Second ELI Nuclear Physics Workshop
Bucharest
–
Magurele, 1
-
2 February 2010
ULTRASHORT PULSE, HIGH INTENSITY LASERS
D
an
C. Dumitras,
Razvan Dabu
Department of Lasers,
National Institute for Laser,
Plasma and Radiation Physics,
Bucharest, Romania
http://www.inflpr.ro
The
relativistic
regime
I
L
>
10
18
W/cm
2
results
in
a
plethora
of
novel
effects
:
X
-
ray
generation,
-
牡y
g敮敲e瑩潮t
牥污li楳瑩t
獥sf
-
景捵獩fg,
h楧h
-
桡牭rn楣
来湥牡ri潮,
electron
and
proton
acceleration,
neutron
and
positron
production,
as
well
as
the
manifestation
of
nonlinear
QED
effects
Intense Laser Fields
Relativistic regime
:
1 <
a
0
< 100,
a
0
2
=
I
L
λ
L
2
/(1.37 x 10
18
Wμm
2
/cm
2
)
where
a
0
is the normalized electric field amplitude,
I
L
and
λ
L
are the laser intensity and wavelength
At
a
0
= 1 the electron mass increases by 2
1/2
; the limit
a
0
~ 100 corresponds to the
100 TW class lasers
Ultra
-
relativistic
regime
:
I
L
>
10
23
W/cm
2
(
a
0
~
10
2
–
10
4
)
in
this
novel
regime,
positrons,
pions,
muons
and
neutrinos
could
be
produced
as
well
as
high
-
energy
photons
this
largely
unexplored
intensity
territory
will
provide
access
to
physical
effects
with
much
higher
characteristic
energies
and
will
regroup
many
subfields
of
contemporary
physics
:
atomic
physics,
plasma
physics,
particle
physics,
nuclear
physics,
gravitational
physics,
nonlinear
field
theory,
ultrahigh
-
pressure
physics,
astrophysics
and
cosmology
the
ultra
-
relativistic
regime
opens
possibilities
of
:
i.
extreme
acceleration
of
matter
so
that
generation
of
very
energetic
particle
beams
of
leptons
and
hadrons
becomes
efficient
ii.
efficient
production
(~
10
%
)
of
attosecond
or
even
zeptosecond
pulses
by
relativistic
compression
occurring
at
rate
of
600
/
a
0
[as]
iii.
study
of
the
field
–
vacuum
interaction
effects
Relativistic/Ultra
-
relativistic Regimes
Interaction Regimes and Targets
Picosecond
science (10 ps
–
to a few hundredth fs): 25 years
Femtosecond
science (from a few hundredths fs to a few fs): 18 years
Attosecond
science (from a few hundredths as to a few as): it will take at least
next 15 years
瑨攠t潳琠業灯牴o湴nc桩eeme湴猠牥⁹e琠瑯tc潭o
⡓(e汴lⰠ
Brasov 2009)
Peak Power
-
Pulse Duration Conjecture
(
Mourou,Brasov
2009)
1) To get high peak laser power
we
must decrease the pulse
duration
2) To get short laser pulses
we
must increase the intensity
Ultra
-
Short Pulses by Laser Mode
-
Locking
1965
1970
1975
1980
1985
1990
1995
2000
Year
Ti:sapphire
Compression
Solid-State Laser
Dye Laser
10 ps
1 ps
100 fs
10 fs
1 fs
10
-14
10
-13
10
-12
10
-11
10
-15
Pulse duration (s)
Optical
-
Fiber Compression:
6 fs (1987)
nJ
Hollow
-
Fiber Compression:
4,5 fs (1997)
mJ
From Femtosecond to Attosecond
80 as
4 fs
Ultrashort Pulse Lasers
Basic elements essential to a fs laser:
-
a broadband gain medium (
㸾 1⁔䡺⤻)
p
ㄯ
Ⱐ瑨t
ultra
-
short pulse
duration is inversely proportional to the phase
-
locked spectral bandwidth
-
a laser cavity
-
an output coupler
-
a dispersive element
-
a phase modulator
-
a gain
-
loss process controlled by the pulse intensity or energy
Ti
-
Sapphire Lasers
The gain rod in a Ti:sapphire laser can cumulate the
functions:
-
gain (source of energy)
-
phase modulator (through the Kerr effect)
-
loss modulation (through self
-
lensing)
-
gain modulation
High Power Amplifiers
In a laser amplifier the energy extraction efficiency is a function of the ratio of
the energy density and the saturation fluence of the laser material
For ultrashort pulses, the energy density of light at the surface and in the
volume of the optical elements is limited by the onset of
nonlinear effects
and
laser damage
due to the high peak power
Hence, an ultrashort pulse cannot be amplified efficiently
Principle of CPA
–
Chirped Pulse Amplification
(Mourou 1985)
Idea: to stretch (and chirp) a fs
pulse from an oscillator (up to
10,000 times), increase the
energy by
linear amplification
,
and thereafter recompress the
