Light propagation in dense and chiral media

Die elektromagnetischen Eigenschaften von Licht werden in der Quantenoptik meist auf die elektrische Komponente reduziert. Ein Medium, das sowohl mit der elektrischen als auch mit der magnetischen Komponente wechselwirkt, wäre jedoch aus technologischer Sicht sehr interessant. Ein vor kurzem vorgeschlagener Ansatz, um die magnetische Antwort zu verstärken, basiert auf hoher Dichte sowie induzierter Chiralität. Eine Kombination von beidem ist jedoch experimentell zur Zeit nicht umsetzbar. Diese Arbeit untersucht Lichtpropagation in dichten und in chiralen Medien, wobei beide Konzepte getrennt und in experimentell zugänglichen Parameterbereichen behandelt werden. Im Einzelnen analysieren wir ein sog. Closed-Loop System, demonstrieren ein Schema zur Kontrolle der Gruppengeschwindigkeit im UV-Bereich, zeigen, wie parametrische Prozesse in der Lichtpropagation verwendet werden können und erläutern den Einfluss hoher Gasdichte auf einen verlangsamten Lichtpuls. Wir leiten die Wellengleichung für Medien mit induzierter Chiralität her und lösen sie auf Basis der allgemeinen Mediumsantwort. In einem konkreten Beispiel verwenden wir die erarbeiteten Konzepte, um Lichtpropagation mit chiraler Wechselwirkung zu untersuchen. Dabei stellen wir fest, dass ein chirales Medium die optimale Umsetzung eines Closed-Loop Phasenkontrollschemas ermöglicht und so die Dynamik eines verlangsamten Lichtpulses während der Propagation kontrolliert werden kann. Außerdem zeigen unsere Ergebnisse, dass bereits mit heutigen experimentellen Methoden Parameter erreichbar sind, bei denen die magnetische Komponente des Probefelds relevant wird

Phase modulation induced by cooperative effects in electromagnetically induced transparency

We analyze the influence of dipole-dipole interactions in an electromagnetically induced transparency setup at high density. We show both analytically and numerically that the polarization contribution to the local field strongly modulates the phase of a weak pulse. We give an intuitive explanation for this local field induced phase modulation and show that it distinctively differs from the nonlinear self-phase modulation a strong pulse experiences in a Kerr medium

Group velocity control in the ultraviolet domain via interacting dark-state resonances

The propagation of a weak probe field in a laser-driven four-level atomic system is investigated. We choose mercury as our model system, where the probe transition is in the ultraviolet region. A high-resolution peak appears in the optical spectra due to the presence of interacting dark resonances. We show that this narrow peak leads to superluminal light propagation with strong absorption, and thus by itself is only of limited interest. But if in addition a weak incoherent pump field is applied to the probe transition, then the peak structure can be changed such that both sub- and superluminal light propagation or a negative group velocity can be achieved without absorption, controlled by the incoherent pumping strength

Nonlinear Effects in Pulse Propagation through Doppler-Broadened Closed-Loop Atomic Media

Nonlinear effects in pulse propagation through a medium consisting of four-level double-$\Lambda$-type systems are studied theoretically. We apply three continous-wave driving fields and a pulsed probe field such that they form a closed interaction loop. Due to the closed loop and the finite frequency width of the probe pulses the multiphoton resonance condition cannot be fulfilled, such that a time-dependent analysis is required. By identifying the different underlying physical processes we determine the parts of the solution relevant to calculate the linear and nonlinear response of the system. We find that the system can exhibit a strong intensity dependent refractive index with small absorption over a range of several natural linewidths. For a realistic example we include Doppler and pressure broadening and calculate the nonlinear selfphase modulation in a gas cell with Sodium vapor and Argon buffer gas. We find that a selfphase modulation of $\pi$ is achieved after a propagation of few centimeters through the medium while the absorption in the corresponding spectral range is small.Comment: 4 figure

Consistent characterization of semiconductor saturable absorber mirrors with singe-pulse and pump-probe spectroscopy

We study the comparability of the two most important measurement methods used for the characterization of semiconductor saturable absorber mirrors (SESAMs). For both methods, single-pulse spectroscopy (SPS) and pump-probe spectroscopy (PPS), we analyze in detail the time-dependent saturation dynamics inside a SESAM. Based on this analysis, we find that fluence-dependent PPS at complete spatial overlap and zero time delay is equivalent to SPS. We confirm our findings experimentally by comparing data from SPS and PPS of two samples. We show how to interpret this data consistently and we give explanations for possible deviations