@article{MenzelHeuerPuhlmannetal.2013, author = {Menzel, Ralf and Heuer, Axel and Puhlmann, Dirk and Dechoum, K. and Hillery, M. and Spaehn, M. J. A. and Schleich, W. P.}, title = {A two-photon double-slit experiment}, series = {Journal of modern optics}, volume = {60}, journal = {Journal of modern optics}, number = {1}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {0950-0340}, doi = {10.1080/09500340.2012.746400}, pages = {86 -- 94}, year = {2013}, abstract = {We employ a photon pair created by spontaneous parametric down conversion (SPDC) where the pump laser is in the TEM01 mode to perform a Young's double-slit experiment. The signal photon illuminates the two slits and displays interference fringes in the far-field while the idler photon measured in the near-field in coincidence with the signal photon provides us with which-slit' information. We explain the results of these experiments with the help of an analytical expression for the second-order correlation function derived from an elementary model of SPDC. Our experiment emphasizes the crucial role of the mode function in the quantum theory of radiation.}, language = {en} } @article{SchwarzeGarzTeuchneretal.2014, author = {Schwarze, Thomas and Garz, Andreas and Teuchner, Klaus and Menzel, Ralf and Holdt, Hans-J{\"u}rgen}, title = {Two-photon probes for metal ions based on phenylaza[18]crown-6 ethers and 1,2,3-triazoles as pi-linkers}, series = {ChemPhysChem : a European journal of chemical physics and physical chemistry}, volume = {15}, journal = {ChemPhysChem : a European journal of chemical physics and physical chemistry}, number = {12}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1439-4235}, doi = {10.1002/cphc.201402232}, pages = {2436 -- 2439}, year = {2014}, language = {en} } @article{HeuerRaabeMenzel2014, author = {Heuer, Axel and Raabe, S. and Menzel, Ralf}, title = {Phase memory across two single-photon interferometers including wavelength conversion}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {90}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {4}, publisher = {American Physical Society}, address = {College Park}, issn = {1050-2947}, doi = {10.1103/PhysRevA.90.045803}, pages = {4}, year = {2014}, abstract = {Spontaneous parametric down-conversion (SPDC) in a nonlinear crystal generates two single photons (signal and idler) with random phases. Thus, no first-order interference between them occurs. However, coherence can be induced in a cascaded setup of two crystals if, e.g., the idler modes of both crystals are aligned to be indistinguishable. Due to the effect of phase memory it is found that the first-order interference of the signal beams can be controlled by the phase delay between the pump beams. Even for pump photon delays much larger than the coherence length of the SPDC photons, the visibility is above 90\%. The high visibilities reported here prove an almost perfect phase memory effect across the two interferometers for the pump and the signal photon modes.}, language = {en} } @article{ZinkWernerJechowetal.2014, author = {Zink, Christof and Werner, Nils and Jechow, Andreas and Heuer, Axel and Menzel, Ralf}, title = {Multi-wavelength operation of a single broad area diode laser by spectral beam combining}, series = {IEEE photonics technology letters}, volume = {26}, journal = {IEEE photonics technology letters}, number = {3}, publisher = {Inst. of Electr. and Electronics Engineers}, address = {Piscataway}, issn = {1041-1135}, doi = {10.1109/LPT.2013.2291963}, pages = {253 -- 256}, year = {2014}, abstract = {Stabilized multi-wavelength emission from a single emitter broad area diode laser (BAL) is realized by utilizing an external cavity with a spectral beam combining architecture. Self-organized emitters that are equidistantly spaced across the slow axis are enforced by the spatially distributed wavelength selectivity of the external cavity. This resulted in an array like near-field emission although the BAL is physically a single emitter without any epitaxial sub-structuring and only one electrical contact. Each of the self-organized emitters is operated at a different wavelength and the emission is multiplexed into one spatial mode with near-diffraction limited beam quality. With this setup, multi-line emission of 31 individual spectral lines centered around and a total spectral width of 3.6 nm is realized with a 1000 mu m wide BAL just above threshold. To the best of our knowledge, this is the first demonstration of such a self-organization of emitters by optical feedback utilizing a spectral beam combining architecture.