Second ELI Nuclear Physics WorkshopBucharest – Magurele, 1-2 February

2010

ULTRASHORT PULSE, HIGH INTENSITY LASERS

Dan C. Dumitras, Razvan Dabu

Department of Lasers,National Institute for Laser,

Plasma and Radiation Physics,Bucharest, Romaniahttp://www.inflpr.ro

The relativistic regime IL > 1018 W/cm2 results in a plethora of novel effects: X-ray generation, -ray generation, relativistic self-focusing, high-harmonic generation, electron and proton acceleration, neutron and positron production, as well as the manifestation of nonlinear QED effects

Intense Laser FieldsIntense Laser Fields

Relativistic regime: 1 < a0 < 100, a02 = ILλL

2/(1.37 x 1018 Wμm2/cm2)where a0 is the normalized electric field amplitude,IL and λL are the laser intensity and wavelength

At a0 = 1 the electron mass increases by 21/2; the limit a0 ~ 100 corresponds to the 100 TW class lasers

Ultra-relativistic regime: IL > 1023 W/cm2 (a0 ~ 102 – 104) 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/a0 [as] iii. study of the field – vacuum interaction effects

Relativistic/Ultra-relativistic RegimesRelativistic/Ultra-relativistic Regimes

Interaction Regimes and TargetsInteraction 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 the most important achievements are yet to come (Svelto, Brasov 2009)

Peak Power -Peak Power - Pulse Duration ConjecturePulse Duration Conjecture(Mourou,Brasov 2009)(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-Ultra-Short Pulses by Laser Mode-LockingLocking

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

Pul

se d

urat

ion

(s)

Optical-Fiber Compression: 6 fs (1987) nJ

Hollow-Fiber Compression: 4,5 fs (1997) mJ

From Femtosecond to AttosecondFrom Femtosecond to Attosecond

80 as

4 fs

Ultrashort Pulse LasersUltrashort Pulse Lasers

Basic elements essential to a fs laser:

- a broadband gain medium ( >> 1 THz); p 1/, the 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 LasersTi-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 AmplifiersHigh 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 Principle of CPA – Chirped Pulse Amplification (Mourou 1985)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 ChirpingPulse 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 + βt

Pulse StretchingPulse 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

sinθ = /d – sinθin

where d is the grating period

• A greater wavelength (red) is diffracted at a larger angle

Pulse CompressionPulse 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 - ASEAmplified 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 (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) gives a ~ 10 ps pre-pulse

- strong nonlinear effects give ps pre-pulses- leakage in the regenerative amplifier gives a ns pre-pulse

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 Optical Parametric Chirped Pulse Amplification – OPCPA (Piskarskas 1992)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 Advantages and disadvantages of OPCPAOPCPA

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 SystemHigh-Intensity Laser System

Front-End:Front-End:

- large bandwidth Ti:sapphire oscillator, optical stretcher and low - large bandwidth Ti:sapphire oscillator, optical stretcher and low energy Ti:sapphire amplifiersenergy Ti:sapphire amplifiers

- large bandwidth Ti:sapphire oscillator, stretcher and ultra-broad-band - large bandwidth Ti:sapphire oscillator, stretcher and ultra-broad-band non-collinear optical parametric chirped pulse amplification (NOPCPA) non-collinear optical parametric chirped pulse amplification (NOPCPA) in BBO, LBO, DKDP crystalsin BBO, LBO, DKDP crystals

Power amplifiers:Power amplifiers:

- Ti:Sapphire power amplifier chain pumped by high-energy nanosecond - Ti:Sapphire power amplifier chain pumped by high-energy nanosecond SHG Nd:YAG, Nd:glass lasersSHG Nd:YAG, Nd:glass lasers

- large aperture DKDP-NOPCPA amplifiers pumped by high energy - large aperture DKDP-NOPCPA amplifiers pumped by high energy nanosecond SHG Nd:glass lasersnanosecond SHG Nd:glass lasers

Pulse compression and beam focusing:Pulse compression and beam focusing:

- large diffraction gratings temporal compressor- large diffraction gratings temporal compressor

- adaptive optics (deformable mirrors)- adaptive optics (deformable mirrors)

100 GW

1 TW

10 TW

100 TW

10 GW

pulse energy

1 ps

10 ps

1 J

10 J

100

J

100 pspulse length

pow

er

1 KJ

1 ns

100 fs

10 fs

100

mJ

10 PW

1 PW

MPQ

CLPU

Sala

man

ca

Peta

l

Jena

GSILULI

RAL

RAL

European PW lasers and projects

And more to come …APOLL

ON

INFL

PR

pulse energy

1 ps

10 ps

1 J

10 J

100

J

100 ps

pulse length

1 KJ

1 ns

Peak power chart:State-of-the-art

MBI

RAL

OSA

KA

Celia

Osa

ka

Live

rmor

e

LULI

RAL

LOA

JAER

IMBI

JenaOsa

ka

LUNDCU

OSCU

OS

LULI

JENA

CUOS

ATLA

SSh

angh

ai

Broo

khav

en100 fs

10 fs

100

mJ

Data fromOECD - Global Science Forum

CPA table top

CPA fusion

100 GW

1 TW

10 TW

100 TW

10 GW

pow

er

10 PW

1 PW

100 GW

1 TW

10 TW

100 TW

10 GW

pow

er

10 PW

1 PWPFS

and European visions

INFL

PR

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 - TEWALASINFLPR - 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

orProposed 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

TCP = 50 ps 0.1-1 kHz

C > 10^12

FE2: > 100 mJ BW > 80 nm

TCP= 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, TCP- chirped pulse duration, TC – re-compressed pulse duration, Φ – focused laser beam diameter, IΣ – intensity on target

Φ = 1-20 μm

IΣ = 3 x 1023 -24 W/cm2

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 !