pulse to the original pulse
duration and shape
During amplification, the laser intensity is significantly decreased in order
-
to avoid the damage of the optical components of the amplifiers;
-
to reduce the temporal and spatial profile distortion by non
-
linear optical
effects during the pulse propagation
For the amplification to be truly
linear
, two essential conditions have to be met
by the amplifier:
-
the amplifier bandwidth exceeds that of the pulse to be amplified;
-
the amplifier is not saturated
Pulse Chirping
A chirped gaussian signal pulse
,
where the instantaneous
frequency grows with time
•
A chirped pulse is a signal
in which the
carrier frequency
has a small time
dependence
•
In particular, it
has a linear
time
-
varying
instantaneous frequency:
•
The chirping results in a spectral broadening
of the pulse, i.e., it extends the range of
frequency components contained in the pulse
•
In general, a pulse can be chirped by passing
it through a medium with a nonlinear refractive
index, i.e., a medium in which the refractive
index depends upon the electric field
•
In a CPA scheme, a large bandwidth
ultrashort pulse is chirped in a stretcher based
on diffraction gratings
i
(
t
) =
0
+
β
t
Pulse Stretching
•
A pair of plane ruled gratings with their faces and rulings parallel has the
property of producing a time delay that is increasing function on wavelengths
•
The grating provides a large negative group
-
velocity dispersion (GVD); if a
telescope is added between the gratings, the sign of the dispersion can be
inverted (positive GVD)
•
Stretching is obtained with a combination of diffraction gratings and a
telescope (such a combination of linear elements does not modify the original
pulse spectrum)
•
During this process the
blue
portion of the pulse travels a longer path length
than the
red
portion of the beam
•
The diffraction angle of the
first order is
sin
θ
=
/
d
–
sin
θ
in
where
d
is the grating period
•
A greater wavelength (red) is
diffracted at a larger angle
Pulse Compression
The red
-
shifted wavelengths of the pulse that arrive at the first grating are
diffracted more than the blue
-
shifted wavelengths, and arrive at different portion
of the second grating than the blue wavelengths
During this process the red portion of the pulse travels a longer path length
than the blue portion of the beam
After diffracting from the second grating and recombining with the blue
wavelengths, the total pulse has been compressed in time since
the blue
components have caught up with the red components
Pulse compression of a chirped pulse
using a grating pair
which provides negative GVD
Amplified Spontaneous Emission
-
ASE
ASE is a severe problem in fs pulse amplification
It is produced because the pump pulse is much longer than the fs pulse to be
amplified
ASE reduces the available gain and decreases the ratio of signal (amplified fs
pulse) to background (contrast), or even can cause lasing of the amplifier,
preventing amplification of the seed pulse
Solutions to reduce ASE: using of saturable absorbers for a favorable
steepening of the leading pulse edge; cross polarized wave (XPW)
generation; segmentation of the amplifier in multiple stages
Prelasing (ns and ps Laser Pre
-
pulses)
Prelasing: laser action, occurring during the pump phase in an amplifier,
resulting from the residual feedback of the various interfaces in the optical path
Pre
-
pulses are produced by:
-
bad orientation of the reflective optics (reflection on the back side)
杩敳 †† †
愠
縠~〠灳⁰牥
-
灵汳l
-
獴s潮朠湯g汩湥n爠敦晥捴c
杩攠灳⁰牥
-
灵汳ls
-
汥l歡来渠瑨攠牥来湥牡瑩t攠慭灬楦i敲
杩敳 愠湳灲p
-
灵汳l
Solutions to reduce pre
-
pulse intensity: the use of Pockels cells and/or Faraday
rotators, ps
-
pumped OPCPA
Spectral shaping using acousto
-
optical
programmable gain control filter
(AOPGCF)
-
Mazzler
(a)
(b)
TEWALAS laser spectra: (a) without active Mazzler; (b) optimized by Mazzler.
