Heterodyne Holographic Interferometry Research Articles

Holographic laser Doppler imaging of pulsatile blood flow.

We report on wide-field imaging of pulsatile motion induced by blood flow using heterodyne holographic interferometry on the thumb of a healthy volunteer, in real time. Optical Doppler images were measured with green laser light by a frequency-shifted Mach-Zehnder interferometer in off-axis configuration. The recorded optical signal was linked to local instantaneous out-of-plane motion of the skin at velocities of a few hundreds of microns per second and compared to blood pulse monitored by plethysmoraphy during an occlusion-reperfusion experiment.

Measurement error caused by speckle noise in heterodyne and quasi-heterodyne holographic interferometry

In heterodyne and quasi-heterodyne holographic interferometry, the measuring accuracy is limited by speckle noise. It is important to know the relation between measurement accuracy and speckle noise in both theory and application. This problem has been discussed in the past under the assumption that the speckle noise produces only a small measuring error. However, this assumption is not reasonable in practice. The effect of speckle noise on the measurement accuracy is analyzed by the use of a general statistical method. The results obtained reveal the general relation between the measuring accuracy and system parameters, and thus constitute important guidelines to the application of these techniques.

Investigation of the population inversion in a He-Ne laser discharge by heterodyne holographic interferometry

Heterodyne holographic interferometry was used for end-on investigation of a He-Ne laser discharge. By tuning an actively stabilized dye laser over the 633 nm neon atomic line the phaseshift was obtained as function of frequency, thus enabling the determination of spatially resolved population inversion.

Tomographic investigation of the particle density distribution of sodium atoms in a glow discharge using resonance heterodyne holographic interferometry

Local particle density distributions in a dc glow discharge causing phaseshifts less than one fringe are determined by resonance heterodyne holographic interferometry and optical tomography. For testing purposes the determination of the number densities of sodium atoms evaporated from an electrode consisting of a sodium intercalation compound (C 64Na) was performed.

Performance of moiré deflectometry with deferred electronic heterodyne readout

Effects of diffraction and nonlinear photographic emulsion characteristics on the performance of deferred electronic heterodyne moiré deflectometry are investigated. The deferred deflectometry is used for measurements of nonsteady phase objects for which it is difficult to complete the analysis of the field in real time. The sensitivity, the accuracy, and the resolution of the system are calculated, and it is shown that they are weakly affected by diffraction and by nonlinear recording. The features of the system are significantly improved compared with those of the conventional deferred intensity moiré technique and are comparable with those of the on-line heterodyne moiré. The system was evaluated experimentally by deferred measurements of the refractive-index gradients of a weak phase object consisting of a large KD*P crystal. This has been done by photographing the phase object through a Ronchi grating and analyzing the transparency with the electronic heterodyne readout system. The results are compared with the measurements performed on the same phase object with on-line heterodyne moiré deflectometry and with heterodyne holographic interferometry methods. Good agreement was observed. Some practical considerations for system improvement are discussed.

Strain measurement by heterodyne holographic interferometry

Heterodyne holographic interferometry provides automated interference phase measurement with high resolution and allows the quantitative evaluation of 3-D displacement and strain on solid objects. The fundamentals of heterodyning in double-exposure holography are reviewed and its possibilities and limitations are discussed in detail. Experimental results of strain measurement on a curved object surface are reported. Three double-exposure hologram recordings with different illuminations are used to get the vector displacement. Based on locally calculated derivatives of the displacement field, a sensitivity for the strain components of 1 microm/m with a spatial resolution of a few millimeters has been achieved. The features of heterodyne holographic interferometry are compared with those of quasiheterodyne (phase stepping) fringe interpolation.

Sensitivity and nonlinearity of optical path difference measurements using triple-exposure heterodyne holographic interferometry

Triple-exposure dual-reference beam holographic recording offers a convenient means by which high-speed transient phenomena may be investigated using heterodyne interferometry. Although convenient, use of the technique imposes certain compromises both in measurement linearity and sensitivity compared with analysis of more conventional double-exposure recordings. Fortunately, linearity can be assumed for events where only small (e.g., one-tenth wavelength) optical path changes are observed. By appropriate control of the intensity ratio of the reconstructed imagewave fronts, the region of linearity may be extended. Furthermore, measurement sensitivity can be optimized by proper control of recording and reconstruction parameters.

Phase stable automatic gain control for heterodyne holographic interferometry

A simple circuit is described which provides a fixed output amplitude for an input variation of 20 dB and with a relative phase shift variation (output versus input) of only 0.12° over the same range. The circuit was developed for use in a heterodyne holographic interferometry system where relative phase measurements to an accuracy of 0.36° are required of signals whose amplitudes may vary by as much as an order of magnitude during a single experiment.

