Phase conjugation

About: Phase conjugation is a research topic. Over the lifetime, 3694 publications have been published within this topic receiving 49099 citations.

Ultrasonic phase conjugation

Abstract: A real‐time ultrasonic phase conjugator is reported. The scheme is based on sampling the wave front in space by means of a transducer array and mixing the signal from each array element with a second harmonic signal using nonlinear circuit components. The same array then retransmits the phase conjugated wave front into the medium. The technique is demonstrated at 300 kHz using a 20‐element transducer array, and it is shown that efficient phase conjugation is possible up to spatial frequencies of ±80°.

Intensity-based adaptive optics with sequential optimization for laser communications

Abstract: Wavefront distortions of optical waves propagating through the turbulent atmosphere are responsible for phase and amplitude fluctuations, causing random fading in the signal coupled into single-mode optical fibers. Wavefront aberrations can be confronted, in principle, with adaptive optics technology that compensates the incoming optical signal by the phase conjugation principle and mitigates the likeliness of fading. However, real-time adaptive optics requires phase wavefront measurements, which are generally difficult under typical propagation conditions for communication scenarios. As an alternative to the conventional adaptive optics approach, here, we discuss a novel phase-retrieval technique that indirectly determines the unknown phase wavefront from focal-plane intensity measurements. The adaptation approach is based on sequential optimization of the speckle pattern in the focal plane and works by iteratively updating the phases of individual speckles to maximize the received power. We found in our analysis that this technique can compensate the distorted phasefront and increase the signal coupled with a significant reduction in the required number of iterations, resulting in a loop bandwidth utilization well within the capacity of commercially available deformable mirrors.

Dye laser amplifiers.

Abstract: A dye laser amplifier is formed by a stimulated brillouin scattering (SBS) dye cell which receives both dye laser light to be amplified and a pump beam along a common optical path. Phase conjugation and amplification of received energy are reflected from the SBS cell. The cell comprises an SBS medium that is a solvent for the laser dye used. Typical SBS mediums are methanol, acetone, isopropyl alcohol, etc. Typical dyes are Rhodamine 6G, Rhodamine B, Rhodamine 560, Rhodamine 575, Sulphorhodamine B, Kiton Red, DCM, Courrarun 523, etc. A plurality of amplifiers may be connected in series to provide increased amplification. The action of the phase conjugation corrects optical distorsions, thereby preserving beam quality and bandwidth even after multiple amplifications. A typical dye laser beam of 590 nm wavelength, about 1 μJ may be amplified to about 120 mJ, with a 17 nsec pulse width, and <500 MHz bandwidth.

Experimental investigations of stimulated Brillouin scattering beam combination

Abstract: We conducted an experimental investigation of beam combination of two beams by stimulated Brillouin scattering (SBS) to determine the conditions under which good phase locking, piston conjugation, and aberration correction could be achieved. Test parameters that were varied included bandwidth, f-number, near- and far-field separation between beams, power ratio between beams, beam aberrations, and polarization mismatch between the beams. The experiments were performed at 532 nm with n-hexane as the SBS medium. Piston-conjugation accuracy was measured by using fringe stability with conventional interferometry and by using extinction in a wave-front-reversing interferometer. The best piston conjugation was obtained when we maximized the overlap of the SBS interaction volumes of the two beams by minimizing the beam separation in the near and the far fields.