HELMHOLTZ GEMEINSCHAFT VUV FEL

HELMHOLTZ GEMEINSCHAFT VUV FEL Streak camera monitoring of the arrival timing jitter Stefan Düsterer for the VUV - FEL Team E. Plönjes, J. Feldhaus and many others + MBI- Berlin + Lund laser center + DCU Dublin + LURE Paris

HELMHOLTZ GEMEINSCHAFT VUV FEL The goal: Time-resolved measurements at the FEL VUV-VUV experiments fs-excitation AND fs – detection is needed VUV-optical experiments  Many interesting processes are triggered by visible rather than by VUV light  The visible laser is much more flexible  larger time-delay (ns...)  variable pulse length / chirping  change color, polarization... Problem: jitter between the two independent sources by BESSY Berlin

HELMHOLTZ GEMEINSCHAFT VUV FEL Layout of the optical laser system Wavelength: 790 nm nm Pulse duration: ~100 fs pulse energy for single laser pulse: µJ Rep rate1 MHz Laser parameters

HELMHOLTZ GEMEINSCHAFT VUV FEL Layout: pump-probe experiments optical laser 5 exp. stations FEL pulse Optical pulse

HELMHOLTZ GEMEINSCHAFT VUV FEL The temporal overlap at the experiment Experimental chamber for the first pump-probe experiments Overlapping the FEL and the optical pulse X-ray streak camera

HELMHOLTZ GEMEINSCHAFT VUV FEL (V)UV streak camera at the experiment With courtesy from Howard Padmore streak camera (Berkeley) ( H. Padmore, R. Falcone, A. MacPhee …) However:we need: Average over 6000 shotssingle shot 266 nm30 nm (+266nm) More about the camera Andrew – next talk The best so far in UV: Zenghu Chang group, Kansas

HELMHOLTZ GEMEINSCHAFT VUV FEL X-ray streak camera at experiment Good idea, however …  Not simple to integrate into experiment ( intensity, geometry …)  great to find temporal overlap at experiment  hard to use as online jitter / drift monitor  User facility  jitter / drift detection should be independent of user experiment

HELMHOLTZ GEMEINSCHAFT VUV FEL What am I gonna talk about ? Using an optical streak camera to monitor the dipole radiation

HELMHOLTZ GEMEINSCHAFT VUV FEL Layout: experimental hall optical laser streak camera 5 exp. stations FEL pulse Optical pulse Dipole radiation Electrons Dipole radiation VUV pulse

HELMHOLTZ GEMEINSCHAFT VUV FEL The problem ms... systematic drifts within the macropulse ~300 fs systematic drifts within the macropulse ~300 fs changes from macropulse to macropulse ~ 600 fs changes from macropulse to macropulse ~ 600 fs...hours... longterm drifts > ps longterm drifts > ps the pulses are NOT drawn to scale ! IR FEL

HELMHOLTZ GEMEINSCHAFT VUV FEL Strategies for using the optical streak camera systematic drifts within the macropulse ~300 fs systematic drifts within the macropulse ~300 fs Macropulse to macropulse ~ 600 fs Macropulse to macropulse ~ 600 fs l ongterm drifts > ps l ongterm drifts > ps  Jitter close to resolution of streak camera (peak detection)  Reprate too low / space charge problems for single shot  Other methods are better suited for 1 MHz detection EOS - Thursday Photoelectron s Reinhard - later  Synchroscan – low camera jitter – integrate over macropulse  10 Hz (1D binning) readout works monitored ( ~300 fs)  rising edge for each macropulse will be monitored ( ~300 fs)  continuous monitoring -> detection of long term drifts feedback  using as feedback signal for RF shifter in laser

HELMHOLTZ GEMEINSCHAFT VUV FEL Two photon Above Threshold Ionization (ATI) Electron spectrometer gas jet Visible fs laser pulse VUV M. Meyer, P.O´Keeffe LURE Superposition of visible and VUV pulse in a nobel gas jet

HELMHOLTZ GEMEINSCHAFT VUV FEL Gas jet FEL SASE pulse visible strong fs- laser pulse (1D) imaging electron spectrometer spatial coordinate Electron energy Photo electrons resolution < 50 fs Parasitic – does not destroy the FEL pulse resolution < 50 fs Parasitic – does not destroy the FEL pulse Photo electrons Single-shot FEL -IR cross correlator

HELMHOLTZ GEMEINSCHAFT VUV FEL Single-shot FEL -IR cross correlator (Proposal by M. Drescher, Universität Bielefeld)

