The Photonic Fence is a system designed to detect mosquitoes and other pestilent flying insects in an active region and to apply lethal doses of laser light to them. Previously, we determined lethal fluence levels for a variety of lasers and pulse conditions on anesthetized Anopheles stephensi mosquitoes. In this work, similar studies were performed while the bugs were freely flying within transparent cages. Dose-response curves were created for various beam diameter, pulse width, and power conditions at 455 nm, 532 nm, 1064nm, and 1540 nm wavelengths. Besides mortality outcomes, the flight behavior of the bugs and the performance of the tracking system were monitored for consistency and to ensure that they had no impact on the mortality outcomes. As in anesthetized experiments, the visible wavelengths required significantly less fluence than near infrared wavelengths to reliably disable bugs. For the visible wavelengths, lethal fluence values were generally equivalent to those found in anesthetized dosing, while near infrared wavelengths required approximately twice the fluence compared with anesthetized experiments. The performance of the optical tracking system remained highly stable throughout the experiments, and it was found not to influence mortality results for pulse widths up to 25 ms. In general, keeping energy constant while decreasing power and increasing pulse width reduced mortality levels. The results of this study further affirm the practicality of using optical approaches to protect people and crops from flying insects.
Infrared neural stimulation (INS) is becoming an important complementary tool to electrical stimulation. Since the mechanism of INS is photothermal, describing the laser-induced heat distribution is fundamental to determining the relationship between stimulation pulses and neural responses. This work developed both a framework describing the time evolution of the heat distribution induced by optical fluence and a new method to extract thermal criteria (e.g., temperature change and rate of change) for neural activation. To solve the general problem of describing the temperature distribution, a Green’s function solution to the heat diffusion equation was determined and convolved with the optical fluence. This provided a solution in the form of a single integral over time, from which closed-form solutions can be determined for special cases. This work also yielded an expression for thermal relaxation time, which provides a rigorous description of thermal confinement for INS. The developed framework was then applied to experimental data from the cochlea to extract the minimum temperature increase and rate of that increase to stimulate the cochlear spiral ganglion. This result, and similar analyses applied to other neural systems, can then shed light on the fundamental mechanism for INS and aid the development of optical neuroprostheses.
Infrared nerve stimulation (INS) is rapidly becoming an important tool for basic research and a promising new clinical
technology to selectively activate nerves to restore function, map the nervous system, and perform diagnostic
procedures. To the best of our understanding, the mechanism of stimulation is photothermal; thus, describing the laserinduced
heat distribution is fundamental to determining the relationship between stimulation pulse and neural
response. This work develops both a framework describing the time evolution of the heat distribution induced by
optical fluence and a novel method to extract thermal criteria for neural activation. We are first concerned with the
general problem of describing the temperature distribution in a homogenous medium. To this end, we determine a
Green’s function solution to the heat diffusion equation and convolve it with the optical fluence. This provides a
general solution to the thermal problem of interest in the form of a single integral over time. Other useful closed form
solutions can be determined for interesting special cases. This pursuit also yields an expression for the thermal
relaxation time, which provides a rigorous description of thermal confinement for INS applications. The insight we
gain from this framework allows us to extract thermal criteria for neural activation from experimental data. Our work
provides both insight into the mechanism for stimulation and understanding sufficient to aid in the development of INS
devices. Thermal criteria values will prove useful for choosing parameters such as spot size, pulse width, stimulation
spacing, and stimulation depth in future INS applications.
We demonstrate control of terahertz (THz) waves developing novel
devices in the THz regime: THz pulse shapers. THz technology is a
relatively unexplored subject, yet the importance of THz wave
manipulation cannot be emphasized enough considering its potential
application to THz imaging systems, ultrafast optical signal
processing, ultrahigh-speed computing, quantum information
science, nanotechnology, and chemical reaction dynamics among
other areas. THz time-domain spectroscopy (THz-TDS) can assess the
performance of the THz pulse shapers monitoring time-dependent THz
wave propagation. THz-TDS permits precise measurements not only of
the amplitude but also of the phase of THz waves, thus a
comprehensive assessment of the THz devices can be achieved. The
phase sensitivity is also vital to many applications such as
high-contrast THz imaging and quantum control of semiconductor
nanostructures. We develop arbitrary THz pulse generators
synthesizing THz waveforms via optical rectification in
pre-engineered domain structures of poled nonlinear crystals using
femtosecond lasers. The terahertz waveforms coincide with the
crystal domain structures. The one dimensional nonlinear wave
equation simulates the experimental results with a good
qualitative agreement. The ratio of the domain length to the
optical pulse length in the crystal turns out to be the crucial
limiting factor to generating optimum terahertz fields and
preventing waveform distortion. Optical pulse shaping techniques
is integrated into the THz pulse generators to extend the scope of
THz pulse shaping control. Continuously tunable narrow-band THz
pulses are generated in a fanned-out periodically-poled lithium
niobate crystal. We measure the free induction decay of rotational
transitions in gas-phase HCl molecules using the narrow-band THz
pulses. The shape of the multi-cycle THz pulses is controlled by
adjusting the relative time delay and intensity between the two
optical pulses.
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