We theoretically discuss the use of holography to achieve the phase conjugation of temporal signals. The reversal of a particular asymmetric pulse envelope is experimentally demonstrated. The holographic material is a photorefractive crystal used in a four-wave mixing configuration.
We describe an experiment in phase conjugation using holographic degenerate four-wave mixing with picosecond pulses. Spatial and temporal distortions are simultaneously introduced on the probe beam, respectively, by a ground glass and a Gires-Tournois interferometer. We experimentally show that after it recrosses the ground glass we obtain a time reversed pulse on the reconstructed beam. Its temporal shape is the same as that without the ground glass. We theoretically discuss this result and show that in our configuration the temporal effect depends only on the hologram dimension parallel to the direction of propagation of the beam, while the spatial phase conjugation is related to the dimensions in the perpendicular plane.
Polarization-preserving phase conjugation of an arbitrarily-polarized multiple-pulse optical signal by using a modified scheme of time-and-space-domain holography is predicted theoretically and demonstrated experimentally. The experimental results obtained by utilizing octaethylporphin-doped polystyrene at 1.8 K as a spectrally-selective recording material indicate that in full accordance with the theory, the reconstructed phase-conjugated replicas of the multiple-pulse optical signal appear temporally reversed and have conjugated wavefronts while the original temporal and spatial dependence of the polarization state is restored. Thus, complete phase conjugation of an optical signal is demonstrated.>
Summary form only given. In this tallk I will try to supplement what I learned in the field. Here are the topics to be touched on. The order is not historical, but serves a tutorial purpose. 1. Time reversibility (TR) of optical wave propagation. 2. Mathematical description of TR in terms of complex amplitudes and complex conjugate amplitudes. 3. Static holography by real and conjugate images. 4.Static holography: illumination by counterpropagating reference waves at the recording and reconstruction stages. 5. Dynamic holography/four-wave mixing for phase conjugation (R. Hellwarth, A. Yariv, Yariv-Pepper instability. 6. Delayed and hidden holograms, photon echoes, electro-acoustic echoes. 7. Two-photon coherence, fast nonlinearities and three-wave mixing via X(2) nonlinearity. 8. Yet unrealized: Bragg (periodic domain). Time-domain phase conjugation: reversal of chirp and compensation of the dispersion spread in fibers. 10. Why a laser may (and may not) oscillate at a single transverse mode: discrimination of gain/loss. 11. Phase conjugation via stimulated Brillouin scattering (V.V. Ragulsky; V.V. Shkunov). 12. Brillouin-enhanced four-wave mixing for phase conjugation, ten to the tenth power amplification of the image (G.A. Pasmanik). 13. Photorefractive crystals: nonlinear response at low intensity at a cost of long build-up time. 14. Double phase conjugation 15. Feinberg's cat and cat conjugator.
A method of polarization (vector) wavefront reversal by four-wave mixing in a photoanisotropic material is described. Jones matrices, describing the dynamic holographic gratings recorded in the material at arbitrary polarization of the signal wave, are derived. They are employed to define the conditions for generating a wave that is fully conjugate (by polarization as well) to the signal wave. The way to achieving these conditions by optically controlling the anisotropy of the nonlinear medium is demonstrated experimentally.
This thesis describes theoretical and experimental aspects as well as potential applications in the field of coherent optics known as Phase Conjugate Optics (PCO). By utilizing nonlinear optical techniques, real-time or wavefront reversal of an arbitrary incident electromagnetic field can be realized. The nonlinear optical interaction gives rise to what is referred to as the phase conjugate (of the incident monochromatic wave) by performing the operation of complex conjugation upon the incident wave's complex spatial amplitude in real time. This conjugate wave, which is also designated as being a wavefront, has the property of exactly retracing the path of the incident field. The ability of the conjugate wave to correct for inhomogeneous linear and nonlinear (intensity-dependent) aberrations as well as polarization distortions is proved. In particular, the theory of a degenerate four-wave nonlinear optical interaction as providing for the conjugator is presented. The effects of linear and nonlinear losses upon this interaction are discussed. The quantum mechanical origin of the third order nonlinear optical susceptibility responsible for the four-wave mixing process is analyzed for both single and two-photon allowed transitions in an atomic (or molecular) system. The analogies of four-wave mixing with that of real-time holography are discussed. The theory of conjugation via four-wave mixing in optical waveguides is presented.
Several of the above characteristics of conjugate fields are verified experimentally where conjugate fields via degenerate four-wave mixing were observed both in the bulk and in waveguide geometries, using carbon disulfide as the nonlinear medium. Amplified time-reversed wavefront generation as well as a mirrorless optical parametric mode of oscillation have been observed, both in agreement with theoretical predictions.
Potential applications of PCO are discussed in three different regimes: spatial-frequency, temporal-frequency, and spatial/temporal frequency domains. In the first category, the ability of PCO to correct for image modal dispersion in optical waveguides as well as the use of PCO to perform real-time coherent image processing and nonlinear microscopy is discussed. Temporal-frequency domain applications of PCO to be analyzed include the use of a nearly degenerate four-wave mixing process as a narrowband, wide field-of-view optical filter, capable of an amplified bandpass. The ability of a PCO interaction to renarrow (transform limited) optical pulses which have been temporally spread due to propagation through (group velocity) dispersive channels is analyzed. A potential application of PCO in the field of nonlinear laser spectroscopy is presented. Specifically, the scattering of a probe photon off a two-photon coherent state (created in a three-level atomic system) is shown to yield a conjugate replica. This conjugate replica is capable of providing sub-Doppler width resolution of the two-photon resonance. Further, in the transient regime, the optical free-induction decay of the conjugate wave is capable of yielding detailed spectral features of the three-level system such as the anharmonic contribution to a (nearly) harmonic potential. This technique, performed in the time domain, is known as [alpha]-beat spectroscopy.
Finally, a detailed theoretical and experimental study is presented of a laser resonator in which one (or both) of the mirror(s) comprising the optical cavity is replaced by a conjugate mirror (PCM). This novel resonator, which is termed a conjugate resonator (PCR), combines many of the spatial- and temporal-frequency aspects of PCO interactions discussed above. The stability criterion, transverse and longitudinal mode spectra, and the PCR output energy, as well as the frequency locking features of the laser modes to the PCM are discussed.