Double-exposure Interferometry Research Articles

Comparison of the results of refractometric measurements in the process of diffusion, obtained by means of the background-oriented schlieren method and the holographic interferometry method

The results of the study of interdiffusion of two liquids, obtained using the holographic recording scheme with a nonstationary reference wave with the frequency linearly varying in space and time are compared with the results of correlation processing of digital photographs, made with a random background screen. The spatio-temporal behaviour of the signal in four basic representations (‘space – temporal frequency’, ‘space – time’, ‘spatial frequency – temporal frequency’ and ‘spatial frequency – time’) is found in the holographic experiment and calculated (in the appropriate coordinates) based on the background-oriented schlieren method. Practical coincidence of the results of the correlation analysis and the holographic double-exposure interferometry is demonstrated.

대형 립 폴리머 광도파로 브래그 격자를 이용한 두 파장 레이저

An external cavity laser supporting two wavelengths is demonstrated by incorporating polymer waveguide Bragg reflectors and a superluminescent light-emitting diode. An oversized rib waveguide structure and Bragg gratings are designed by using the effective-index and transmission-matrix methods. Bragg gratings with different periods are inscribed on a polymer waveguide through double-exposure laser interferometry. In order to tune the cavity loss affected by the reflectivity of Bragg gratings, a Bragg reflectors with varying length is incorporated. Two-wavelength-mode lasing is achieved for the device consisting of 2-mm long, 537-nm period gratings and 2.2-mm long, 540-nm period gratings; the lasing wavelengths are 1554 nm and 1564 nm, with an output power close to 0 dBm, a 20-dB bandwidth of 0.2 nm, and a side-mode suppression ratio of 45 dB.Keywords: Polymeric optical waveguide, Bragg reflection grating, External cavity laser, Multi-wavelength laserOCIS codes: (130.5460) Polymer waveguides; (230.1480) Bragg reflectors; (140.3070) Infrared and far-infrared lasers; (140.3460) Lasers

Nanoscale interlayer that raises response rate in photorefractive liquid crystal polymer composites

By depositing a nanoscale photoconductive layer on a stable photorefractive (PR) polymeric film, consisting of the polymer poly[N-vinylcarbazole] (PVK) doped with 4,4'-n-pentylcyanobiphenyl (5CB) and C60, both the response rate and beam coupling properties were improved greatly. Systematic measurements and observations unveiled the role played by the additive layer in preventing ion injection from the ITO layer into the PR film and hence in mitigating the charge compensation. A strong fanning effect and high diffraction orders at small angles have demonstrated the excellent PR property in the modified samples used. To demonstrate great potential of the PR composite in the updatable applications, real time double exposure interferometry was performed accordingly with good results.

Holographic Analysis of the Initial Canine Displacement Produced by Four Different Retraction Springs

To estimate and compare the magnitude and direction of initial displacement of the canine produced by four different canine retraction springs. A freshly macerated mandible was used as an experimental model. First premolars were extracted, and strap-up was done with a 0.018 inch Roth Preadjusted Edgewise System (3M Unitek, Monrovia, Calif). The canine was subjected to loads of 4 oz, 5 oz, and 6 oz, each applied by four different canine retraction springs, that is, closed coil spring, open coil spring, PG spring, and T-loop retraction spring. The magnitude and direction of the initial displacement of the canine were studied by means of double-exposure interferometry. The PG spring produced the highest initial displacement for a given force among the force systems used, followed by open coil, closed coil, and T-loop. Maximum tipping was observed with the open coil spring, followed by the PG spring, the closed coil spring, and the T-spring. The T-loop may be preferred whenever minimal tipping is performed. The PG spring may be preferred over other springs whenever a higher magnitude of displacement is desired. Closed coil springs may be preferred whenever a reasonable magnitude of displacement is required and reasonable tipping is allowed.

Reflection holograms in sillenite crystals for double-exposure interferometry

Holographic recording in reflection geometry offers high lateral image resolution (necessary to analyze microscopically structured objects, e.g. biological cellular structures) and a compact and simple setup (Denisyuk holography). Our aim is to combine this high resolution three-dimensional imaging with holographic double-exposure interferometry to allow the analysis of a dynamic process on the microscopic scale. We derive analytic expressions for gain and diffraction efficiency valid for arbitrary optical activity (and thus not only for Bi 12 SiO 20 but also for Bi 12 TiO 20 crystals). The theoretical predictions agree convincingly both with the experimental data published in [J. Opt. Soc. Am. B 14 (1997) 1179] and with our experimental data.

Utilization of photorefractive crystals for holographic double-exposure interferometry with nanosecond laser pulses

A holographic double-exposure interferometer for deformation and vibration analysis of diffusely reflecting objects in quasi real-time is presented. Writing of holographic gratings with 3 ns laser pulses in photorefractive sillenite-type crystals enables recording of sequences of double-exposure interferograms. A repetition rate of 12.5 Hz is achieved with the set-up used. Automatic phase evaluation of the interferograms is performed with a spatial-heterodyne technique. Photorefractive recording in a BTO:Cd crystal with pulsed illumination is investigated and discussed in view of the application in double-exposure interferometry. The performance of the interferometer is investigated by observing deformations of a vibrating test object.

Some characteristics of relief formation on photothermoplastic carriers used in double-exposure interferometry

An analysis is made of the main trends in the development of a surface relief on photothermoplastic carriers of optical information used to record double-exposure holographic interferograms. It is shown that high-quality interferograms require recording conditions (taking into account the composition of the material and the heating temperature of the thermoplastic carrier layer, as well as the parameters of the sensitizing corona discharge) where the surface of the photothermoplastic carrier can be treated in the equipotential approximation.

