Applications of Lasers at Accelerators A general overview Matthias - - PowerPoint PPT Presentation

Applications of Lasers at Accelerators

Matthias Gross for the PITZ team Nakhon Ratchasima, 01. November 2018 A general overview

Introduction of DESY “Deutsches Elektronen- Synchrotron”

Page 3

DESY – Overview

| Overview | 2018

Deutsches Elektronen-Synchrotron

• National research centre of Germany
• Member of the Helmholtz Association
• Two sites: Hamburg and Zeuthen
• Hamburg since 1959, Zeuthen since 1992 DESY
• Together 2300 employees + more than 3000

guest scientists from over 40 countries each year Research Topics

• Accelerators
• Photon Science
• Particle Physics / Astroparticle Physics

Page 4

Research in Zeuthen

| Overview | 2018

Astroparticle Physics

• Role of high-energy particles in the cosmic

evolution

• Neutrino astronomy/cosmology, gamma astronomy,

theoretical astroparticle physics, multimessenger astronomy Particle Physics

• Search for the fundamental building blocks of

nature and their interaction

• Experimental and theoretical particle physics

Accelerators

• Development of tomorrow's accelerators
• Photoinjector Test Facility in Zeuthen (PITZ)

Page 5

Latest Science News from DESY in Zeuthen

| Overview | 2018

12 July 2018: Breakthrough in the search for cosmic particle accelerators

• Scientists trace a single neutrino back to a galaxy

billions of light years away 13 August 2018: World record – Low-draft electron bunches drive high plasma wakes

• Scientists achieve highest ratio of acceleration to

deceleration in plasma wakes yet 10 October 2018: First CTA telescope inaugurated

• LST-1 makes its debut on the northern Cherenkov

Telescope Array site

Page 6

Lasers and Accelerators

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Example: FEL – FLASH at DESY, Hamburg site

Photocathode laser Could be used:  Laser heater  Diagnostics (Laser wire…) Seed laser Drive laser / Ionization laser for Plasma acceleration Pump-probe laser Optical synchronization

• f the whole

setup

Page 7

Contents

Introduction / Basics

• Laser principle / properties
• Important laser types

Photoinjector

• Example: PITZ
• Laser pulse shaping

Seeding

• Working principle
• Example: sFLASH

Pump-probe laser

• Working principle
• Possible experiments

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Applications of Lasers at Accelerators Synchronization

• Basics
• Example: European XFEL

Laser-beam interactions

• Diagnostics
• Compton Back Scattering

Novel acceleration

• Introduction
• Plasma electron acceleration
• Alternative Schemes

Outlook / Summary

Introduction / Basics

Page 9

Laser Working Principle

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

• General setup

Light Amplification by Stimulated Emission of Radiation

Gain medium

Cavity Pump

partially transparent

Page 10

Properties of Laser Light

• Diagram courtesy Prof. Simon Hooker

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

• They have a narrow spectrum

(bandwidth).

• They are spatially and temporally

coherent.

• They produce highly directional

beams.

Page 11

Laser Basics

• Wavelength
• From THz to X-ray. Most common: visible and near infrared
• Temporal structure
• cw (e.g. laser pointer) or pulsed (e.g. data transmission)
• Accelerator lasers: typically pulsed with lengths of ps to fs
• Output power
• Very low (e.g. barcode scanner) to very high (e.g. laser welding)
• Pulse energies for accelerators: typically J (photocathode laser) to J (laser driven plasma acceleration)
• Gain medium
• Solid: crystal, glass (most important for accelerators)
• Semiconductor: pump laser
• Gas, liquid, …
• Electrons: free electron laser (FEL)

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Properties cover a wide range

Page 12

Ti:Sapphire Laser

• Gain medium: a crystal of sapphire (Al2O3) that is

doped with titanium ions

• Pump: typically a frequency doubled Nd:YAG laser

(532 nm)

• Tunable over wide wavelength range (650 nm to

1100 nm); most efficient around 800 nm

•  good for ultrashort pulses (down to a few fs)
• High output power reachable with Chirped Pulse

Amplification

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Short pulses, high output power

Typical setup of Ti:Sapphire laser Energy level diagram of Ti:sapphire laser

From: Renk K.F. (2012) Titanium–Sapphire Laser. In: Basics of Laser Physics. Springer

Page 13

Optical Parametric Chirped Pulse Amplification (OPCPA)

