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Diagnostics & Lasers R&D at Daresbury S.P. Jamison Accelerator Science and Technology Centre, STFC Daresbury Laboratory Preparing for the needs of an ultrafast FEL facility

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Page 1: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Diagnostics & Lasers R&D at Daresbury

S.P. Jamison Accelerator Science and Technology Centre,

STFC Daresbury Laboratory

Preparing for the needs of an ultrafast FEL facility

Page 2: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Diagnostics & Lasers • Fast beam position monitors

• Timing distribution & beam arrival monitors

• Electro-optic longitudinal profile diagnostics

• THz driven modulation of electron beam

• Ultrafast Photon diagnostics

Daresbury accelerator projects • ALICE - Accelerators and Lasers in Combined Experiments

• EMMA - non-scaling FFAG demonstrator

• VELA -

• CLARA - planned FEL test facility

Page 3: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

ALICE Accelerator and Lasers in Combined Experiments

30MeV Energy recovery linac

• Initial motivation as testbed for planned 100mA ERL

• Principally for accelerator and light source R&D • Some light-source user experiments

60pC, 81MHz, 100us train @10Hz (8000bunches, 5mA peak)

CSR THz source

60pC, 16MHz, 100us train @10Hz IR FEL

10-40pC, single bunch @ 5Hz

EMMA injector

• Mid-IR FEL • THz for cell irradiation

• “DICC” high current cryo-module currently being installed for with-beam testing

• Synchronised lasers available – including 20 TW TiS (Compton scattering expt)

Typical operating

modes

Page 4: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

EMMA Electron Model for Many Applications

First demonstration of non-scaling FFAG acceleration

Single bunch injection from ALICE Acceleration from 10MeV – 20MeV in Serpentine acceleration mode

• 42 cells in 16m circumference • One cell for each of injection, extraction • 50+ BPMs, single bunch, multiple-turn readout

Very compact & dense accelerator:

Page 5: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

VELA formally Electron Beam Test Facility

• High brightness RF Photoinjector • Available for industry to develop new accelerator-based

technologies • Healthcare • Security scanners • Water treatment • ….

• Two independent beam areas available

• Funded August 2011 • Commissioning has started

Parameter Value Units

Frequency 2998.5 MHz

Bandwidth < 5 MHz

Accelerating Voltage < 6 MeV

Accelerating Gradient <100 MV/m

Peak RF Input Power up to 10 MW

Beam charge 250 pC

Page 6: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

VELA Beam Transport Layout

Beam Enclosure 1

Beam Enclosure 2

Beam Injector

Photoinjector laser • 11 mJ @ 800nm • 2 mJ @266nm • Up to 400Hz

Page 7: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Photoinjector laser transport

• l = 266 nm • ~8.5 mm FWHM • M2 ≈ 3.5 • ZR ~ 175 m • 180 fs FWHM • 1 mJ (2 mJ) • 400 Hz

• ~1 mm FWHM • ZR ~ 2.5 m

~14

m

source

cathode

Page 8: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Laser Transport Design • The beam focusing done in stages

– Minimum 3 optics to achieve required demagnification – Mirror Box 2 compresses beam (two optics) – Mirror Box 3 makes final demagnification (single optic)

• “off-the-shelf” spherical mirrors – not a true image at the cathode – Build-up of astigmatism from successive spheres even – Main aim is for an illuminated spot of about the correct size

• custom toroids required for true image relay

FM1 = 750 mm FL

FM2 = 100 mm FL

FM3 = 2500 mm FL

Wavefront propagation

using FOCUS code

Ideal Source, Spherical Mirrors

Page 9: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

To develop a normal conducting test accelerator able to generate longitudinally and transversely bright electron bunches and to use these bunches in the

experimental production of stable, synchronised, ultra short photon pulses of coherent light from a single pass FEL with techniques directly applicable to the

future generation of light source facilities.

