Fresnel Biprism Research Articles

Optical-sectioning microscopy by patterned illumination

We propose a very simple method for the flexible production of 1D structured illumination for high resolution 3D microscopy. Specifically, we propose the insertion of a Fresnel biprism after a monochromatic point source for producing a pair of twin, fully coherent, virtual point sources. The resulting interference fringes are projected into the 3D sample and, by simply varying the distance between the biprism and the point source, one can tune the period of the fringes, while keeping their contrast, in a very versatile and efficient way.

Illustration of quantum complementarity using single photons interfering on a grating

A recent experiment performed by Afshar et al (2007 Found. Phys. 37 295–305) has been interpreted as a violation of Bohr's complementarity principle between interference visibility and which-path information (WPI) in a two-path interferometer. We have reproduced this experiment, using true single-photon pulses propagating in a two-path wavefront-splitting interferometer realized with a Fresnel's biprism, and followed by a grating with adjustable transmitting slits. The measured values of interference visibility V and WPI, characterized by the distinguishability parameter D, are found to obey the complementarity relation V2+D2⩽1. This result demonstrates that the experiment can be perfectly explained by the standard interpretation of quantum mechanics.

Design, Construction and Calibration of a GRENOUILLE, Single-Shot, Ultrashort-Pulse Measurement System

A detailed explanation is provided for the design, construction and calibration of a GRENOUILLE system, an ultra-short pulse measurement system based on a single-shot second-harmonic-generation frequency-resolved optical gating method. Its main components are a Fresnel bi-prism, a thick beta barium borate (BBO) and a charge coupled device (CCD) camera, together with some ancillary optical components. Because there is no moving part in this system, ultrashort laser pulses of a few tens of femtosecond duration can be characterized in real time and even a single pulse can be characterized if it has su cient energy.

Interferometric method of determining the refraction index of two-dimensional sonic crystals

Sonic crystals are defined as materials consisting of periodic distributions of acoustic scatterers in another medium with different elastic properties. These materials present two main acoustical features: they present ranges of frequencies where the acoustic wave propagation is forbidden and, moreover, they can be used to construct acoustical refractive devices. We present here an interferometric method of characterizing directly the refraction index of these materials. We focused our research on sonic crystals constructed with a periodic distribution of rigid cylinders in air. The interferometric method used is based on the acoustical analog of an optical device called Fresnel's biprism. Our numerical predictions are in good agreement with the experimental results obtained and allow us to estimate the refraction index for very low frequencies. Moreover, in this range we show the nonlinear behavior in the dispersion relation refraction index versus frequency. Finally, we analyze the relationship between the refraction index and some typical sonic crystal parameters. In view of the results we can conclude that this method offers certain advantages with respect to the classical method used to obtain the refraction index in sonic crystals with airborne propagation: the phase delay method.

Experimentally simple, extremely broadband transient-grating frequency-resolved-opticalgating arrangement

We demonstrate a simple, essentially alignment-free Transient-Grating Frequency-Resolved-Optical-Gating arrangement using a simple input mask that separates the input beam into three beams and a Fresnel biprism that crosses and delays them. It naturally operates single shot and has no moving parts. It is also extremely broadband and hence should be ideal for measuring pulses from optical parametric amplifiers.

Fringes demodulation in time-averaged digital shearography using genetic algorithms

This paper presents a phase recovery method, based on genetic algorithms, in time-average shearography. It is proved that a single Bessel fringe pattern obtained under a subtraction operation could be enough to calculate the phase. A merit function is solved iteratively using genetic operator like selection, reproduction and mutation. Experimental results are presented in this paper using a simple shearing system based on a Fresnel biprism.

Single-photon wavefront-splitting interference

We present a new realization of the textbook experiment consisting in single-photon interference based on the pulsed, optically excited photoluminescence of a single colour centre in a diamond nanocrystal. Interferences are created by wavefront-splitting with a Fresnel's biprism and observed by registering the "single-photon clicks" with an intensified CCD camera. This imaging detector provides also a real-time movie of the build-up of the single-photon fringes. We perform a second experiment with two detectors sensitive to photons that follow either one or the other interference path. Evidence for single photon behaviour is then obtained from the absence of time coincidence between detections in these two paths.

