Strong fields in laser plasmas - an introduction to high intensity laser plasma interaction -

Transcription

1 Strong fields in laser plasmas - an introduction to high intensity laser plasma interaction - 1 Laser acceleration experiments Experimental techniques & measurement of strong fields 2 Electron kinematics and laser absorption 3 Principles of laser particle acceleration - overview of some subjects concerning actual application of high intensity lasers - few basic considerations (not a consistent theoretical approach) - overview of experiments and techniques Centers in Germany: FSU, FZD, GSI, HHU, LMU-MPQ, MBI european activities cf. e.g.: Matthias SchnÇrer: schnuerer@mbi-berlin.de lecture is a compilation out of books, PhD-thesis, articles, (DonÅt blame me for footnotes )

2 Laser-Plasma-Interaction Experiment focussing mirror laser pulse target pulse duration s plasma neutrons target photons ions unique property: focussing of laser light electrons hot dense plasma can produce very high intensities

3 Essential steps in laser technology triggered new fields in laser plasma physics Q-switching ns > W/cm 2 plasma ablation (concept of inertial confinement fusion) laser plasma soft x-ray sources Mode locking ps > W/cm 2 strong field physics nonlinear effects (observation of high harmonics) laser plasma hard x-ray sources spectral control, fs > W/cm 2 chirped pulse amplification relativistic plasma physics particle acceleration (observation and prediction)

4 Chirped Pulse Amplification creation of highest light intensities

5 Prerequisites for experiments and examples: First: the laser example: view to the High Field Laser Laboratory at Max-Born-Institut Outline: temporal contrast, focusing, beam synchronization, ion diagnostic mixed with experiment examples

6 High Field Laser System XPW-frontend MBI-development LA 1 MBI-development output 80 mj bandwidth 80 nm LA 2 Amplitude Technology only multi-pass amplification with old frontend: pulse duration 45 fs 30 TW on target (contrast 10-7 ) 15 TW on target (contrast 10-11, with plasma mirror ) regenerative- and multi-pass amplification pulse duration 25 fs 100 TW at compressor output (contrast 10-9, AT- frontend) (contrast 10-11,XPW- frontend)

7 Experimental areas

8 Setting an experiment for high-intensity laser solid matter interaction Prerequisites: temporal contrast focusing laser beam synchronization ion detection contrast issue: ns pedestal launches shock and heat waves K Zeil et al. New Journal of Physics 12 (2010)

9 Examples Shock Wave S. Eliezer The interaction of high-power laser pulses with plasmas

10 Temporal contrast of a multi-pass Ti:Sapph laser system ~ W/cm 2 ~ W/cm 2 plasma creation threshold for ~ ns pulses Improvement necessary, otherwise interaction with low density plasma at pulse peak

11 Pulse duration and contrast measurement correlators (examples) second order third order

12 Ultra-high temporal contrast of the laser pulse is the critical issue - plasma mirror - Initial Parameter pulse energy: 1.2 J pulse duration 45 fs ns - ASE contrast: 5 x 10-8 Double Plasma Mirror (DPM) energy throughput ~60 % no decrease of focusability Target chamber focused with f /2.5 Off-Axis Parabola (OAP) Focus Diameter 3.6 Öm Intensity ~ 5 x W/cm 2 a 0 ~ 5 Data from literature and qualitative comparison suggest I pedestal < I peak

13 Plasma Mirror: ultra-high temporal contrast E ~ 1.3 J, 45 fs Interaction with nm-thick foils: contrast > E ~ 0.7 J, 45 fs, I Lpeak ~ 5 x W/cm 2 Henig et al. PRL 2009 Steinke et al. LPB 2010 plasma mirror - coated substrates view inside: plasma mirror in vacuum chamber best with XPW-frontend perfect shot series degradation due to debris damage of test coating

14 Example: change of the temporal laser contrast effect on fast ion emission Front-side and back-side emitted ions Ti (thickness ~ 5 micron ), 45 deg. irradiation, a 0 ~ 3 (no PM), a 0 ~ (1-2) (PM) laser fs-protons counts (protons) shot without pm (2.7 J b.c.) bs fs files bs/fs mcp bs/fs 40/16 counts/ion fs-counts*1/3 due bs/fs trace width energy (MeV) signal cutoff bs-protons ASE-contrast: with double plasma mirror < energy (MeV) shot with pm (2.6 J b.c.) bs fs files bs/fs mcp bs/fs 40/16 counts/ion fs-counts*1/3 due bs/fs trace width

