ELI Summer School, 2015 Projekt: Výzkum a vývoj femtosekundových laserových systému a pokročilých optických technologií (CZ.1.07/2.3.00/20.0091)
ELI Summer School Lasers Institute of Physics of the Czech Academy of Sciences
Jonathan Tyler Green
Lasers at ELI
Section
Energy / pulse length
Rep. rate
Peak power
Expected max. focused intensity
L1
100 mJ / 20 fs
1 kHz
5 TW
1019 Wcm-2
L2
10 J / 20 fs
10 Hz
0.5 PW
1021 Wcm-2
L3
30 J / 25 fs
10 Hz
1.5 PW
>1022 Wcm-2
L4
1.5 kJ / <150 fs
0.016 Hz
10 PW
>1023 Wcm-2
Principle of laser operation
mirror
Amplifying medium
mirror
Single mode laser
mirror
Amplifying medium
mirror
Diode Lasers Image: photonicssociety.org
Intensity 1.5
|E|2
1
0.5 n = 3.4
Image: Brittanyspears.ac
0
n = 3.2 -1
-0.5
0
0.5 1 x (microns)
1.5
2
2.5
Diode Lasers
Diode Lasers Applications of diode lasers • Spectroscopy research • CD, DVD, printing technology
• Materials Processing • Optically pumping solid state / fiber lasers
Fiber Lasers
Figure: University of Southampton Optoelectronics Research Center
Solid State Lasers Solid State Laser
Image: Lambda Optics
Image: QRBiz
Solid State Lasers Titanium Sapphire
Image: Laser Quantum
Image: Wall, Sanchez, Lincoln Lab Journal, 3 (1990)
Solid State Lasers Neodymium-doped materials
Nd:YAG Energy level diagram
Solid State Lasers Neodymium-doped materials
Solid State Lasers Ytterbium-doped materials
Smaller quantum defect and larger amplification bandwidth than Nd-doped materials
Efficient cooling in SS lasers 10 Hz rep. rates Pulse energy 10J
kHz rep. rates kW average power
10 Hz rep. rate High pulse energy >100J
multislab
Courtesy T. Metzger (MPQ Garching)
Courtesy K. Ertel and J. Collier (RAL/STFC)
SS and Fiber Lasers Applications of diode lasers • • • • •
LIDAR Defense Machining / Materials Processing Ultra-fast science High field physics
Mode locking
=
Mode locking
Mode locking: Kerr Lens Saturable Absorber
Keller, Nature 424, 831-838 (2003)
Precision Dimensional Metrology based on a femtosecond pulse laser, DOI: 10.5772/7950
Amplification methods
To amplify ultra-short pulses it is necessary to
1. Amplify all wavelengths 2. Control the relative phase of all wavelengths
Amplification methods Extremely high peak intensities of short pulses will destroy amplifier material. How can we amplify the pulses? Chirped Pulse Amplification (CPA)
Amplification methods “Chirping” a pulse is a method for stretching the pulse in time and decreasing the peak pulse power.
Amplification methods Stretcher
Amplifier
Compressor
Temporal dispersion
𝜔 𝑛(𝜔) 𝛽 𝜔 = 𝑐 𝛽 𝜔 = 𝛽 𝜔𝑜 Related to phase velocity
L
𝜕𝛽 1 𝜕 2𝛽 + 𝜔 − 𝜔𝑜 + 𝜔 − 𝜔𝑜 2 𝜕𝜔 2 𝜕𝜔
Inverse group velocity
2
+ ⋯
Temporal dispersion
𝜔 𝑛(𝜔) 𝛽 𝜔 = 𝑐 𝛽 𝜔 = 𝛽 𝜔𝑜 Related to phase velocity
L
𝜕𝛽 1 𝜕 2𝛽 + 𝜔 − 𝜔𝑜 + 𝜔 − 𝜔𝑜 2 𝜕𝜔 2 𝜕𝜔
Inverse group velocity
2
+ ⋯
Group velocity dispersion (GVD)
Temporal dispersion
Number of higher order dispersion terms to account for depends on bandwidth of optical pulse.
