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Julie Cass SULI Program 2011 SLAC National Accelerator Center Advisor Josef Frisch

Calculations and Simulations of an Infrared Prism Spectrometer for Ultra-Fast Bunch Length Diagnosis at LCLS. Julie Cass SULI Program 2011 SLAC National Accelerator Center Advisor Josef Frisch. 1. Overview of Spectrometer Optics . 90° off-axis parabolic mirrors (OAP)

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Julie Cass SULI Program 2011 SLAC National Accelerator Center Advisor Josef Frisch

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  1. Calculations and Simulations of an Infrared Prism Spectrometer for Ultra-Fast Bunch Length Diagnosis at LCLS Julie Cass SULI Program 2011 SLAC National Accelerator Center Advisor Josef Frisch

  2. 1 Overview of Spectrometer Optics • 90° off-axis parabolic mirrors (OAP) • HeNe laser at 632.816 nm (visible) to align optics • Alignment complicated when infrared laser is used • KRS-5 crystal acts as spectrometer prism, dispersing transition radiation

  3. 2 MATLAB Model: Ray Transfer Matrix Analysis • MATLAB used to model beam size with ray transfer matrix analysis • Ray transfer matrix: 2 x 2 matrices describing each optical element or free space propagated by beam Passage through a lens of focal length f Free space propagation

  4. 3 Gaussian Ray Transfer Matrix Analysis • Designed for modeling light rays of negligible waist size • HeNe laser is Gaussian - generated a vector to represent the initial beam in terms of a complex beam parameter q R – radius of curvature w – beam width k – normalization constant for second component of beam vector • MATLAB code calculates and graphs beam waists

  5. 4 Log of Beam Width Optical Element Number* *including free spaces of step size 100um

  6. 5 ZEMAX Simulation • Study spectrometer resolution achievable: simulation using optics modeling software ZEMAX • ZEMAX offers ray-tracing computations, following paths of perfect • geometric rays as they are reflected and refracted • Spot size analyzed at two points: • (1) Focal point of first OAP • (2) Detector surface (focal point of 3rd OAP)

  7. 6 ZEMAX: Adding Mirror Tilts • Mirror tilts in increments of 0.05° along optical, horizontal and vertical axes • Angles adjusted until beam size similar to measured beam size reached, then compared with estimated misalignment error

  8. 7 ZEMAX: Detector Tilt • Dispersion causes chromatic aberrations • Detector tilt required • New simulationto account for differences in design parameters C. Behrens et al., “Design of a Single-Shot Prism Spectrometer in the Near- and Mid-Infrared Wavelength Range for Ultra-Short Bunch Length Diagnostics”

  9. Results and Analysis

  10. 8 Results: Beam Size at First OAP Focus • Measured: 172 um • MATLAB: 65 um • ZEMAX:Tilts of ~0.4° to change beam size at focus from 0 to 172um • Consistent withhuman error in alignment

  11. 9 Results: Beam Size at Detector Surface • Measured: 280 um • MATLAB: 38 um • Much larger degree of error • (~ 7x magnification) • ZEMAX:14 um • Tilts of ~1.03° about horizontal/vertical axes needed to achieve measured size • Tilts of ~1.07° about optical axis needed to achieve measured size • This measurement is much more complicated

  12. 10 Updated Detector Tilt • Detector tilt of 45° for optimal focusing • All wavelengths will not fit on detector surface: range limited by this size rather than KRS-5 transmission 14mm

  13. 11 Conclusions • Current alignment leaves significant aberrations • Development of alignment procedures with greater precision • Addition of lasers with a range of wavelengths • Detector range limited by its size unless: • Adjustments are made to current design

  14. 12 Acknowledgements • Advisor: Joe Frisch • ZEMAX advising : Alan Fischer • Colleagues: Kiel Williams and Gilles Dongmo-Momo • SULI Program Director: Steve Rock • DOE and SLAC National Accelerator Laboratory for funding and direction of SULI Program

  15. References [1] Y. Ding et al., “Measurements and Simulations of Ultralow Emittance and Ultrashort Electron Beams in the Linas Coherent Light Source”, PRL 102, 254801, 2009  [2] Linear Coherent Light Source http://lcls.slac.stanford.edu/ [3] K. Williams, “Optical Design of a Broadband Infrared Spectrometer for Bunch Length Measurement at the Linac Coherent Light Source,” SLAC National Accelerator Laboratory SULI Program 2011, Palo Alto, CA  [4] Pyreos Ltd, http://www.pyreos.com/ [5] G. Dongmo-Momo, “Calibration of the Heat Sensor for the Free Electron Laser Bunch Length Measurements,” SLAC National Accelerator Laboratory SULI Program, Palo Alto, CA 2011 [6] MATLAB 7.0.4, The MathWorks Inc. [7] Bahaa E. A. Saleh and Malvin Carl Teich (1991). Fundamentals of Photonics. New York: John Wiley & Sons. Section 1.4, pp. 26-36 [8] Gaussian Beams http://www.rp-photonics.com/ [9] Radiant ZEMAX LLC, http://www.zemax.com [10] C. Behrens et al., “Design of a Single-Shot Prism Spectrometer in the Near- and Mid-Infrared Wavelength Range for Ultra-Short Bunch Length Diagnostics”, DIPAC'11, Hamburg, Germany, 201

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