Interference (wave propagation)

About: Interference (wave propagation) is a research topic. Over the lifetime, 26086 publications have been published within this topic receiving 321110 citations.

Beating the standard quantum limit: phase super-sensitivity of N-photon interferometers

Abstract: Quantum metrology promises greater sensitivity for optical phase measurements than could ever be achieved classically. Here, we present a theory of the phase sensitivity for the general case where the detection probability is given by an N photon interference fringe. We find that the phase sensitivity has a complicated dependence on both the intrinsic efficiency of detection and the interference fringe visibility V. Most importantly, the phase that gives maximum phase sensitivity is in general not the same as the phase at which the slope of the interference fringe is a maximum, as has previously been assumed. We determine the parameter range where quantum enhanced sensitivity can be achieved. In order to illustrate these theoretical results, we perform a four-photon experiment with = 3/4 and V = 82±6% (an extension of our previous work (Nagata et al 2007 Science 316 726)) and find a phase sensitivity 1.3 times greater than the standard quantum limit at a phase different to that which gives maximum slope of the interference fringe.

Event-synchronous cancellation of the heart interference in biomedical signals

Abstract: A two-pass adaptive filtering algorithm is proposed for cancellation of recurrent interferences such as the heart interference in biomedical signals. In the first pass, an average waveform in one period of the interference is estimated by event-synchronous (QRS-synchronous) averaging of the corrupted signal. In a second pass, an adaptive Schur recursive least squares (RLS) lattice filter is used to cancel the interference by using the event synchronously repeated estimated average waveform of the interference as an artificial reference signal. One key feature of this approach is that the ECG is only used for QRS synchronization and not directly as a reference signal for adaptive filtering. Thus the proposed algorithm can be applied to interference problems where ECG and true interference are almost synchronous but show considerably different waveforms. This is usually the case with the heart interference in biomedical signals. Both off-line and real-time implementations of the event synchronous interference canceller are described. The method is applied to the cancellation of the heart interference in magnetoencephalogram (MEG) signals and to the effective isolation of ventricular extrasystoles (VES) in magnetocardiogram (MCG) signals. Experimental results are shown. The new method typically attenuates the amplitudes of R-wave and T-wave interference components by an amplitude factor of 30 without influencing the MEG events of interest. >

Lau effect and grating imaging

Abstract: Lau imaging is shown to be a special case of generalized two-grating interference and is explained in terms of the phenomenon of grating imaging, wherein a grating is imaged by a second grating.

Topological Singularities in Wave Fields

Abstract: This thesis is a study of the natural geometric structures, arising through interference, in fields of complex waves (scalars, vectors or tensors), where certain parameters describing the wave are singular. In scalar waves, these are phase singularities (also called wave dislocations), which are also nodes (zeros of amplitude): in two dimensional fields they are points, and in three dimensions, lines. The morphology of dislocation points and lines is studied in detail, and averages of their geometrical properties (such as density, speed, curvature and twistedness) are calculated analytically for isotropically random gaussian ensembles (superpositions of plane waves equidistributed in direction, but with random phases). It is also shown how dislocation lines may be knotted and linked, and a construction of torus knots in monochromatic waves is studied in detail, using experimentally realisable beams. In vector waves, the appropriate fields are described geometrically by an ellipse at each point (the polarization ellipse). Their singularities, occurring along lines in three dimensions, are where the ellipse is circular (C lines) and linear (L lines); in two dimensional fields, possibly representing the transverse plane of paraxial polarized light waves, there are C points, but still L lines. The geometry of these singularities is considered, and analytical calculations for their densities in isotropic gaussian random vector waves are performed. The C and L singularity structures are generalised to fields of spinors using the Majorana sphere (vector fields have spin 1), and singularities in rank two tensor waves (spin 2) are briefly discussed.

Frequency modulated lasar radar

Abstract: An apparatus and a method for measuring the distance to an arbitrary target includes a radiation source producing a beam of coherent radiation the frequency of which is continuously varied. The beam is divided into a ranging beam and a reference beam. The ranging beam is coupled to a ranging interferometer, which directs a portion of the ranging beam at the target. The ranging interferometer produces a first signal indicative of the phase difference between a portion of the ranging beam directed at and scattered by the target and another portion of the ranging beam which has traveled over a path of fixed length. The reference beam is coupled to a reference interferometer. A portion of the reference beam is directed by the reference interferometer along a reference path of a predetermined length, and the phase difference between the portion of the reference beam directed along the reference path and another portion of the reference beam which has travelled over a path of a fixed length is measured. The number of fringes resulting from the wave interference produced in the ranging interferometer and the number of fringes in the wave interference pattern produced by the reference interferometer are counted and used, together with the known length of the reference path, to determine the distance of the target from the ranging interferometer.