms)
Gas flow = 8.7 m/s
for 5 Hz operation
Discharge
Gas flow
3D orthogonal system
in high rep. rate discharge laser
KrF, ArF, XeCl laser TEA CO2 laser
Laser beam
Cooling section
Most efficient cooling is achieved by exhauting hot material from lasing volume.
Comparison between Nd:YAG, Nd:glass, Yb:YAG, Ti:sapphire, KrF, and CO2 lasers
Solid state lasers
High efficiency pumping
High density pumping
High density heating
Small volume
Thermal lens problem
Operating in
thermal
equilibrium
condition
Gas lasers
Low density
Low efficiency pumping
Large volume
Low distortion
Heat (removal) capacity is large in solid state.
1. Solid state laser vs Gas laser
YAG
KrF
Ratio
density [g/cc]
4.55
0.00498
914
Specific heat [J/g/K]
0.59
0.33
1.79
Specific heat [J/cc/K]
2.68
0.00164
1634
14 m/s
7.8 ms
for 3.5”” HD drive
@7200 rpm
in ELECTRA @
5 Hz operation
Typical moving speed [m/s]
comparable
2. Solid state laser vs Liquid laser
Optical distortion
Disk rotation
Liquid circulation
Nothing
n  P (pressure drop)
Pressure gap is a driving force of liquid flow. Unavoidable!
Moving active medium lasers: glass laser system
Thermal conductivity is low
Byer/HOYA moving slab
SIOM/China
Rotation
Active area
Moving slab
50cm/s
Cooling
Lamp pumping
Cooling chamber
Lamp house
Tube‐type glass laser
Moving speed is not so high, because the active media are so heavy.
Merging of electronics and laser tech.: Is it possible?
High technology in opto‐electronics area might be available for our future.
High Speed Rotary Thin Disk
for efficient cooling of solid state lasers
Most efficient cooling is fast movement of hot material from lasing volume. High speed rotation of thin disk laser is one of the good ideas.
What is a commercial Hard Disk Device?
Effect of mass production.
500 GB HD: Only $50
3.5 inch in diameter
High speed motor 7200 rpm
power 2.4 – 4 W @120 Hz
Edge speed
>14 m/s
Gap space: 10 nm
A commercial Hard Disk technology is available for transmissiontype thin disk laser amplifiers.
Al -> glass -> ceramic : existing technology
Platter, ceramic disk
3.5 inches 0.63 mm thick
Mirror finish < nm
YAG ceramic disk is available.
10 times larger thermal conductivity.
Al
Glass
15 nm
Composed from two original images IBM Corporation
Cooling power of high speed rotary thin disk laser
R=1600 for 5mm beam, 5 Hz pumping
For short pulse pumping
No thermal lensing is possible
Dynamic scaling for pulse pumping
Transmission thin
disk laser
He gas
N Hz rotation
Ceramic laser
Cooling plate
Lasing Hard Disk Driver:
Basic Components for Coherent Beam Combining.
Multiple transparent thin disks
Multiple Lasing HD stages
We need new ideas for our future.
Laser plasma accelerator is a really new regime.
We need new technology for new science.
How to realize a photonic century?
温故知新
We learn a lot from past, knowledge and
experiences.
They are always fresh enough.