• Amplifying an ultrashort laser

pulse up to petawatt level

• Typical: Ti:Sapphire laser as

seed

• Main idea: keep laser pulse

intensity at a manageable level in the amplifier crystal

• After compressor: light

transport in vacuum only (filamentation)

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Reaching very high pulse energies

Source: Wikipedia

Page 14

Solid State Photocathode Laser at PITZ

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Built and maintained by Max Born Institute

• Basic principle
• Solid state: Yb:KGW oscillator, Yb:YAG amplifier,

2x frequency doubling

• Basic parameters
• Wavelengths: 1030/515/257 nm
• Pulse length: 2…25 ps
• Pulse energy: <5 µJ in the UV
• Repetition rate: 10 Hz (1 MHz in burst)
• Manufacturer
• Max Born Institute, Berlin (custom product)
• Application
• Photocathode laser

Laser pulse timing structure: 100ms (10 Hz) 1 s up to 600 pulses

Page 15

Fiber Laser

• Optical fiber: guiding light by difference in refractive

indices of core and cladding

• Advantages:
• Compact
• High electrical and optical efficiency
• Reliable (24/7 operation of accelerators)
• Excellent beam quality
•  Use as oscillator of solid state laser systems

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

http://www.fiberlaser.fujikura.jp/eng/products/about-fiber-laser.html

Page 16

Diode Laser

• Advantages
• High efficiency (direct

conversion from electrical current to light)

• Cheap
• Small
• Direct modulation is possible
• Disadvantages
• Low beam quality
• Not easy to produce

ultrashort pulses

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Used as pump laser for solid state laser systems current active zone metal cleaved facet Schematic of a p-n diode laser eV Fn Fp hf active zone p-n junction forward biased with voltage V n p

Page 17

Free Electron Laser (FEL)

SASE = self amplified spontaneous emission

• Highly energetic electrons are forced onto a slalom

course in a magnetic structure (undulator) and are emitting synchrotron radiation

• Photons and electrons interact, leading to a density

modulation in the electron bunch

• Radiation is stimulated in the disks, leading to

lasing

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Principle

Power Distance

Photoinjector

Page 19

Photoinjector

• Photocathode laser must be

stable and locked to RF.

• Light needed at energies

>photocathode work function, generally UV.

• > Laser needs third or fourth

harmonic frequency conversion.

• Laser requirements:
• High pulse energy
• Reliable running
• Excellent pointing stability
• Properties of the bunch can be

controlled by the laser pulse shape in time and space.

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Setup at PITZ (Photoinjector Test Facility at DESY, Zeuthen Site)

RFgun: L-band (1.3 GHz) nc (copper) standing wave 1½-cell cavity Main solenoid, Bz_peak~0.2T Bucking solenoid Photo cathode (Cs2Te) Coaxial RF coupler Cathode laser 257nm ~20ps (FWHM) Vacuum mirror Electron bunch 1nC, ~6.7MeV/c

UHV

Laser pulse timing structure:

Page 20

Laser Pulse Shaping

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Important to optimize electron bunch quality (at PITZ and elsewhere)

10 20 30 40 50 60 0.2 0.4 0.6 0.8 1 1.2

• 5
• 4
• 3
• 2
• 1

1 2 3 4 5 6 current (A) slice emittance (mm mrad) z-<z> (mm)

Simulated slice emittance (1nC)

emittance (Gaussian) emittance (flattop) emittance (3D-ellipsoidal) current (flattop)

• Laser shaping  key for optimizing photoinjector brightness (Q/x y z).
• Ellipsoidal laser shaping benefits high bunch charge beams or CW guns (lower gun gradients).

PITZ holds WR on lowest measured projected emittances

Experiments (projected emittance):

Projected emittance:

Page 21

2D Shaping (Transverse Shape Constant in Time): Pulse Shaper

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Installed in PITZ photocathode laser (MBI)

• Contains 13 birefringent YVO4 crystals. Pulses are split according to polarization. Delay is given by crystal

thickness; relative amplitude can be varied freely by adjusting relative angle between crystals

• Basic process
• Free pulse shaping, e.g. flat top

t

• eo

eo

Page 22

3D Shaping: Developments at PITZ

• Besides further improvement of projected and

slice emittance:

• Ellipsoidal beams  less transverse halo
• More regular (sinusoidal) long. phase space 

shorter bunches!

