TECHNOLOGY AREA(S): Materials OBJECTIVE: To have a microstructure designed for dielectric optically transparent materials to act as a narrowband (1030 to 1070 nm) high reflector (HR) for continuous wave (CW) laser light, while maintaining high transmission for the remaining wavelengths - visible into the infrared. Such structures should be designed to withstand high powers, into the kilowatts. DESCRIPTION: There is a need to develop narrowband high reflector microstructures for the 1030 to 1070 nm range for continuous wave (cw) laser light to protect and allow uninterrupted operation of visible, MWIR and LWIR sensors. Such microstructures will efficiently block the specified range of wavelengths while transmitting light in the rest of the spectral region and maintaining good optical imaging quality. The primary goal of the current SBIR is to develop a microstructure, which can be etched onto a variety of dielectric optical materials whose transparency regions span the visible through infrared (e.g. fused silica, zinc sulfide, zinc selenide, silicon, germanium, etc.), that will be capable of reflecting greater than 99.5% of 1030 to 1070 nm light while not reducing the transmission of the substrate by more than 10% and maintaining good optical imaging quality in the rest of the visible, MWIR and LWIR spectral regions. A microstructure capable of handling optical powers of up to 10 MW/cm2 is preferred, with an acceptance angle up to +/- 45 degrees over a one-inch clear aperture. Proposed microstructures should clearly include an efficient mechanism for dissipating the absorbed or reflected optical energy at the specified wavelength range. Materials should not be limited to traditional optical materials; instead exploitation of compatible material platforms suitable for operation in the visible to LWIR spectral range is encouraged. Ability of the chosen material to dissipate the required optical power and operate under standard military specification should be addressed. The proposed designs should be both polarization and vibration insensitive. Fabrication techniques needed to realize proposed filter designs should be clearly defined in the Phase I effort. Such structures should be scalable for dielectric optics with a diameter up to 4 inches. Such cw microstructures are useful for commercial applications that use 1030 to 1070nm lasers for manufacturing, as well as other industrial applications where protection of the operator and the environment is required to avoid damage from high intensity laser radiation. The cw high reflector microstructure filters will provide uninterrupted, enhanced force protection and day/night situational awareness. Military applications for this technology include laser safety devices for Mounted/Dismounted Ground System thermal sensors, and for thermal imaging systems on manned aircraft, unmanned aerial vehicles, and unattended ground sensors. PHASE I: Feasibility study for design and analysis of a cw high reflector microstructure for dielectric optical materials capable of reflecting greater than 99.5% of 1030 to 1070 nm light, while not reducing the transmission of the unaltered substrate in the rest of the visible, MWIR, and LWIR (400 nm to 12 m) spectral regions by more than 10%. A microstructure capable of handling optical power densities up to 10 MW/cm2 is preferable with an acceptance angle of 10 degrees over a one-inch clear aperture. These filters should be both polarization and vibration insensitive. The deliverables shall include a detailed design for a high reflector microstructure on four of the substrate materials (e.g. fused silica, zinc sulfide, zinc selenide, silicon, germanium, etc.). Include simulation results of the transmittance and reflectance spectra spanning the full spectral range (400 nm through 12 m) along with a best-effort coupon that demonstrates critical aspects of the manufacturing, and clearly demonstrates the capability to actualize the proposed reflectors. PHASE II: Fabrication and demonstration of prototype cw high reflector microstructures with a one-inch clear aperture (but scalable up to a 4 inch clear aperture), with an acceptance angle of 45 degrees, on four of the substrate materials. The filter should be capable of rejecting greater than 99.5% of 1030 to 1070 nm continuous wave light, while not reducing the transmission in the rest of the 400 nm to 12 m spectral region by more than 10%, and show that the reflectance is polarization insensitive. They should also be capable of handling optical power densities up to 10 MW/cm2. Damage testing will be conducted at the U.S. Army Research Laboratory with a 200 m to 900 m beam spot size. The expected deliverables are at least four fully-operational prototype cw high reflector microstructures on four different materials covering the spectral range of 400 nm to 12 m. Also, potential commercial and military transition partners for a Phase III effort shall be identified. PHASE III: Further research and development during Phase III efforts will be directed towards a final deployable design, incorporating design modifications based on results from tests conducted during Phase II, and improving engineering/form-factors, equipment hardening, and manufacturability designs to meet the U.S. Army CONOPS and end-user requirements. Manufactured cw high reflector microstructures shall be integrated into military systems utilizing visible, MWIR and LWIR sensor technologies. Potential commercial applications include laser protection of thermal security cameras for use in Homeland Security applications (perimeter security at airports, coastal ports, nuclear power installations), UAV sensor protection, as well as satellite sensor protection. The possibility to incorporate these structures onto windshield glass could also be explored, for the potential protection of both ground vehicles and aircrafts. REFERENCES: 1: Magnusson, R., "Wideband reflectors with zero-contrast gratings," Optics Letters 39, (15) 4337 (2014)2: Zhang, S., et. al., "Broadband guided-mode resonant reflectors with quasi-equilateral triangle grating profiles," Opt. Exp. 25 (23), 28451 (2017)3: Hobbs, D.S., MacLeod, B.D., and Manni, A.D., "Pulsed laser damage resistance of nanostructured high reflectors for 355nm" Proc. SPIE 10447, 104470W (2017) LASER DAMAGE SYMPOSIUM XLIX4: Chen, G., et. al., "Period photonic filters: theory and experiment, " Opt. Eng. 55 (3), 037108 (2016)KEYWORDS: High Power, Continuous Wave, Microstructure, 1 Micron, Optics, Infrared, Visible, High Reflector, Dielectric, High Transmission, MWIR, LWIR, Reflective
