Talbot Interferometer Research Articles

UV-assisted selective chemical etching of relief gratings in Er/Yb-codoped IOG1 phosphate glass

The patterning of sub-micron periodicity Bragg reflectors in Er/Yb-codoped IOG1, phosphate glass is demonstrated. A high yield patterning technique is presented, wherein high volume damage is induced into the glass matrix by exposure to intense UV radiation, and subsequently a chemical development in a strong acid selectively etches the exposed areas. The grating reflectors were fabricated by employing an elliptical Talbot interferometer and the output of a 213nm, 150ps frequency quintupled Nd:YAG laser. The grating depth of the etched relief pattern in time was measured at fixed time intervals and the dependence is presented in upon the etching time and exposure conditions. The gratings fabricated are examined by atomic and scanning electron microscopy for revealing the topology of the relief structure. Gratings with period of the order of 500nm were fabricated, having a maximum depth of 60nm.

Fabrication of diffraction grating for X-ray Talbot interferometer

Imaging technology using the phase data attracts attention from many researchers as the observation technique of a biomechanical material. We produced a diffraction grating for obtaining high-resolution phase data. We designed the new process flow and developed the fabrication technique composed of MEMS technology, X-ray lithography, and micro electroplating. The X-ray lithography process was performed using the NewSUBARU synchrotron radiation facility. The line and the aspect ratio of this grating were 4 μm and above 5 μm, respectively. We evaluated the diffraction grating in SPring-8.

Phase Tomography by X-ray Talbot Interferometry for Biological Imaging

The X-ray phase tomography of biological samples is reported, which is based on X-ray Talbot interferometry. Its imaging principle is described in detail, and imaging results obtained for a cancerous rabbit liver and a mouse tail with synchrotron radiation are presented. Because an amplitude grating is needed to construct an X-ray Talbot interferometer, a high-aspect-ratio grating pattern was fabricated by X-ray lithography and gold electroplating. X-ray Talbot interferometry has an advantage that it functions with polychromatic cone-beam X-rays. Finally, the compatibility with a compact X-ray source is discussed.

The Turning Error Effect of Reflectors in the Talbot Interferometer used for Writing Fiber Bragg Grating

The Talbot interferometer used for writing fiber Bragg grating (FBG) is analyzed effectively in this paper. Based on electromagnetic theory, a computing model of the Talbot interferometer is established with the temporal and the spatial coherence taken into account and with the turning angle of the reflectors as a critical parameter. The model can provide a more detailed and precise information about the interference field and is used to study the effect of the turning error of the reflectors in writing FBG. The calculation result shows that the turning error has an important effect on the visibility of the far interference field.

X-ray Talbot Interferometry with Capillary Plates

An X-ray Talbot interferometer consisting of two capillary plates, which were used as X-ray amplitude gratings, was evaluated for X-ray phase imaging. A theoretical aspect of capillary X-ray Talbot interferometry is presented with a preliminary operation result using synchrotron radiation. A two-dimensional X-ray Talbot effect, or self-imaging effect, which was the basis of Talbot interferometry, was observed with the capillary plate, and moiré images formed by the X-ray Talbot interferometer exhibited contrasts corresponding to the differential phase shift caused by phase objects placed in front of the interferometer. Finally, the possibility of quantitative phase measurement with a fringe scanning technique is discussed.

D012 Phase Imaging with an X-ray Talbot Interferometer—Invited

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Changing photo-written Bragg wavelengths of fiber gratings via one phase mask and four mirrors

A phase mask interferometer is developed to photo-write long gratings with arbitrary Bragg wavelengths. In this system, the fiber Bragg grating is photo-written by UV interference stripes of 193 nm reflected from two rotatable mirrors and two fixed mirrors, where the phase mask is not only used as a beam splitter, but also initialized the reference quantity of Bragg wavelength; the fixed mirrors are used for reducing the incident angle; the rotatable mirrors are used for adjusting the corresponding photo-written Bragg wavelength. It is worth noting that the photo-written length is fourfold as high as the length in the Talbot interferometer with the same mirror size.

