Significance: The optical properties of biological samples provide information about the structural characteristics of the tissue and any changes arising from pathological conditions. Optical coherence tomography (OCT) has proven to be capable of extracting tissue’s optical properties using a model that combines the exponential decay due to tissue scattering and the axial point spread function that arises from the confocal nature of the detection system, particularly for higher numerical aperture (NA) measurements. A weakness in estimating the optical properties is the inter-parameter cross-talk between tissue scattering and the confocal parameters defined by the Rayleigh range and the focus depth.
Aim: In this study, we develop a systematic method to improve the characterization of optical properties with high-NA OCT.
Approach: We developed a method that spatially parameterizes the confocal parameters in a previously established model for estimating the optical properties from the depth profiles of high-NA OCT.
Results: The proposed parametrization model was first evaluated on a set of intralipid phantoms and then validated using a low-NA objective in which cross-talk from the confocal parameters is negligible. We then utilize our spatially parameterized model to characterize optical property changes introduced by a tissue index matching process using a simple immersion agent, 2,2’-thiodiethonal.
Conclusions: Our approach improves the confidence of parameter estimation by reducing the degrees of freedom in the non-linear fitting model.
Animal models of stroke are used extensively to study the mechanisms involved in the acute and chronic phases of recovery following stroke. A translatable animal model that closely mimics the mechanisms of a human stroke is essential in understanding recovery processes as well as developing therapies that improve functional outcomes. We describe a photothrombosis stroke model that is capable of targeting a single distal pial branch of the middle cerebral artery with minimal damage to the surrounding parenchyma in awake head-fixed mice. Mice are implanted with chronic cranial windows above one hemisphere of the brain that allow optical access to study recovery mechanisms for over a month following occlusion. Additionally, we study the effect of laser spot size used for occlusion and demonstrate that a spot size with small axial and lateral resolution has the advantage of minimizing unwanted photodamage while still monitoring macroscopic changes to cerebral blood flow during photothrombosis. We show that temporally guiding illumination using real-time feedback of blood flow dynamics also minimized unwanted photodamage to the vascular network. Finally, through quantifiable behavior deficits and chronic imaging we show that this model can be used to study recovery mechanisms or the effects of therapeutics longitudinally.
Wavefront-shaping devices incorporated into optical microscopy systems are capable of correcting sample-induced aberrations and recovering diffraction-limited imaging performance. The widespread dissemination and application of adaptive optical techniques, however, requires easy integration of adaptive optical modules, both in terms of hardware and software, into existing microscopes. We built an adaptive optical module with reduced complexity and simplified integration by utilizing a novel segmented deformable mirror and a standalone control software program. We demonstrated its ability to improve image brightness and resolution at depth in the mouse, zebrafish, and fly brains in vivo.
A solar simulator capable of producing an irradiance of 300 suns is reported. Technical challenges were not limited to optical design; developing a methodology to measuring 300 suns was difficult. This document reports on the design of the custom fabricated solar simulator, the measurement methodology for high-powered solar concentrator measurements and empirical results validating the desired simulated power density as well as the irradiance stability, spectral accuracy, beam uniformity and irradiance beam size.
Wavelength conversion (WC) imaging is a methodology that employs temperature sensitive detectors to convert photoinduced
termperature into a detectable optical signal. One specific method is to use molecular detectors such as
thermochromic liquid crystals (TLC), which exhibits thermochromism to observe the surface temperature of an area by
observing the apparent color in the visible spectrum. Utilizing this methodology, an ultra-broadband room temperature
imaging system was envisioned and realized using off the shelf thermochromic liquid crystals. The thermochromic
properties of the sensor were characterized to show a thermochromic coefficient α = 10%/°K and a noise equivalent
power (NEP) of 64 μW. With the TLC camera, images of both pulsed and continuous wave (CW) sources spanning 0.6
μm to 150 μm wavelengths were captured to demonstrate its potential as a portable, low-cost, and ultra-broadband
THz optics has experienced a tremendous increase in interest among the scientific community as
better THz sources and detection schemes are discovered. With recent studies in THz modulation
experiment using optically excited Si opens a new possibility in constructing THz optics using an
optically controlled THz SLM. Thus, various patterns, such as zone lenses, could be optically
constructed and tuned in real time for used in THz beam correction. For example, optically
constructed Fresnel zone lenses on high-resistivity Si can be actively tuned for focal length and
chromatic aberration, which are just some possible applications of this methodology. In this paper,
we will present results for an optically controlled single pixeled THz semiconductor SLM for use as
a modulator and discuss extensions to applications in zone lenses, diffraction gratings, and other
Optically controlled modulation of broadband THz radiation with a comparably uniform spatial distribution is demonstrated in a Si-based semiconductor structure with moderate doping. Using THz Time-Domain Spectroscopy a maximum intensity modulation of more than 99% was demonstrated for a spectrum ranging from 50GHz to 3.5THz with 3dB attenuation already for optical excitation as low as only 5mW. The uniformity of the modulation was measured and compared to the THz beam profile.