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Ultimate performance with ellipsoidal laser pulses

• Basic principle:
• Generate energy chirped pulse

(time-energy correlation)

• Spatial spreading with dispersive

element

• 3D Spatial shaping
• Two methods to generate

ellipsoidal photo cathode laser pulses are under study at PITZ:

• Spatial Light Modulator (SLM):

Mironov et al., Appl. Opt. 55, p. 1630 (2016)

• Volume Bragg Grating (VBG):

Mironov et al., Laser Phys. Lett. 13, p. 055003 (2016)

Seeding

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What is Seeding and Why do You Want to do it? (1)

• Standard process to generate FEL radiation:
• Self Amplified Spontaneous Emission (SASE)
• Fast realization  just send electron beam through

undulator

• But: laser light is originating from noise

fluctuations, which are not controllable

•  strong shot-to-shot fluctuation of spectral properties
• Idea: seeding  provide seed photons with a

defined wavelength and phase to have a better control of the process and improve the FEL properties

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Comparison to SASE

Typical SASE spectrum

Serkez, Svitozar et al. arXiv:1308.0172

Typical seeded spectrum

Page 25

What is Seeding and Why do You Want to do it? (2)

• A suitable seeding source for FELs must be a coherent and stable source in the

wavelength range where one is interested to operate the FEL or at longer wavelength if one use the harmonic conversion in the FEL

• Possible sources are:
• An external seed laser (visible to UV)
• FEL wavelength equals fundamental seed laser wavelength
• Harmonic emission produced by lasers, HHG (UV-VUV)
• Weak coherent pulses are amplified by the FEL process
• A free electron laser (IR-X-ray)
• Radiation from a FEL is used as a seed for another FEL (self seeding, two stages HG, oscillator seeding, ...)

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

How to seed an FEL In general: seeding gets more complicated with shorter FEL wavelengths

Page 26

Seeded EUV-FEL at FLASH

• The Seed Laser
• 267 nm seed pulses are

generated by third- harmonic generation (THG) of near-infrared (NIR) Ti:sapphire laser pulses

• Maximum energy of these

UV seed pulses: 500μJ

• Seed laser provides fixed

wavelength and phase

• FEL radiates at higher

harmonic e.g. at 7th harmonic (38 nm)

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

High-Gain Harmonic Generation (HGHG)

https://sflash.desy.de/

from Grattoni et al. FEL2017, MOP042

Pump-probe Laser

Page 28

What is Pump-probe?

• Basic modes for laser based analysis
• Static
• A cw laser is pointed on the sample and the output (spectrum, spatial

distribution etc. is analyzed)

• Dynamic
• A short pulse laser is used to investigate transient phenomena
• Pump-probe
• 2 laser pulses are used*
• The first laser pulse (pump) triggers a reaction from the sample
• The second pulse (probe) is used to characterize the sample
• The delay between the pulses is scanned to investigate sample dynamics

(other properties e.g. pulse energies can be scanned, too)

• The 2 pulses can be from the same laser or from different lasers (with

different wavelengths)

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

A method for time-resolved measurements

from DOI: 10.1155/2013/104806 *one pulse could be also e.g. an electron bunch

Page 29

FLASH 1 Pump-probe Laser

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

High power 10 Hz and low power 1 MHz optical pulses

http://photon-science.desy.de/facilities/flash/beamlines/optical_laser_systems/index_eng.html

Page 30

Examples of Pump-probe Investigations at FLASH

• Laser ablation with XUV pulses (probe reflection with optical laser)
• Characterization: cross-correlating VUV with optical pulses
• Single-shot photoelectron spectroscopy on free atoms and molecules
• Two-color multiphoton ionization of atomic helium by combining XUV

pulses with optical laser

• Investigating transient condensed phase dynamics (crack formation,

phase separation, nucleation…)

• Diffractive imaging of small objects  pre-align the molecules in the

sample with optical laser; characterize by ionizing and dissociating the molecules with a time-delayed XUV pulse

• X-ray induced transient optical reflectivity change of solids
• Atomic inner-shell relaxation dynamics (optical probe pulse)

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

XUV/VUV FEL and optical laser pulses – FEL radiation can be both pump or probe

References in: https://doi.org/10.1016/j.nima.2010.09.159

Synchronization

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Timing Distribution and Synchronization

• FELs can produce laser pulses with a

length down to a few fs

• Subsystems (distributed over 100s of

meters to kilometers) have to be synchronized to that time frame

• Practical limit for RF timing systems 50

to 100 fs – not sufficient!

