Beyond 1 PW:

What is the next step in ultraintense laser physics and technology?

Presented by: Todd Ditmire Center for High Energy Density Science Department of Physics University of Texas at Austin

The power that a laser can deliver has increased roughly by a factor of 1000 every 10 years

for λ = 1 µm

Electron Quiver Energy (eV)

New and Exotic Physical Regimes Can Be Accessed With Ultra-High Intensity Lasers









10 10 10 10 10 10 10 10

2000 1990


Relativistic Plasmas Hard X-ray Generation



Tunnel Ionization High Temperature Plasma Formation Bright X-ray Generation

3 2





Nonperturbative Atomic Physics High Order Nonlinear Optics



Fast Ignition e +e- Production Weapons Physics Nuclear reactions

Relativistic ions Nonlinearity of Vacuum Multi-GeV elecs.

Current Technology Perturbative Atomic Physics Nonlinear Optics










Laser Intensity (W/cm2)






The science enabled by an exawatt laser is likely to be exotic and exciting

Focused intensity: > 1025 W/cm2

Electron quiver energy: ~ 10 GeV

Light pressure: ~ 1015 bar

Proton quiver energy: ~ 100 MeV

• Macroscopic relativistic electron plasmas (pair plasmas) • Relativistic ion plasmas • TeV electron acceleration • Hawking Unruh radiation • Vacuum birefringence • Vacuum pair production (“boiling” the vacuum)

The quiver energy of electrons at relativistic intensity mimics MeV temperatures and lead to pair plasmas Solid Target

Pair production in relativistic plasma

e- e+ fireball a0 = 10 - 30 yields strongly relativistic plasma I ~ 1021 W/cm2 over 10 - 100µm → P = 10 - 100 PW

dN/dEdΩ Ω


e ns e t In

ra ult

fa s

e uls p t

Hot electron and positron spectrum measured from the LLNL PW laser


e- at 30o

1010 9


e- at 95o

Relativistic pair plasmas near energetic objects like black holes are thought to lead to gamma ray bursts

e+ at 30 o

Note a0 ~ 1 for protons when I = 2 x 1024



107 106 5



Positron spectrum


Energy (MeV)


A multi- PW laser could enable wakefield acceleration to > 10 GeV

Multi-PW lasers may lead to multi-GeV electron ejection upon highly charged ion production Ultra-relativistic “Above Threshold Ionization” • Ionization "injects" electrons right at the peak of the field

Electrons with large longitudinal momentum can “ride” the laser wave



• This yields much greater energies than if the laser interacts with free electrons


Monte Carlo simulation using a focused PW beam

c z

Ar17+ ionization I = 5 x 1021 W/cm2

T /4 time needed to slide off the peak is τ ≅ γ Electron where T - period of the laser light. dephasing time

test electrons Maximum ejected electron energy

tan2 θ = 2/(γ-1)

Max Electron Energy (GeV)

Near GeV electrons ejected within 4° of the laser axis 10 PW laser 1 EW laser


At sufficient intensities it should be possible to observe the optical nonlinearity of vacuum Atom/vacuum subject to an oscillating field E=E0sin(ωt - kz)

Atom Distorted potential


Oscillating laser field

mc2 -mc2 Electron can tunnel into a physical energy state


Wavepacket can tunnel into continuum

Positive energy states

s = 2mc2/eE Dirac sea of filled negative energy states

Laser polarization

Tunnel ionization rate

=1.3 x 1016 V/cm Intensity ~ 2.2 1029 W/cm2

Eat = 5 x 109 V/cm Intensity~ 3.5 1016 W/cm2 Polarization of atoms gives rise to nonlinearities with E ~ 0.1% Eat I ~ 109 W/cm2

Polarization of vacuum gives rise to nonlinearities with E ~ 0.1% ES I ~ 1022 W/cm2

With a 10 PW laser it might be possible to observe birefringence of the vacuum

Reaching how powers in CPA require temporal phase control and broad bandwidth gain

Petawatt lasers of differing specifications are needed to access a wide variety of science applications Increasing compactness

Increasing aperture

10 TW




Ultrafast x-ray isochoric heating of solids (w/ Ka radiation) Radiative blast waves


Direct isochoric heating of solids to 1 keV

Laser driven cluster explosions 1-D Wakefield acceleration of e-

Pair plasma production (gamma ray burst physics

Strongly relativistic interactions (GeV) electrons In pe cr ak ea po sin w g er

100 PW

HEPW systems

Z-Petawatt at SNL

Ultrafast xray melting of solids


Fast ignitor physics

Proton isochoric heating

Relativistic atom, e- and plasma interactions


“ARC” Petawatt on NIF (future)

1st generation PW lasers (LLNL, Osaka, RAL etc.)

