The increased performance and versatility of epitaxially grown III-V Type II strained layer superlattice (T2SLS) materials led to disruption of the IR sensor industry over the last decade. Increased performance at reduced cost are highly attractive to many end customers. Access to this detector material combined with the L3Harris front-side illuminated FPA structure lend to mechanically robust FPAs with array size only limited by source detector wafer size. This paper will present an overview of the technology development at L3Harris and the progress that has been made introducing SLS material into high operating temperature (HOT) MWIR sensors, LWIR sensors and dual-band (MW/MW & MW/LW) sensors.
L3Harris has developed a multispectral sensor architecture that opens doors to the incorporation of enabling functionality for future applications. This sensor architecture, while detector material agnostic in nature, builds upon our type-II superlattice (T2SL) technology, which was originally developed through the tri-service Vital Infrared Sensor Technology Acceleration (VISTA) program. The sensor architecture consists of stacked absorber layers that can be individually processed as they are integrated into the sensor stack. This layer-based approach enables the insertion of additional functional structures to enhance performance, such as embedded dielectric filters for efficient spectral separation, which would not be possible in a monolithic design. Due to the additional degrees of freedom with this configuration, it is necessary to design the filter such that it is compatible with the process required to functionalize each absorber while simultaneously meeting performance requirements. In this work, we report on various filter designs impacting the performance of focal plane arrays (FPAs) having embedded dielectric filters, under various practical constraints.
The nonlinear optical properties of a series of substituted thiophene oligomers have been investigated using the Z-scan technique. As the length of the thiophene increases from the monomer to an oligomer containing nine thiophene units, the absorption spectrum shifts to longer wavelength. This shift in wavelength moves the absorption band into resonance with the laser wavelength and the nonlinear optical properties of these materials change. In the samples where there is no linear absorption at the laser wavelength, the nonlinear absorption appears to originate from a two-photon absorption process. The nonlinear refraction observed is dominated by the contributions of the solvent. In the samples where there is linear absorption at the laser wavelength, several competing mechanisms appear to be responsible for the nonlinear response observed. At low laser irradiance, saturable absorption is observed. As the laser irradiance is increased, a decrease in the transmitted energy is observed. The nonlinear refraction in these materials is now large and negative.
KEYWORDS: Absorption, Optical limiting, Metals, Molecules, Pulsed laser operation, Chemical species, Picosecond phenomena, Chemical elements, Time resolved spectroscopy, Data modeling
We study one free base and seven metallo- octabromotetraphenylporphyrins by several techniques. In a pico-second pump-probe experiment, we monitor the transient transmission of each sample up to 11 ns after it is irradiated by an intense laser pulse. Combined with the results from time-resolved fluorescence spectroscopy, we propose a simple model to interpret the transmission data. We attribute the reduction in the transmission to triplet state absorption and extract the triplet state absorption cross-sections, as well as the lifetimes from the time dependent transmission data. In a separate experiment where the transmission of a nanosecond laser pulse is measured with various input energies, our measurement in the cross- sections predicts the correct optical limiting behavior. We assess the overall optical limiting performance of all 8 samples by direct comparison with C60 at the same ground state transmission.
We measure the magnitude and phase of the degenerate third-order nonlinear optical susceptibility (chi) (3)llll of solutions of various bis-thienyl polyenes (n-BTP) with the number n of the conjugated double bonds ranging from 3 to 9. We study both neutral and bipolaronic (i.e., doubly ionized) forms of n-BTP. We find that, within experimental error, (chi) (3)llll is proportional to nb where b-5.5 at 532 nm for our neutral n-BTP samples which have 3 <EQ n <EQ 9, and b-14 at 1.06 micrometers for the bipolaron state samples which have 6 <EQ n <EQ 9 where the probing laser wavelength is close to an absorption band. We calculate (chi) (3)llll of the bipolaronic n-BTP assuming it is associated with this absorption band acting as a two-level system and find good agreement with experiment.
We use a pump-probe technique to measure the change in optical transmission through a 1 cm C60/benzene (0.58 g/l) solution caused by a 532 nm 25 ps `pump' pulse having fluence up to approximately 10 mJ/cm2. Temporal dependence indicates that transmission drops within the pump pulse width and stays at the reduced level up to our maximum delay time (approximately 10 ns). If we use the standard three-level model for the C60 molecule we deduce that either the excited-singlet-to-triplet crossing happens faster than our pulse width or the two states have indistinguishable absorption cross-sections ((sigma) S approximately equals (sigma) T) at our laser wavelength. We believe that the latter assumption is more probable, and interpret our data by a simple two-cross-section ((sigma) O, (sigma) T) model. We find that the difference (sigma) T - (sigma) O is (3.5 +/- 0.2) X 10-17 cm2. We measure the ground state absorption cross-section (sigma) O to be (3.5 +/- 0.3) X 10-18 cm2 in an independent experiment.
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