OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Directed Energy (DE) OBJECTIVE: Develop an optical diagnostic system capable of measuring the time evolution of a high-energy laser beam at two or more axial positions on the beam path simultaneously. Priority will be given to instrumentation concepts that can capture the 2-dimensional cross-section of a laser beam profile such that it is completely non-interfering to the optical path of the laser DESCRIPTION: The Air Force is interested in characterizing the space-time evolution of high-energy lasers (HELs) in the field and in the laboratory. HEL beams are degraded by atmospheric scatter due to water vapor, salt particles, dust and other particulate matter, and distorted by thermal blooming within the HEL beam. These distortions and degradations negatively affect the intensity of the beam on target, reducing kill-chain effectiveness. AFRL has a charter (DAFI 49-401) to characterize the performance of new HEL systems prior to releasing them into service, and a multi-point beam profiler is seen as a necessary diagnostic to that end. Predictive models leading to improved adaptive-optics solutions would benefit from measuring the time evolution of the 2-D irradiance profile at one or more axial locations simultaneously before measuring the downrange irradiance profile on target using conventional means; however, doing this would require a noninvasive method which is not currently available. Most commercially available beam profilers are either scanning-slit or CMOS camera profilers, both of which are placed within the path of the beam and are fully destructive to it downrange. Commercially available non-contact beam profilers are designed for very high local intensity and small beam waist and are largely unsuited for the scale of HEL beams; furthermore, they only characterize the radial profile from a 1-D integrated viewing angle. A specific need remains to characterize the 2-D irradiance profile nonperturbatively. The requirements for the system are the following: a. Beam cross-section between 10 and 50cm (T=O) b. Nominal laser wavelength 1.07 micron (T), extendable to 1.07 micron and 2 micron (O) c. Cross-sectional spatial resolution 1.25cm (T) 2.5mm (O) d. Measurement must be nonperturbing / noninvasive to the beam path e. Minimum peak irradiance 20kW/cm2 (T), 2kWcm2 (O) f. Beam cross-section dynamic range 20dB (T), 35dB (O) g. Usable in the laboratory or field (T), and over water (O) h. Minimum time resolution 100ms (T), 10ms (O) i. Must operate outdoors in full sunlight (T=O) j. Simultaneous multi-point measurements on the laser propagation axis between 10m and 200m (T) to 10km (O) k. Combination of background clutter (solar, HEL multipath backscatter, etc) must be <5% (T) or <1% (O) that of the measured beam. i. Must not rely on aerosol backscatter (fog, dust, etc) for off-axis beam characterization. m. Preference will be given to devices capable of measuring without intervening optics (such as beam splitters). n. System should demonstrate a path to multiple simultaneous measurements along the beam path at separations between 100m (T) and 5km (O) PHASE I: As this is a Direct-to-Phase-II (D2P2) topic, no Phase I awards will be made as a result of this topic. To qualify for this D2P2 topic, the Air Force expects the applicant(s) to demonstrate feasibility by means of a prior Phase I-type effort that does not constitute work undertaken as part of a prior or ongoing SBIR/STTR funding agreement. Applicant(s) is required to provide detail and documentation in the Direct to Phase II proposal which demonstrates accomplishment of a Phase I-like effort, including a feasibility study. This includes determining, insofar as possible, the scientific and technical merit and feasibility of ideas appearing to have commercial potential. The "Phase-I-type" study should minimally demonstrate: a. That the diagnostic mechanism, through a combination of analysis and/or measurement, is sustainable. b. A path to a 2-D beam profile measurement, whether through direct measurement or mathematical algorithmic reconstruction techniques. c. Evidence that the background clutter is bounded to less than 5% of the measured signal. d. A proposed system architecture that, through combination of system engineering and bench testing, substantiates Requirements a-n listed in the Topic Description. PHASE II: Build a single TRL6-level platform relevant to the Air Force's HEL beam diagnostic needs. Demonstrate and evaluate, with support of a government furnished laboratory- or field-based HEL system, the system's ability to image the HEL 2-D irradiance profile under a variety of conditions. Compare measured performance against preliminary modeling, analysis and measurement. Refine and update imaging capability as necessary. Design a preliminary workstation, including display, graphical interface and system controls to enable an operator to configure the diagnostic optimally. Ultimately demonstrate that the diagnostic either meets all system threshold requirements or shows a clear path to meeting requirements through a cost-reasonable Phase II enhancement or Phase III transition plan. PHASE III DUAL USE APPLICATIONS: Complete system diagnostic, including building multiple units for simultaneous measurements along the HEL beam path. Facilitate a transition plan that provisions for future fielding of units for dual-use applications, such as real-time diagnostic feedback and adaptive optics for improved beam control. REFERENCES: 1. KLEINMAN R.E. and SENIOR T.B.A.; "Chapter 1 - Rayleigh Scattering", Mechanics and Mathematical Methods - Series of Handbooks, Vol 2, 1986, pages 1-70 2. NIETO-VESPERINAS M. "2-Fundamentals of Mie Scattering", Dielectric Metamaterials, Fundamentals, Design, and Applications; Woodhead Publishing Series in Electronic and Optical Materials, 2020, pages 39-72 3. GARDNER R.J. "Geometric Tomography", Notices of the AMS, 1995, pages 1-429 4. SMITH D.J. "High Power Laser Propagation: Thermal Blooming", Proceedings of the IEEE, Volume: 65, Issue: 12, December 1977, Pages: 1679 - 1714 5. High Power Optical Splitter for Laser Weapons Systems (SBIR N241-041), https://www.navysbir.com/n24_1/N241-041.htm 6. CMOS Camera Beam Profilers that measure reliably but dump the beam on the output: https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=3483 7. One resource for a non-contact beam profiler that measures only the integrated transverse profile (one view from the camera angle): https://www.ophiropt.com/en/p/SP90623 8. "An application of a tomographic scattering detection system": https://opg.optica.org/optcon/fulltext.cfm?uri=optcon-1-5-949&id=471728 KEYWORDS: HEL Weapon; Beam Profiler; Thermal Blooming; Atmospheric Propagation; Beam Cross section; HEL Irradiance; HEL Spot Size, Tomographic high energy laser transverse irradiance profile
