Phase-conjugate Replica Research Articles

Self-pumped phase conjugation in a liquid crystal light valve with a tilted feedback mirror

We report self-pumped phase conjugation in a photorefractive liquid crystal light valve with a tilted feedback mirror. This is a new scheme for the self-generation of a phase-conjugate replica and can in general be applied to thin nonlinear layers, opening the way to distortion-correction applications of thin media.

Real-time pseudoscopic image reconstruction by a conjugate wave in LiNbO3:Fe

Experimental scheme to generate phase conjugate or pseudoscopic replica of the object wave by illuminating the hologram with a conjugate of the reference wave is carried out. The hologram is formed in the photorefractive LiNbO3:Fe crystal by the interference of an object wave and a converging reference wave. Subsequently the hologram on illumination with the conjugate diverging wave forms the desired pseudoscopic replica of the object wave. This scheme is then extended to an interferometric application.

Self‐reading geometry conjugators with copper‐doped photorefractive (K<sub>0.5</sub>Na<sub>0.5</sub>)<sub>0.2</sub>(Sr<sub>0.75</sub>Ba<sub>0.25 </sub>)<sub>0.9</sub>Nb<sub>2</sub>O<sub>6</sub> crystals and their applications

The dependence of the reflectivity on the distance of the spots corresponding to the two incident beams on crystals is measured and analyzed in self-reading geometry conjugators (SRGCS) with Cu-doped single-domain photorefractive (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 CrYStals. Double peaks in some dependence are observed and used to investigate the mechanism of SRGCS. The dynamic features of the two phase-conjugate beams and the decrease of the specular reflectivity of the probing beam in SRGCS are observed and analyzed. A bump in the probing beam’s phase-conjugate replica as a result of a short pause of the incident pumping beam is analyzed in terms of the pyroelectric effect and photovoltaic effect. A comparison of results on conjugation fidelity, response rate, and threshold between CAT self-pumped phase conjugators and SRGCS is given. Real-time vertical and horizontal high-pass filtering, real-time double-exposure interferometry, and detection of the blemishes caused by amplitude defects in optical systems are demonstrated experimentally. The corresponding theoretical analyses are also given.

Resonance fluorescence spectrum of an atom near a phase conjugator

Resonance fluorescence by an atom near the surface of a phase conjugator is studied. The atom is irradiated by a finite-linewidth laser beam, and the bandwidth is modelled by a randomly fluctuating phase. Expressions for the steady-state atomic density operator and the resonance fluorescence spectrum are obtained. For a small laser linewidth the spectrum contains two delta peaks: the usual peak at the laser frequency and its phase-conjugate image. In the limit of separated lines the spectrum consists of the Mollow triplet and its phase-conjugate replica. In the image triplet the positions of the fluorescence line and the three-photon line are reversed, as compared with the original triplet. Also, the intensity of the image spectrum is distributed differently over the three lines.

Mutually pumped phase conjugation in photorefractive strontium barium niobate: theory and experiment

Two mutually incoherent laser beams can generate each other’s phase-conjugate replica by sharing holograms in a photorefractive strontium barium niobate (SBN) crystal. The path of each beam inside the SBN crystal uses three internal reflections at the crystal faces. We discuss phase-conjugate imaging, moving gratings induced by an applied electric field, the time response of grating formation, and the dependence of the phase-conjugate reflectivity on the incident-beam ratio. Also, we derive the amplitude coupled-wave solutions for mutually pumped phase conjugators with two coupled gratings, and we compare the theoretical results with our experimental results.