• Stable in terms of transverse position, angle, and intensity from shot to shot. • A target synchronisation level for the photon pulse ‘arrival time’ of better than 10 fs

rms is proposed. • In this context “ultra short” means less than the FEL cooperation length, which is

typically ~100 wavelengths long (i.e. this equates to a pulse length of 400 as at 1keV, or 40 as at 10 keV). A SASE FEL normally generates pulses that are dictated by the electron bunch length, which can be orders of magnitude larger than the cooperation length.

CLARA Compact Linear Accelerator for Research and Applications

Major upgrade of VELA

Page 10: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Other Aims and Prerequisites To deliver the ultimate objectives of CLARA will encompass development across many areas:

NC RF photoinjectors and

seed laser systems

Generation and control of bright electron

bunches – manipulation by externally injected

radiation fields – mitigation against unwanted short

electron bunch effects High temporal coherence and wavelength stability through seeding or other

methods Generation of coherent higher harmonics of a

seed source

Photon pulse diagnostics for single shot

characterisation and arrival time monitoring

Low charge single bunch

diagnostics

Synchronisation systems

Advanced low level RF systems Novel short period

undulators

Page 11: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

CLARA Flexible FEL Layout

Chicane (1m long)

Diagnostic/Matching Section

Modulator Undulator (1.5m long)

Radiator Undulator (2.5m long)

e-beam

Laser seed

0m 3m 6m 9m 12m 15m 18m 21m

• By implementing a flexible FEL layout, especially in the modulator region, it will be possible to test several of the most promising schemes.

• We are carefully comparing the various schemes and their detailed requirements – we do not anticipate testing them all!

• We aim to design in this flexibility from the start.

Current principle seed/modulation wavelengths • 30um-50um. Difference frequency generation & OPA • 800nm & harmonics

Page 12: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

EXAMPLES OF FEL SCHEMES ON CLARA

SINGLE SPIKE SASE 100pC tracked bunch compressed via velocity bunching

SLICING + CHIRP/TAPER Short pulse generation using an energy chirped electron bunch and a tapered undulator E. L. Saldin et al, Phys. Rev. STAB 9, 050702, 2006

MODE-LOCKING Mode-locked amplifier FEL using the standard CLARA lattice with electron beam delays between undulators N. R. Thompson and B. W. J. McNeil, Phys. Rev. Lett. 100, 203901, 2008

MATCHED MODE-LOCKING Electron beam delays matched to the rms electron bunch length to distinguish a single spike from the pulse train

Plots courtesy of Ian Martin and Neil Thompson

Page 13: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Parameters

The parameters have now been broken down to cover 5 different operating modes. This helps us understand which parameters we need simultaneously.

FEL output wavelengths from 400nm to 100nm • Can make use of 800nm laser for harmonic generation experiments • Can use well established laser diagnostics for single shot pulse length measurements • No need for long photon beamlines, can deflect by 90 degrees

Operating Mode Seeded (long pulse) Unseeded (SASE) Ultra Short Pulse Multibunch High Rep Rate

Motivation Flat top for seeded FEL experiments

SASE FEL Single Spike SASE FEL Oscillator FEL (RAFEL)

Technology demonstration & commercial applications

Max Beam Energy (MeV)

250 250 250 250 100

Max Macropule Rep Rate (Hz)

100 100 100 100 400

Bunch Charge (pC) 250 250 20 to 100 25 250

Number of Bunches per macropulse

1 + pilot 1 + pilot 1 + pilot 20 1

Peak Current at FEL Entrance (A)

400/125 400 1500 25 N/A

Nominal Bunch Length (fs)

250/800 (flat region) 250 (rms) <30 250 (rms)

Page 14: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

CLARA Layout

Gun

2m linac

VELA exploitation

area

4m linac

Bunch Compressor

Laser Heater 4m linacs

4th Harmonic

Cavity

TDC1

TDC2

FEL modulators

Further exploitation

line

FEL radiators

FEL afterburner

Dump

Photon Diagnostics

70MeV 250MeV

Total Length ~ 90m

Page 15: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

CLARA - Next Steps

CDR now being drafted

TDR will follow

CLARA funding still to be secured

If procurement starts April 2014 then could install in first half of 2016

CLARA first commissioning – mid 2016

Page 16: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Diagnostics & Lasers • Fast beam position monitors

