Amplificarea pulsurilor laser ultrascurte. CPA in Ti:safir sau OPCPA? Solutii pentru laserul ELI-RO. - PowerPoint PPT Presentation

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Amplificarea pulsurilor laser ultrascurte. CPA in Ti:safir sau OPCPA? Solutii pentru laserul ELI-RO.

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... Non-critical synchronization ... Fs nJ Oscillator Ps Stretcher mJ Amplifier Fs compressor XPW 1-2 ns Stretcher High-energy ten-hundred J amplifier chain High ... – PowerPoint PPT presentation

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Title: Amplificarea pulsurilor laser ultrascurte. CPA in Ti:safir sau OPCPA? Solutii pentru laserul ELI-RO.


1
Amplificarea pulsurilor laser ultrascurte. CPA in
Tisafir sau OPCPA? Solutii pentru laserul
ELI-RO. (Partea I)
R. Dabu Sectia Laseri, INFLPR
2
  • De ce aceasta prezentare?
  • Cunoasterea stadiului actual pe plan mondial in
    domeniul laserilor de mare putere in femtosecunde
  • Incercam sa dam un raspuns privind solutia
    tehnica potrivita pentru laserul ELI-RO
  • Ce putem face ca sa ne incadram in efortul
    stiintific necesar pentru realizarea acestui
    laser
  • Sa facem un pas mai departe in pregatirea unor
    specialisti in domeniul laseri in femtosecunde
    de mare putere si directii de cercetare bazate pe
    acesti laseri
  • Sa atragem in echipa de lucru tineri cu un
    background care sa le permita incadrarea rapida
    in acest domeniu

3
  • CUPRINS
  • 1. Amplificarea pulsurilor laser cu deriva de
    frecventa (chirped pulse amplification - CPA)
    in Tisafir.
  • - Caractersiticile Tisafir ca mediu
    amplificator laser.
  • - Probleme legate de amplificarea pulsurilor
    de femtosecunde de mare energie.
  • 2. Ce este amplificarea parametrica si, in
    particular, OPCPA.
  • - Oscilatia, generarea si amplificarea
    parametrica ca fenomene in optica neliniara.
  • - Relatiile care guverneaza fenomenele
    parametrice.
  • - Castigul unui amplificator parametric, banda
    de frecventa.
  • 3. Amplificare parametrica optica (OPA) de banda
    larga si de banda foarte larga.
  • - Conditiile de obtinere a amplificarii
    parametrice de banda larga sau foarte larga.
  • - Cum se calculeaza pentru un cristal dat
    parametrii de functionare in cele doua cazuri.
  • - Potentialul aplicarii pentru laserii cu
    pulsuri ultrascurte de mare putere.
  • - Amplificarea parametrica a pulsurilor
    largite cu deriva de frecventa OPCPA.
  • - Metode de obtinere a amplificarii de banda
    larga la degenerescenta, amplificare
    necoliniara, folosirea mai multor laseri de
    pompaj. Exemple.
  • - Metode de obtinere a amplificarii de banda
    foarte larga. Benzile de amplificare foarte larga
    in cristale BBO si DKDP pentru laserii din clasa
    PW.
  • 4. Prezentarea unor sisteme laser amplificatoare
    in domeniul PW
  • - Laserul rusesc cu oscilator in fs la 1250 nm
    (Crforsterite) si amplificare in cristale DKDP.
  • Laserul englez (910 nm) cu amplificare de mare
    energie in DKDP.

