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Published byBeverley Griffin Modified over 6 years ago
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Optical Design of a Broadband IR Spectrometer
Kiel Williams, With Julie Cass & Gilles Dongmo-Momo Mentor Josef Frisch 8/11/2011 Courtesy lightsources.org
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LCLS Bunch Length Tens of femtoseconds in duration (sheet of paper and a photon) Direct Measurement Methods Fail Important to understanding biological processes Courtesty LCLS
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Spectral Measurements
Optical Transition Radiation (OTR) produced by by bunches Spectrum of OTR contains bunch length information Primarily within IR spectrum Courtesy H. Loos
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Constraints of Spectral Range
Normal optics fail to transmit over relevant range Gold-Coated Optics for beam direction KRS-5 Prism for beam decomposition Zinc Selenide for testing Off-axis parabolic (OAP) mirrors for expansion Transmittance (%) Wavelength (Microns) Courtesy of International Crystal Laboratories Transmittance (%) Wavelength (Microns)
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Prism Structure Diffraction gratings fail to transmit over wide range
Nice symmetry permits easier aberration reduction Bends emerging beam at odd angles Courtesy of C. Behrens
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Experiment Objectives
Calibration of pyroelectic thermal sensor Improve methods for OAP alignment Multiple lasers to allow for superior calibration CCD for imaging beam profile
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Optical Layout Design Need to fit multiple lasers on narrow optical table Combine beams to prevent redundancy Use optics that transmit over far range Courtesy C. Behrens
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Initial Alignment Irises for initial alignment of beam
Rigorous checking of OAP Orientation Tilting of prism and CCD to optimum angles
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Slit Calibration Adjustable Slit Used to Measure Beam
Calibrated due to uncertainty about inch-based scale Varied linearly across tested range
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Correction of Optical Aberrations
Dramatic aberrations for minor misalignments or height errors Aberrant effect inherent to parabolic optics Many degrees of freedom, coupled X-Y movement complicates process
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Beam Profile Measurements
Check Gaussian beam profile as good assumption Simulation suggests idealized ~50 micron diameter Half-Power Beam occurring for microns Alternates between several hundred and tens of microns based on OAP positioning Courtesy of ZEMAX Users’ Knowledge Base
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Results and Future Goals
Obtainment of thermal imaging for IR lasers Integration of thermal sensor into system More rigorous comparison to simulation
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Acknowledgements Many thanks to Mentor Josef Frisch Alan Fisher
Mark Petree George Burgueno US Department of Energy
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Questions?
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