• Timing distribution & beam arrival monitors

• Electro-optic longitudinal profile diagnostics

• THz driven modulation of electron beam

• Ultrafast Photon diagnostics

Daresbury accelerator projects • ALICE - Accelerators and Lasers in Combined Experiments

• EMMA - non-scaling FFAG demonstrator

• VELA -

• CLARA - planned FEL test facility

Page 17: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

rapid serpentine acceleration with large tune variation.

EMMA was constructed for study of non-scaling FFAG acceleration

During accelerating the bunch executes up to ten turns

• Expanding trajectory sweeps about a half of the pickup aperture. • For machine tuning, the bunch can be kept circulating >1000turns. • Revolution period is T=55.2ns, • bunch charge is up to 30pC, the bunch length is about 10ps.

The rapid dynamics needs advanced diagnostics.

EMMA Diagnostics

The trajectory should be measured on each turn, in each of 42 F-D cells.

Page 18: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

EMMA Beam Position Monitor System

world-fastest-rate BPM system, ASTeC designed, built and commissioned

The system is applicable to ERL machines for bunch-by-bunch-in-train measurements, in particular, to ALICE.

faced a problem of a BPM noise caused by a RF power leakage from the EMMA RF system waveguide. Noise suppression required improvement to Front-End module shielding.

Meeting requirements of EMMA beam diagnostics.

Commissioning issues

Page 19: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

hor. and vert. time-multiplexed converter outputs (4ns/div)

• developed concept of BPM self-synchronisation with beam, when the BPM detector reference signals and the ADC clock are being manufactured from the BPM input signal, which makes them automatically synchronous with the beam signal.

• We devised a way of use of a fast and precise pipe-line-type ADC chip for single bunch/train measurements which opened a possibility to use such ADCs in fast-rate BPMs.

pickup signal (0.5ns/div)

Page 20: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

• The system comprises total 53 of BPMs that is about 400 boards & cards.

• Functional architecture, solutions and design of electronics was done by ASTeC.

• In-house EPICS implementation

• In collaboration, a VME interface and its firmware was designed by WareWorks Ltd (UK).

Poincare map.

Board/card fabrication was done by UK Electronics Ltd. Components & fabrication cost is about 150kGBP.

Page 21: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

* Leakage in vertical plane due to pick-up geometry and spurious vertical dispersion

Combined BPM/BAM/FEL Diagnostics at ALICE

"20121213"" ""22:30:57.522037"

0 500 1000 15001.5

2.0

2.5

3.0

3.5

4.0

4.5

Horizontal BPM

0 500 1000 15000.4

0.3

0.2

0.1

0.0

Vertical BPM

0

0

0

0

0

Horizontal BPM

Charge

Bunch Number Bunch Number

Bunch Number

Posit

ion

(mm

)

0 500 1000 150045

50

55

60

65Charge

Vertical BPM* FEL Output

Bunch Number

* Leakage in vertical plane due to pick-up geometry and spurious vertical dispersion

Charge

Page 22: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

22

Optical Clock Distribution & beam arrival monitors

Single Mode Distribution Fibre (100m)

Dispersion Comp. Fibre

Faraday Rotating Mirror (50:50)

RF pickup

Beamline

BEAM ARRIVAL MONITOR

MZM

Scope

PLL

Fibre Stretcher

STABILIZED FIBRE LINK

Mode-locked fibre ring laser

(81.25MHz)

~

RF crystal oscillator

(81.25MHz)

Pol. Contr. λ/2

A pulsed timing system, similar to DESY, is being used to deliver short pulses for accelerator diagnostics. Currently linked to ALICE, will migrate to VELA/CLARA The delivered clock stability is aimed at the few femtosecond level.