Characterization of ultrashort pulses by a modified grating-eliminated no-nonsense observation of ultrafast incident laser light E fields (GRENOUILLE) method

The measurement and characterization of ultrashort laser pulses remains an arduous task. The most commonly used pulse-measurement method is known as frequency-resolved optical gating (FROG), and another version with great experimental simplification and low-priced setup is known as grating-eliminated no-nonsense observation of ultrafast incident laser light E fields (GRENOUILLE). Nevertheless, there is interest in elaborating other, more accessible or simpler and cheaper, setups with equal or better assets. We explored modification of the GRENOUILLE method in which we replaced the original Fresnel biprism with a beam splitter and two mirrors and used a cheap webcam to measure the pulse traces. We have evaluated our system, and we propose a method to correct border effects caused by the beam intensity's profile based on the characterization of three pulse classes: Fourier-transform limited, double, and chirped. We compare the recovered electric field with further spectral and second-order correlation data of the corresponding pulses.

Strong reduction of the degree of spatial coherence of a laser beam propagating through a preformed plasma.

A strong reduction of the spatial coherence of a laser beam after its propagation through a plasma has been measured using a Fresnel biprism interferometer. The laser beam was diffraction limited; the coherence width was reduced from 40 mm in vacuum down to a few mm with the plasma. Numerical results based on a paraxial model exhibit a coherence degree close to the experimental one; they also prove the importance of taking into account the nonlocal transport effects in numerical simulations for such plasma conditions.

Increased phase-matching bandwidth in simple ultrashort-laser-pulse measurements

Recently we introduced an extremely simple device for measuring ultrashort laser pulses, which utilizes a thick nonlinear-optical crystal, that replaces the usual thin nonlinear-optical medium and spectrometer simultaneously. It also replaces the usual beamsplitter and delay line with a single optic, a Fresnel biprism, which requires no alignment. Here we review the operation of the device and show that dithering the lateral position of the input beam in such a device increases the spectral range of the device with no loss in spectral resolution. Furthermore, we show that it separates the two constraints on crystal selection, allowing the measurement of a wider range of spectrally broader and/or more complicated pulses.

Highly simplified device for ultrashort-pulse measurement

We show that a frequency-resolved optical gating device using (1) a thick nonlinear crystal to replace the usual thin crystal and spectrometer and (2) a Fresnel biprism to replace the beam splitter and delay line yields a remarkably simple single-shot ultrashort-pulse intensity-and-phase measurement device with no sensitive alignment parameters and significantly greater sensitivity.

Fringe localization in wavefront division interferometers

Abstract When an amplitude division interferometer is illuminated by an extended incoherent source the fringes are localized. If the incoherent source is a periodic array of sources or if it continuous, there is a fundamental difference at the observation space and this is the appearance of several (more than one) localization surfaces. In the present paper it is stated that localized fringes can also be obtained in wavefront division interferometers provided the source is incoherent and periodic. As an example, the multiple localization planes in Fresnel's biprism are shown and experimental results are compared to the theoretical ones.

Studies in synchrotron x-ray microradiography: observation ofbiprism-type interference

Synchrotron x-ray microradiographic imaging is a routine and indeed essential prerequisite for the collection of diffraction data from a particular single small crystallite embedded within a mat containing thousands of similarly small-sized individuals when that particular small crystallite has been earmarked for a diffraction study, by reason of its special morphological features or optical properties, for example. The combination of optical microscopic, microradiographic and microdiffraction topographic techniques is proving fruitful in studies of CVD diamond crystallites. The simplest radiographic contrast mechanism applying in the case of negligibly-absorbing objects is refractive deviation of the transmitted beams. However, the optimization of experimental parameters for microradiography brings in factors such as Fresnel diffraction effects and incident-beam uniformity. When faceted objects are radiographed, re-entrants between facets produce the x-ray analogue of the Fresnel biprism. Radiographic experiments are illustrated that plausibly demonstrate biprism interference, on the evidence of the fringe patterns observed.

