Air Force Research Laboratory and MetroLaser, Inc. researchers have completed the initial development and transition to operational use of portable field holography systems. This paper documents the first fully operational use of a novel and unique experimental capability for remote field holography. In this paper we document the field trials and initial experiments that were performed with the Remote Holographic Interferometry System (RHIS) at the Munitions Directorate, Air Force Research Laboratory Site at Eglin, AFB, Florida. These experiments were performed to assess the effectiveness of remote pulsed laser holography combined with high-speed videography to document the formation and propagation of plumes of materials created by impact of high-speed projectiles. This paper details the development of the experimental procedures and initial results of this new tool.
Development of an aero-optics simulation code is reviewed. When completed, the code will contain three elements, 1) an algorithm for producing physically plausible aero-optical properties and bounds on properties characterizing flows of interest, 2) an algorithm for converting these into aero-optical features of a flow described by a set of time varying, random, phase masks, and 3) a code that will integrate these and propagate a wavefront through a typical test scenario with an output similar to that provided by the test diagnostics. The resultant aero-optics computational simulator will allow an aerodynamicist to simulate and run aero-optical tests that will be useful for test planning and data interpretation. This paper reviews the approach taken by the author in modeling aero-optic phenomena and presents initial results based on a simplified model of a turbulent condition through which point source wavefront is propagated.
A method is presented to store biometric and/or other important information on an ID card in the form of a Card Hologram that cannot be read or duplicated without the use of a special Key Hologram that is secured inside of an automated reader. The Key Hologram produces the unique wavefront required to release the information contained in a complex, 3- D diffraction pattern recorded in a volume hologram attached to the card. Experimental results are presented in which the image of an Air Force resolution target are recorded and reconstructed in a volume material using a random speckle wavefront and that cannot be viewed using a simple wavefront such as a collimated or diverging laser beam.
This paper presents experimental results using a ZnSe Risley prism scanner in which diffractive gratings were etched into the prism faces to correct for chromatic aberrations. Risley prism scanners, which consist of independently rotating prisms, offer distinct advantages over mirrored systems. The faces of the two scanner elements are parallel and adjacent to one another, resulting in a simple, lightweight, and compact system with extremely high pointing stability and accuracy. Laboratory results for the scanner, when used in a midwave infrared imaging system, demonstrated a total field of view +/- 22.5 degrees with almost no aberrations. The optical performance of the scanner demonstrated a factor of two improvement in resolution when compared to an equivalent scanner using no diffractive correction. We conclude that the use of diffractively corrected prisms offer a new potential for using Risley prisms as a alternative lightweight scanner in missile seekers.
A method is presented to store biometric and/or other important information on an ID card in the form of a Card Hologram that cannot be read or duplicated without the use of a special Key Hologram that is secured inside of an automated reader. The Key Hologram produces the unique wavefront required to release the information contained in a complex, 3D diffraction pattern recorded in a volume hologram attached to the card. Experimental results are presented in which the image of an Air Force resolution target are recorded and reconstructed in a volume material using a random speckle wavefront and that cannot be viewed using a simple wavefront such as a collimated or diverging laser beam.
Emblems using holograms or other diffractive devices have long been used to mark cards and other objects as a means of authentication. The effectiveness of such emblems as a security device is ultimately determined by the inspection system. Due to the expense and highly variable performance of the human inspector, automated machine reading devices are an attractive alternative for performing the verification task. An additional advantage of the machine reader is that information regarding the card or its holder may be stored covertly. A security verification system is presented consisting of a holographic security emblem in which information is covertly stored, and an automated reader based on a joint transform correlator (JTC). A holographic encoding method is used to produce an emblem that stores the required phase and/or amplitude information in the form of a complex, 3-D diffraction pattern that can only be interpreted through the use of a second 'key' hologram. The reader incorporates the use of the non-linear material, Bacteriorhodopsin, as a means of miniaturizing the system, reducing system cost, and improving system performance. Experimental results are presented that demonstrate the feasibility of the approach for security applications.
Holographic interferometry can be used to examine minute changes in the surface of components as they undergo stress, thermal expansion, erosion, growth, and vibration. Such changes often can be used to identify the presence of a defect beneath the surface, because of the anomalous microscopic behavior of the surface. In addition, the mechanical characteristics of the component, such as vibrational modes, expansion, and residual stress can be identified through holographic inspection. Over the past 30 years a wide range of methods have evolved as new hardware and technology becomes available. The wide range of procedures, including electronic holography, multiwavelength recording thermoplastic recording, time-averaged holography, real-time holographic interferometry, cineholography, and other methods can be revisited each time a new development is made in lasers, computers, and recording materials. Methods that once held only academic interest often become practical with newly available hardware and software.
There is a need to perform modal analysis upon large structures such as buildings and bridges to understand and predict their behavior during earthquakes. Conventional holographic techniques cannot practically be used. Time average holography on glass plates and thermoplastic film requires vibration isolation. Double pulse holography on glass plates is time consuming in the processing of the plates and locating resonance frequencies and requires an in field darkroom. Conventional electronic speckle pattern interferometry (ESPI) normally requires vibration isolation and is limited to frequencies above 30 hertz. And also ESPI normally produces undesirable noisy looking images. Techniques for performing double pulsed ESPI with fringe enhancement and no vibration isolation have been developed to study these large structures. The work in progress on these techniques is presented.
Holography concepts have been evaluated as nonintrusive tools that can measure earthquake effects and earthquake resistance of structures. The methods offer potential toward the application of advanced design techniques in civil and earthquake engineering. Our study produced methods to holographically monitor large, distant surfaces, which could be used to inspect buildings, bridges, storage tanks, or dams during interaction with geological or meteorological forces. This work included the successful demonstration of holography in obtaining modal information of a 3.4-m-tall liquid storage tank at a distance of 20 m.
The use of pulsed laser holography in analyzing the atomization of impinging jets is evaluated using a holographic camera system capable of recording a 3D image of the atomization process in 3 x 10 exp -8 seconds. The holocamera and the experimental configuration and procedure are described in detail. Two nozzles were fabricated to produce 1-mm diameter liquid water jets that impinged at 60 and 90 deg. Holograms were obtained for each nozzle at liquid velocities of 20 and 40 m/s. Analysis of the holograms revealed the evolution of the jets from the plane of emergence through the region of droplet formation. Features of interest included the growth of disturbances prior to the breakup region and the effect of these disturbances on the formation of ligaments and liquid globules. Preliminary analyses show that waves of atomized liquid formed after impingement are closely correlated to waves measured on the jets, leading to the possibility of controlling the atomization process at the nozzle.