University scale laser systems

Pulse duration (s)

1 PW

1 EW

Petawatt at Omega EP


Titan at LLNL



Diocles at U. Nebraska

Realistic bandwidth limit for high energy (optical) lasers

Texas Petawatt











Laser Energy (J)







We are presently at a cross roads in examining how to get to move beyond 1 PW powers

• Can 10 PW be built in 5 years and can exawatt be built in a decade? • Push to shorter pulses or higher pulse energy? • Utilize Ti:sapphire or some other gain medium? • Can OPCPA be employed all the way to an exawatt? • How can 10 PW to exawatt pulses be compressed? • What will it cost to build a 10 PW laser or an exawatt?

Using hybrid OPCPA/Mixed laser glass technology, ~100 fs PW lasers at E> 100 J are possible and it is possible to build a 10 PW laser on this technology now

The Europeans have initiated an EU funded project to build multiple 10 PW-class lasers

Three ELI Pillars • Bucharest, Romania: ELI - NP Devoted to nuclear physics with intense lasers and gamma beams • Prague, Czech Republic: ELI - CZ Devoted to work on electron acceleration • Szeged, Hungary; ELI - AS Devoted to attosecond pulse generation

The current state-of-the-art ultrafast, ultraintense lasers tends to fall into two categories

Ti:sapphire based CPA lasers: Pulse energy ~ .001 - 30 J, Pulse duration <30 - 100 fs, Peak Power < 100 TW; 1 PW Repetition Rate ~ 1 kHz - 1 Hz Shortest pulse systems and most “table-top” CPA lasers

Nd:glass based CPA lasers Pulse energy 10 - 1000 J Pulse duration > 100 fs Peak power 10 - 1000 TW Repetition rate ~ 1 shot/min - 1 shot/hr Highest energy systems, many of “facility” scale

Ti:sapphire has advantages and disadvantages in high power CPA lasers Absorption and emission spectrum of Ti:sapphire Large scale Ti:sapphire crystals

Gain bandwidth in Ti:sapphire is very large → amplification of pulses as short as 20 fs

High quality Ti:sapphire can only be produced with aperture up to ~10 cm

Nd:glass is very attractive for high power lasers because it can be fabricated with large aperture

Direct flashlamp pumping (and ultimately direct diode pumping) have many attractions for high peak power

The first Petawatt laser was demonstrated at LLNL by implementing CPA on the Nd:glass NOVA laser The Petawatt at LLNL Nova laser

90 cm gratings to compress Nova pulses

Petawatt specs: 500 J energy 500 fs pulse duration Peak intensity > 1020 W/cm2 Information derived from M. D. Perry et al “Petawatt Laser Report” LLNL Internal report UCRL-ID-124933.

The principal limitation to the use of Nd:glass in CPA lasers is that it exhibits limited gain bandwidth Gain spectrum of two kinds of laser glass

Calculation of the effects of gain narrowing in Nd:glass

Spectrum reduced to 7 nm bandwith

Gain narrowing of the ultrafast pulse spectrum tends to limit Nd:glass CPA lasers to pulse duration of 500 fs

We have chosen a route to 1 PW by mixing glasses and aiming for ~ 100 fs pulses

Optical parametric amplification in CPA (OPCPA) offers the potential for very broadband amplification

The Texas Petawatt design is based on a 3-stage OPCPA amp and a mixed glass chain

The layout of the amplifier section is compact and rests on four interlocking tables

4J opcpa pump

~9m ~ 200 J out

The MLD gratings in the TPW perform well with high diffraction efficiency and ~90% throughput

We presently we shoot >1.3 PW on target during the last experimental run Seed spectrum before power amps

Spectral Intensity (arb. units)

Spectrum at full energy

14 nm bandwidth

Wavelength (nm)

The hybrid mixed glass architecture can be scaled to 10 PW with existing technology System elements with estimated energies Femtosecond oscillator 1 nJ

Pre-amp pulse cleaner

• operating at 1057 nm • >13 nm bandwidth

OPCPA amplifiers

Pulse stretcher 1 µJ

100 nJ

• Stretch to 3 ns • Disperson of >200 ps/nm • Pass >50nm of total bandwidth

• Boost energy to > 1 µJ • Saturable absorber

3.3 J

Nd:silicate glass amplifier

110 J

Nd: phosphate glass amplifier

• Total gain ~ 35 • Pulse fluence <3J/cm2

• Amplify to ~2.5 J • Retain full BW • Spectrally shape seed for Nd:glass amps • Spatially shape beam for power amps Design considerations