15 Contrast enhancement with non-linear optical methods: XPW Principle cross-polarized wave generation 10 0 results with XPW saturable absorber degenerated four wave mixing process in non-linear media layout stretcher 10 ps multipass amplifier 1 mj, 50 nm booster amplifier 1 mj, 70 nm Oscillator 15 fs XPW temporal filter (vacuum) 80 nm, contrast > Offner stretcher to 'Amplitude' amplifier (20 J) to HFL amplifier (1mJ) intensity time, ps Open question: influence of ps-wings, PM necessary? YES!

16 Setting an experiment for high-intensity laser solid matter interaction Prerequisites: temporal contrast focusing laser beam synchronization ion detection focus issue : - need well defined intensity distribution focus quality - CPA systems with a grating compressor require simultaneous optimization of focus and compression (compensation of slight grating mismatches)

17 adaptive (or deformible) mirror simple and robust measurement: row example: f/70 focussing exposure of high dynamic range CCD col

18 Far field improvement of the MBI high field Ti:Sapph laser with appropriate grating alignement and an adaptive optical mirror system row 280 row col col attoff_adapt_off_singleshot_dif_x ATTOFF_ADAPT_On_SINGLESHOT_DIF_x energy content determination with a f=4000 mm lens, focussed directly on a CCD: 27% diffraction limited (AOM-off) 50% diffraction limited (AOM-on)

19 Setting an experiment for high-intensity laser solid matter interaction Prerequisites: temporal contrast focusing laser beam synchronization ion detection setting of 2 beam experiments (pump probe) HFL-facility at MBI two pulses at relativistic intensity level: primary goal: imaging of strong fields further possibilities: particle acceleration schemes with two beams particle bunch laser pulse scattering

20 Example of an 2 beam experiment

21 A simple method for beam (2 colors) synchronization with plasma shadow Ti:Sa = 35 fs Nd:glass = 1 ps time resolution 1 ps

22 Synchronization of femtosecond pulses spectral interference Gerhard Kampert, PhD-Thesis, Würzburg

23 Setting an experiment for high-intensity laser solid matter interaction Prerequisites: temporal contrast focusing laser beam synchronization ion detection two principle techniques are in use: - recording storage media ( plastic plates CR39, films, GAF-chromic image plates) >> robust solution, need certain flux and energy, not online - electronic detectors (mainly MCP, CCD in test, other from HEP may come in use) >> on-line, high sensitivity is a pro & con

24 Spectrometry with orthochromic films a simple an robust test experiment to check the ion beam characteristic T Paasch-Colberg Diploma Thesis MBI 2009 High proton flux e.g. F Nürnberg et al. Rev.Sci.Instrum. 2009

25 Ion detection MCP detection and Thomson spectrometer Paasch-Colberg Diploma Thesis MBI 2009

26 MCP Test and Calibration response of a single ion source: Am241 (5,486 MeV) alpha response concerning a certain ion flux comprehensive calibration (proton beam from laser plasma) e.g. K Harres et al. Rev.Sci.Instrum other sources proton cyclotrons

27 Calibration of Thomson Parabola MCP assembly R Prasad et al.: Nuclear Instruments and Methods in Physics Research A 623 (2010)

28 Gating of particle detectors (MCPs) Recording of 2D images with temporal information (resolution) obtained with particle beam dispersed in time (particles with different kinetic energies and different time of flights) requires gating of the detector (snapshot) film (stack) detector - gating corresponds to energy detection interval MCP detector - need temporal gating

29 Proton imaging with online readout Al-target object plane Laser beam proton beam MCP mm aperture 660 mm advantages of the MCP detector: high sensitivity low flux density possible data acquisition at high repetition rates electric gating background reduction (XUV, X-ray, electrons, low energy particles) high energy/time resolution How does the gating of the MCP work?

