Phase-conjugate Interferometer Research Articles

Laser-diode phase-conjugate interferometer for distance measurement

A laser-diode (LD) phase-conjugate interferometer with two self-pumped (cat) phase-conjugate mirrors instead of two ordinary mirrors is constructed for distance measurement over extended ranges. The measurement is based on frequency-modulated continuous-wave techniques. A wide-tunable LD with an external cavity is used as a light source in a phase-conjugate wavefront-matched interferometer. The interferometer is insensitive to spatially nonuniform phase distortion, but can only detect the spatially uniform phase change introduced by the displacement of one cat mirror. The linear regression of the measured beat frequency as a function of the distance has been ascertained.

A phase-conjugate Twyman-Green interferometer with increased sensitivity for laser beam collimation

A Twyman-Green interferometer having a phase-conjugate mirror in one arm and double mirror in another arm is described to measure divergence and to check the collimation of a laser beam. It uses an internally self-pumped phase conjugation in BaTiO3 crystal as phase-conjugate mirror. The use of double mirror gives a dual interference field which results in improved sensitivity in collimation testing. The dual-field interferogram is also useful in easily distinguishing between the divergent and convergent nature of the test beam. Measurement results are presented.

A phase-conjugate Twyman-Green interferometer with increased sensitivity for laser beam collimation

A phase-conjugate Twyman-Green interferometer with increased sensitivity for laser beam collimation

Self-pumped phase-conjugate interferometer with a photorefractive iron-doped lithium-niobate crystal

A single object wave is amplitude divided by a beam splitter into two waves of equal intensity that are made to interfere at the back surface of an iron-doped lithium-niobate crystal so that the normal to the back surface is the angular bisector of the input waves. The interference results in the formation of a phase grating (Bragg grating) in the volume of the crystal. These waves are diffracted at the Bragg grating on both the front focal plane and the back focal plane of the crystal. The wave diffracted in the back focal plane from the Bragg grating and counterpropagating to the incident wave is observed to be the phase conjugate of the input object wave. The wave diffracted in the front focal plane of the Bragg grating is incorporated into the design of an interferometer to measure a specific in-plane displacement of the object wave. It is theoretically evaluated and experimentally demonstrated that interferometers such as those that incorporate conjugate-wave pairs are highly sensitive.

Exact measurement of flat surface profiles by object shifts in a phase-conjugate Fizeau interferometer

We propose a method of exact measurement of flat surface profiles in a phase-conjugate Fizeau interferometer. Aberration of lenses causes an undesirable phase distribution in the interference signal of the phase-conjugate Fizeau interferometer. To eliminate this phase distribution, we shift the object in two directions orthogonal to each other and we get difference values of the surface profile of the object. Additional displacements of the object surface involved in the shifts lead to some small errors in the difference values. We estimate an exact surface profile by solving the difference equations. Characteristics of the method are made clear through computer simulations and measurements of a 40-mm-diam flat mirror.

Response characteristics of a self-pumped phase-conjugate mirror to spatially nonuniform phase changes of an incident wave and their applications

The response of a self-pumped phase-conjugate mirror to spatially nonuniform phase change of incident wave is examined with a phase-conjugate Fizeau interferometer. The experimental results make it clear that the spatially nonuniform phase change of the incident wave is not reversed by the self-pumped phase-conjugate wave (SPPCW) immediately after the phase change, and the decrease of phase-conjugate reflectivity caused by the nonuniform phase change is proportional to the nonuniformity of the phase change. The phase characteristic of the SPPcw makes the phase-conjugate Fizeau interferometer for surface profile measurements insensitive to object vibrations. The reflectivity characteristics enable us to measure the nonuniform phase change by detecting the intensity of the SPPCW.

Phase-conjugate shear interferometer with multiple wavelengths

Optical phase conjugation and two-wavelength recording in a photorefractive crystal BaTiO 3 is used for real-time lateral-shear interferometry. Dispersion in uniaxial BaTiO 3 crystal is used to provide perfect phase matching for two gratings of different spatial frequencies. Theoretical predictions of possible geometries are experimentally verified. The magnification effect and modulation of diffraction efficiency due to recording-reconstruction with different wavelengths are also presented.

Determination of resonant and nonresonant third-order nonlinearities of organic molecules by phase-conjugate interferometry

We have used a phase-conjugate interferometer to determine the real and imaginary parts of the third-order hyperpolarizability of 3,3'-diethyloxadicarbocyanine iodide (DODCI) and 4-methoxy-4'-nitrostilbene (MONS) at 1064 nm. For DODCI the values are enhanced by a two-photon resonance, and the two-photon extinction coefficient is determined. However, the nonlinear loss of DODCI is dominated by linear absorption from the two-photon excited state. We could not observe linear or nonlinear absorption for the MONS solutions, and we have determined the nonresonant third-order hyperpolarizability for this molecule.

