Strained superlattice with and without DBR From Wikipedia
Strained superlattice with and without DBR From Wikipedia, the free encyclopedia A distributed Bragg reflector (DBR) is a reflector used in waveguides, such as optical fibers. It is a structure formed from multiple layers of alternating materials with varying refractive index, or by periodic variation of some characteristic (such as height) of a dielectric waveguide, resulting in periodic variation in the effective refractive index in the guide. Each layer boundary causes a partial reflection of an optical wave. For waves whose wavelength is close to four times the optical thickness of the layers, the many reflections combine with constructive interference, and the layers act as a high-quality reflector. Hope to enhance QE in SSL photocathodes, while maintaining high polarization
DBR photocathode results Sample# 75102 (DBR): H 1 chamber, best result 4 3. 5 Polarization (%) 3 2. 5 2 1. 5 1 0. 5 0 700 720 740 760 Wavelength (nm) 780 800
DBR QE: micro-Mott vs. H 1 chamber Sample# 75102 (DBR) 4 QE enhanced High polarization wavelength 3. 5 Polarization (%) 3 2. 5 QE_H 1 DBR 11/2014 2 after running all weekend QE 1. 5 qe after 2 hr heat 1 0. 5 0 700 710 720 730 740 750 760 770 Wavelength (nm) 780 790 800
Effect of heating on polarization Sample# 75102 (DBR) 100 2. 5 Pol_DBR 1 st heat 610 2 pol after running all weekend 90 80 pol after 2 hour heat Polarization (%) 70 60 1. 5 50 40 1 30 20 0. 5 10 0 0 750 760 770 780 Wavelength (nm) 790 800
Analyzing power DBR 75102 analyzing power 1. 3 1. 25 QE(%) 1. 2 1. 15 1. 1 1. 05 1 0 20 40 60 80 100 halfwave angle 120 140 160 180
Standard SSL formula Sample# 75102 (DBR) 100 2. 5 90 630 C, 15 min 80 2 70 Polarization (%) 75102 best 630 C, 30 min 640 C 30 min 60 1. 5 50 40 1 30 20 0. 5 10 0 0 750 760 770 780 Wavelength (nm) 790 800
Conclusions • QE in micro-Mott slightly lower than in H 1 chamber (load-locked system makes changing cathodes much easier though) • DBR polarization excellent – comparable to best cathodes we’ve seen • DBR enhancement is at wavelength where polarization isn’t maximum. • Standard cathode has thus far yielded poor QE – our fault or the cathode? (working to resolve)
Full pile data sets, 75102 DBR Sample# 75102 (DBR) 100 2. 5 90 80 2 Polarization (%) 70 60 1. 5 50 Pol_DBR 1 st heat 610 pol 3 rd heat (610+630) pol after running all weekend second autoscan pol after 2 hour heat 40 1 30 20 0. 5 10 0 0 750 760 770 780 Wavelength (nm) 790 800 QE_H 1 DBR 11/2014
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