Fringe modulation in shifted reference holography of fine motions

Abstract The holographic fringe contrast in shifted reference double-exposure interferometry of very small changes has been described. Two cases, that is linearized subfringe holographic interferometry and holographic subtraction have been considered. The study aims at establishing unit reference to object beam intensity ratio for hologram recording in these situations.

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.

Holographic double-exposure interferometry with tetragonal KTa 1− xNb xO 3: Fe crystals

Iron-doped tetragonal potassium tantalate-niobate (KTN:Fe) crystals are used as photorefractive storage media for holographic double-exposure interferometry. Holographic recording in the investigated crystals is influenced by thermal treatments. Deformations of a diffusely reflecting test target are observed with the help of holographic interferograms utilizing a phase-stepping technique.

Holographic double-exposure interferometry in near real time with photorefractive crystals

A holographic interferometric technique based on fast sequences of double exposures in photorefractive crystals for the dynamic analysis of reflection-type objects is presented. Methods for optimizing the diffraction efficiency and the decay time of the holographic gratings recorded at short exposure times are discussed. Special attention is paid to the use of external electrical fields. The maximization of fringe contrast in double-exposed interferograms is investigated both theoretically and experimentally. Finally, the automatic evaluation of interferograms is demonstrated by use of a sample sequence of interferograms.

Holographic interferometry for the display of shock wave induced deformations and vibrations—A contribution to laser lithotripsy

The physical effects involved during the fragmentation of a urinary or gall stone by laser lithotripsy are not yet completely understood. We present the first in vitro experiments which display the deformations and vibrations produced by a shock wave in such a stone by means of holographic double-exposure interferometry. In the shell of an egg used as test object a slowly decreasing eigen vibration resulting from the shock wave can be observed. A gall stone shows a strongly inhomogeneous short-time deformation equalizing after some microseconds. The display of these deformations and vibrations may lead to a better understanding of the fundamental physical involved in stone fragmentation.

Measuring the spatial coherence from an extended quasi-monochromatic source by double-exposure speckle interferometry

Double-exposure speckle interferometry is used to measure the degree of spatial coherence from an extended quasi-monochromatic source. The method closely follows the theory of spatial coherence and allows easy interpretation of results; it can be implemented with a compact interferometer based on laser speckle patterns.

Speckle interferometry: noise reduction by correlation fringe averaging

A method for noise reduction in double-exposure speckle interferometry is proposed, based on averaging independent spatially filtered correlation fringe patterns.

Real-time double-exposure interferometry using self-pumped conjugator with Cu: KNSBN

A simple real-time double-exposure interferometry employed by an internally self-pumped conjugator Cu: KNSBN is demonstrated. The device can perform a real-time nondestructive test of object.

Double-exposure interferometric measurements for determining phase changes produced by transparent media

A simple experiment to record phase changes produced by transparent objects using holographic double-exposure interferometry is described. An ordinary white light source is used to analyse the fringes on the photographic plate of the double-exposure interferogram. A theory is developed to estimate the phase shift between the two object waves without reconstructing the object and it agrees well with the experimental observations.

Improvements In The Experimental Techniques Of Moire Interferometry

The paper presents some developments in the application techniques of double-exposure moire interferometry, with the aims of simplifying the technique and overcoming some of its current drawbacks. The main proposed development is the substitution of the classic interferometric setup, which records a high density grating on the specimen, by a high density, highly efficient double (crossed) holographic grating, clamped onto the object just in front of it. The following main advantages are recognized: Since the holographic grating is clamped onto the object and follows its rigid motion, the corresponding effect on the fringes Fs minimized. The coherence length requirements for the laser are minimized to a fraction of the distance from the grating to the object. An argon laser without etalon can be used, an obvious advantage given the low sensitivity of the photosensitive coatings. The specimen needs to be (doubly) exposed only once to obtain the two orthogonal sets of displacement fringes, thanks to the use of a crossed grating. Thus, errors due to the low repeatability of the test are avoided. Some applications, including the use of unusual photosensitive coatings and processing procedures, are presented.

Determination of Arbitrary Tooth Displacements

The noninvasive, modern technique based on the method of double-exposure hologram interferometry was used to measure arbitrary displacements of teeth in the three dimensional space. The experimental studies were carried out on an idealized model of the maxillary central incisor. The results show that the experimental data, based on component loading, are inadequate to accurately predict tooth displacement from an arbitrary force acting in the three dimensional space.

Determination of slope and strain contours by double-exposure shearing interferometry

An interferometric technique is used to determine directly patterns of derivatives of displacements. In the case of plate models, the fringes are loci of equal slope; for specimens provided with surface gratings, one forms patterns of partial derivatives of in-plane displacements. A theory for the interpretation of the interference fringes in terms of displacements is outlined; some experimental applications illustrate the paper.

Acoustical Holographic Interferometry

Experiments on acoustical holographic interferometry were performed by scanned acoustical holography with 3 MHz sound waves. Interferometric imaging of tilted objects was performed and clear fringes corresponding to the height difference in the objects were observed in double-exposure interferometry and in two-hologram interferometry. Capability of acoustical interferometry to measure inclination of flaws in massive material has been shown in the double-exposure interferometry experiment. Two-frequency interferometry experiments were also performed and contour lines were superimposed on the reconstructed images. Good agreement between calculated and measured height differences in the object was obtained.