•  Fiber-optics with short pulse lasers:

sub-fs timing stability possible

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Conventional RF timing systems are not sufficient

Page 33

Laser-based Synchronization System @ E-XFEL

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

• Master for accelerator synchronization, slave system for experiment lasers
• Up to 24 + 20 fs-stable optical links (mass production, cost optimized, robust)
• End-stations:
• different laser systems (injector, pump-probe, …)
• RF re-synchronization
• bunch arrival time diagnostics
• Jitter performance < 10 fs (rms), world wide largest installation, in operation

Courtesy: Jost Müller, Matthias Felber

Laser-Beam Interactions

Page 35

Electro-optic Bunch Characterization

• Electro-optic effect: electric field
• f electron bunch changes
• ptical properties of nonlinear

crystal

• Polarization of probe laser pulse

is rotated due to Pockels-effect in GaP crystal

• Probe pulse is linearly chirped
• Measurement of electron bunch

arrival time and bunch structure with spectrometer

• Use of e.g. Ti:Sapphire laser
• Advantage: method is non-

destructive (parasitic)

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Beam Diagnostics

From: Arsov et al., Electro-optic bunch arrival time measurement at FLASH, Proc. EPAC08, p. 3348

Page 36

Laser Wire Scanner

• Principle (like wire scanner):
• Focused laser beam is scanned across electron

beam

• Interaction via Compton scattering  laser

photons are scattered to higher energies, almost parallel to incident electron beam

• Main advantage to wire scanner and screens:
• Higher resolution (<1 m) - needs good focusing
• f laser beam
• Noninvasive
• Can be used with high charge density (no risk of

material damage)

• Ion beams can also be measured

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Beam diagnostics: measurement of transverse size of electron beams

• From: Boogert et al. “Micron-scale laser-wire

scanner for the KEK Accelerator Test Facility extraction line”, PRST-AB 13, 122801 (2010)

• Laser system:
• Nd:VAN oscillator and Nd:YAG amplifiers
• Frequency doubling (532 nm output wavelength) 

better focusing

• Pulse energy: 400 mJ

Page 37

Compton Back Scattering (CBS)  Inverse Compton Scattering

• Basic idea:
• Set up counterpropagating electron and laser beams
• Electron-photon collisions  photon back scattering
• Very efficient photon energy amplifier: CBS = 42 laser
• E.g. hard x-rays can be produced with low energy (e.g.  = 100) electron

machine and standard optical laser

• The catch:
• The scattering cross section is very low
• Need highly brilliant electron source and high power optical laser
• Compact Compton projects
• Several projects are in operation or are projected
• Applications: medical (radiotherapy), crystallography …
• Other applications
• Can be used also for beam diagnostics (e.g. beam energy and energy spread)

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

A compact X-ray source

From: A. Variola, LA3NET Topical Workshop: Beam Diagnostics (March 2015)

e.g. Ti:Sapphire

Page 38

Example: MIT Compact Compton Project

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

From: A. Variola, LA3NET Topical Workshop: Beam Diagnostics (March 2015)

Novel acceleration

Page 40

Motivation for Developing Plasma Acceleration

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

• Why novel accelerators? – we are already very good in accelerator technology!
• Conventional accelerators work well but they are very large
• Conventional accelerator cavities: about 100 MV/m
• Possible with plasma acceleration: larger than 100 GV/m !!!

Name Final energy Size HERA 27.5 GeV 6 km length SLAC (SLC linac) 50 GeV 3.2 km length European XFEL (linac) 17.5 GeV 2.1 km length

1000x

Page 41

Problem of Conventional Accelerators

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

• Basic problem: microscopic particles are accelerated with macroscopically generated fields
• Small field gradient  Large accelerator
• New Idea: Plasma accelerator
• Utilize microscopic fields (fields between electrons and ions in a plasma) – these are big since the charges can be

close together without destroying the building materials

• Ionization of a gas, creating a plasma with advantageous properties for acceleration
• How to drive a plasma wake?
• With a strong laser pulse (laser driven plasma wakefield accelerator – LDPWA)
• With a particle beam (particle driven plasma wakefield accelerator – PDPWA)

