Lifetime measurements of DBR and nondbr photocathodes at high laser intensities PST 2009 - Ferrara Eric J. Riehn Collaboration B2 Institut für Kernphysik Johannes Gutenberg-Universität Mainz September 10, 2009
Table of contents 1 Introduction 2 Reflectivity Measurements 3 Heating Experiments 4 Summary & Outlook
Photo current photo current laser power Definition of the quantum yield: QY (λ) = N e = h c N hν e I photo λ laser P laser (1) N e : number of electrons N hν : number of photons I photo : photo current λ laser : wavelength of laser light P laser : power of laser light h, c, e : fundamental constants
Heating of nondbr photo cathodes caused by irradiation Figure: Plot taken from K. Winkler (2002; Mainz)
Structure of a nondbr - photocathode Figure: Structure of SL 7-395 (nondbr)
Structure of a nondbr - photocathode Figure: Structure of SL 7-395 (nondbr)
Structure of a nondbr - photocathode Figure: Structure of SL 7-395 (nondbr)
Structure of a DBR - photocathode Figure: Structure of SL 7-396 (DBR)
Experimental Setup Figure: Setup of the polarized test source PKAT
Determination of the reflectivity in vacuo Reflectivity of the cathode: r cathode = P D1 r glas P D2 (1 r glas ) 2 (2) Reflectivity of the glas: r glas = P D2 P 0 (3)
Determination of the reflectivity in vacuo Reflectivity of the cathode: r cathode = P D1 r glas P D2 (1 r glas ) 2 (2) Reflectivity of the glas: r glas = P D2 P 0 (3)
Results Figure: Reflectivity curves for DBR and nondbr cathodes
Results Figure: Reflectivity curves for DBR and nondbr cathodes
DBR - photocathode as Fabry-Pérot-Interferometer Figure: Structure of SL 7-396 (DBR)
Spectral Quantum Yield Figure: DBR-related resonance features in Quantum Yield
Heating Experiments In a specific wavelength region (here: 780 nm to 860 nm) DBR photo cathodes should not heat as much as a corresponding crystal without mirror and therefore have an extended lifetime.
Lifetime Figure: Lifetime of DBR SL 7-396H @ 600 mw
Special features to pay attention to The Plateau: no decrease in quantum yield during the first hours/days after activation
Special features to pay attention to The Bump: temporary rise of the quantum yield after increasing the irradiation power
Special features to pay attention to The Drop-Off: continuing (even accelerated) decrease of the quantum yield after decreasing the irradiation power
Lifetime Measurements Figure: Results from irradiation measurements
Lifetime Measurements Figure: Results from irradiation measurements
Lifetime Measurements Figure: Results from irradiation measurements
Summary & Outlook DBR-crystals show a resonance caused enhancement of the quantum yield at the working point no difference in polarisation between DBR and nondbr samples Effects of highly intense laser irradiation on DBR-crystals lifetime of DBR-crystals is 6 times higher in comparison to the nondbr-crystals respectively laser power can be increased without reducing the lifetime that much DBR s are a very promising addition to active cooling
Summary & Outlook DBR-crystals show a resonance caused enhancement of the quantum yield at the working point no difference in polarisation between DBR and nondbr samples Effects of highly intense laser irradiation on DBR-crystals lifetime of DBR-crystals is 6 times higher in comparison to the nondbr-crystals respectively laser power can be increased without reducing the lifetime that much DBR s are a very promising addition to active cooling
Summary & Outlook DBR-crystals show a resonance caused enhancement of the quantum yield at the working point no difference in polarisation between DBR and nondbr samples Effects of highly intense laser irradiation on DBR-crystals lifetime of DBR-crystals is 6 times higher in comparison to the nondbr-crystals respectively laser power can be increased without reducing the lifetime that much DBR s are a very promising addition to active cooling
Summary & Outlook DBR-crystals show a resonance caused enhancement of the quantum yield at the working point no difference in polarisation between DBR and nondbr samples Effects of highly intense laser irradiation on DBR-crystals lifetime of DBR-crystals is 6 times higher in comparison to the nondbr-crystals respectively laser power can be increased without reducing the lifetime that much DBR s are a very promising addition to active cooling
Appendix Nonlinear Q.Y. at different laser powers
Appendix Comparison of DBR and nondbr (St. Petersburg)
Appendix Asymmetry Figure: Asymmetry of SL 7-395 and SL 7-395H vs. Wavelenght
Appendix Quantum Yield Figure: Quantum Yield of SL 7-395 and SL 7-395H vs. Wavelenght
Appendix Lifetime of the Cleaning Effekt Figure: QE @ 630 nm vs. the Number of Preparations
Appendix First own Results with Spectrometer
Appendix Thermal Conductivity of the Mount Figure: Standard cathode Mount