This paper describes research conducted by the U.S. Army Combat Capabilities Development Command (DEVCOM) Analysis Center (DAC) to characterize the supercontinuum (SC) effect generated from interactions between ultrashort pulsed lasers (USPL) and commonly used optical materials. The well-known supercontinuum effect occurs when an optical material is irradiated by a laser with pulses of temporal width typically in the femtosecond regime. Interactions between the laser pulses and the material will induce a time dependent self-phase modulation, which leads to an apparent frequency modulation resulting in radiation emitted from the material as a “white light” laser.
Supercontinuum can be generated in many commonly used dielectric materials, otherwise known as bulk materials. The generation of SC in these bulk materials has been well documented and is easily achieved in an indoor laboratory setting. However, inducing SC generation (SCG) in an outdoor setting through atmosphere has not been reported as frequently. We conducted an outdoor experiment at DAC’s Electro-Optical Vulnerability Analysis Facility (EOVAF) laser range in July of 2023. An USPL was used to irradiate an optical collimating system several hundred meters from the USPL with several different bulk materials placed at its exit aperture using a spectrometer system to measure the SCG induced in the materials. After the outdoor experiment was completed, the spectrometer was calibrated using a quartz tungsten halogen (QTH) lamp. The calibration data were used to create a spectral response function which was applied to the uncalibrated spectral data of the SCG resulting in calibrated measurements of spectral fluence.
This paper describes a novel mathematical approach for correcting image distortions created with an optical laser scanning system employing a two-dimensional rotatable plane mirror. The image distortions are created by the movement of the plane mirror during the scanning process. Scanning mirror systems are frequently used in a variety of fields, such as medical imaging, material processing, device measurement, and three-dimensional scanning. The case of a fast steering scanning mirror used for low energy material retro-reflection measurements is studied. The system described suffers from distortions. This paper presents the derivation of a novel mathematical model used to correct the distortions. The corrections obtained from the model are tested and verified by application to an experimentally acquired data set.
Unique laboratory experiments are conducted using multiple waveband passive polarimetric and active infrared imaging systems to measure the optical signature of a diverse sample set in support of innovative research in material classification. The primary objective of this work is to explore the feasibility of utilizing multiple sensors of varying waveband or modality to enable or improve classification of common materials relevant in remote sensing applications. This objective includes current remote sensing technologies such as passive polarimetric imaging across multiple infrared wavebands, and light detection and ranging (LiDAR) active imaging. Therefore, to fully explore this objective, representative measurements of diverse materials are collected with three passive polarimeters and a LiDAR system. The measurements characterize material properties such as bidirectional reflectivity, directional emissivity, and surface roughness, which can be used for material classification. Typical passive polarimetric classification techniques assume the polarized signature is generated by reflection, and the imaging geometry is known. We propose to utilize both the polarized signature created by reflections as well as self-emission from the material. The reflectivity and imaging geometry estimations are assisted with the inclusion of LiDAR measurements. We present details of the experiment setup, sample set, analysis of imagery, and observations drawn from experimental results. The capability of classifying materials using passive polarimetric and active infrared imaging systems is investigated.
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