Second ELI Nuclear Physics Workshop

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nc桩eeme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 !