Delay

detector

The laser master oscillator is a mode-locked fibre ring laser at 81.25 MHz (81.08MHz for CLARA)

Mode-locked Eribum laser from Toptica Photonics

65fs output pulses

An actively stabilized fibre delivers the short pulses to diagnostic locations

Beam arrival monitors have

been implemented using the delivered short pulses

Fast BPM electronics will be modified for use in BAM

Laser Master Oscillator

Page 23: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Dt

RF pickup

Beamline

Mod. Scope

From stabilized link

The Optical Link Link stabilization is currently achieved using a

balanced optical cross-correlator to measure the group delay between the reference and reflected beams

10.2fs jitter in link (some issues with the RF master oscillator at time of experiment)

The links on ALICE are ~100m long and run though the basement (no environmental control)

Beam Arrival Monitors Beam arrival monitors convert the timing jitter

information into amplitude jitter

Some issues with sensitivity at low bunch charges since we are using existing stripline BPM.

Optical Clock Distribution System

phase noise.

103 104 105 106 102 101 100

Page 24: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Carrier-phase studies – towards 1fs links

Monitoring effect of fibre stretching on changes in carrier phase offset

Deliberate stretching of fibre enable studies of fibre response at different frequencies

Feasibility study on locking both group and phase velocity in distribution link.

Pulsed interferometric system can potentially give higher locking resolution while maintaining short pulse delivery.

Page 25: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

ALICE

Study of beam dynamics with combined diagnostics

As well as clock delivery, the distributed femtosecond pulses are used to implement beam arrival monitoring. A combined experiment using multiple diagnostics was performed to study instabilities in the FEL and ALICE

as a whole.

Developing bunch-by-bunch understanding of how beam affects FEL and how FEL affects beam

Changes in timing, charge and position along a train were measured with optical BAMs and BPMs. Simultaneous recordings of these signals were correlated with FEL output power to measure effects due to beam jitter.

Page 26: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

26

Study of FEL with combined diagnostics

Combine with fast FEL detector and BAM measurements, similar instabilities observed

Correlations of diagnostics give information about Arc 2

Tracing of trends though pre-lasing and lasing parts of pulse train.

position charge

Frequency (MHz)

FEL pulse energy

Frequency (MHz)

Several instabilities observed in beam by fast BPM system 100 kHz bunch position oscillation 300 kHz charge oscillation. Confirmed

in faraday cup and PI laser power On-going investigation into laser position

stability courtesy F. Jackson

Beam arrival time

Page 27: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Electro-Optic temporal profile monitors

Spectral Decoding

Spatial Encoding

Temporal Decoding

Spectral upconversion**

o Chirped optical input o Spectral readout o Use time-wavelength relationship o >1ps limited

o Ultrashort optical input o Spatial readout (EO crystal) o Use time-space relationship

o Long pulse + ultrashort pulse gate o Spatial readout (cross-correlator crystal) o Use time-space relationship

o monochomatic optical input (long pulse) o Spectral readout o **Implicit time domain information only

• Deconvolution for ~100fs resolution

• In beamline BAMs

• Robust EO systems (no fs lasers required!)

• Extension to time domain readout (FROG)

(?)

Page 28: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

χ (2)(ω;ωthz,ωopt)

ωopt + ωthz

convolution over all combinations of optical

and Coulomb frequencies

Electro-optic detection bandwidth

ωthz

ωopt

ωopt - ωthz

ωopt

description of EO detection as sum- and difference-frequency mixing

THz spectrum (complex)

propagation & nonlinear efficiency

geometry dependent

(repeat for each principle axis)

optical probe spectrum (complex)

EO c

ryst

al

This is “Small signal” solution. High field effects c.f. Jamison Appl Phys B 91 241 (2008)

Page 29: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

DC “THz” field.... phase shift (pockels cell)

temporal sampling

of THz field

Monochromatic THz & optical

Chirped optical Parameter dependent results

optical sidebands

Delta-Fnc ultrafast pulse...

