DOD STTR 24.B Annual

Active
No
Status
Open
Release Date
April 17th, 2024
Open Date
May 15th, 2024
Due Date(s)
June 12th, 2024
Close Date
June 12th, 2024
Topic No.
A24B-T003

Topic

High Reflector Microstructure for 1 Micron Continuous Wave Light and Mid to Long Wave Transmission

Agency

Department of DefenseN/A

Program

Type: STTRPhase: Phase IYear: 2024

Summary

The Department of Defense (DOD) is seeking proposals for a Small Business Innovation Research (SBIR) program focused on the development of a high reflector microstructure for 1 micron continuous wave light and mid to long wave transmission. The objective is to build a microstructure that can efficiently block the specified range of wavelengths (1030 to 1070 nm) for continuous wave laser light while maintaining high transmission in the mid-wave to long-wave infrared (MWIR to LWIR) spectral region. The microstructure should be capable of reflecting greater than 99.5% of the specified light while not reducing the transmission of the substrate by more than 10% and maintaining good optical imaging quality. The proposed microstructures should be scalable for dielectric optics with a diameter up to 5 inches. The Phase I effort involves the design, analysis, and fabrication of a high reflector microstructure, while Phase II focuses on the fabrication and demonstration of a prototype microstructure. Phase III efforts will involve further research and development to finalize the design and integrate the microstructures into relevant systems. The potential applications of this technology include protection of thermal cameras for private security and the potential protection of any infrared systems. The solicitation is open, with a close date of June 12, 2024. More information can be found on the grants.gov website or the DOD SBIR/STTR Opportunities page.

Description

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Directed Energy (DE), Space Technology, Advanced Materials

 

OBJECTIVE: Build a microstructure designed for dielectric optically-transparent materials to act as a narrowband (1030 to 1070nm) high-reflector for cw laser light, while maintaining high transmission in the MWIR to LWIR.

 

DESCRIPTION: There is a need to develop highly reflective microstructures for the 1030 to 1070 nm range for continuous wave (cw) laser light to protect and allow uninterrupted operation of mid-wave to long-wave infrared sensors.  Such microstructures will efficiently block the specified range of wavelengths while transmitting light in the rest of the infrared spectral region and maintaining good optical imaging quality. 

 

The primary goal of the current STTR is to develop a microstructure, which can be etched onto a variety of dielectric optical materials whose transparency regions span the infrared (specifically ZnS, ZnSe, BaF2, Silicon, Ge, and other such optics), 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 (structural similarity index measure (SSIM) greater than 0.9) in the infrared spectral region.  A microstructure capable of handling optical powers of up to 10 MW/cm2 is preferred, with an acceptance angle of at least +/- 15 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 infrared 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 5 inches.

 

Nano-structure resonant surfaces, a type of microstructure, consist of an array of index variations formed by holes or mesas.  Typically, the array is etched into a substrate like fused silica and then conformally coated with a thin layer of higher index material like aluminum oxide or tantalum pentoxide.  This gives a high low index contrast and periodic variation in a direction transverse to the beam propagation direction.  In this way you can set-up a filter function in a single structured surface that performs as well as 50 to 200 thin-film layers typical of an interference filter.  Interference Filters accumulate their resonance in the longitudinal direction. This is one of the major advantages of nano-structure resonant (NSR) reflection (notch transmission) filters. 

 

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.  There exist numerous military applications for this technology which can be further discussed at the CUI and higher levels.

 

PHASE I: Design, analysis and fabrication 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 MWIR, and LWIR (3 µm to 12 µm) spectral regions by more than 10% and not degrading the optical quality of the transmitted light significantly (SSIM greater than 0.9).  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 (zinc selenide, and three of the following: zinc sulfide, barium fluoride, silicon, and germanium). Include simulation results of the transmittance and reflectance spectra spanning the full spectral range (400 nm through 12 µm) along with a prototype coupon, i.e. a small-scale device 1in2 or larger with full functionality, as a proof of concept 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 2 inch clear aperture (but scalable up to a 4 inch clear aperture), with an acceptance angle of ± 15 degrees, on four of the substrate materials (including ZnSe). 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 3 µm to 12 µm spectral region by more than 10% and not degrading the optical quality of the transmitted light significantly (SSIM greater than 0.9).  Additionally, the reflectance should be 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 µm to 900 µm 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 3 µm to 12 µm.  Deliverables will be tested for cw damage threshold and within sensor systems.  Also, potential commercial and military transition partners for a Phase III effort shall be identified.

 

PHASE III DUAL USE APPLICATIONS: 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 relevant systems.  

 

Potential commercial applications include protection of thermal cameras for Private security.  The possibility to incorporate these structures onto other glasses could also be explored, for the potential protection of any infrared systems.

 

REFERENCES:

Magnusson, R., “Wideband reflectors with zero-contrast gratings,” Optics Letters 39, (15) 4337 (2014) Chen, G., et. al., “Period photonic filters: theory and experiment,” Opt. Eng. 55 (3), 037108 (2016) http://spie.org/Publications/Journal/10.1117/1.OE.55.3.037108?SSO=1; 
Zhang, S., et. al., “Broadband guided-mode resonant reflectors with quasi-equilateral triangle grating profiles,” Opt. Exp. 25 (23), 28451 (2017) https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-23-28451; 
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 XLIX

 

KEYWORDS: high power, continuous wave, microstructure, 1 micron, optics, infrared, high reflector, dielectric, high transmission, MWIR, LWIR, reflective