}, language = {en} } @article{ZinkNiebuhrJechowetal.2014, author = {Zink, Christof and Niebuhr, Mario and Jechow, Andreas and Heuer, Axel and Menzel, Ralf}, title = {Broad area diode laser with on-chip transverse Bragg grating stabilized in an off-axis external cavity}, series = {Optics express : the international electronic journal of optics}, volume = {22}, journal = {Optics express : the international electronic journal of optics}, number = {12}, publisher = {Optical Society of America}, address = {Washington}, issn = {1094-4087}, doi = {10.1364/OE.22.014108}, pages = {14108 -- 14113}, year = {2014}, abstract = {The emission characteristics of a novel, specially designed broad area diode laser (BAL) with on-chip transversal Bragg resonance (TBR) grating in lateral direction were investigated in an off-axis external cavity setup. The internal TBR grating defines a low loss transversal mode at a specific angle of incidence and a certain wavelength. By providing feedback at this specific angle with an external mirror, it is possible to select this low loss transverse mode and stabilize the BAL. Near diffraction limited emission with an almost single lobed far field pattern could be realized, in contrast to the double lobed far field pattern of similar setups using standard BALs or phase-locked diode laser arrays. Furthermore, we could achieve a narrow bandwidth emission with a simplified setup without external frequency selective elements. (C) 2014 Optical Society of America}, language = {en} } @article{NiebuhrZinkJechowetal.2015, author = {Niebuhr, Mario and Zink, Christof and Jechow, Andreas and Heuer, Axel and Glebov, Leonid B. and Menzel, Ralf}, title = {Mode stabilization of a laterally structured broad area diode laser using an external volume Bragg grating}, series = {Optics express : the international electronic journal of optics}, volume = {23}, journal = {Optics express : the international electronic journal of optics}, number = {9}, publisher = {Optical Society of America}, address = {Washington}, issn = {1094-4087}, doi = {10.1364/OE.23.012394}, pages = {12394 -- 12400}, year = {2015}, abstract = {An external volume Bragg grating (VBG) is used for transverse and longitudinal mode stabilization of a broad area diode laser (BAL) with an on-chip transverse Bragg resonance (TBR) grating. The internal TBR grating defines a transverse low-loss mode at a specific propagation angle inside the BAL. Selection of the TBR mode was realized via the angular geometry of an external resonator assembly consisting of the TBR BAL and a feedback element. A feedback mirror provides near diffraction limited and spectral narrow output in the TBR mode albeit requiring an intricate alignment procedure. If feedback is provided via a VBG, adjustment proves to be far less critical and higher output powers were achieved. Moreover, additional modulation in the far field distribution became discernible allowing for a better study of the TBR concept. (C) 2015 Optical Society of America}, language = {en} } @article{HeuerMenzelMilonni2015, author = {Heuer, Axel and Menzel, Ralf and Milonni, P. W.}, title = {Complementarity in biphoton generation with stimulated or induced coherence}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {92}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {3}, publisher = {American Physical Society}, address = {College Park}, issn = {1050-2947}, doi = {10.1103/PhysRevA.92.033834}, pages = {8}, year = {2015}, abstract = {Coherence can be induced or stimulated in parametric down-conversion using two or three crystals when, for example, the idler modes of the crystals are aligned. Previous experiments with induced coherence [Phys. Rev. Lett. 114, 053601 (2015)] focused on which-path information and the role of vacuum fields in realizing complementarity via reduced visibility in single-photon interference. Here we describe experiments comparing induced and stimulated coherence. Different single-photon interference experiments were performed by blocking one of the pump beams in a three-crystal setup. Each counted photon is emitted from one of two crystals and which-way information may or not be available, depending on the setup. Distinctly different results are obtained in the induced and stimulated cases, especially when a variable transmission filter is inserted between the crystals. A simplified theoretical model accounts for all the experimental results and is also used to address the question of whether the phases of the signal and idler fields in parametric down-conversion are correlated.