Use of a phase type elongated circular grating in Talbot moiré deflectometry

Summary We analyze theoretically and experimentally the self-image of a phase type elongated circular (EC) grating which has a periodic structure of rectangular type, so that it can be employed in Talbot moire deflectometry. We examine the visibility of a self-imaged phase EC grating while the optical phase difference of the grating is varied. We show that the self-image of a phase EC grating of rectangular type is slightly aberrated around the center of the interface of linear and semicircular parts but moire fringes by self-imaging a phase EC grating on a reference EC grating are little influenced by the image aberration. We conclude that a phase EC grating as well as an amplitude EC grating in our earlier work [Optik 113 (2002) 285] can be effectively applied to a Talbot interferometer when the phase difference of the grating is prepared close to 90°.

Study of wedge-adjusted Talbot interferometer for writing fiber gratings with variable inscribed Bragg wavelengths

A wedge-adjusted Talbot interferometer is presented to change the inscribed Bragg wavelength of fiber Bragg gratings. In this system, the grating is written by UV interference stripes of 193 nm derived from two combined mirrors, where a phase mask is used as a beamsplitter of ±1 order of diffraction light. It is noteworthy that the adjustor transforms the shift of wedge into the rotation of the two mirrors, and alters the mutual angle of two interfering beams in writing fiber Bragg gratings.

A simple method for the fabrication of intrinsically apodized chirped fibre Bragg gratings

A new and simple fabrication technique is reported for the UV inscription of intrinsically apodized chirped fibre gratings at an arbitrary Bragg wavelength employing a single chirped phase-mask in a scanning Talbot interferometer set-up. Chirped gratings have been successfully produced over a large wavelength range and with bandwidths up to 5 nm. These gratings exhibit the time-delay response of a small ripple effect. In the present paper a comparison with previously reported fabrication methods is given, showing the advantages and disadvantages of the different methods.

Talbot interferometer as a time filter

Abstract The Talbot interferometer is analyzed with regards to its temporal characteristics. An expression for its impulse response is derived. The use of the Talbot interferometer as a time filter in optical communications systems is suggested.

Modified Talbot interferometer for fabrication of fiber-optic grating filter over a wide range of Bragg wavelength and bandwidth using a single phase mask

A technique involving a compact apparatus that combines the phase mask and two-beam interferometric techniques is presented. It involves the use of a phase mask to diffract the ultraviolet (UV) beam and a cylindrical lens combined with a pair of mirrors to produce two symmetric virtual line sources of UV light. Bragg wavelength and bandwidth of the fiber gratings can be controlled with a simple translation of the fiber and/or the phase mask. Using a 40-mw continuous-wave frequency-doubled argon-ion laser at 244 mm and a single phase mask, a series of chirped fiber gratings with the Bragg wavelength in a wide range around 600 nm and 1300 nm are fabricated in hydrogen-loaded ordinary fibers.

Talbot interferometer based on a birefringence grating

A 1-D coarse grating imaged onto a photorefractive Bi 12SiO 20 crystal is stored as modulation of birefringence. On this basis, the self-imaging phenomenon is implemented. When an analyzer is placed at the output of the crystal, the modulation of birefringence is converted into a modulation of transmission. In this case in the read-out process, self-images are generated and distributed along the propagation direction at those positions which coincide with the loci that the self-images occupy in case that an amplitude grating would be used instead of the combination of the birefringence grating and the analyzer. Moreover, it is demonstrated that by maintaining the read-out polarization state and the crystal configuration it is not necessary to convert the modulation of birefringence into a modulation of transmission to generate self-images. Its means that no matter the analyzer is removed, self-images are generated as well. In this case, the planes of highest visibility coincide with those planes corresponding to a conventional phase grating. It is well known that Talbot interferometers built in with ordinary gratings are not sensitive to polarization changes. On the other hand, it is showed that the birefringence grating stored in the crystal allows to implement a polarization sensitive interferometer. It means that if a birefringence material is tested, then the shifting introduced in the self-images can be used for quantitative determination of the material birefringence.

