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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.

 

We simulate the possibility of scaling channel formation to low density plasmas of low atomic number gas over a large range of pulse duration including (1) pulses up to 300 ps in duration, using inverse bremsstrahlung (IB) heating and (2) ultrashort pulses up to 100s of femtoseconds for generating tenuous plasmas of centimeter to meter lengths by optical field ionization (OFI). Results show IB heating up to tens of eV, and channels formed from an initial density of 1e18 cm-􀀀3 with axial densities as low as 1e17cm-3 and radius of 50 microns. It has been shown that centimeter-scale waveguides can be generated via OFI heating at densities of approximately 1e17 cm-􀀀3. Lastly, we outline the experimental setup to be used in future experiments at the University of Texas Tabletop Terawatt (UT3) facility. 

Heteroepitaxial crystalline films underlie many electronic and optical technologies but are prone to forming defects at their heterointerfaces. Atomic‐scale defects such as threading dislocations that propagate into a film impede the flow of charge carriers and light degrading electrical/optical performance of devices. Diagnosis of subsurface defects traditionally requires time‐consuming invasive techniques such as cross‐sectional transmission electron microscopy. Using III–V films grown on Si, noninvasive, bench‐top diagnosis of subsurface defects have been demonstrated by optical second‐harmonic scanning probe microscope. A high‐contrast pattern is observed of subwavelength “hot spots” caused by scattering and localization of fundamental light by defect scattering sites. Size of these observed hotspots are strongly correlated to the density of dislocation defects. The results not only demonstrate a global and versatile method for diagnosing subsurface scattering sites but uniquely elucidate optical properties of disordered media. An extension to third harmonics would enable irregularities detection in non‐χ⁽²⁾materials making the technique universally applicable.