Abstract. 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.Group velocity control in the ultraviolet domain via interacting dark-state resonances 2
We discuss in-medium propagation dynamics in a white light cavity that leads to an enhancement of the cavity's bandwidth without reducing its maximum intensity buildup. We analyze the spatiotemporal dynamics of our system with a full simulation of the field propagation in a regime that leads to strong absorption of the control fields. We find that an additional coherent field is generated within the medium via four-wave mixing. This self-generated field leads to a backaction of the medium onto the probe field. Counter intuitively, this pronounced in-medium dynamics throughout the propagation leads to an additional enhancement of the cavity bandwidth. PACS numbers: 42.65.Sf, 42.50.Nm, 42.60.Da, 04.80.Nn In an optical cavity, the bandwidth of supported frequencies and the intensity buildup are inversely proportional [1]. Increasing the cavity's finesse, e.g., via the reflectivity of the mirrors, leads to a higher buildup for a smaller range of frequencies and vice versa. The reason is that frequencies away from the cavity resonance correspond to different wavelengths which do not exactly fulfill the resonance condition. Thus, they acquire a phase shift with respect to the resonance frequency and experience loss at the mirrors. In terms of applications, this inverse dependence is a limiting factor for a number of schemes. Perhaps most prominently, gravitational wave detectors (GWD) aim at detecting tiny oscillations that ideally could be amplified by the power buildup in a high-quality cavity with large bandwidth [2]. To overcome this problem, the concept of a so-called white-light cavity (WLC) was developed [3]. Its basic idea is to employ a mechanism inside the cavity that cancels the phase shift for offresonant frequencies, thereby improving the bandwidth of a cavity without the drawback of reducing its maximum buildup. In the case of GWD one could increase sensitivity without restricting detection bandwidth.It may seem that the simplest implementation of a WLC would be to introduce a pair of plain parallel gratings such that their diffraction leads to a frequency dependent path length inside the cavity [4], which, however, is not feasible [5]. A grating causes a phase shift that depends on the position where the wave is diffracted. Since different frequencies are diffracted at different positions at one of the gratings, an additional frequency dependent phase shift occurs and prohibits canceling the frequency dependent phase shift in the cavity.A different implementation of WLC uses a medium with negative dispersion inside the cavity. In such a medium, phase shifts due to wavelength mismatch can be compensated by suitable phase shifts generated via a frequency-dependent index of refraction. Proposed systems include a strongly driven double-Λ system with incoherent pumping [3], a strongly driven two-level atomic resonance, and a Λ-system off-resonantly driven by two strong fields [6]. In the latter case, the negative disper-sion occurs between two gain lines. This has also been used in an experiment to demonst...
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.