Mauve line
–
FEMTOLASERS oscillator; yellow line
–
after first multi
-
pass amplifier;
white line
–
after second multi
-
pass amplifier
Correction of spectral phase dispersion
using
acousto
-
optical programmable dispersion filter
(AOPDF)
-
Dazzler
Temporal distortion of the amplified re
-
compressed pulse is produced by:
-
dispersion and phase distortions introduced by the laser amplifier system
-
spectral gain narrowing in Ti:sapphire amplifiers
(a)
(b)
TEWALAS:
Pulse duration measurements using SPIDER (a) with Dazzler phase correction;
(b) without phase correction. All cases: with spectrum correction by Mazzler
Optical Parametric Chirped Pulse Amplification
–
OPCPA (Piskarskas 1992)
Idea: to replace the laser gain media of a CPA system by a nonlinear crystal
Key principle of OPCPA
: A broad bandwidth linearly chirped signal pulse is
amplified with an energetic and relatively narrow
-
band pump pulse of
approximately same duration
Amplification by stimulated emission is substituted by optical parametric
amplification of the signal pulse in the presence of a pump pulse
Requirements
: precise time/space synchronization of signal and pump pulses;
high intensity and high quality pump beams; short pump pulse duration
Advantages and disadvantages of OPCPA
Advantages:
•
High gain in a single pass (up to ten orders of magnitude per cm)
•
Broad bandwidth (ultrashort re
-
compressed pulses)
•
Parametric amplification is possible in a wide range of wavelengths
•
Negligible thermal loading
•
High signal
–
noise contrast ratio
•
High energy and peak power levels in available large nonlinear crystals,
no transversal lasing
•
One avoids the problems of power losses by ASE in high
-
gain laser
amplifiers
Disadvantages:
•
The requirement to match the pump and signal pulse duration
•
The requirement for a high intensity and high beam quality for pump pulse
•
The limited aperture of most available nonlinear crystals
•
The complicated details of phase
-
matching issues
High
-
Intensity Laser System
Front
-
End:
-
large bandwidth
Ti:sapphire
oscillator, optical stretcher and low
energy
Ti:sapphire
amplifiers
-
large bandwidth
Ti:sapphire
oscillator, stretcher and ultra
-
broad
-
band
non
-
collinear optical parametric chirped pulse amplification (NOPCPA)
in BBO, LBO, DKDP crystals
Power amplifiers:
-
Ti:Sapphire
power amplifier chain pumped by high
-
energy nanosecond
SHG
Nd:YAG
,
Nd:glass
lasers
-
large aperture DKDP
-
NOPCPA amplifiers pumped by high energy
nanosecond SHG
Nd:glass
lasers
Pulse compression and beam focusing:
-
large diffraction gratings temporal compressor
-
adaptive optics (deformable mirrors)
100 GW
1 TW
10 TW
100 TW
10 GW
pulse energy
pulse length
10 PW
1 PW
European PW
lasers
and
projects
And more to come …
pulse energy
pulse length
Peak power chart:
State
-
of
-
the
-
art
Data from
OECD
-
Global
Science Forum
CPA table top
CPA fusion
100 GW
1 TW
10 TW
100 TW
10 GW
10 PW