Gas

Plasma Plasma wake

Page 42

Plasma Acceleration: Basic Principle

• Beam driven

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Courtesy: Patric Muggli

Typical length scale: Plas asma a wavele eleng ngth

wake Plasma Ez ~ TV/m ~ 5 fs fs

PIC simulation (M. Geissler)

• Laser driven

Page 43

Laser Driven Plasma Wakefield Acceleration (LWFA)

• Utilizing ponderomotive forces (electric

field of laser wave)

• Electric field has to be strong enough to

move electrons far enough away from axis during one half-cycle

• Gas is ionized by the same laser pulse
• Laser of choice: Ti:Sapphire with

OPCPA

• Typical peak power: >100 TW (currently

up to 1 PW)

• One of the highest gradient demonstrated

so far: 200 GV/m with 1 PW power* (Kim et al.)

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

From: Kim et al., DOI:10.1038/s41598-017-09267-1 *30 fs pulses with 30 J pulse energy

Page 44

LAOLA@PITZ: Plasma Wakefield Acceleration Experiments

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

• Self-Modulation
• Motivation: AWAKE experiment at CERN  Single stage

electron acceleration with self modulated proton beam

• Demonstration at PITZ: characterization of

self-modulation with flexible electron beam

• Successful experimental results:
• High Transformer Ratio
• Idea: Increase ratio of witness energy gain to driver energy

loss with asymmetric drivers

• Demonstration at PITZ: Time resolved energy

measurement (slice energy) by using double triangular drive bunch

• Successful

experimental results:

Measured electron bunch profile

driver witness Time resolved bunch x vs. t

• Long. phase space

pz vs. t

• 4

x, mm

• 2

2 4 6 t, ps 30 20 10 22.8 pz, MeV/c t, ps 30 20 10 22 np~4x1014 cm-3 np~3x1014 cm-3

• M. Gross et al, Phys. Rev. Lett. 120, 144802 (2018)

TR = 𝟓. 𝟕+𝟑.𝟑 𝟓. 𝟕−𝟏.𝟖

• G. Loisch et al, Phys. Rev. Lett. 121, 064801 (2018)

Page 45

> FLASH and FLASHForward‣‣ share the FEL-quality accelerator.

• ≲ 1.25 GeV energy, a few 100 pC at ~100 fs rms bunch duration
• ~2 µm trans. norm. emittance

FLASHFORWARD‣‣

BEAMS FROM FLASH

A next-generation experiment for plasma wakefield accelerator science

> Unique beamline features:

• X-band deflector with ~1 fs resolution

(in collaboration with CERN, PSI)

• 3rd harmonic cavity for phase-space linearization

→ shaping of current profile for driver and witness

• ≤ 800 bunches (at ≥ 1/MHz spacing) at 10 Hz rate,

a few 10 kW average power

→ A. Aschikhin et al., NIM A 806, 175 (2016)

Courtesy: Jens Osterhoff For ionization: Ti:Sapphire laser OPCPA system 25fs, 800mJ 60m beam transport line from laser lab to plasma cell

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Page 46

Alternative Schemes

• Electron accelerators
• Dielectric structures
• Direct laser driven
• Proton accelerators
• Target Normal Sheath Acceleration (TNSA)

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Page 47

Dielectric Laser Acceleration (DLA)

• Same basic geometry as RF

acceleration structures (but: much smaller!)

• Electric field is generated by

laser (accelerating phase for electron bunch)

• Advantage: no metals needed

– dielectrics have higher breakdown thresholds  higher gradients (1 to 10 GV/m) can be reached

• Laser
• High power
• High repetition rate
• e. g. Ti:Sapphire laser
• Also possible: use as deflector

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

From: R.J. England, 60th Advanced beam dynamics workshop on future light sources (2018)

Page 48

Direct Laser Driven Acceleration in Vacuum

• Electric field distribution is

circularly symmetric

• Strong, on-axis acceleration

field near focus

• Laser for experiment:
• Ti:Sapphire
•  = 810 nm;  = 8 fs;

E = 0.85 mJ

• Simple setup, but not very

efficient

• Acceleration gradients in the

GV/m range, but short interaction length (a few micrometer near focus point)  small energy gain

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Basic principle: use radially polarized light  strong longitudinal field in focus

From: Carbajo et al., PRAB 19, 021303 (2016)

• Electron momentum:
• Input: 40 keV/c
• Output: up to 52 keV/c

Page 49

Ion acceleration: Principle

• Laser pre-pulse creates pre-plasma on target front

side

• Main pulse interacts with plasma; accelerates

electrons to MeV energies mainly in forward direction

• Electrons propagate through target (collisions with

material increases divergence)

