Topic
Signal beam
About: Signal beam is a research topic. Over the lifetime, 1881 publications have been published within this topic receiving 20717 citations.
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27 Apr 2007
TL;DR: In this paper, the authors proposed a multi-conjugate adaptive optics system consisting of two phase correctors, each of which is driven by a pair of wavefront sensor phase measurements, along with an internal probe beam that samples the beam train along a common path while propagating in the opposite direction as the external signal beam or beacon wavefront that sample the turbulence.
Abstract: Imaging through turbulence using adaptive optics is limited by scintillation, even with perfect wavefront sensing and reconstruction. Such errors can be mitigated in closed loop by multi-conjugate adaptive optics systems consisting of two phase correctors, each of which is driven by a pair of wavefront sensor phase measurements, along with an internal probe beam that samples the beam train along a common path while propagating in the opposite direction as the external signal beam or beacon wavefront that samples the turbulence. With this arrangement, not only direct measurement and feedback of irradiance but also intensive and/or highly coupled nonlinear control algorithms can be avoided in favor of more conventional, simple, decentralized linear control laws. Linear stability analysis of such systems is feasible in spatial frequency domain, and nonlinear wave-optic simulations in time domain suggest that, given sufficient temporal bandwidth, rejection of combined phase and amplitude disturbances can be enhanced by a factor of two or more (as quantified by error variances or Strehl ratio logarithms). Previous studies by other authors are extended using simplified regularization methods.
3 citations
TL;DR: Not only is the two-wave mixing gain important when the photorefractive effect is used for dynamic phase demodulation, but so are the polarization shifts occurring from the mixing process.
Abstract: We studied the two-wave mixing anisotropic diffraction process in
GaAs for demodulation of static and dynamic phase encoded
signals. The static results quantitatively agreed with a previous
theoretical model for cubic crystals. This model has been described
explicitly for all beam polarizations and crystal rotation angles with
respect to the plane of incidence. Dynamic phase modulation, in
which the signal beam was phase modulated at frequency
fs and the reference beam at
fr = fs + Δf, produced a
signal at Δf that was proportional to the difference
between the static beam intensities with and without two-wave mixing
under all conditions of polarization and crystal orientation
studied. A significant dynamic output signal was produced even when
only a shift in polarization but no energy transfer occurred as a
result of the anisotropic two-wave mixing process. Therefore not
only is the two-wave mixing gain important when the photorefractive
effect is used for dynamic phase demodulation, but so are the
polarization shifts occurring from the mixing process.
3 citations
TL;DR: In this paper, the information loss due to superimposing a quasi-monochromatic thermal-noise beam on a similar signal beam is investigated for two types of noise beams, sample noise, and path noise.
Abstract: The fluctuations in a thermal beam due to the superposition of two similar thermal beams are computed. The information loss due to superimposing a quasi-monochromatic thermal-noise beam on a similar signal beam is investigated for two types of noise beams, sample noise, and path noise. In the Wien and Rayleigh–Jeans limits, the information loss j23 per macrocell is found to depend only on the signal-to-noise ratio. The relative loss in maximum obtainable information, I3,max/I2,max, for given signal and noise beams is given as well as some numerical examples.
3 citations
TL;DR: In this paper, two self-pumped phase-conjugated images at different wavelengths were successfully generated using an undoped barium titanate crystal with an offset of 2 mm.
Abstract: Two self-pumped phase-conjugated waves at different wavelengths are successfully generated using an undoped barium titanate crystal. With one signal beam at a wavelength of 514.5 nm incident to the (100) face of the crystal and the other at a wavelength of 488.0 nm incident to the opposite (100) face with an offset of 2 mm, two phase-conjugated images are produced even at high power ratios between the signal beams. The use of two different wavelengths prevents interference between the two signal beams, resulting in the generation of phase-conjugated waves over a wide dynamic range.
3 citations
TL;DR: In this paper, a broadband, nano-vibration measuring method based on the photoelectromotive force (photo-EMF) effect of semiconductor crystal was presented, where a He-Ne-laser homodyne interferometer system was used as a light source and a GaAs crystal is used as photodetector.
Abstract: A broadband, nano-vibration measuring method based on the photoelectromotive force (photo-EMF) effect of semiconductor crystal is presented. A He-Ne-laser homodyne interferometer system is used as a light source and a GaAs crystal is used as a photodetector. The signal beam, which is modulated by the vibration, interferes with the reference beam, and a vibrating interference pattern is created on the surface of the GaAs crystal. Due to the photo-EMF effect, an alternating current signal, which relates to the vibration, is produced. We found the optimum parameters for the measurements by adjustments of the intensity ratio of the two beams, the angle between the beams and the interelectrode spacing on the GaAs crystal. The system can detect the vibration amplitude about several nanometers. The results of measurements of the vibrations of the PZT sample are well coincided with those obtained by TEMPO200 (Bossa Nova Technologies, America) system.
3 citations