Rachel Sidebottom, Jason Allison, Ethan Aulwes, Brittany Broder, Matthew Freeman, Per Magnelind, Fesseha Mariam, Frank Merrill, Levi Neukirch, Tamsen Schurman, James Sinnis, Zhaowen Tang, Dale Tupa, Joshua Tybo, Carl Wilde, Michelle Espy
Purpose: Proton radiography may guide proton therapy cancer treatments with beam’s-eye-view anatomical images and a proton-based estimation of proton stopping power. However, without contrast enhancement, proton radiography will not be able to distinguish tumor from tissue. To provide this contrast, functionalized, high-Z nanoparticles that specifically target a tumor could be injected into a patient before imaging. We conducted this study to understand the ability of gold, as a high-Z, biologically compatible tracer, to differentiate tumors from surrounding tissue.
Approach: Acrylic and gold phantoms simulate a tumor tagged with gold nanoparticles (AuNPs). Calculations correlate a given thickness of gold to levels of tumor AuNP uptake reported in the literature. An identity, ×3, and ×7 proton magnifying lens acquired lens-refocused proton radiographs at the 800-MeV LANSCE proton beam. The effects of gold in the phantoms, in terms of percent density change, were observed as changes in measured transmission. Variable areal densities of acrylic modeled the thickness of the human body.
Results: A 1-μm-thick gold strip was discernible within 1 cm of acrylic, an areal density change of 0.2%. Behind 20 cm of acrylic, a 40-μm gold strip was visible. A 1-cm-diameter tumor tagged with 1 × 105 50-nm AuNPs per cell has an amount of contrast agent embedded within it that is equivalent to a 65-μm thickness of gold, an areal density change of 0.63% in a tissue thickness of 20 cm, which is expected to be visible in a typical proton radiograph.
Conclusions: We indicate that AuNP-enhanced proton radiography might be a feasible technology to provide image-guidance to proton therapy, potentially reducing off-target effects and sparing nearby tissue. These data can be used to develop treatment plans and clinical applications can be derived from the simulations.
We report the development of a phonon laser based on the center-of-mass oscillation of an optically levitated silica nanosphere in a free-space optical dipole trap. A parametric feedback scheme based on the detection of the oscillator’s center-of-mass is used to provide a cooling signal that intrinsically depends on the oscillator’s mean phonon occupation. When an amplification signal is added to the feedback at the mechanical resonance, these two signals produce center-of-mass dynamics that are analogous to those of a single-mode optical laser. Observed phenomena include a threshold in oscillation amplification, a transition from Brownian motion below threshold to coherent oscillation above threshold, reduction in the linewidth of the oscillation spectrum, and gain saturation. We also analyze the statistical phonon number distributions above and below threshold. The observed dynamics are described by a model that includes both stimulated and spontaneous emission of center-of-mass phonons. Importantly, the operation of this phonon laser relies on externally controllable, feedback-based parameters and therefore allows tuning of the threshold via these parameters. We also explore the use of the levitated nanoparticle phonon laser as a detector of weak external forces via injection locking.
KEYWORDS: Near field optics, Free space optics, Singular optics, Nanocrystals, Optical tweezers, Diamond, Luminescence, Optomechanical design, Near field, Plasmonics
Nitrogen-vacancy (NV) centers in diamond provide a platform for room temperature spin manipulation, making them a strong candidate for inclusion in optical levitation experiments seeking to couple mechanical and spin degrees of freedom. Here, we report progress on the coherent manipulation of single NV center spins contained within optically levitated nanodiamond in a free-space optical dipole trap. The NV center spin is coherently manipulated at both atmospheric pressure and low vacuum, and while the trapping beam causes a reduction in the fluorescence emitted by the center, no reduction in the spin coherence is observed. Further, after an initial exposure to low vacuum, the nanodiamond remains at near room temperatures at all pressures and trapping powers considered in these experiments.
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