Hirofumi Fujiwara

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.

Transient phase conjugation by degenerate four-wave mixing in saturable dyes

Transient phase conjugation by degenerate four-wave mixing in saturable dyes is investigated theoretically and experimentally. Two special cases are examined: (1) the case in which two pump waves and a probe wave are simultaneously turned on and (2) the case in which the pump waves are turned on well before the incidence of the probe wave. For case (1) a peak appears in the transient reflectivity for high pump intensity, while for case (2) the reflectivity increases monotonically with time up to the steady-state value irrespective of the value of the pump intensity.

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 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.

Excited-state absorption and pump propagation effects on optical phase conjugation in a saturable absorber

Phase conjugation by degenerate four-wave mixing in a saturable absorbing medium with a relatively long-lived excited state is analyzed; the analytical results are compared with experimental results. We propose a four-level model and take into account the effects of both excited-state absorption and pump propagation to explain the experimental results, which could not be explained by the models proposed previously. The numerical result predicts that the value of the phase-conjugate reflectivity as a function of the pump intensity is maximum at a certain absorbance (as absorbance increases) that is dependent on the cross section of the excited-state absorption. The present analysis explains most observations in the experiment, which was performed with a saturable-dye-doped polymer film as the saturable absorbing medium.

Effects of absorption on the propagation constants of guided modes in an asymmetric slab optical waveguide

Abstract We investigate how bulk losses of the thin film waveguide core influence the propagation constants of the modes of an asymmetric slab waveguide. Film absorption of a few hundreds inverse centimeters causes measurable shifts of the effective refractive indices, particularly for modes of higher order. We evaluate the error, that would be introduced into measurements of the refractive index and film thickness by the prism coupler method, if existing film losses were to be ignored.

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.

Power transfer by nearly degenerate two-wave mixing in a saturable dye-doped film

We analyze power transfer by nearly degenerate two-wave mixing (TWM) in a saturable absorbing medium by assuming a three-level model for the saturable absorbing medium. The theoretical results are compared with the experimental ones by using an erythrosin-B-doped polymer film as the saturable absorbing medium. Pump-intensity-dependent behavior of the TWM gain that is predicted by the theory was experimentally verified with this dye-doped film. The saturation intensity Is and the detuning parameter δ of erythrosin B were estimated by the comparison of the theory and the experiment: Is ≈ 1.6 W/cm2, δ ≈ 1.1. The theoretical curves calculated from these values are in good agreement with the experimental curves near resonance, whereas they disagree with the experimental results as the laser frequency shifts off resonance.

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.