ps pulses: track up to TOD fs pulses: track up to fifth order or higher
Stretchers / Compressors Bulk Material: n = n(ω)
Stretchers / Compressors Chirped Mirrors
Stretchers / Compressors Control GDD and TOD with incidence angle and grating separation
L1 kW compressor
L1 kW compressor
OPCPA
Titanium Sapphire
Amplification methods
Used in L3
Used in L1, L2
OPCPA Optical Parametric chirped pulse amplification Requirements for phase matching: Signal
Ep = Es+Ei kp = ks + ki
Pump Idler
OPCPA Broad phase matching bandwidth in non-collinear configuration Crystal optical axis
θ α
kp ks Bandwidth of signal
ki
OPCPA Broad phase matching bandwidth in non-collinear configuration
Optimum phase matching angle = 515 nm, Material: 3, Phase Matching Type: 1 p
25.8
= 2.25o
25.6
= 2.375o = 2.5o
Phase matching in BBO crystal Pump: 515nm Signal: ~800nm
Phase Matching Angle (deg)
25.4
= 2.625o
25.2
= 2.75o
25 24.8 24.6 24.4 24.2 24 23.8 650
700
750
800
(nm)
850
900
950
1000
OPCPA OPCPA is less developed than Ti:Sapphire amplification, but offers important advantages:
1. Very large amplification bandwidth 2. No energy stored in crystal (no heating due to quantum defect) 3. No amplified spontaneous emission; however parametric super-flourescence can occur
Example: L1 laser system
Thin Disk Regenerative Amplifier
Compressor + SHG
1030 nm
Oscillator
OPCPA
Broadband 800 nm
Example: L1 Thin disk lasers
Pump laser: 100mJ @ 1kHz
Example: L1 Thin disk lasers Compressor efficiency: 90.5%
56% conversion efficiency giving 16 mJ at 515 nm 20
1
18
0.9
16
0.8
14
0.7
12
0.6
10
0.5
8
0.4
0.2
6
0.3
0.1
4
0.2
2
0.1
Autocorrelation trace (AU)
0.6 0.5
data fitted curve
pulse duration: 1.8 ps
515 nm pulse energy
0.7
0.4 0.3
0 -20
-15
-10
-5
0 t (ps)
5
10
15
20
0
0
5
10
15 20 1030 nm pulse energy
25
0 30
Efficiency
0.8
Example: L1 Thin disk lasers Second Harmonic Generation in LBO
Example: L1 Thin disk pumped OPCPA Pulses synchronized to 14 fs RMS. Loop is robust and remains locked for hours.
F. Batysta, et al., Opt. Exp., 22, 30281 (2015)
L2 Beamline
Kryogenně chlazený čerpací 10 J laser pro OPCPA
120 mm
Yb:YAG monokrystal firmy Crytur
Špičkový výkon
1 PW (15 nul)
Energie v pulsu
15 J
Délka pulsu
15 fs
Výstřelů
10 / vteřinu
Dodavatel
Tým ELI + Rutherford Appleton Laboratory
Technologie
Diodové čerpání, OPCPA
L3 Beamline
Diagnostika svazku
L3 Front end
Diodami čerpané Nd:sklo – čerpací laser
Špičkový výkon
1 PW (15 nul)
Energie v pulsu
30 J
Délka pulsu
30 fs
Výstřelů
10 / vteřinu
Dodavatel
Livermore National Energetics + Tým ELI
Technologie
Čtvercový svazek 214mm x 214mm, Ti:safírové zesilovače a diodové i Nd:skleněné čerpací lasery
Ti:safírový zesilovač
Front end, Ti:safírový oscilátor, stretcher,...
PW kompresor a diagnostika
L4 Beamline Špičkový výkon
10 PW (16 nul)
Energie v pulsu
1,5 kJ a 150 J
Délka pulsu
1 ns a 150 fs
Výstřelů
1 / minutu
Dodavatel
National Energetics + Ekspla + Tým ELI
Technologie
Výbojkově čerpané Nd:skleněné zesilovače + OPCPA předzesilovač
Thank you for your attention! Thanks to Lasers & Control Team Pavel Bakule Roman Antipenkov Jakub Novak Frantisek Batysta Robert Boge Jack Naylon Tomas Mazanec Martin Horacek Marc-Andre Drouin