Effects of nonlinear phase shifts on the performance of a phase-conjugate interferometer

We present a theory of the effects of various sources of nonlinear phase shifts on the performance of a phase-conjugate interferometer that uses degenerate four-wave mixing in the retroreflected pump-beam configuration in determining the complex (magnitude and phase) third-order nonlinear susceptibility of novel nonlinear optical materials. Our analysis reveals that the performance of the interferometer is insensitive to the net nonlinear phase shift acquired by the pump wave in a double pass through the nonlinear material. However, the interferometer is susceptible to nonlinear phase shifts through the four-wave mixing process. As a consequence, under certain conditions a finite phase is measured by the interferometer for the real third-order susceptibility of a lossless nonlinear material. This measured phase depends on the intensity imbalance between the forward and the backward pump beams as well as the intensity of the probe beam. The effects of the intensity imbalance between the pump beams on the measured phase can be compensated for by a judicious choice of the intensity of the probe beam.

Time-delay Fizeau phase-conjugate interferometer

A time-delay Fizeau phase-conjugate interferometer is constructed by using a BaTiO(3) crystal in a degenerate four-wave-mixing configuration. The slow response time of BaTiO(3) is used to build a phase-conjugate mirror that functions as a holographic memory. An optical wave and its time-delayed version are stored inside the crystal sequentially while their phase-conjugate waves are generated simultaneously. Superposition of the two phase-conjugate waves produces an interferogram as a result of the relative phase change of the input waves. The simplicity and real-time operation of this technique lead to several advantages over the conventional holographic interferometry. The use of photorefractive crystal eliminates the darkroom process and reposition procedure. A higher accuracy can be achieved because the interfering waves are phase-conjugate waves. The principle of this technique is presented and the experimental results and its applications are discussed.

Tunable self-reference phase conjugate interferometer

We propose a versatile self-reference phase conjugate interferometer which is based on degenerate four-wave mixing in a photorefractive crystal. A crystal of BaTiO(3) is used to store a wavefront which is compared to its displaced version at a later time. Tunable transverse and longitudinal displacements can be easily given to a wavefront. A theoretical description and experimental results of this interferometer are presented.

Laser beam collimation using a phase conjugate Twyman-Green interferometer

This paper presents an improved technique for testing laser beam collimation using a phase conjugate Twyman-Green interferometer. The technique is useful for measuring laser beam divergence. It is possible using this technique to detect the defocusing of the order of one micrometer for a well corrected collimating lens. A relation is derived for the defocusing that can be detected by the phase conjugate interferometer.

Phase conjugate Twyman-Green interferometer for testing spherical surfaces and lenses and for measuring refractive indices of liquids or solid transparent materials

The present paper describes an application of a phase conjugate Twyman-Green interferometer using barium titanate as a self-pumping mirror for testing optical components like concave and convex spherical mirrors, and lenses. The aberrations introduced by the beam splitter while testing concave or convex spherical mirrors of large aperture are automatically eliminated due to self-focussing property of the phase conjugate mirror. There is no necessity for a good spherical surface as a reference surface unlike in classical Twyman-Green interferometer or Williams interferometer. The phase conjugate Twyman Green interferometer with a divergent illumination can be used as a test plate for checking spherical surfaces. A non-destructive technique for measuring the refractive indices of a Fabry Perot etalon by using a phase conjugate interferometer is also suggested. The interferometer is found to be useful for measuring the refractive indices of liquids and solid transparent materials with an accuracy of the order of ± 0.0004.

Phase measurement of a Fourier spectrum by a fringe-scanning phase-conjugate interferometer

We present a novel method for obtaining the phase distribution of an object spectrum by using a fringe-scanning phase-conjugate interferometer. A detailed analysis of the proposed technique is provided, and experimental demonstrations for validating this technique are also given. The major advantages of this method are its potentially high accuracy and its low space-bandwidth-product requirement for the detection system.

Phase-conjugate Fizeau interferometer

We describe a phase-conjugate interferometer that consists of a partially transmitting conventional mirror placed in front of and in close proximity to a phase-conjugate mirror. The interferometer is self-referencing, compact, and insensitive to environmental disturbances, provides twice the sensitivity of conventional (nonphase-conjugate) interferometers, and produces a direct representation of an incident wave front. We have constructed such a device using internally self-pumped phase conjugation in barium titanate and have used the device to characterize the wave front produced by an aberrated optical system.

Measurement of χ^(3) and phase shift of nonlinear media by means of a phase-conjugate interferometer

We have constructed a new interferometer that uses two phase-conjugate mirrors. This device allows for the measurement of the relative phase shift and the ratio of the nonlinear susceptibilities of materials. We have been able to measure weak reflectivity signals not detectable by normal degenerate four-wave mixing methods. It has been determined that the x((3)) value of colloid semiconductor glass OG530 at 532 nm is 7 x 10(-12) esu.

Strictly Real-time Image Differentiation in Photorefractive BSO

Abstract Strictly real-time image differentiation is demonstrated using a phase-conjugate interferometer based on simultaneous phase conjugate generation in photorefractive bismuth silicon oxide (BSO).

Dual-wave-front phase-conjugate interferometer and measurements of flame-temperature.

A new interferometer by dual-wave-front generation in degenerate four-wave mixing is described with measurements of flame-temperature. The dual wave front created in a nonlinear medium automatically yields a self-referencing operation for a given phase of an incident probe beam. A phase-mismatching problem for nonconjugate wave generation is also considered. The experimental observations are shown using a dye-laser and Na-vapor system.