Page 30: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Spectral decoding as optical Fourier transform Why does it work, when does it fail?

Consider (positive) optical frequencies from mixing Positive and negative Coulomb (THz) frequencies; sum and diff mixing

Linear chirped pulse:

Assume broad input probe spectrum Fourier transform form

Convolution function limits time resolution…

… but will aid in identifying the arrival time

Page 31: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

ALICE Electro-optic experiments o Energy recovery test-accelerator intratrain diagnostics must be non-invasive

o low charge, high repetition rate operation typically 40pC, 81MHz trains for 100us

Spectral decoding results for 40pC bunch

o confirming compression for FEL commissioning o examine compression and arrival timing along train o demonstrated significant reduction in charge requirements

Page 32: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Deconvolution possible.

“Balanced detection” χ(2) optical pulse interferes with input probe (phase information retained)

“Crossed polariser detection” input probe extinguished...phase information lost

Deconvolution not possible [ Kramers-Kronig(?)]

Oscillations from interference with probe bandwidth ⇒ resolution limited to probe duration

Spectral decoding deconvolution

Page 33: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Spectral decoding Kramer-Kronig deconvolution

Phase inferred from measured amplitude spectrum

Widely used in CSR/CTR temporal diagnostic… …can it work for spectral decoding?

“measured” spectral amplitude

KKphase actual phase (chirp removed)

Surprisingly close retrieval of phase information

- Does not recover chirp - Some turning points missing

“known” & retrieved temporal profiles

Linear chirp phase reintroduced - independently

measurable quantity

Page 34: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Spectral upconversion diagnostic measure the bunch Fourier spectrum...

... accepting loss of phase information & explicit temporal information

... gaining potential for determining information on even shorter structure

... gaining measurement simplicity

Long pulse, narrow bandwidth, probe laser

→ δ-function

NOTE: the long probe is still converted to optical replica

same physics as “standard” EO

different observational outcome

Page 35: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Spectral upconversion

difference frequency mixing

sum frequency mixing Spectral sidebands contain the

temporal (phase) information

ALICE single shot CTR expt

• Femtosecond diagnostic without femtosecond laser • Capability for <20fs resolution

FE

LIX

FE

L ex

pt

Ap

p P

hys

Let

t (2

01

0)

Sidebands generated by 2.0THz FEL output

• Measure octave spanning THz spectrum in single optical spectrometer

• Add temporal readout as extension. (FROG, SPIDER)

0-10 THz ( λ= mm – 30um) → 800nm �20nm

Page 36: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Wavelength [um]

Observe non-propagating spectral components which are

not accessible to radiative techniques (CSR/CTR/SP)

Expected Upconversion

spectra for short bunches

& narrow bandwidth probe

Ti:S probe, ~5ps duration, transform limited.

Spectral upconversion

Page 37: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Δν <50GHz (Δ t >9ps)

Laser based test-bed at Daresbury

Femtosecond laser pulse spectrally filtered to produce narrow bandwidth probe

• Photoconductive antenna THz source mimics Coulomb field. • Field strengths up to 1 MV/cm.

1.5mm 150μm Asymmetry in sum and difference spectra - not explainable by (co-linear) phase matching

Due angular separation of sum & difference waves - general implications for THz-TDS and EO diagnostics

ZnTe Probe

Sum Freq.

THz Diff Freq. Detection

Followed to by NC-CPOPA & FROG

Page 38: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

fs time domain diagnostic without fs laser

Problem: Up-conversion is relatively weak – our calculations suggest energies of a few nJ. Signal needs amplifying without loss of information. Solution: Non-collinear Chirped Pulse Amplification (NCPA)

~800nm femtosecond signal

Stretcher Compressor

Stretching factor 103 or more to prevent saturation, damage, NL effects

Amplified pulse then recompressed BBO

Routinely used to produce “single-cycle” optical pulses Amplification with robust nanosecond pulse lasers High gains of 107 or more Gain bandwidths >100nm (50THz) Preservation of phase of pulse is possible