4
Nuclear Laser Facility Layout (as presented in
the ELI Cz-Hu-Ro proposal)
5
Time schedule for ELI-RO Laser
HIGH ENERGY AMPLIFIERS, COMPRESSOR, BEAM
TRANSPORT AND FOCUSING
MEDIUM ENERGY AMPLIFIERS
FRONT-END
E 200 mJ B 100 nm (compressible down to 15
fs) Tstretched 2 ns Ns ps contrast gt 1012 Rep
rate 10 Hz
E gt 300 J Compressible to lt 20 fs and gt 200 J
Ns ps contrast gt 1012 Rep rate 0.1- 0.02 Hz I
FOCUSED 1023-24 W/cm2
E gt 4 J Compressible down to 15 fs Ns ps
contrast gt 1012 Rep rate 10 Hz
2010- Middle of 2012
End of 2013
End of 2015
2010
2011
2012
2013
2014
2015
6
10 PW laser, a very difficult task (high risk
project) X 50 more powerful than any existing
femtosecond commercial laser X 20 more powerful
than any existing femtosecond laboratory laser
system X 500 more powerful than femtosecond
TEWALAS laser at INFLPR Factors of (high) risk -
high energy (200-300 J/pulse) laser amplifier -
re-compression of stretched amplified pulses and
laser beam focusing - expected results of
nuclear physics experiments
Two possible solutions for high energy
femtosecond pulses amplification
Optical Parametric Chirped Pulse Amplification - OPCPA Tisapphire Chirped Pulse Amplification TiS_CPA
Amplifier media DKDP crystals - 20-30 cm diameter, already available No significant thermal problems Expected pulse duration 5-15 fs Relatively cheap crystals Central wavelength of the amplified pulse 910 nm 20 cm TiS crystals probably available in the next 1-2 years Efficient cooling required Transversal lasing problems Expected pulse duration 15-25 fs More expensive crystals Central wavelength 800 nm
Pump lasers Very precise synchronization Short pump pulse (2-3 ns) Conversion efficiency (pump to amplified signal radiation) 10-20 Non-critical synchronization Pump pulse duration non-critical in the nanosecond range (10-30 nsec) Conversion efficiency (from pump to amplified radiation) 30-40
7
Selection criteria for ELI-RO laser system
  • 1. Able to fulfill required specifications
  • Peak pulse power 10 PW per one amplifier chain
  • Pulse-width of the re-compressed amplified pulse
    lt 20 fs
  • Rep-rate 1/10 1/60 Hz
  • Ns ps contrast gt 1012
  • Focused laser intensity 1023-24 W/cm2 (Laser
    beam focused near the diffraction limit)
  • 2. Existing techniques proved by the long term
    laser facilities operation (200 TW Tisapphire
    CPA laser systems)
  • 3. Existing laser components and devices
    necessary to reach 10 PW power (e.g. 30 cm
    diameter DKDP crystals)
  • 4. Required laser components and devices that
    could be probably developed in the next years
    (20-cm diameter TiS rods NdYAG, YbYAG,
    Ndglass, diode pump lasers diffraction
    gratings, etc.)
  • 5. Conditions of operation and expected laser
    system long-term stability
  • 6. Costs of the whole laser system
  • First target 2012 ? Front-End able to satisfy
    the required laser specifications to be installed
    in Bucharest-Magurele.

8
Principle of Chirped Pulse Amplification (CPA)
for Gaussian temporal and spectral pulse profile
- ultra-short pulse duration, -
phase-locked spectral band-width
CPA technique involves the temporal stretching of
ultra-short pulses with a large spectral
bandwidth delivered by an oscillator. This way,
the laser intensity is significantly reduced in
order o avoid the damage of the optical
components of the amplifiers and the temporal and
spatial profile distortion by non-linear optical
effects during the pulse propagation. After
amplification, the laser pulse is compressed back
to a pulse duration very closed to its initial
value
9
Definitions related to the broad-band ultrashort
pulses
  • Ultrashort laser pulse is characterized by
  • Central frequency and corresponding
    wave-number
  • - Frequency spread arround and
    corresponding spread in wave-number
  • Evolution in time of the pulse is related to

