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Laser needs for interferometry based beam size measurements

Laser needs for interferometry based beam size measurements. Axel Brachmann SLAC 01/30/06. Fringe spacing as function of laser beam crossing angle for 1064, 532, 355 and 266 nm. Smallest measurable spotsize. For 355 nm, 174 degree crossing angle and 90 % Modulation depth (best case):.

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Laser needs for interferometry based beam size measurements

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  1. Laser needs for interferometry based beam size measurements Axel Brachmann SLAC 01/30/06

  2. Fringe spacing as function of laser beam crossing angle for 1064, 532, 355 and 266 nm Axel Brachmann, SLAC, 01/30/2006

  3. Smallest measurable spotsize For 355 nm, 174 degree crossing angle and 90 % Modulation depth (best case): σy = 12 .6 nm Axel Brachmann, SLAC, 01/30/2006

  4. Obtainable spot sizes using 532 nm laser (Numbers in parenthesis are for 1064 nm) Axel Brachmann, SLAC, 01/30/2006

  5. How many Compton photons do we get ? 1. Order Example laser spot size (D) at interference point of 10 µm laser peak power is 10 MW (10µJ/10ps) laser wavelength is 532 nm Electron energy is 1.54 GeV Number of electrons (ne) is 1*1010 Fringe spacing (174 degree laser beam crossing) is 0.266 μm Smallest measurable spotsize is 0.1 μm Laser photon density (np) 1.14* 1027 m-3 Compton cross section (σc) is 6.474 *10-25 cm2 Number of Compton photons: Nγ = σc* np* D *ne 7353 Axel Brachmann, SLAC, 01/30/2006

  6. Confirm attainable interference pattern and stability and modulation depth • HeNe 543.1 nm • Resolution target • Microskop objective + CCD camera • Calibrate spacial resolution with resolution target • Up to 228 lines per mm • Line width = 1/2LP = 2 μm • e.g. NEWPORT RES1/2 • FFTB: 40 micron spotsize Axel Brachmann, SLAC, 01/30/2006

  7. Laser system choices (I) • Single bunch system – commercially available • Multibunch system – development necessary First question : Which wavelength? • Nd:YAG 532, 355 nm • Nd:YLF 527, 351 nm • Ti:Sapphire 350-450 nm Axel Brachmann, SLAC, 01/30/2006

  8. Laser system choices (II) • Second question: Choice of mode-locked oscillator for 3 MHz bunch train generation • Nd:YAG, Nd:YLF,Ti:Sapphire modelocked oscillator are commercially available, however at higher rep rates (70+ MHz) • Cavity dumped low rep rate oscillators with limited commercial availability (1 MHz) • http://www.gmp.ch/, http://www.highqlaser.com, • Fiber laser as pulse train source are also possible (e.g. Er-doped fiber lasers – frequency doubled could be a seed for a Ti:Sapphire amplifier Axel Brachmann, SLAC, 01/30/2006

  9. External EO pulse train generation • Pockels cells (and driver electronics) at 3 MHz are being developed by the laser industry  not mainstream yet • Issues for EO driver electronics : fast rise/fall times at kV levels • Issues for EO devices: piezoelectric resonances • For ILC e- source we anticipate development of a system based on external pulse chopping Ti:Sapphire but upgrade to cavity dumped modelocked oscillator is planned Axel Brachmann, SLAC, 01/30/2006

  10. Pulse train amplification • Direct Diode pumping: • Nd:YAG, Nd:YLF • high power still requires flashlamps due to high cost of laser diodes • Pumping by Solid State Laser • Ti:Sapphire • doubled Nd:YAG, Nd:YLF, ND:VAD, Yb:YAG lasers • Thin disk laser technology currently most powerful pump source with low M2 (1.1, e.g 50 W cw, 515 nm, ELS Lasers) • Cryogenically cooled Ti:Sapphire allows high power densities in Ti:Sapphire amplifier crystals Axel Brachmann, SLAC, 01/30/2006

  11. Mode-locked Fiber lasers • Emerging technology: • 1 GW, 1 MHz, 600 fs, 5 nm bandwidth • E.g. www.polaronyx.com Axel Brachmann, SLAC, 01/30/2006

  12. PITZ – DESY/Zeuthen : Axel Brachmann, SLAC, 01/30/2006

  13. LW Interferometer Possibility Pulse Picker SHG Axel Brachmann, SLAC, 01/30/2006

  14. References • P. Tenenbaum, T. Shintake; Measurement of Small Electron Beam Spots. 1999; SLAC Pub 8057. • T. Shintake; Nanometer Spot Size Monitor using Laser Interferometry. US-CERN-Japan Joint Accelerator School: Topical Course: Frontiers of Accelerator Technology, Maui, Hawaii, 3-9 Nov 1994. In *Maui 1994, Frontiers of accelerator Technology 437 – 459. • M. Woods, T. Kotseroglou, R. Alley, J. Frisch, A. Hayakawa, T. Shintake; Stability and modulation depth of Interference Fringes of the FFTB BSM. FFTB 98-02. • M. Woods, T. Kotseroglou, T. Shintake; Vertical position stability of the FFTB electron beam measured by the KEK BSM monitor. FFTB 98-03 Axel Brachmann, SLAC, 01/30/2006

  15. Axel Brachmann, SLAC, 01/30/2006

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