Advanced nanostructured antireflection coatings for high performances IR detector and imaging applications

Abstract

The growth and development of antireflection (AR) coatings comprising alternating optical layers has enabled reduced losses due to reflection of radiation off substrates and optical components, with associated substantial improvements in overall optical and imaging performance for a wide range of devices and applications. A novel means of enhancing transmission for improved detector and system performance has involved the growth of nanostructured optical layers offering tunable refractive index properties that provide broadband and omnidirectional suppression of light reflection/scattering while increasing transmission. These nanostructured AR coatings can be custom designed for specific wavebands from the ultraviolet (UV) to long-wave infrared (LWIR) for various photonic applications, such as when the need for increased sensitivity over a given wavelength range requires maximizing the transmission of light, e.g., onto the surfaces of detectors and imaging devices. We have developed advanced, optimized nanostructured AR coatings fabricated using a proprietary e-beam deposition process on GaSb, Si and various other types of substrates and sensors to provide broadband high AR performance, particularly for IR band sensing applications. These nanostructured coatings provide substantial improvements over conventional thin film AR coating technologies including quarter wavelength stacks by further minimizing reflection losses and increasing transmission over a wide range of light incidence angles on optical detectors and focal plane array (FPA) imaging devices. Here we review the latest developments of this high-performance nanoengineered AR coating technology in view of advancing NASA Earth Science sensing and imaging infrared (IR) band applications.

Advanced MWIR and LWIR band detection and imaging with nanostructured antireflection coating technology

“…9,10 (For example we previously have developed MWIR AR coatings for the 3-5 µm, 2-5 µm, and also more recently for the 1.5-5.0 µm range of wavelenths.) 2 For MWIR band AR coatings the ability to employ SiO2, a low-index and effective e-beam comparable material, is critical for high performance over this potentially extended or broad wavelength band.…”

“…High resolution imaging in infrared (IR) and ultraviolet (UV) bands has numerous applications in NASA space and commercial systems. [1][2][3] The performance of imaging sensor systems is limited by loss of incident signals from Fresnel reflection that occurs on both sides of optical components as well as from the front surfaces of imaging sensor arrays. This loss is significantly large due to the high refractive index of substrates used for IR and UV detector arrays and optical systems of interest to NASA.…”

High-performance graphene-enhanced HgCdTe photodetectors for uncooled extended infrared band sensing and imaging

“…1,2 The 2-5 μm MWIR spectral band is similarly suitable for various NASA Earth Science applications. 3,4 Using low size, weight, power, and cost MWIR sensors on smaller platforms in space can provide improved measurement and mission capabilities. 5 As cryogenic cooling is often utilized to minimize thermally generated dark current, and since dark current increases with longer cutoff wavelengths, this requirement becomes even more important for MWIR and long-wave infrared (LWIR) sensors.…”