We report a functional optical coherence tomography cross-sectional scanner to detect neural activity using unmyelinated nerves dissected from squid. The nerves, unstained or stained with a voltage-sensitive dye, were imaged in a nerve chamber. Transient phase changes from backscattered light were detected during action potential propagation. The results show that the scanner can provide high spatiotemporal resolution cross-sectional images of neural activity (15 μs/A-line; 0.25 ms/B-scan; ∼8.5×5.5 μm2 in xz). The advantage of this method compared to monitoring a single depth profile z is a dramatic increase in the number of available sites that can be measured in two spatial dimensions xz with lateral scanning; therefore, the study demonstrates that two-dimensional monitoring of small-scale functional activity would also be feasible.
We report terahertz (THz) emission from magnesium doped a-plane indium nitride (a-InN:Mg) films with different
background carrier density, relative to the Mg-doped InN films grown along the c-axis (c-InN:Mg). Due to its high
electron affinity, as-grown InN film is typically n-type and it has extremely high background carrier density, which
causes much weaker THz emission than that from other semiconductors, such as InAs. The background carrier density of
Mg-doped InN can be widely changed by adjusting the Mg doping level. For c-InN:Mg, THz emission is dramatically
enhanced (×500 than that of undoped c-InN) as the background carrier density decreases to a critical value of ~1×1018cm-3, which is due to the reduced screening of the photo-Dember field at the lower carrier density. For a-InN, however,
intense THz emission (×400 than that of undoped c-InN) is observed for both undoped and Mg-doped a-InN and the
enhancement is weakly dependent on the background carrier density. The primary THz radiation mechanism of the aplane
InN film is found to be due to the acceleration of photoexcited carriers under the polarization-induced in-plane
electric field perpendicular to the a-axis, which effectively enhances the geometrical coupling of the radiation out of
semiconductor. The weak dependence of THz radiation on the background carrier density for a-InN shows that in-plane
surface field induced-terahertz emission is not affected by the background carrier density. Small, but apparent azimuthal
angle dependence of terahertz emission is also observed for a-InN, indicating the additional contribution of nonlinear
optical processes on terahertz emission.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.