Beamsplitting Interference phenomena are certainly among the most exciting phenomena in the whole of physics. In the following we will concentrate mainly on interference of weak fields; i.e. the beams contain, on average, only a few photons. The principle of classical interference is as follows: a light beam is split by an optical element, for example by a semitransparent mirror or a screen with several very small apertures, into two or more partial beams. These beams will take different paths and are then reunited and form interference patterns. The first step, the splitting of the beam into partial beams, plays a decisive role; light beams coming from different sources (or from different spatial areas of the same source) do not interfere with each other! We start our discussion of interference with an analysis of the action of a beamsplitter. To form a realistic idea of this device, let us imagine a semitransparent mirror. (Our considerations apply equally well to a screen with two apertures. We could also generalize to cases of unbalanced mirrors, with reflectivity different from 1/2, or screens with apertures of different size.) The classical wave picture can describe interference phenomena without any great effort: the incoming beam is split into the reflected and the transmitted partial wave, and each of these waves contains half of the energy. The process of splitting becomes conceptually difficult only when we think of the beam as consisting of spatially localized energy packets, or photons.
Motivated by the fact that the null shell of a collapsing black hole can be described by a perfectly reflecting accelerating mirror, we investigate an extension of this model to mirror semitransparency and derive a general implicit expression for the corresponding Bogolyubov coefficients. Then, we turn this into an explicit analytical form by focusing on mirrors that are accelerated via an impulsive force. From the so-obtained Bogolyubov coefficients we derive the particle production. Finally, we realize the field coming from the left-past spacetime region, passing through the semitransparent moving mirror and ending up to the right-future spacetime region as undergoing the action of a Gaussian quantum channel. We study the transmission and noisy generation properties of this channel, relating them to the Bogolyubov coefficients of the mirror's motion, through which we evaluate capacities in transmitting classical and quantum information.
Summarywe report on the development of a power efficient Faraday laser working at 780nm Rb transition using an atomic vapor Faraday filter as a frequency-selecting element. In the routine linear-cavity of Faraday laser, a partial reflectivity cavity mirror was used as output coupler. In this work, a high-reflection mirror (R>99.98%) replaces the partial reflectivity cavity mirror, the transmitted light of the Faraday optical filter is fully used as feedback beam and for frequency selection, while the light with polarization perpendicular to the transmitted part from the second polarizing beam splitter (PBS2) of Faraday anomalous dispersion optical filter (FADOF) is output. Single frequency laser is obtained at 780 nm Rb transition over a range of laser diode (LD) current from 60 to 140 mA. Such a single-frequency laser will be an excellent optical frequency standard by frequency stabilization technique.