Dual Hologram Research Articles

Post-Process of Density Streaks Image of Flow Field in Supersonic Jet Device Captured by Laser Dual Hologram Interferometry

Wind tunnel test can not simulate effectively the flow field of fuze electrical machinery at flight test conditions. In order to deeply research the structure of flow field and measure the flow field density out of fuze electrical machinery, the laser dual hologram interferometry was applied and the streaks photos were obtained clearly. To recognize the contours of density field, identification is needed to deal with interference streaks, and the density of local streaks is calculated with interference principle. The hologram interferometry photos of density field were pro-processed in the thesis, for the problem of photos that the left part was much brighter than the right, the method of multiple threshold was used to binary image. It can be seen that the method gives consistent results to a certain extent of human perception and gives ideal results to find uniform regions in the image plane. Then the binary image is thinned by pixels searching algorithm according to the lines to get coordinates of the pixels of each streak and to lay the foundation for extracting density field from density interference streak in future research.

射流密度场激光双曝光全息干涉图像的后处理

射流密度场激光双曝光全息干涉图像的后处理

Dual hologram shearing interference technique with enhanced sensitivity for wind tunnel testing

A novel optical diagnostic approach, namely, a dual hologram shearing interferometry with enhanced sensitivity, is proposed for visualization, and for measuring the density gradients of the flow in wind tunnels. The technique is especially useful for strong turbulent and/or unsteady regions flows. The features of the technique make it tolerant to vibrational disturbances typical to many wind tunnel facilities. The method was demonstrated by its application to a supersonic flow over a spherically blunted nose cone/cylinder model.

Dual hologram shearing interference technique for wind tunnel flow fields testing

A novel optical diagnostic technique, dual hologram shearing interferometry, for measuring density gradients of different phase objects is proposed and demonstrated. The lateral shearing is achieved by using a phase grating. A holographic interferometer has been developed and designed on the base of a single pass Z type conventional schlieren device. The interferometer’s scheme is insensitive to acoustical disturbances, similarly to the conventional schlieren layout, and is capable of recording holograms with a continuous wave laser during the wind tunnel run.

Dual hologram technique with enhanced sensitivity for measurements of weak phase objects

Conventional interferometric measurements of weak phase objects run into serious accuracy problems due to low sensitivity and/or optical aberrations.

Holographic study of suspended vaporizing volatile liquid droplets in still air

The data presented here describe the dynamics of vaporization of a single suspended droplet of chloroform, acetone and diethyl ether at room temperature and pressure in still air. The dual hologram technique was applied for direct measurements of the radial distribution of the change in the refractive index caused by the vapor molecules, Δn, in the vicinity of the vaporizing volatile liquid droplets as a function of time and droplet size. Δn was found to be a function of the similar dimensionless variable r a where a is the droplet radius. Δn drops exponentially and exhibits an effect of free convection. In addition, it was found for all three substances that b, the radial distance at which the abrupt vapor concentration decrease occurs, is independent of drop size, i.e. the boundary of convection does not change in time. The reduction of interferometric data made it possible to determine saturation pressures, vapor densities and temperatures at the droplet surface. The variation of vapor density versus the dimensionless variable r a was obtained from the interferometric measurements by assuming a theoretical temperature distribution. The vaporizing rate constants, K, and internal droplet temperatures T i were measured at conditions where intensive heat transfer through the suspending fiber and thermocouple took place.

Dual Computer-generated Holograms for Testing Aspherical Surfaces

The use of a dual computer-generated hologram for performing interferometric testing of aspherical surfaces is described. The dual hologram consists of apertures whose positions are modulated along two different directions. The dual hologram allows the simultaneous generation of two different wavefronts whose sum and difference can be obtained with appropriate spatial filtering. This has been proved theoretically and verified experimentally. Finally, the dual hologram is utilized to test steep aspherics, and some practical advances of the dual hologram are mentioned.

Application of Dual Hologram Interferometry to Wind-Tunnel Testing

T study shows that dual hologram interferometry can be used to accurately measure local densities in wind-tunnel experiments, and that this technique does not suffer from some of the serious limitations of previous interferometric methods. A pulsed ruby laser is used as the light source so that highfrequency turbulence in the flow can be instantaneously recorded, and hence, frozen in time. The unique feature of dual hologram interferometry is that the no flow and flow conditions are recorded at different times on separate holograms. Because of this, movement between exposures is not recorded in the interferogram, and therefore, the method is not sensitive to wind-tunnel vibration. The images are interfered upon reconstruction, and the fringe configuration is controlled by precisely varying the orientation of the two holograms with respect to each other. ~ The heart of a practical, operational system is the dual hologram plate holder which is used to hold and precisely align the two holograms during image reconstruction. To demonstrate the accuracy and versatility of this method, three separate Mach 3 flowfields were considered in the original paper, but only the flat plate turbulent boundary-layer results are presented here.

Dual hologram interferometry

This report describes dual hologram interferometry, a new electro-optic technique used to calculate two-dimensional density distributions from measurable changes in index of refraction. Using this technique, two scenes recorded at different times are stored in separate holograms. One hologram contains reference data depicting the subject in an undisturbed state and the other hologram describes the same subject in a test or disturbed condition. Desired interference patterns are obtained by super-imposing the two separate scenes which are simultaneously reconstructed from each hologram. Specific interferograms, infinite fringe and various finite fringe patterns, are obtained by carefully regulating the optical attitude between the holograms and the reference beam during reconstruction of the scenes. In this project, dual hologram interferometry is used to describe quantitatively free convection from a uniformly heated right circular cylinder. Temperature distributions through the boundary layer and local heat transfer coefficients are determined at different azimuth positions. The results are compared both to experimental data obtained from another holographic technique and to a theoretical prediction of this specific test. This investigation shows that dual hologram interferometry accurately records changes in index of refraction which means the technique can be used to accurately measure experimental fluid flow data.