30 Gating of MCP detector U MCP (-1 kv) MCP at L=0.69m particles MCP radiation e - Phosphor-screen proton energy [MeV] Phosphor-screen voltage MCP voltage ΔE ΔT U Phosphor (+5 kv) proton arrival time [ns] gating sets the energy interval ΔE of the protons time resolution (exposure time) highly important for imaging of dynamical processes new device fast pulser from Kentech rectangular voltage pulse on MCP

31 Proton Imaging scheme scientific application for laser driven proton beams diagnostic tool for imaging of internal field structures in relativistic plasmas Laser 1 mesh Laser 2 ultra low emittance h ~ p mm mrad t 3 t 2 energy t 1 proton beam 2D snapshots exposure time depends on energy interval detector: MCP

32 2D Proton Imaging with MCP no interaction Nd: glass laser target surface 300Öm parameter magnification: ~10 observed area: ~3 mm proton energy: MeV exposure time: 400 ps TiSa: 40 fs, ~ W/cm 2 Nd:glass 1.5 ps ~10 18 W/cm 2

33 Streaking transient strong electric fields principle of proton streak deflectometry: (T. Sokollik et al. APL, 2008) pump proton beam probe - short proton burst (~ ps emission) - laminar beam (projection imaging) E (x,t) deflection at x i,t 2 probed with v 2 -protons deflection at x i,t 1 probed with v 1 -protons Measurement Raytracing Field configuration

34 no interaction with combination of the imaging setup with a the magnet glass and laser a thin slit leads to: continuous temporal record observation of one spatial dimension Proton Streak Camera Spatial dimension Proton Energy

35 Specific target systems mass limited targets Foil targets: beam attributes: high laminarity short bunches broad spectra divergence 2ç-20ç Micro droplets: mass-limited target lateral electron spread is limited ion source size correlates with droplet size unique phenomena due to geometry and size

36 Generation of micro droplets proton images 45 µm Ø16µm Animation: Th. Sokollik

37 Proton imaging of mass limited targets 40fs, 600mJ 1 x W/cm 2 60fs, 150mJ 2 x W/cm 2 Magnification: ~70 fold M L d MCP gating: ΔT gate ~ 5-15 ns T gate L v L 2 v 1 Time resolution: Δt ps t t d v d 2 v 1 T M gate CPA2 CPA2 Δt=65 ps Δt=150 ps

38 Proton imaging of mass limited targets reveals directional ion emission 3D particle tracing experiment 1/6 Q 0 2/3 Q 0 1/6 Q 0 + moving ion front PIC- simulation by T. Toncian Sokollik et al., PRL 193, (2009) t= 220 fs electric field distribution

39 Isolated mass-limited targets The idea: Investigation of a real isolated mass-limited spherical target Without the influence of: ambient plasma adjacent objects mounting stripes The approach: Single sphere in a Paul trap upper endcap trap rods microsphere target supply lower endcap Benchmark for theoretical predictions 10 mm

40 Laser Experiment with trapped MLT

41 Experiment: Ion acceleration

42 Example: Ultra-high temporal laser contrast light sail of ultra-thin foils Henig PRL 103, (2009). Steinke LPB 28, 215 (2010). experiments with few nm-thick diamond like carbon foils stable acceleration to GeV energies laser : 2 6 x10 22 Wcm2 simulation: B. Qiao et al, PRL 2009)

43 Some references Books Shalom Elizier The interaction of high-power lasers with plasmas IoP Publishing, 2002 Paul Gibbon Short pulse laser interaction with matter Imperial College Press, 2005 Thesis Thomas Sokollik Sven Steinke Andreas Henig Rainer Hörlein Sebastian Pfotenhauer Oliver Jäckel

44 Credits: HFL team Lasers: Laser development: G. Priebe, L. Ehrentraut M.K. Kalachnikov Technical Infrastructure: G. Kommol, J. Meißner, P. Friedrich IT&Electronics: D. Rohloff Experimental infrastructure (plasma dynamics): S. Steinke, F. Abicht, J. Bränzel, M. Schnürer (Th. Sokollik now at LBNL, T. Paasch-Colberg now at MPQ) Theory: A.A. Andreev TR18 collaboration: HHU, MPQ/LMU, FSU Director MBI Division B: W. Sandner