TY  - GEN
A1  - Niebuhr, Mario
A1  - Heuer, Axel
T1  - Phase measurement and far-field reconstruction on externally coupled laser diode arrays
N2  - Passive coherent combination of several discrete low power laser diodes is a promising way to overcome the issue of degrading beam quality when scaling single emitters to > 10W output power. Such systems would be an efficient alternative to current high power sources, yet they suffer from fatal coherence loss when operated well above threshold. We present a new way to obtain detailed coherence information for laser diode arrays using a spatial light modulator to help identify the underlying decoherence processes. Reconstruction tests of the emitted far-field distribution are conducted to evaluate the performance of our setup.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 383 
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-402140
ER  - 
TY  - GEN
A1  - Menzel, Ralf
A1  - Puhlmann, Dirk
A1  - Heuer, Axel
T1  - Complementarity in single photon interference – the role of the mode function and vacuum fields
N2  - Background 
In earlier experiments the role of the vacuum fields could be demonstrated as the source of complementarity with respect to the temporal properties (Heuer et al., Phys. Rev. Lett. 114:053601, 2015). 

Methods 
Single photon first order interferences of spatially separated regions from the cone structure of spontaneous parametric down conversion allow for analyzing the role of the mode function in quantum optics regarding the complementarity principle. 

Results 
Here the spatial coherence properties of these vacuum fields are demonstrated as the physical reason for complementarity in these single photon quantum optical experiments. These results are directly connected to the mode picture in classical optics. 

Conclusion 
The properties of the involved vacuum fields selected via the measurement process are the physical background of the complementarity principle in quantum optics.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 333 
KW  - Complementarity
KW  - Mode function
KW  - Quantum optics
KW  - Vacuum fields
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-395210
ER  - 
TY  - GEN
A1  - Menzel, Ralf
A1  - Heuer, Axel
A1  - Milonni, Peter W.
T1  - Entanglement, complementarity, and vacuum fields in spontaneous parametric down-conversion
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Using two crystals for spontaneous parametric down-conversion in a parallel setup, we observe two-photon interference with high visibility. The high visibility is consistent with complementarity and the absence of which-path information. The observations are explained as the effects of entanglement or equivalently in terms of interfering probability amplitudes and also by the calculation of a second-order field correlation function in the Heisenberg picture. The latter approach brings out explicitly the role of the vacuum fields in the down-conversion at the crystals and in the photon coincidence counting. For comparison, we show that the Hong–Ou–Mandel dip can be explained by the same approach in which the role of the vacuum signal and idler fields, as opposed to entanglement involving vacuum states, is emphasized. We discuss the fundamental limitations of a theory in which these vacuum fields are treated as classical, stochastic fields.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1077 
KW  - complementarity
KW  - vacuum fields
KW  - entanglement
KW  - Hong-Ou-Mandel effect
KW  - spontaneous parametric down-conversion
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-473542
SN  - 1866-8372
IS  - 1077
ER  -