A Fresnel bi-prism device for atomic matter waves

The principle of a simple bi-prism for coherent atomic translational waves is studied. The scheme of the experiment consists of a diffracting slit, in front of which the evanescent wave running along a tapered optical fibre provides a converging gradient of optical potential for two-level atoms. The combined effects of Fresnel diffraction and bi-prism interferences are described in different experimental configurations. The influence of gravitation is outlined. Orders of magnitude and feasibility are discussed in the case of thermal neon atoms, for which experiments are under consideration.

Spatial modulation of the pump in the ultrabroadband dye laser with a “spatially-dispersive” resonator

The ultrabroadband nanosecond dye laser with a prism-based “spatially-dispersive” resonator, and a transverse pump being spatially modulated by Fresnel biprism, has been investigated. The influence of the lateral shift between the frequency components, the pumped zone dimension and the divergence on the laser bandwidth has been analyzed and experimentally demonstrated. The possibility to manipulate the shape of the laser spectrum by spatial modulation of the pump has been estimated. The biprism delivers a specific pump intensity distribution of the active medium, thus it compensates the lower emission cross-section in the wings of the dye gain profile and expands the laser bandwidth. Ultrabroadband generation (FWHM = 45 nm) is obtained.

A compound interferometer for angle measurement

The present paper reports a compound interferometer where the output of a Fresnel biprism is made the input to a shearing interferometer. Thus a study of a four-beam interference pattern under the background of a two beam interferometric fringes is made. An analysis of fringe formation together with the experimental observations of the above interferometers has also been discussed. The interesting observations on changing the relative axial position of the biprism with respect to direction of shear can be used for angle measurement or angular calibration. Moreover, the combined fringe system shows some self-imaging properties which also exhibit some interesting effects. Both theoretical analysis as well as some experimental results are presented.

Device for reflective dividing of a laser beam with adjustable distance between the two focus spots

For reflective dividing of a laser beam and focusing in two spots with a fixed distance between, a Fresnel biprism is used. When there is a need for a more frequent change of distance between the spots, a new solution is proposed.

Polarisation experiments with a Fresnel biprism

Polarisation experiments with a Fresnel biprism I S Ruddock Optical diffraction patterns displayed by microcomputer A R Allen Analogue-to-digital conversion made easy T E Jenkins and S R Goodes Microcomputer measurement of the velocity of sound in air P A Bates Using the BBC micro as a frequency meter Richard Bishop Measuring speed using a computer several techniques Jon M Pearce A versatile optical multichannel analyser system for use with picosecond streak cameras Guoguang Shen, W M Dennis and W Blau How to use your BBC computer as a cheap storage oscilloscope

Investigation of the moment distribution in a bent circular plate by speckle-shearing interferometry

This paper describes the application of a simple speckle-shearing interferometric method for the determination of moment distribution in a clamped circular plate under a concentrated transverse load at its center. The present system consists of an image-shearing camera using a Fresnel biprism of small angle. Reduction of spurious speckle- noise and enhancement in the clarity of the fringe was achieved by using a white light source at the Fourier filtering stage. Experimental values have been compared with the existing analytical solution. Fairly close agreement between the experimental and theoretical values shows the accuracy and reliability of the method.

Digital speckle-pattern shearing interferometry

An application of digital image processing techniques to speckle-shearing interferometry is described. A present system consists of an image-shearing camera using a Fresnel biprism of small angles and a digital TV-image processing facility. This interferometer makes it easy to measure in quasi-real-time spatial derivatives of surface displacement and modal vibration amplitude of objects. A statistical theory is applied to analyze the formations of these fringes due to 3-D displacement. Interpretation of the result leads to conditions of maximum fringe contrast and the limitation of this technique. Experimental results in the three cases of slope of normal displacement, surface strain, and slope of vibration amplitude measurements are presented.