• Electrons leave rear side and create sheath
• An electric field (order of laser field ~TV/m) is

created due to charge separation; ionizes atoms at surface

• Ions are accelerated in the sheath field

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

TNSA: Target Normal Sheath Acceleration

• Thin target foil: 5-50 m
• Laser: Ti:Sapphire with 10-100 fs pulse length;

~1-10 J pulse energy

• M. Roth et al., Proc. CAS, CERN-2016-001

Outlook

Page 51

The FS-LA Group at DESY

• Group is dedicated for laser

developments around accelerators

• Group leader: Ingmar Hartl
• Small overview of lasers and

activities within the FS-LA Laser Science and Technology Group

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Laser R&D, operations and applications

Now: main E-XFEL photocathode laser

Page 52

The Ultrafast Optics and X-Rays Group at DESY

• Group is dedicated to contribute

enabling technologies for large- scale x-ray free- electron lasers

• Group leader: Franz Kärtner
• Small overview of lasers and

activities within the Group

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Developing novel table-top ultrafast light sources from the THz through the x-ray wavelength range

Page 53

Summary

• Lasers are an important part of a lot of accelerators
• From the beginning… (Photoinjector laser)
• …to the end (Pump-probe laser)
• Most important laser type:
• Short pulse solid state laser
• DESY has rich experience in developing and operating lasers in the accelerator environment
• State of the art RF accelerators
• Novel accelerators (plasma…)
• There is laser expertise at PITZ and contacts to specialist groups at DESY and elsewhere

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Applications of Lasers at Accelerators

Thank you

Contact Deutsches Elektronen-Synchrotron www.desy.de Matthias Gross PITZ matthias.gross@desy.de +49 33762 77323

Backup slides

Page 57

DESY in Zeuthen – Overview

| Overview | 2018

Modern research centre

• More than 280 employees
• International participation in

science and research

• Construction and development
• Mechanical and electronic

workshops

• Computer centre
• Detector development
• Libraries, administration,

communication

• School labs

Page 58

Coherence: Temporal and Spatial

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

What only a laser can do

• Red: single frequency wave
• Blue: copy of the same wave delayed by 
• Sine wave: infinite temporal coherence

A plane wave: infinite spatial coherence (flat phase front)

Temporal coherence Spatial coherence

Fixed phase relations in time and space

Page 59

Diffraction at a Slit: Interference Pattern

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Spatial and temporal coherence is needed

Page 60

Examples for High Power OPCPA Lasers

• BELLA laser at Berkeley lab (USA)
• Pulse energy/length: >40 J / <30 fs
•  peak power: 1 PW
• Repetition rate: 1 Hz
• http://bella.lbl.gov/facilities/bella-center-facilities-

bella-laser/

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

• ELI beamlines (Czech republic)
• L3: Pulse energy/length: >30 J / <30 fs
•  peak power: 1 PW
• Repetition rate: 10 Hz
• https://www.eli-beams.eu/en/facility/lasers/

Page 61

Max Born Institute Laser - Setup

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Oscillator Pulse picker #1 Pulse shaper Regenerative amplifier Booster amplifier Optical Sampling System (OSS) regen amplifier OSS mixer L B O B B O Pulse picker #2 Accelerator tunnel Attenuator

Page 62

Example: Free-electron LASer in Hamburg (FLASH)

Parameter FLASH1 FLASH2 Electron beam energy 0.35 - 1.25 GeV 0.4 - 1.25 GeV Normalised emittance at 1 nC (rms) 1.4 mm mrad 1.4 mm mrad Energy spread 200 keV 500 keV Electron bunch charge 0.1 - 1.2 nC 0.02 - 1 nC Peak current 1 - 2.5 kA 1 - 2.5 kA Electron bunches per second (typ./max) 300 / 5000 300 / 5000

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

World's first soft X-ray FEL – user facility since 2005

• Also available now: FELs for hard x-rays e.g. LCLS,

SACLA, E-XFEL etc. Parameter FLASH1 FLASH2 Photon wavelength 51 - 4.2 nm 90 - 4 nm Photon pulse duration (FWHM) <30 - 200 fs <10 - 200 fs Peak Power (from av.) 1 - 5 GW 1 - 5 GW Single photon pulse energy (average) 1 - 500 µJ 1 - 1000 µJ Spectral Width (FWHM) 0.7 - 2 % 0.5 - 2 %