Pulse compressor 1920 J


• Beam size ~ 40 x 40 cm • Compensate disperson of 200 ps/nm • Pass >24nm of total bandwidth • High efficiency

• Stretch to >2 ns • Disperson of >200 ps/nm • Pass >25nm of total bandwidth

High energy amplification occurs in two stages employing silicate and phosphate slab amps


The OPCPA section can be staged with Intrepid pump lasers arranged as spokes off the main chain OPCPA Output: 3 J; 20 nm bandwidth

Temporally shaped pump pulses for spectral shaping of the seed BBO Amp1 2 paired crystals BBO Amp2 2 paired crystals Stretched seed pulse Rectangular apodized aperture

Relay image telescope Relay image telescope KDP Amp1 single crystal KDP Amp2 single crystal

OPCPA crystals

KDP Amp3 single crystal

Intrepid 4

Intrepid 3

Intrepid 2

Intrepid 1

The silicate and phosphate glass amplifiers are arranged in a double pass configuration

Nd:phosphate head


Deformable mirror

Nd:silicate head

We are investigating liquid cooling the faces of glass slabs as a means for dramatically increasing rep. rate

This technology will permit operation of large aperture (~ 30 cm) Nd:glass slab amplifiers with rep. rate at least one shot per minute Viewgraph credit: Jon Zuegel (LLE Rochester)

The compressor is constructed from 4 pairs of phased MLD gratings

40 x 40 cm beam in w/1.9 kJ

2 x each 50 x 90 cm phased gratings

The hybrid mixed glass architecture would enable construction of a compact 10 PW laser Mechanical Engineering conception of the 10 PW Hybrid Mixed glass laser 30 cm amp power conditioning 30 cm phosphate disk amp

10 cm silicate disk amp

final amp double pass telescope

Oscillator, pulse cleaner and stretcher

OPCPA stages

Pulse shaped OPCPA pump lasers

Laser output: Energy: 1500 J, Pulse duration: <150 fs repetition rate: 1 shot/min Laser Wavlength: 1054 nm Temporal pulse contrast: 1010:1 at > 10 ps

8-grating pulse compressor

The high energy amplifier architecture of a near term mixed-glass 10 PW laser could be based on Beamlet Z-Beamlet laser at Sandia National Laboratories

The idea of tiling multiple gratings for compression of 1 µm pulses has been demonstrated at Omega EP Two-grating phased array at the U. of Rochester

Pulse compression data using the two grating array (U. of Rochester)

Commonly available Nd:glass is NOT the optimum glass for broadband CPA

LG-680 Silicate glass Relative Fluorescence

Relative Fluorescence

LG-760 Phosphate glass

Wavelength (µ µm)

Wavelength (µ µm)

Peak Wavelength: 1054 nm

Peak Wavelength: 1061 nm

Peak cross section: 4.3 x 10-20 cm2

Peak cross section: 2.9 x 10-20 cm2

Linewidth (FWHM): 21.1 nm ______________________________

Linewidth (FWHM): 28.2 nm ______________________________

Nd2O3 ~3% P2O5 ~ 97%

Nd2O3 ~3% SiO2 ~ 97%

Different laser glasses could enhance the bandwidth of a mixed glass laser chain These alternative glasses have gain shifted further into the red, broader linewidths and reasonable gain cross sections


Modified recipe Nd:silicate


Standard Nd:silicate

This glass could enable sub-100 fs large scale lasers

Novel glass bandwidth FWHM: 38 nm (x2 that of Phosphate) Realistic amplified bandwidth: >20 nm Corresponding best compressed pulse: 80 fs

New glass performance could make rep-rated glassbased systems operating at 80 fs

Using these new glasses, a 120 fs, 120 kJ exawatt laser should be possible with existing technology

a ilic s d

te pha s o h te/p

igh hhg t i w B ate shapin h p os al /ph pectr e t s ca sili A and d e P ix c m y OPC i s Ba nerg e cm asi


dvanced Mixed a osphate glass/ph

The architecture of a mixed glass exawatt laser would be straightforward

Final gain would be in 8 NIF-style beamlines

8x 15 kJ = 120 kJ in 120 fsx8

A key element would be in the successful tiling of 15 MLD gratings for each compressor

A hybrid approach to an Exawatt laser has many advantages to other approaches

Thoughts on the future

• The science case for moving toward 10 PW needs to be ascertained • New materials should be explored for potential push toward 1 EW • More work needed on tiling large number (~9 or more) of gratings for large aperture compressors • Phasing numerous CPA beams to increase on-target intensity • Liquid cooling of glass slab amplifiers for development of ~ 1shot/min multi-PW to EW lasers


Texas Petawatt

Beyond 1 PW - The National Academies of Sciences, Engineering ...

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