Phase velocity
Group velocity
If second, third order terms are negligible, the
laser pulse travels undistorted in shape with the
goup velocity VG.
10
Definitions related to the broad-band ultrashort
pulses
Group velocity mismatch
Group velocity dispersion
Electric field of the laser pulse in the
frequency domain where
Group delay
L, medium length
Group delay dispersion
Third order dispersion
11
Tisapphire amplification
Polarized fluorescence spectra and calculated
gain line for a optical c-axis normal cut
Tisapphire rod p c-axis parallel polarized
radiation s c-axis normal polarization
Stimulated emission cross section at 795 nm
(c-axis parallel polarized radiation)
P. F. Moulton, JOSA B, Vol. 3, 125 (1986)
12
Pulse amplification in Tisapphire
Energy gain
where Fin is the input pulse fluence, Foutis the
output pulse fluence,
is the saturation fluence of Tisapphire,
, n is the inverted population, l is the medium
length.
Very low input signal, Fin/Fs ltlt 1, small signal
gain
High-level energy densities, Fin /Fs gtgt 1,
saturated gain
Damage threshold fluence at 532 nm, 10 ns pulse
duration, 5-10 J/cm2 Conservative fluence at 532
nm, 10 ns pulse duration, 1-1.5 J/cm2
W. Koechner, Solid-State Laser Engineering,
Springer Verlag, Germany, 1996
13
TEWALAS - schematic drawing of the laser system
14
TEWALAS - Laser system layout
15
Critical characteristics of Tisapphire amplifiers
  1. Spectral band-width of the amplified pulses
    (re-compressed pulse duration)
  2. Intensity contrast of femtosecond pulses versus
    amplified spontaneous emission (ASE) and
    nanosecond pre-pulses
  3. Strehl ratio, focused spot

16
Pulse spectrum narrowing during TiS
amplification TEWALAS_INFLPR
(a)

(b)
TEWALAS laser spectra (a) without active
Mazzler (b) optimized by Mazzler. Mauve line
FEMTOLASERS oscillator yellow line after first
multi-pass amplifier after second multi-pass
amplifier.
17
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18
TEWALAS beam profiles
(a) MP1, (b) MP2
19
(a)
(b)
(c)
Pulse duration measurements using SPIDER. (a),
(b) with Dazzler phase correction (c) without
phase correction. All cases with spectrum
correction by Mazzler.
20
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21
ASE contrast improvement by cross-polarized wave
(XPW) generation
XPW generation four-wave mixing process
governed by the thirdorder nonlinearity
XPW generated wave has the same wavelength as the
input pulse and a cubic dependence on the
intensity
2 mm BaF2
Lens
P1, P2 crossed polarizers Energetic efficiency
10-30 Contrast improvement 3-5 orders of
magnitude
P1
Y
P2
X
Z
ß angle
f
Peak intensity level 3 x 1012 W/cm2
Fs nJ Oscillator
Ps Stretcher
mJ Amplifier
Fs compressor
1-2 ns Stretcher
XPW
High-energy ten-hundred J amplifier chain
Double CPA PW laser
High-energy fs compressor
PW fs pulses
A. Jullien et al, Opt. Lett. 30, 920 (2005) A.
Jullien et al, Appl. Pys. B, 84, 409 (2006) L.
Canova et al, Appl. Phys. B, 93, 443 (2008)
22
Nanosecond Contrast
Nanosecond Contrast _at_600mJ 8x10-8
23
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24
Problems of Tisapphire laser amplifiers for PW
femtosecond laser facilities
Gain narrowing due to the high factor
amplification, 5 nJ ? 250 J, M 5 x
1010 Amplified pulse duration expected not
shorter than 15-20 fs Required nanosecond and
picosecond intensity contrast for a 10 PW laser
(1023-24 W/cm2 focused peak power density) gt
1012-13 Thermal loading (532, 527 nm ? 800
nm) Tisapphire rods, 200 cm diameter required
(currently available 100 cm diameter) Transversa
l lasing in large diameter Tisapphire
rods. Development of high energy, high repetition
rate nanosecond green lasers, with smooth,
uniform spatial intensity profile. Strehl ratio
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