Page 63

Photoinjector: High Brightness Electron Beam Source

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Principle

Laser pulse Electrons

Page 64

What is Seeding and Why do You Want to do it? (1a)

• Seeding controls the start-up of the FEL pulse within the electron bunch and helps to

produce:

• Temporal coherence of the FEL pulse
• Control of the time duration, wavelength and bandwidth of the coherent FEL pulse
• More stable pulse energy
• Natural synchronization of the FEL pulse to the seed laser ( pump-probe experiments)
• Reduction in undulator length needed to achieve saturation
• High peak flux and brightness
• Disadvantages:
• Need extra high power laser
• Seeded FELs are more sensitive to electron beam energy and phase space distortion than SASE

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

How to seed an FEL

Page 65

E-XFEL: Laser Synchronization

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

• laser synchronization schemes
• “conventional” PLL-type RF locking
• MZI-based Laser-2-RF phase detection -> low-drift,

low-noise (3fs!)

• all-optical scheme based on balanced optical cross-

correlation -> lowest drift, ultra-low jitter: 1.3fs!

• MTCA.4-based controls
• engineered design
• robust
• 24/7 operation

Origami-10 all-optical locking performance

<1.3fs rms

CAD drawing of balanced

• ptical cross-correlator

Courtesy: Jost Müller, Matthias Felber

Page 66

Laser Heater

• Electron beams from high brilliance photo-cathode

guns have an extremely small energy spread (few keV)

• This causes random intensity variations, which can be

amplified significantly due to coherent synchrotron radiation (CSR) in bunch compressors

•  Micro-bunching instability
• Momentum modulations  drastic increase of

momentum spread

• SASE radiation is reduced or prevented completely
• Solution: introduce small incoherent energy spread

by overlapping IR laser with electron beam in an undulator before bunch compression

• Inverse FEL process  random energy transfer to

electrons

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Method to prevent micro-bunching instability at an XFEL

Laser heater setup

(Angelova et al, Proc of EPAC08, WEPP077)

• Laser used at European XFEL:
• Unconverted IR light ( = 1030 nm) from photocathode

laser, amplified to 200 J per pulse

• Pulse length  36 ps
• Inherently synchronized to electron bunch

Page 67

Example: AXSIS (Attosecond X-ray Science)

• Key aspects:
• Miniature gun driven by THz radiation
• Inverse Compton scattering creates x-ray pulses with

attosecond pulse length

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

Attosecond X-ray source based on coherent inverse Compton scattering

• Main application: crystallography and spectroscopy

with extremely high resolution

• https://axsis.desy.de/

Page 68

Plasma Wakefield Accelerator

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

• Acceleration of an electron with a (travelling) wakefield
• With optimal utilization of nonlinearities we can achieve extremely strong acceleration

+ + + + + + + + + + + + +

Page 69

Beam Driven Plasma Wakefield Acceleration (PWFA)

• Utilizing Coulomb forces (electric field of

particle bunch)

• Electric field to drive wake can be much

less than for LWFA (bunch charge has constant sign)

• Ionization of gas:
• By particle bunch itself (field ionization); but:

bunch head erosion. Better:

• Laser ionization. Laser of choice:

Ti:Sapphire with OPCPA (field ionization). Alternatively: UV laser (direct ionization)

• Highest gradient demonstrated so far:

50 GV/m with (Blumenfeld et al.)

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

From: Blumenfeld et al. Nature 445, p. 741

Page 70

PWFA Research at PITZ (Beam Driven Plasma Acceleration)

| Applications of Lasers at Accelerators | Matthias Gross for the PITZ team, 01. November 2018

A flexible platform for exploring beam-plasma interactions

• Flexible temporal bunch forms (advanced photocathode laser pulse shaper)
• Developed and benchmarked beam diagnostics in place (RF deflector, dipole spectrometer, …)

Novel cross-shaped lithium heat pipe oven

• Ionization laser (ArF excimer laser) is coupled in through side windows

 flexibility in plasma channel length and density profile Discharge plasma cell (argon)

• Simple setup
• Scalable in plasma density

pz

• O. Lishilin et al., Proc. of IPAC2017, TUPIK017
• G. Loisch et al., “Jitter mitigation in low density plasma sources for

wakefield accelerators”, NIM A, to be published