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Optically Pumped FIR Lasers
Published in Peter K. Cheo, Handbook of Molecular Lasers, 2018
First predicted in 1954, superradiance is a collective emission process whereby N atoms or molecules radiate in phase much like the mobile carriers that comprise the current in a classical antenna [49]. By in-phase we mean that the electric fields from the oscillating dipoles add, implying that the radiated power scales as N2. Naturally, only N photons can be emitted, so the system must radiate in this manner for a time which must scale as 1/N. For large N, the emission time must be less than T1. To detect this effect, the system has to be excited in a time short compared to an anticipated emission time, which means that the initial evolution of the system occurs on a very short time scale compared to the naturally decaying time scale. Since the system does not know its ultimate fate, it will initially evolve normally, which means by emitting a weak spontaneous emission noise field. Some of this noise predisposes further emission, and eventually a strong field evolves. This oversimplified picture thus suggests a delay between when the system is excited and when it radiates.
Introduction to Lasers
Published in F.J. Duarte, Tunable Laser Optics, 2017
Although most lasers do need efficient and well-designed optical resonators, some lasers have such high gain factors that they tend to emit laser like radiation sometimes called superradiant emission or superfluorescence with only one mirror, or even without external mirrors. This means that the intrinsic reflection factors from flat windows provide the necessary feedback for powerful emission albeit with poor coherence properties. More specifically, this emission tends to be broadband and highly divergent. One additional advantage of using inclined windows, when using high gain laser media, is to reduce parasitic reflections that tend to contribute to output noise. Some laser media that produce very high gains include copper vapor, molecular nitrogen, and laser dyes.
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Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
superposition integral superheterodyne an architecture used in virtually all modern-day receivers. In the early days of radio, tuned stages of amplification were cascaded in order to secure a sufficiently high level of signal for detection (demodulation). superheterodyne receiver most receivers employ the superheterodyne receiving technique, which consists of either down-converting or upconverting the input signal to some convenient frequency band, called the intermediate frequency band, and then extracting the information (or modulation) by using an appropriate detector. This basic receiver structure is used for the reception of all types of bandpass signals, such as television, FM < AM < satellite, and radar signals. superinterleaving See interleaved memory. is 50 MHz). Superpipeline processors usually have a relatively deep pipeline, of about 7 stages or more (8 stages on the R4000). superpipelining a pipeline design technique in which the pipeline units are also pipelined internally so that multiple instructions are in various stages of processing within the units. The clock rate is increased accordingly. superpolish methods for producing a surface of low RMS roughness, typically 10 angstroms RMS or less; methods include special mechanical, chemical, and ion polishing techniques. superposition coding multiple-access channel coding technique in which each user encodes independently, such that at the receiver, the transmitted signals may be estimated using successive cancellation. See also successive cancellation. superradiance usually refers to the strongly enhanced spontaneous emission that is emitted by a coherently prepared system of atoms or molecules. superscalar processor a processor where more than one instruction is fetched, decoded, and executed simultaneously. If n instructions are fetched and processed simultaneously, it is called an nissue superscalar processor. For example, the Pentium is a two-issue, and the DEC 61164 is a fourissue superscalar processor. This feature was implemented both on CISC (Pentium) and RISC (61164) processors. superposition for a system T [], the property that T [a1 x1 (t) + a2 x2 (t)] = a1 t[x1 (t)] + a2 t[x2 (t)]. superposition integral for a linear shiftinvariant system characterized by an impulse response, h(t), the output, y(t), for a given input, x(t), is calculated as y(t) = - x(s)h(t - s)ds. Also called the convolution integral.
Photon bunching from an equilateral triangle of atoms
Published in Journal of Modern Optics, 2023
The study of characteristics of emitted radiation from a system of interacting atoms is an important research area in the realm of quantum computing and optics. The interactions that exist in such few-atom radiative ensembles lead to the collective behaviour which can alter the traits of emission and can give rise to increased rates of spontaneous emission, commonly known as superradiance. The topic has been studied in [1–6]. It is found that atoms positioned in a line [7–18] or arranged as arrays in two spatial dimensions [19–22] depict collective behaviour. Such geometric arrangements of atoms can be realized in an experiment if closely-separated trapped atoms interact with each other via a common reservoir field [23–26]. If the interatomic separation is kept short, usually on the order of or less than the involved atomic transition wavelength, the dipole–dipole interaction and the collective decay occur as a result of the interaction through the common continuum of reservoir field modes. The analysis of the emitted electric field correlation functions is a tool that enables the understanding of the radiative characteristics of the atomic ensemble. The first-order correlation function evaluated at one-time determines the intensity of the fluorescence field radiated by the system of atoms. The two-time correlation function [27] yields the spectral characteristics of the emitted radiation. It helps to distinguish whether the emitted field behaves non-classically or classically [28]. Based on this knowledge the existence of a correlation or an anti-correlation in the emitted photon pair can be determined.