Signal beam

About: Signal beam is a research topic. Over the lifetime, 1881 publications have been published within this topic receiving 20717 citations.

Time gated imaging through scattering material using polarization and stimulated raman amplification

Abstract: An apparatus for imaging into or through scattering materials (17) includes a source (20) for producing a broadband laser reference beam (R) and a Stokes illumination beam (Si) correlated to the reference beam The Stokes illumination beam is transmitted into the scattering material to obtain a Stokes signal beam (Ss) having a first image carrying component and a first nonimage component The reference beam and the Stokes signal beam are then separately delayed (Rd, Sd) and polarized (Rp, Sp), after which they are combined to produce a combined beam (C) having a Stokes component and a reference component A Stimulated Raman amplifier (30) responsive to the combined beam produces an amplified signal beam (A) in which the image carrying component has been amplified by a higher gain factor than the nonimage component

Device for coherent addition of laser beams

Abstract: Device for coherent addition of laser beams including several optical amplifiers in parallel pumped by a beam coming from a master laser. The beams emitted by these amplifiers are transmitted to a non-linear material and play the role of pump beams. The non-linear material also receives a signal beam derived from the master laser. The various beams of the amplifiers are therefore added in the non-linear material along the direction of the signal beam.

Two‐wave mixing with time‐modulated signal in Bi12SiO20 theory and application to homodyne wave‐front detection

Abstract: We theoretically analyze a two‐wave mixing interaction in photorefractive Bi12SiO20 crystals in which the amplitude of the signal beam is time modulated at high frequency. Calculations of the photoinduced space‐charge field are derived for a sinusoidal modulation of the input signal. Due to the time‐integrating properties of the nonlinear crystal, the transmitted signal exhibits a differential gain when the modulating frequency is much greater than the inverse of the material response time. Application to coherent homodyne detection of wave fronts carrying spatial and temporal information is also presented.

Beam intensity striations and applications.

Abstract: The single-element spectrogram for a continuous broadband signal, plotted as a function of range, has been shown to exhibit striated bands of intensity maxima and minima. The slope of the striations is an invariant of the modal interference and is described by a waveguide invariant parameter “beta.” The striation pattern is analyzed and modeled in this paper for the beam outputs of a horizontal line array obtained by conventional beamforming. Array beamforming makes it possible to measure the waveguide invariant parameter for weak signals due to the enhancement of signal levels by the array gain over that of a single element. It is shown that the signal beam spectrogram as a function of range exhibits the same striation pattern as that (predicted) for a single element. Specifically, for a broadside signal, the beam striation is identical to that of a single-element plus a constant signal gain. For a nonbroadside target, the signal beam intensity will be modified by a frequency-bearing dependent signal gain due to the signal spread over multiple beams, nevertheless the beam spectrogram retains the same striation pattern (slope) as for a single element. The sidelobe beams (outside the canonical cones containing the signal arrivals) exhibit an entirely different striation pattern as a function of frequency and range. For array processing, it is shown that a fast range-rate, close range target and a distant, slow range-rate interference source will have a different striation pattern (slope) in the corresponding beam spectrograms as a function of time, assuming no prior knowledge of the source ranges. The difference in the striations between the beam spectrograms can be used in array processing to suppress the interference contribution. A 5–7 dB interference suppression is demonstrated using simulated data.

Contour mapping of the spatiotemporal state of polarization of light.

Abstract: A novel interferometric polarimeter capable of mapping a spatiotemporal change in the state of polarization (SOP) of light is described. The polarimeter has a reference beam of light with two orthogonal linearly polarized components that interfere with the counterpart components of an elliptically polarized signal beam. The resultant interference pattern is recorded by a computer by the use of a wideband metal-oxide semiconductor video camera. The interference pattern reduces to the ellipticity and azimuth of the ellipse at an instant of time, by which the spatiotemporal change in the SOP is mapped. No optical elements are used for the control of polarization in the polarimeter, and this allows for the mapping of a rapid change in the SOP. Successful experiments are demonstrated by generating an elliptically polarized beam whose SOP varies in space and time.