}, language = {en} } @article{ElsnerPuhlmannPieplowetal.2015, author = {Elsner, Robert and Puhlmann, Dirk and Pieplow, Gregor and Heuer, Axel and Menzel, Ralf}, title = {Transverse distinguishability of entangled photons with arbitrarily shaped spatial near- and far-field distributions}, series = {Journal of the Optical Society of America : B, Optical physics}, volume = {32}, journal = {Journal of the Optical Society of America : B, Optical physics}, number = {9}, publisher = {Optical Society of America}, address = {Washington}, issn = {0740-3224}, doi = {10.1364/JOSAB.32.001910}, pages = {1910 -- 1919}, year = {2015}, abstract = {Entangled photons generated by spontaneous parametric downconversion are ubiquitous in quantum optics. In general, they exhibit a complex spatial photon count distribution. This spatial structure is responsible for seemingly surprising results concerning, e.g., complementarity such as the apparent simultaneous observation of interference fringes V and which-way information D at a double slit, as recently reported by Menzel et al. [Proc. Natl. Acad. Sci. USA 109, 9314 (2012)]. We implement a complete quantitative model of the SPDC interaction that fully incorporates the effects of crystal anisotropies, phase matching, and the pump beam structure and allows for arbitrary manipulations of the SPDC light in the near and far fields. This enables us to establish an upper bound D-2 + V-2 <= 1.47 for the experimental parameters reported by Menzel et al. We report new experimental results that agree excellently with these theoretical predictions. The new model enables a detailed quantitative analysis of this surprising result and the fair sampling interpretation of biphotons passing a double slit. (C) 2015 Optical Society of America}, language = {en} } @misc{RaetzelWilkensMenzel2016, author = {R{\"a}tzel, Dennis and Wilkens, Martin and Menzel, Ralf}, title = {Gravitational properties of light}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-90553}, year = {2016}, abstract = {The gravitational field of a laser pulse of finite lifetime, is investigated in the framework of linearized gravity. Although the effects are very small, they may be of fundamental physical interest. It is shown that the gravitational field of a linearly polarized light pulse is modulated as the norm of the corresponding electric field strength, while no modulations arise for circular polarization. In general, the gravitational field is independent of the polarization direction. It is shown that all physical effects are confined to spherical shells expanding with the speed of light, and that these shells are imprints of the spacetime events representing emission and absorption of the pulse. Nearby test particles at rest are attracted towards the pulse trajectory by the gravitational field due to the emission of the pulse, and they are repelled from the pulse trajectory by the gravitational field due to its absorption. Examples are given for the size of the attractive effect. It is recovered that massless test particles do not experience any physical effect if they are co-propagating with the pulse, and that the acceleration of massless test particles counter-propagating with respect to the pulse is four times stronger than for massive particles at rest. The similarities between the gravitational effect of a laser pulse and Newtonian gravity in two dimensions are pointed out. The spacetime curvature close to the pulse is compared to that induced by gravitational waves from astronomical sources.}, language = {en} } @article{RaetzelWilkensMenzel2016, author = {R{\"a}tzel, Dennis and Wilkens, Martin and Menzel, Ralf}, title = {Gravitational properties of light}, series = {New journal of physics : the open-access journal for physics}, volume = {18}, journal = {New journal of physics : the open-access journal for physics}, publisher = {IOP Science}, address = {London}, issn = {1367-2630}, doi = {10.1088/1367-2630/18/2/023009}, pages = {1 -- 16}, year = {2016}, abstract = {The gravitational field of a laser pulse of finite lifetime, is investigated in the framework of linearized gravity. Although the effects are very small, they may be of fundamental physical interest. It is shown that the gravitational field of a linearly polarized light pulse is modulated as the norm of the corresponding electric field strength, while no modulations arise for circular polarization. In general, the gravitational field is independent of the polarization direction. It is shown that all physical effects are confined to spherical shells expanding with the speed of light, and that these shells are imprints of the spacetime events representing emission and absorption of the pulse. Nearby test particles at rest are attracted towards the pulse trajectory by the gravitational field due to the emission of the pulse, and they are repelled from the pulse trajectory by the gravitational field due to its absorption. Examples are given for the size of the attractive effect. It is recovered that massless test particles do not experience any physical effect if they are co-propagating with the pulse, and that the acceleration of massless test particles counter-propagating with respect to the pulse is four times stronger than for massive particles at rest. The similarities between the gravitational effect of a laser pulse and Newtonian gravity in two dimensions are pointed out. The spacetime curvature close to the pulse is compared to that induced by gravitational waves from astronomical sources.}, language = {en} }