HELMHOLTZ GEMEINSCHAFT VUV FEL Strategies for using the optical streak camera systematic drifts within the macropulse ~300 fs systematic drifts within the macropulse ~300 fs Macropulse to macropulse ~ 600 fs Macropulse to macropulse ~ 600 fs l ongterm drifts > ps l ongterm drifts > ps  Jitter close to resolution of streak camera (peak detection)  Reprate too low / space charge problems for single shot  Other methods are better suited for 1 MHz detection  Synchroscan – low camera jitter – integrate over macropulse  10 Hz (1D binning) readout works monitored ( ~300 fs)  rising edge for each macropulse will be monitored ( ~300 fs)  continuous monitoring -> detection of long term drifts feedback  using as feedback signal for RF shifter in laser

HELMHOLTZ GEMEINSCHAFT VUV FEL Layout of the dipole radiation beam line electrons 45 m evacuated beamline Spherical collection mirror 2” diameter – 2.3 m focal length → → 20 mrad acceptance ~ visible photons

HELMHOLTZ GEMEINSCHAFT VUV FEL Location of the “dipole experiments” 90° off-axis parabola (4”) to focus on slit Laser hutch 40 µm spot size - ZEMAX simulation-

HELMHOLTZ GEMEINSCHAFT VUV FEL Emission geometry – principle limits ? R=3.6 m Collecting mirror Path length difference between different rays on the arc 3 fs < 3 fs Rays projected to object plane Path length difference between Different rays projected to object plane 3 ~ opening angle 3 10 mrad → 4 fs 20 mrad → 30 fs Electron trajectory → the electron bunch shape is accurately mapped onto the dipole light

HELMHOLTZ GEMEINSCHAFT VUV FEL Dipole light is white light Another problem: Dispersion Bandwidth: temporal spread temporal spread 400 nm400 fs 12 ps 50 nm50 fs 1.7 ps 10 nm10 fs 0.3ps Ways around :● use band-pass filter (tremendous loss of photons) ● all reflective optics (expensive) ● focus directly onto the cathode (??) ● don’t use a streak camera …. Vacuum window (3mm) Streak camera lens Measurements : TTF Phase I by Ch. Gerth

HELMHOLTZ GEMEINSCHAFT VUV FEL Streak camera test – synchroscan, 2ps resolution measurements by Ingo Will, MBI Berlin 100 fs (FWHM) The delay between two short laserpulses can be determined with a reproducability of <100 fs (FWHM) – despite a camera resolution of 2 ps ! Resolution of arrival time jitter expected to be 300 fs

HELMHOLTZ GEMEINSCHAFT VUV FEL What am I gonna talk about ? Next topic optical correlation between optical correlation between the dipole light and the laser

HELMHOLTZ GEMEINSCHAFT VUV FEL Optical correlation Dipole radiation fs-laser Line focus Non-linear crystal

HELMHOLTZ GEMEINSCHAFT VUV FEL Timing from 800 nm, 80 fs., 10 Hz repetition rate, ~2 mJ Ti:Sapphire laser. CCD, PSD Oscilloscope KDP β SHG Delay stage, ΔL BS Variable Attenuator τ = ΔL/ccos(β/2) t 0 Freq. Doubled light t 0 +τ SHG imagine lens Test experiment - setup

HELMHOLTZ GEMEINSCHAFT VUV FEL 5x10 7 photons → photons + 5x10 7 photons → 10 6 sum frequency photons Single shot1 MHz readout Single shot detection with 1 MHz readout 30 fs resolution 6 ps window 30 fs resolution (in demo experiment) in 6 ps window 5x10 7 photons → photons + 5x10 7 photons → 10 6 sum frequency photons Single shot1 MHz readout Single shot detection with 1 MHz readout 30 fs resolution 6 ps window 30 fs resolution (in demo experiment) in 6 ps window Test experiment having 5x10 7 photons /pulse

HELMHOLTZ GEMEINSCHAFT VUV FEL time overlap at the experiments –Use x-ray streak camera “downstream” experiment (<1 ps res.) Optical streak cameraOptical streak camera –Monitor macro pulse to macro pulse jitter ( ~300 fs res.) –Use as feedback for long term drifts Optical correlation +FEL and Dipole radiationOptical correlation +FEL and Dipole radiation –~ 30 fs resolution –Detection at 1 MHz Conclusions Multiple (redundant) jitter diagnostics will be used (2 EOS, Dipole radiation, Photoelectrons, x-ray streak) to find out which is best suited ( XFEL)

HELMHOLTZ GEMEINSCHAFT VUV FEL......

HELMHOLTZ GEMEINSCHAFT VUV FEL ps - timing tool Holzman et al. Appl. Phys Lett. 76, 134 (2000) Simple way to get ps overlap – just measuring charge ? Single photoconductive switch 2 switches second one grounds the first at ps delay