Beams ~1.5mm diameter

Gain >1000x (~300MW/cm2)

Spectral upconversion & FROG extension

Page 39: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Laser-lab development system

(2) Amplification

Stretcher Compressor Single Shot FROG

NL crystal

(3) Measure: 𝐸� 𝜔 = 𝑆 𝜔 𝑒−𝑖𝜑 𝜔

(4) Calculate properties at NL crystal (to remove remaining spectral amplitude and any residual phase distortion)

50ps 60mJ 1064nm Nd:YAG (doubled)

Spectrally filtered Ti:Sapphire

THz Source (Spectral intensity and phase distortions can be both modelled and measured)

Page 40: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

(2) Amplification

Stretcher Compressor Single Shot FROG

NL crystal

(3) Measure: 𝐸� 𝜔 = 𝑆 𝜔 𝑒−𝑖𝜑 𝜔

(4) Calculate properties at NL crystal (to remove remaining spectral amplitude and any residual phase distortion)

(1) up-convert Coulomb field

(Spectral intensity and phase distortions can be both modelled and measured)

In beam pipe

Commercial nanosecond Nd Laser Integrated frequency conversion

(OPO)

Envisaged integrated system

Page 41: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Picosecond periods match time scale of compressed bunches lengths in conventional accelerators.

• No oscillatory smearing as in optical bunch slicing

• Controllable field profile on sub-ps time scale.

• Octave spanning spectrum possible

Terahertz carrier-phase is synchronised to laser pulse envelope

• Potential for the whole bunch to be “resynchronised” or compressed (in contrast to the selection/tagging from within the bunch)

Laser driven synchronisation ?

Laser driven THz sources for electron-beam manipulation

Page 42: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Energy gain for 20 MeV beam

AEMITR ALICE Energy Modulation by Interaction with THz Radiation

Vacuum acceleration of bunch with TEM10-like single-cycle THz pulses

100 MV/m fields achievable long slippage period ~1 m for 20 MeV (β = 1 - 10-3 )

Page 43: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Ey

Radial bias (120kV pulse)

Longitudinal polarised THz pulses from Photoconductive antenna

Ex

Simple & efficient but Lacks temporal shaping capability

Transverse field from current surge

generates charge separation

origin of longitudinal

field

Longitudinal field implicit from

now working on nonlinear generation of longitudinal beams temporal shaping capability

Page 44: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

AEMITR layout

Energy spread diagnostic

• Two-bunch train, separation

• 790ns (reference & modulated)

• YAG:Ce screen (t~100ns)

• Double shutter gated camera, measuring both reference & modulated bunches

• 20MeV, 20pC

• Minimising projected energy spread “on-crest” acceleration. <50keV spread

Electron beam parameters

• THz generation adjacent to accelerator f~1.5 m

• <2 mJ, 50 fs TiS & photoconductive antenna

THz generation

Two experimental periods completed, no acceleration observed yet • Many issues resolved, improvement made • Synchronisation significant remaining issue

Page 45: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

CLARA FEL Photon diagnostics

Expected FEL output from CLARA: 100nm-250 nm, <10 fs pulse duration.

Schematic of SDFG setup: DF output is generated by bringing test and probe pulses to focus on metal mirror.

ΘΘ θ

ω1

ω2

ω3

Metal mirror

Potential solution: surface sum/difference frequency generation

Test system currently under development:

– Use SDFG to characterise EBTF photo-injector laser: 266 nm, ~180 fs

Photon temporal characterisation ? - characterisation of the FEL schemes

Challenges in bandwidth, phase-matching, absorption

• Removes practical phase-matching requirement.

• Amplitude and phase possible using SPIDER or similar

3rd order autocorrelation from Au, from Dia et al. (2005)

Page 46: Diagnostics & Lasers R&D at Daresbury · 2018-12-10 · ultra short. photon pulses of coherent light from a single pass FEL with techniques directly applicable to the future generation

Thank you