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High Energy Laser Beam Absorption Diagnostics and Thermal Blooming Prediction System

Description:

TECHNOLOGY AREA(S): Weapons, 

OBJECTIVE: To develop an atmospheric absorption spectroscopy measurement system capable of measuring the absorption properties of atmospheric gases and particles in the 1000-1100 nanometer near infrared wavelength band, and predict the occurrence and degree of thermal blooming due to high energy laser beam propagation. 

DESCRIPTION: The objective of this effort is to create a portable measurement system to characterize the spectral absorption in numerous deployable environments over the wavelengths of 1030 – 1080nm, and make predictions on thermal blooming effects. These measurements will be utilized to characterize the specific mechanisms that give rise to thermal blooming as well as to determine the maximum amount of laser energy that can be utilized for a given engagement before thermal blooming effects create diminishing returns on increased laser power. Since the instrumentation will be used in the field, it must be designed such that it is immune to the effects of turbulence which can be severe over long near ground paths. The measurement path length must be optimized to balance the need for adequate atmospheric sampling, measurement accuracy, and immunity to turbulence. The measurement system should be validated through modeling and laboratory experimentation before it is taken out of a controlled lab environment to support field tests. Below is a set of threshold and objective requirement for the final field test instrument. Wavelength Range (nm): T: 1030-1070; O: 1000-1100 Spectral Resolution (nm): T: 0.1; O: 0.01 Absorption accuracy (%): T: 5; O: 1 Environment: T: 24/7 Outdoor operation, Temperature 0-50C; O: 24/7 Outdoor operation, Temperature -15-60C Atmospheric Turbulence (worst case): T: Cn2 < 1x10^-13; O: Cn2 < 1x10^-12 Eye safety: Eye safe operation (no PPE required) Size/Weight/Ruggedized: T: Field Test Transportable; O: Tripod Mountable 

PHASE I: The phase I effort will focus on the design of measurement system and analysis of the thermal blooming prediction model theory. This effort should result in a preliminary design that has been analyzed using modeling and simulation to establish high confidence that the instrument will be capable of meeting the requirements in the field test environment described above, and the theoretical process for determining thermal blooming based on measurements from the system. 

PHASE II: The Phase I designs will be utilized to fabricate, test and evaluate a breadboard system. The designs will then be modified as necessary to produce a final prototype. The final prototype will be demonstrated in a field test or controlled environmental chamber to validate its thermal blooming prediction accuracy. 

PHASE III: High energy DoD laser weapons offer benefits of graduated lethality, rapid deployment to counter time-sensitive targets, and the ability to deliver significant force either at great distance or to nearby threats with high accuracy for minimal collateral damage. Future laser weapon applications will include very high power devices used for air defense to detect, track, and destroy incoming rockets, artillery, and mortars and it is expected that thermal blooming will be a significant limiting factor. The utilized laser power will need to be managed to keep it just below the level that would produce thermal blooming. The Phase III effort would be to design and build a sensor that could be integrated into an Army’s High Energy Laser Weapon System for real time use as part of the fire control system. Military funding for this Phase III effort would be executed by the US Army Space and Missile Defense Technical Center as part of its Directed Energy research. 

REFERENCES: 

1: J. I. Steinfeld, "Molecules and Radiation: Introduction to Modern Molecular Spectroscopy", Dover Publications, (1974)

KEYWORDS: High Energy Lasers, Thermal Blooming, Absorption Spectroscopy, Spectral Transmission, Spectrometer, Spectrophotometer 

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