Kazuo Nakagawa

Phase conjugation in fluorescein film by degenerate four-wave mixing and holographic process

Abstract Phase conjugation is performed in a fluorescein film by a cw Ar ion laser of the wavelength 0.488 μm in a degenerate four-wave mixing (DFWM) configuration. It becomes apparent that the phase conjugate wave is generated simultaneously by not only DFWM but also a holographic process and that the DFWM and holographic components of the phase conjugate wave have different time constants.

Generation of a phase-conjugate wave in methylred-doped PMMA and gelatin

Abstract Methylred-doped polymethyl methacrylate (PMMA) can generate a phase-conjugate wave due to degenerate four-wave mixing (DFWM) and holographic processes while methylred-doped gelatin can generate only through the DFWM process. The phase-conjugate wave due to the holographic process differs from that due to the DFWM process in the respect that light induces longlived photochemical changes of host matrix and/or guest dye in refractive index and/or absorption coefficient.

Real-time image subtraction and addition using two cross-polarized phase-conjugate waves

Abstract A method of real-time image subtraction and addition is demonstrated with an erythrosin-B-doped polyvinyl alcohol film. In a degenerate four-wave mixing configuration consisting of two-step processing, this dye-doped film acts as an image-encoded hologram in the first step and also as a phase conjugator in the second step. In the second step, an image subtraction or addition can be performed by observing two mutually cross-polarized phase-conjugate waves through an analyzer.

Real-time and double-exposure phase-conjugate interferometries using eosin-doped gelatin film

Abstract Both real-time and double-exposure phase-conjugate interferometries are demonstrated with an eosin-doped gelatin film. The eosin-doped film can generate phase conjugate waves simultaneously or separately by degenerate four-wave mixing (DFWM) and holographic processes. The holographic process differs from the DFWM process in the respect that the eosin-doped film can record spatial information on light like a hologram. The DFWM component has a response time in the order of milliseconds, which is by a factor of four faster than that of the holographic component. The difference in their response times in the two processes is important in real-time and double-exposure phase-conjugate interferometries.

Phase conjugation in methyl-orange-doped PVA films by photoinduced anisotropy

The influence of photoinduced anisotropy (dichroism and birefringence) in methyl-orange-doped polyvinyl alcohol film upon optical phase conjugation is investigated. The reflectivity of the phase-conjugate (PC) beam due to degenerate four-wave mixing (DFWM) is measured under the condition that the polarization states of a probe and two pump beams are mutually orthogonal. The more efficient PC beam generates at 515 nm rather than at 488 nm. At 515 nm, the reflectivity of the PC beam exceeds 10 percent about 30 minutes after the initiation of DFWM. It was found that birefringence rather than dichroism contributes to the generation of the PC beam at 515 nm.

Efficient Optical Phase Conjugation in Methyl-Orange-Doped Polyvinyl Alcohol Film

An efficient optical phase conjugate (PC) wave in methyl-orange (MO)-doped polyvinyl alcohol (PVA) films by degenerate four-wave mixing (DFWM) is reported. As the wavelength concerned was far from the absorption center of the MO dye, a PC wave was generated more efficiently. For the configuration of mutually orthogonal-polarized pump and probe waves the PC reflectivity reached 30% at a wavelength of 531 nm and an intensity of 1 W/cm2 of a cw krypton-ion laser, by using a film with absorbance (=the product of the small-intensity absorption coefficient and the film thickness) of 2.1 at 531 nm. It was found that the photoinduced birefringence resulting from trans-cis isomerization, i.e., the real part of the nonlinear susceptibility χ2112, mainly contributed to generation of the PC wave at 531 nm.

Contribution of population or thermal grating to phase conjugation in saturable xanthene-dye-doped polymer films

The time constant of a decaying phase-conjugate (PC) signal was measured as a function of a grating period in polyvinyl alcohol films doped with xanthene dyes such as erythrosin B, eosin Y, and uranin. The time constant was independent of the grating period and was of the same order as the time required for the population grating of each dye to decay. These experimental results indicated that there was a population grating contribution but not a thermal grating contribution in the generation of PC signals by these saturable xanthene-dye films.

Phase-Conjugate Interferometry Using Degenerate Four-Wave Mixing And Holography

An erythrosin-doped polyvinyl alcohol (PVA) film can generate phase-conjugate (PC) waves simultaneously by degenerate four-wave mixing (DFWM) process with a fast response time and holographic process with a slow one. The DFWM component with a response time of about 1 msec results from saturable absorption in erythrosin dyes, while the holographic component with a response time of tens sec is generated from a hologram recorded in the erythrosin/ PVA film. The PC reflectivities for both components exceed one percent. In combination of these two processes, we demonstrate that the erythrosin/PVA film is available for real-time and double exposure PC interferometries with a cw argonion laser.

Real-time image subtraction by phase conjugation using an erythrosin-B-doped-PVA film

Polymer lightguides ofPMMA, doped with azo dyes are investigated with respect to their opto-optical or all optical properties. The TRANS-CIS photoisomerisation of the azo dyes leads to reasonable polarization dependent optically induced refractive index changes. These are studied in planar lightguides and in leaky guides. With light at the absorption edge all optical properties are studied leading to a possible application as bistable device.

Polarization-dependent phase-conjugate reflectivity in randomly oriented saturable absorbers

Polarization dependence of phase-conjugate reflectivity by degenerate four-wave mixing is clarified theoretically and experimentally in a saturable-dye-doped polymer film. 1. _INTRODUCTLON A dyedoped film in which optically anisotropic saturable dye molecules are rigidly fixed and are randomly oriented has been used as a nonlinear material which can generate a phase-conjugate (PC) wave by degenerate four-wave mixing13 (DFWM). Such a film can generate a PC wave which has the same polarization state as the probe wave even for a probe wave orthogonally polarized to two pump waves. Tompkin et. al. 4 showed that in such a phase conjugator the nearly perfect vectorial phase conjugation can be obtained at the pump intensity near the saturation intensity of the phase conjugator. In this work following the analysis of Tompkin et. al. 4 closed-form solutions for the PC reflectivities in the dye-doped film are derived for two states of the polarization: the probe wave is polarized parallel and perpendicular to the pump waves. Some experimental results are also demonstrated in an eosin-Y-doped poly-vinyl alcohol (PVA) film and are compared with the theoretical results. 2. POLARIZATION DEPENDENT PC REFLECTIVITIES Dye molecules are modeled as dipoles which are randomly and uniformly oriented and are rigidly fixed in a solid matrix. We assume that each dye molecule has only one component of transition dipole moments at a wavelength considered5. An induced dipole moment of each dye molecule by