Differential Excitation Spectroscopy (DES) is a new pump-probe detection technique (patent-pending) which characterizes molecules based on a multi-dimensional parameterization of the rovibrational excited state structure, pump and probe interrogation frequencies, as well as the lifetimes of the excited states. Under appropriate conditions, significant modulation of the ground state can result. DES results provide a unique, simple mechanism to probe various molecules. In addition, the DES multi-dimensional parameterization provides an identification signature that is highly unique and has demonstrated high levels of immunity from interferents, providing significant practical value for highspecificity material identification. Dimethyl methylphosphonate (DMMP) is used as a simulant for G series nerve agents and thiodiglycol as a simulant for sulfur mustard (HD). Ab initio calculations were performed on DMMP for various rovibrational states up to J’ ≤ 3 and validated experimentally, demonstrating good agreement between theory and experiment and the very specific responses generated. Thiodiglycol was investigated empirically. Optimal detection parameters were determined and mixtures of the two materials were used to demonstrate the immunity of the DES technique to interference from other materials, even those whose IR spectra show significant overlap.
Differential Excitation Spectroscopy (DES) is a new pump-probe detection technique (patent-pending) which characterizes molecules based on a multi-dimensional parameterization of the rovibrational excited state structure, pump and probe interrogation frequencies, as well as the lifetimes of the excited states. Under appropriate conditions, significant modulation of the ground state can result. DES results provide a unique, simple mechanism to probe various molecules. In addition, the DES multi-dimensional parameterization provides an identification signature that is highly unique and has demonstrated high levels of immunity from interferents, providing significant practical value for high-specificity material identification. Ammonium nitrate (AN) and urea nitrate (UN) are both components commonly used in IEDs; the ability to reliably detect these chemicals is key to finding, identifying and defeating IEDs. AN and UN are complicated materials, having a number of different phases and because they are molecular crystals, there are a number of different types of interactions between the constituent atoms which must be characterized in order to understand their DES behavior. Ab initio calculations were performed on both AN and UN for various rovibrational states up to J’ ≤ 3 and validated experimentally, demonstrating good agreement between theory and experiment and the very specific responses generated.
Kestrel Corporation has previously demonstrated that the Distorted Grating Wavefront Sensor (DGWFS) can successfully reconstruct wavefronts in severely scintillated conditions, and has an ongoing experiment investigating aberrations in the eye using a DGWFS. Existing aberrometers cannot accurately reconstruct wavefronts when large amounts of scattering or scintillation are present and so cannot be used with subjects who have conditions such as cataracts (opacification of the ocular lens). Consequently a large proportion of the population cannot utilize today's diagnostic aberrometers and so do not benefit from otherwise available treatments. As previously reported, a DGWFS has been integrated into an Shack-Hartmann based aberrometer provided by the International Laser Center, Moscow State University, however several issues became apparent regarding data collection from the human eye. Results from laboratory experiments intended to investigate and resolve these data collection issues will be discussed.
Earlier research reported a comparison of the wavefronts recorded simultaneously by a Shack-Hartmann and a Distorted Grating Wavefront Sensor (DGWFS). In this paper we present the results of a continuation of this earlier work where we have now closed an adaptive optics loop under simulated propagation conditions using the Advanced Concept Laboratory (ACL) at Lincoln Laboratory. For these measurements only one wavefront sensor controlled the deformable mirror at a time. To make direct comparisons between the sensors we took advantage of the ACL's ability to exactly replicate a time varying propagation simulation. Time varying and static comparisons of the two sensors controlling the ACL adaptive system under conditions that ranged from a benign path, D/r0 = 2, to a propagation condition with significant scintillation, D/r0 =9, will be shown using the corrected far field spot as a measure of performance. The paper includes a description of the DGWFS used for these tests and describes the procedure used to align and calibrate the sensor.
The concept of a curvature-based wavefront sensor using a distorted grating as the imaging element to capture images of two spatially separated planes onto a single detector has been reported previously. This presentation reports on simulations comparing a Shack-Hartmann (S-H) sensor with a distorted grating wavefront sensor (DGWFS) for a generic adaptive optics (AO) system using a Clear-1 atmospheric model. Using WaveTrainTM simulation software a model of the DGWFS has been developed and integrated into the software. A simulation of a complete AO system including a tip/tilt system, high order correction system, atmospheric model, and a back-propagating laser system has been constructed. The model has then been exercised using various seeing conditions, noise levels, WFS sensitivities, camera systems, and other parameters. A comparison between the performance of the AO system using the S-H sensor and the DGWFS is presented, both in terms of wavefront measurement accuracy, image quality, and as a beam delivery system.
A key element in any adaptive optics system is the deformable mirror used to introduce the conjugate correction. In this paper we will present the results from characterizing a pair of custom 20 element, 38 mm diameter, bimorph deformable mirrors that were specifically designed to provide unusually large stroke to allow correction of significant focus and astigmatism terms in a human fundus adaptive optics imager. Data on the measured correction capability and inherent hysteresis of the mirror shown that the mirrors have 40 μm waves of defocus correction and 20 μm waves of astigmatism correction at 760 nm, with a typical hysteresis at full deflection of 15%. This technology is patented under Patent # 6,331,059 B1.
Earlier research reported a comparison of the wavefronts recorded simultaneously by a Shack-Hartmann and a Distorted Grating Wavefront Sensor (DGWFS). In this paper we present the results of a continuation of this earlier work where we have now closed an adaptive optics loop under simulated propagation conditions using the Advanced Concept Laboratory (ACL) at Lincoln Laboratory. For these measurements only one wavefront sensor controlled the deformable mirror at a time. To make direct comparisons between the sensors we took advantage of the ACL’s ability to exactly replicate a time varying propagation simulation. Time varying and static comparisons of the two sensors controlling the ACL adaptive system under conditions that ranged from a benign path, D/r0 = 2, to a propagation condition with significant scintillation, D/r0 =9, will be shown using the corrected far field spot as a measure of performance. The paper includes a description of the DGWFS used for these tests and describes the procedure used to align and calibrate the sensor.
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