Measurement of apparent young's modulus in the bending of cantilever beam by heterodyne holographic interferometry

Detection of micromechanical phenomena in material requires a sufficiently high-accuracy measurement. This paper shows the possibility of applying heterodyne holographic interferometry to such experimental verification. The effects of the ratios of thickness to grain size on the apparent Young's modulus are evaluated based on the deflection patterns of the cantilever beam. The characteristic length l of couple-stress theory is calculated by applying the analytical results of Koiter to our experimental results. This value is about one fifth of the grain size.

Heterodyne And Quasi-Heterodyne Holographic Interferometry

The use of heterodyne and quasi-heterodyne techniques in holographic interferometry allows a quantitative evaluation of the interference phase with high accuracy and offers the possibility of automated interferogram processing. In this paper, the fundamentals of these electronic methods are reviewed, the possibilities and limitations are discussed, and some applications in the field of displacement and strain measurement are presented. Heterodyne holographic interferometry is well suited for scientific applications in which very high accuracy (1/1000 of a fringe) is needed. Quasi-heterodyne holographic interferometry with video processing is adequate for industrial applica-tions in which high speed and medium accuracy (1/100 of a fringe) are required.

Measurement of three components of a displacement vector using heterodyne holographic interferometry

A new method for measuring a displacement vector using a single hologram is discussed. The method realizes the measurement by observing the object through three or more points on the hologram using a single lens and by using a heterodyne technique to detect accurate phase differences. In order to establish the optimum optical system of this method, it is necessary to estimate the measuring errors caused by fringe reading error and optical setting error. These two errors are calculated for a typical optical system. On the basis of the results of the analysis, an experimental result was evaluated.

Natural convection boundary layers adjacent to pyrolyzing surfaces

The temperature, velocity, and concentration distributions were measured in boundary layers adjacent to heated vertical polymethyl methacrylate (PMMA) and wood (Southern Pine) surfaces, and next to a heated, vertical, sintered bronze plate through which propane was injected. The temperature, velocity, and concentration were measured as functions of position and time using thermocouple probes, flow visualization techniques, and heterodyne holographic interferometry, respectively. The measured distributions were compared to the results of a simple model. The agreement between the measured values and the results of the model was generally good and was within the experimental uncertainty.

Heterodyne interferometry and holography for vibration measurements

Two frequency or heterodyne interferometry transforms the optical interference phase into the phase of an electronically detectable beat‐frequency signal. This allows to use powerful signal processing for increased sensitivity far below the optical wavelength λ and high temporal resolution, especially for vibration analysis. The principle and the properties of this heterodyne technique will be illustrated by presenting laser interferometry for displacement and velocity measurements. With an extended version [R. Dändliker and J.‐F. Willemin, Opt. Lett. 6, 165–167 (1981)] amplitude and phase of in‐plane and out‐of‐plane microvibrations (amplitudes 1 nm, spatial resolution 30 μm) at frequencies from 5 kHz to 5 MHz can be analyzed in real time. Experimental results for piezoelectric ultrasound transducers will be presented. Two‐reference‐beam holographic interferometry allows to use the heterodyne technique for accurate fringe evaluation and interpolation (λ/1000), since the two object fields are stored and accessible independently by the corresponding reference beam [R. Dändliker, Progress in Optics (North‐Holland, Amsterdam, 1980), Vol. 17, pp. 1–84.]. For vibration analysis, however, the object has to be recorded holographically by two or more coherent light pulses, synchronized to the object movement, using pulsed lasers or stroboscopic light modulation. Experimental results of deformation measurements by heterodyne holographic interferometry will be presented. The strength and weakness of this technique applied to vibration analysis will be discussed in particular.

Heterodyne holographic interferometry: concentration and temperature measurements in gas mixtures

Heterodyne holographic interferometry is employed to measure refractive-index distributions in transparent media. A system using a He-Ne laser and relatively modest electronic instrumentation is described. The system was used to measure temperature and specie-concentration distribution in natural convection boundary layers in air adjacent to heated surfaces through which a second gas is emitted or injected.

Accuracy of heterodyne holographic strain and stress determination

The basic equations for the evaluation of surface displacement, strain and stress from holographic interferograms are derived. The object shape and the geometry of the optical setup are taken in to account. A corresponding computer program is described. Heterodyne holographic interferometry is used for fringe interpolation (better than 1/1000 of a fringe) to get sufficient accuracy and spatial resolution. Errors and accuracy of holographic strain and stress determination are discussed with the aid of the computer program. A cylindrical tube under pressure load is presented as a numerical example. © 1979 Society for Experimental Mechanics, Inc.

Nonlinear cross-talk in two-reference-beam holographic interferometry

Nonlinear hologram recording leads to cross-talk in two-reference-beam holographic interferometry. This cross-talk generates spurious interference fringes and introduces an error in heterodyne holographic interferometry. It is shown that the cross-talk depends essentially on the recorded scence between the two exposures and can be eliminated by clearing the scene from any visible parts which remain unchanged in position.