Mutually pumped phase conjugation in Kerr media and the effects of external seeding

Mutually pumped phase conjugation, a process by which two incident laser beams can mutually pump each other to generate the phase-conjugate replica of the other beam, is studied in a transparent Kerr medium with an electrostrictive nonlinearity. The nonlinear medium acts as a phase-conjugating mirror to both of the incident beams and generates their Stokes-shifted phase-conjugated outputs by the nearly degenerate four-wave mixing process. Our results show that this process will occur only if the coupling strength, defined by the product of the Kerr amplitude gain coefficient, the total input intensity, and the interaction length, is above the threshold value of 2. If the intensity of one of the input beams exceeds the threshold value and the second input beam is weaker than the first, then the weak beam is phase conjugated with a large reflectivity that has a maximum value of the intensity ratio of the strong to the weak input beam. For negligible absorption in the medium, a complete transfer of energy of both the incident beams into the phase-conjugate beams can occur for finite interaction lengths that are only slightly larger than the threshold value. Seeding the oscillation beams tends to lower the phase-conjugate power reflectivities, probably because of increased contribution from the competing two-wave mixing process.

Storage and phase conjugation of multiple images using backward-stimulated echoes in Pr^3+:LaF_3

We have observed long-term storage and phase conjugation of multiple images by using a backward-stimulated echo scheme in the 3H4 -3Po transition of Pr3+:LaF3 crystal. The temporal order of the multiple-echo images is the reverse of that of the input images. Each of the echo images is a phase-conjugate replica of the input images and lasts as long as IS sec. This constitutes, in principle, the movie using a stimulated photon echo.

Phase conjugation in an optical fibre

We report experimental studies of phase conjugation by stimulated Mandelstam Brillouin scattering in multimode fibres. A dramatic decrease in the threshold power as compared to that (104 to 105 W) typically observed in conventional media was achieved. A ruby pulsed pump with ∼ 500-ns pulses was used. For the 7-m-long fibre, the threshold power was ≈ 50 W, the degree of phase conjugation was almost one, the pump-to-Stokes conversion efficiency was about 80%. For the 130-m-long fibre, the threshold power decreased to ≈ 10 W and the pump-to-Stokes conversion efficiency reached 100%. Polarization scrambling was observed in the 130-m-long fibre, but the Stokes wave with polarization coinciding with that of the pump wave was a phase-conjugate replica of the pump, as before.

Four wave mixing in a waveguide — Two radiation and two guided modes interaction

The theory of nonlinear interaction between two radiation modes as a pump waves and two guided modes: the input beam and the generated backward beam, is presented. In the degenerate case, for all waves at the same frequency, we demonstrate the possibility of the input wave amplification and the phase conjugate replica generation as well as of the interaction between modes of different polarization. The nondegenerate case, with the phase matching achieved by pump waves amplitude modulation is also considered.

Degenerate forward four-wave mixing in LiNbO3

Abstract Forward four-wave mixing in LiNbO3:Fe is used for generation of a phase-conjugate replica of unfocused beams of a CW He-Cd laser. The possibility of partial self-compensation for static and light-induced optical inhomogeneities of a nonlinear sample is demonstrated.

Theory of a self-pumped phase conjugator with two coupled interaction regions

We present a plane-wave analysis of a recently demonstrated self-pumped phase conjugator. This device uses four-wave mixing to produce the phase-conjugate replica of an incident optical wave. All the waves are derived from the single incident wave: there are no externally supplied pumping beams. We consider the case of four-wave mixing in two interaction regions coupled by simple reflection. We calculate the phase-conjugate reflectivity as a function of coupling strength, taking into account imperfect coupling between the two interaction regions, and show that there is a threshold coupling strength below which the reflectivity is zero and above which the reflectivity is multiple valued. We also compute the coupling strength per unit length for a photorefractive crystal of barium titanate.

Phase-conjugate reflection from a temporal dielectric boundary

Electromagnetic theory predicts the generation of a backward-traveling wave when the velocity of a forward-propagating electromagnetic field inside a dielectric medium varies as a function of time. The backward wave is a phase-conjugate replica of the incident field and possesses some interesting properties. The mechanism giving rise to the phase-conjugate wave is a temporal analog of the Fresnel reflection that occurs when an electromagnetic field encounters a spatial dielectric boundary. We derive the dependence of the phase-conjugate reflectivity on the rate of change of the dielectric constant and show the difficulty of observing this type of phase-conjugate wave.