Analysis and application of a [formula omitted] order Talbot interferometer for 193 nm laser grating formation

We report the analysis, design and application of a Talbot interferometer in which the zero and first order beam from a grating are recombined. This interferometer produces fringes of the same period, d, as the master grating or phase mask rather than d 2 when the ±1 orders are employed. Experiments using the 0 1 Talbot interferometer with 193 nm ArF laser illumination to write gratings on polymers by ablation and photosensitive Bragg gratings in fibres are reported.

Interferometer based on the Talbot effect in holography

This paper discloses an interferometer based on the Talbot effect in holography and combining in itself properties of the Talbot and of the holographic interferometers. The second grating is replaced with the hologram of the first grating in the interferometer proposed, which constitutes its difference from the Talbot interferometer and which results in an interferometer having four output informational channels with different sensitivities.

Talbot interferometer with circular gratings for the measurement of temperature in axisymmetric gaseous flames

A detailed study for measuring the temperature distribution in axisymmetric flames by using a Talbot interferometer with circular gratings is presented. We increased the sensitivity of the interferometer by optimizing the pitch of the grating and the Talbot plane. We compare the experimental results with the values that were measured with a thermocouple to an accuracy of ±0.2% of full scale ±4 digits. Good agreement is seen between the temperatures measured by use of a thermocouple and those measured by use of Talbot interferometry.

Measurement of the temperature profile of an atomic absorption spectrophotometer burner using a Talbot interferometer with circular gratings

A Talbot interferometer with circular grids is used to measure the temperature profile inside a premixed laminar flow slot burner used in an atomic absorption spectrophotometer. The experimentally measured results using the Talbot interferometry are compared with the values measured by a platinum-platinum-rhodium thermocouple with accuracy of measurement of ±0.2% full scale ±four digits and good agreement is found. The effect on the temperature profile of aspirating water through the nebulizer is also investigated.

Fringe processing and analysis with a neural network

Optical testing involving interferometric fringes is often adequate to obtain a quantitative estimate of a critical parameter such as asphericity, i.e., the deviation of a surface from a perfect sphere at a specific radial distance. We propose a two-stage neural network solution that can provide such a quantitative output. The first stage is a self-organizing map network that efficiently performs fringe thinning by detecting fringe maxima even in the case of noisy low-contrast images. The second stage is a back-propagation-trained neural network that learns to interpret the thinned fringes represented by polynomial coefficients. Fringe patterns from a sample set of optical components, with known parameters that cover a wide range, are used for training. Experimental results were obtained in the case of fringe patterns from a Talbot interferometer for testing aspheric glass molds used in ophthalmic lens making. On test molds with asphericity values close to 0.050 mm, the difference between values obtained from the neural network and by contact measurement was less than 0.002 mm.

Measurement of a transparent object by using an automated Talbot interferometer

It is reported that the first partial derivative of the phase distribution for a transparent object can be measured automatically by a personal computer with an image processor. The moire pattern is formed by superimposing the Fourier image distorted by the transparent object on the master grating. But if only the moire patterns are observed, it is not shown if the fringe order numbers increase or decrease. The fringe scanning method is presented to overcome the fringe order numbers. The four-step method is used to calculate the first partial derivative. By a simple experiment, the first partial derivative can be shown in the three dimensional graphics.

Talbot interferometry using logic-operated moiré

A new kind of Talbot interferometer is proposed in this paper on the basis of real-time logic-operated moiré using the joint self-imaging effect. Therefore, grating-carriers eliminated and fringes sharpened moiré difference-beat interferograms can be yielded. Theoretical analyses and experimental verifications are given.