The Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket payload flew for the second time on 2014 December 11. To enable direct Hard X-Ray (HXR) imaging spectroscopy, FOXSI makes use of grazing-incidence replicated focusing optics combined with fine-pitch solid-state detectors. FOXSI’s first flight provided the first HXR focused images of the Sun. For FOXSI’s second flight several updates were made to the instrument including updating the optics and detectors as well as adding a new Solar Aspect and Alignment System (SAAS). This paper provides an overview of these updates as well as a discussion of their measured performance.

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Optical second-harmonic generation (SHG) in reflection characterized variations in the second-order nonlinear optical susceptibility χ(2) of Ba1−xSrxTiO3 (BSTO) alloy films grown epitaxially on SrTiO3(001) (STO) as Sr molar ratio x changed from 0 to 1 and thickness from 10 to 50 nm. X-ray diffraction showed that BSTO films with x ≳ 0.1 were highly crystalline and compressively strained with out-of-plane (in-plane) lattice constant 4.09 > c > 3.97 (3.903 < a < 3.907 Å, pinned to substrate) for 0 < x < 1. Spectroscopic ellipsometry showed that the BSTO dielectric function was nearly x-invariant in the range of fundamental (780 nm) and SH (390 nm) wavelengths. SHG intensity peaked at x ∼ 0.3 for a given film thickness, suggesting that composition control can optimize ferroelectric and electro-optic properties of BSTO films grown on STO buffer layers.

A preliminary measurement of the second‐order nonlinear optical susceptibility of symmetric, coupled, InAs/AlSb multiple quantum well (MQW) structures is acquired through optical second‐harmonic generation (SHG) at fundamental wavelength 1.55 µm. High quality crystalline MQW structures of variable thickness and corresponding bulk AlSb control samples are achieved using a digital alloy epitaxial growth technique that avoids cluster formation and phase segregation. All samples are grown in between a GaSb cap and substrate layer. To isolate SHG from the MQW (or control) layers of interest from cap and substrate contributions, a multilayer optical response matrix model is built and independently tested by accurately reproducing linear reflectivity spectra. While a simplified response matrix analysis of SHG based solely on bulk χ(2)s does not reproduce the distinct SHG responses of the two sets of samples, the inclusion of an additional interface SHG contribution leads to a successful fit of the data and implies . The results demonstrate a proof‐of‐concept quantification of χ(2) in symmetric MQWs and suggest the possibility of engineering χ(2) in these structures, particularly with the introduction of well asymmetries.

The nuclear spins of low-density implanted Ga atoms in Ge are interesting candidates for solid state-based qubits. To date, activation studies of implanted Ga in Ge have focused on high densities. Here, we extend activation studies into the low-density regime. We use spreading resistance profiling and secondary ion mass spectrometry to derive electrical activation of Ga ions implanted into Ge as a function of the rapid thermal anneal temperature and implant density. We show that for our implant conditions, the activation is best for anneal temperatures between 400 and 650 °C with a maximum activation of 69% at the highest fluence. Below 400 °C, remaining implant damage results in defects that act as superfluous carriers, and above 650 °C, surface roughening and loss of Ga ions are observed. The activation increased monotonically from 10% to 69% as the implant fluence increased from [Formula: see text] to [Formula: see text] cm−2. The results provide thermal anneal conditions to be used for initial studies of using low-density Ga atoms in Ge as nuclear spin qubits.