1 PW
100 GW
1 TW
10 TW
100 TW
10 GW
10 PW
1 PW
PFS
and
European visions
Laser system
Amplification
Reported characteristics
Project
Concept
PEARL
-
Russia
OPCPA
-
DKDP
λ
= 910 nm,
τ
= 43 fs,
R = 1shot/30 min, P = 0.56 PW
P = 2 PW
PFS
-
Germany
OPCPA
-
DKDP
λ
= 900 nm,
τ
= 5 fs,
R = 10 Hz, P ≈ 1 PW
RAL
-
UK
OPCPA
-
DKDP
λ
= 910 nm,
τ
= 15
-
30 fs,
R =1 shot/30 min, P ≈ 10 PW
XL III
-
China
Ti:sapphire
λ
= 800 nm,
τ
= 31 fs,
R = 1shot/20 min, P = 0.72 PW
P > 1 PW
APRI
-
Korea
Ti:sapphire
λ
= 800 nm,
τ
= 30 fs,
R = 10 Hz, P = 100 TW
P = 1.1 PW,
R = 0.1 Hz
P
→
10 PW
JAERI
-
Japan
Ti:sapphire
λ
= 800 nm,
τ
= 33 fs,
R=Few shots/hour, P = 0.85 PW
APOLLON
-
France
Hybrid:
OPCPA&Ti:S
λ
= 800 nm,
τ
= 15
-
20 fs,
R = 1 shot/min, P ≈ 10 PW
LLNL
-
USA
Nd:glass
λ
= 1053 nm,
τ
= 440 fs,
R = 1
-
2 shots/hour, P = 1.5 PW
POLARIS
-
Germany
Yb: fluoride
phosphate glass
λ
= 1032 nm,
τ
= 150 fs,
R = 0.1 Hz, P = 1 PW
N
-
Novgorod,
Russia
Cr
-
doped
ceramics
λ
= 1378 nm,
τ
= 25 fs,
R ≈ 1 shot/hour, P → 100 PW
λ
= central wavelength,
τ
=
pulse duration, R = repetition rate, P = peak power
PW Laser Systems: reported, projects, concepts
INFLPR
-
TEWALAS
Possible solutions for 10
-
PW ELI
-
RO laser
B1) Hybrid laser system at 800 nm central wavelength:
-
Front
-
End based on OPCPA in nonlinear crystals (BBO, LBO)
-
High power amplification in Ti:sapphire crystals
B2) Ti:sapphire amplifiers at 800 nm central wavelength :
-
Front
-
End based on Ti:sapphire amplification
-
High power amplification in Ti:sapphire crystals
or
Proposed
solution
A) OPCPA based laser system (910
-
nm central wavelength):
Front
-
End → very broad
-
band signal radiation at 910
-
nm central
wavelength generated by chirp
-
compensated collinear OPA.
High power OPCPA in large aperture DKDP crystals
ELI
-
RO Nuclear Laser Facility Layout
Concept of 3 x 10 PW amplifier chains
2xFRONT
END
DPSL
-
pumped
OPCPA
FE1:
10
-
20 mJ
BW > 120 nm
T
CP
= 50 ps
0.1
-
1 kHz
C > 10^12
FE2:
> 100 mJ
BW > 80 nm
T
CP
= 1
-
2 ns
10
-
100 Hz
C > 10^12
TEST
COMPRESSOR
AMPLIFIERS
Ti:Sapphire pumped by ns
Nd:YAG & Nd:Glass lasers
A1 + A2
BOOSTERS
> 4 J, 10Hz
DIAGNOSTICS
TARGETS
DIAGNOSTICS
BW
–
Spectral bandwidth, C
–
intensity contrast, T
CP
-
chirped
pulse duration, T
C
–
re
-
compressed pulse duration,
Φ
–
focused
laser beam diameter, I
Σ
–
intensity on target
Φ
= 1
-
20
μ
m
I
Σ
= 3 x 10
23
-
24
W/cm
2
BEAM
TRANSPORT
IN VACUUM
TARGETS
A3 +A4+ A5
POWER
AMPLIFIERS
>300 J
A3 +A4+ A5
POWER
AMPLIFIERS
>300 J
A3 +A4+ A5
POWER
AMPLIFIERS
>300 J
A1 + A2
BOOSTERS
> 4 J, 10Hz
A1 + A2
BOOSTERS
> 4 J, 10Hz
COMPRESSOR
200 J
COMPRESSOR
>200 J
COMPRESSOR
200 J
COMPRESSOR
>200 J
COMPRESSOR
200 J
COMPRESSOR
>200 J
BEAM
TRANSPORT
IN VACUUM
BEAM
TRANSPORT
IN VACUUM
2 x FRONT END
DPSSL
-
pumped
OPCPA / ns SHG
Nd:YAG pumped Ti:S
3
-
chains AMPLIFIERS
Ti:Sapphire pumped by ns SHG
Nd:YAG & Nd:Glass lasers
ELI
-
NP
Thank You !
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