1. Optical Design of a Broadband IR Spectrometer
Kiel Williams,
With Julie Cass & Gilles Dongmo-Momo
Mentor Josef Frisch
8/11/2011
Courtesy lightsources.org

2. 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

3. Spectral Measurements
Optical Transition Radiation (OTR) produced by by bunches
Spectrum of OTR contains bunch length information
Primarily within IR spectrum
Courtesy H. Loos

4. 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)

5. 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

6. Experiment Objectives
Calibration of pyroelectic thermal sensor
Improve methods for OAP alignment
Multiple lasers to allow for superior calibration
CCD for imaging beam profile

7. 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

8. Initial Alignment Irises for initial alignment of beam
Rigorous checking of OAP Orientation
Tilting of prism and CCD to optimum angles

9. Slit Calibration Adjustable Slit Used to Measure Beam
Calibrated due to uncertainty about inch-based scale
Varied linearly across tested range

10. 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

11. 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

12. Results and Future Goals
Obtainment of thermal imaging for IR lasers
Integration of thermal sensor into system
More rigorous comparison to simulation

13. Acknowledgements Many thanks to Mentor Josef Frisch Alan Fisher
Mark Petree
George Burgueno
US Department of Energy

14. Questions?