Selective laser sintering (SLS) is an efficient process in additive manufacturing that enables rapid part production from computer-based designs. However, SLS is limited by its notable lack of in situ process monitoring when compared with other manufacturing processes. We report the incorporation of optical coherence tomography (OCT) into an SLS system in detail and demonstrate access to surface and subsurface features. Video frame rate cross-sectional imaging reveals areas of sintering uniformity and areas of excessive heat error with high temporal resolution. We propose a set of image processing techniques for SLS process monitoring with OCT and report the limitations and obstacles for further OCT integration with SLS systems.
Neurological cancer surgeries require specialized tools that enhance imaging for precise cutting and removal of tissue without damaging adjacent neurological structures. The novel combination of high-resolution fast optical coherence tomography (OCT) alongside short pulsed nanosecond thulium (Tm) lasers offers stark advantages utilizing the superior beam quality, high volumetric tissue removal rates of thulium lasers with minimal residual thermal footprint in the tissue and avoiding damage to delicate sub-surface structures (e.g., nerves and microvessels); which has not been showcased before. A bench-top system is constructed, using a 15W 1940nm nanosecond pulsed Tm fiber laser (500uJ pulse energy, 100ns pulse duration, 30kHz repetition rate) for removing tissue and a swept source laser (1310±70nm, 100kHz sweep rate) is utilized for OCT imaging, forming a combined Tm/OCT system – a smart laser knife. The OCT image-guidance informs the Tm laser for cutting/removal of targeted tissue structures. Tissue phantoms were constructed to demonstrate surgical incision with blood vessel avoidance on the surface where 2mm wide 600um deep cuts are executed around the vessel using OCT to guide the procedure. Cutting up to delicate subsurface blood vessels (2mm deep) is demonstrated while avoiding damage to their walls. A tissue removal rate of 5mm^3/sec is obtained from the bench-top system. We constructed a blow-off model to characterize Tm cut depths taking into account the absorption coefficients and beam delivery systems to compute Arrhenius damage integrals. The model is used to compare predicted tissue removal rate and residual thermal injury with experimental values in response to Tm laser-tissue modification.
We present development of a nanosecond Q-switched Tm<sup>3+</sup>-doped fiber laser with 16 W average power and 4.4 kW peak power operating at 1940 nm. The laser has a master oscillator power amplifier design, and uses large mode area Tm<sup>3+</sup>-doped fibers as the gain medium. Special techniques are used to splice Tm<sup>3+</sup>-doped fibers to minimize splice loss. The laser design is optimized to reduce non-linear effects, including modulation instability. Pulse width broadening due to high gain is observed and studied in detail. Medical surgery is a field of application where this laser may be able to improve clinical practice. The laser together with scanning galvanometer mirrors is used to cut precisely around small footprint vessels in tissue phantoms without leaving any visible residual thermal damage. These experiments provide proof-of-principle that this laser has promising potential in the laser surgery application space.
Little numerical analysis has been done on in vivo vascular fluorescence imaging. Here, we use a 3D fluorescence
Monte Carlo model to evaluate a microvasculature geometry obtained via two-photon microscopy. We found that
a bulk-vascularization assumption does not pro- vide an accurate picture of penetration depth of the collected
fluorescence signal. Instead the degree of absorption difference between extravascular and intravascular space,
and the degree of stokes shift must be taken into account to determine the depth distribution. Additionally,
we found that using targeted illumination can provide for superior surface vessel sensi- tivity over wide-field
illumination, with small area detection offering an even greater amount of sensitivity to surface vasculature.
Depth sensitivity can be enhanced by either increasing the detector area or increasing the illumination area.
Finally, we see that excitation wavelength and vessel size can affect intra-vessel sampling distribution, as well as
the amount of signal that originates from inside the vessel under targeted illumination conditions.
Given their tunable optical properties and high optical absorption and scattering cross sections, gold nanoshells (GNS) have been explored for a number of <i>in vitro</i> and <i>in vivo</i> imaging contrast and cancer therapy agents. While it has been shown that GNSs preferentially accumulate at the tumor site, little is known about the accumulation kinetics within the tumor. We demonstrate accumulation kinetics of GNSs in bulk tumors and histology slides using two-photon induced photoluminescence (TPIP) imaging. We found that GNSs had a heterogeneous distribution with higher accumulation at the tumor cortex. In addition, GNSs were observed in unique patterns surrounding the perivascular region. These results demonstrate that direct luminescence based imaging of metal nanoparticles provides high resolution and molecular specific multiplexed images.
Gold nanoshells are a novel class of hybrid metal nanoparticles whose unique optical properties have spawned new
applications including more sensitive molecular assays and cancer therapy. We report a new photo-physical property of
nanoshells (NS) whereby these particles glow brightly when excited by near-infrared light. Specifically, we demonstrate
NS excited at 780 nm produce strong two-photon induced photoluminescence (TPIP). We characterized the
luminescence brightness of NS, comparing to that of fluorescein-labeled fluorescent beads (FB). We find that NS are 140
times brighter than FB. To demonstrate the potential application of this bright TPIP signal for biological imaging, we
imaged the 3D distribution of gold nanoshells targeted to murine tumors.
Optical changes in skin blood flow due to the presence of glycerol were measured from a two-dimensional map of blood
flow in skin blood vessels with a dynamic imaging technique using laser speckle. In this study a dorsal skin-flap window
was implanted on the hamster skin with and without a hyper-osmotic agent i.e. glycerol. The hyper-osmotic drug was
delivered to the skin through the open dermal end of the window model. A two-dimensional map of blood flow in skin
blood vessels were obtained with very high spatial and temporal resolution by imaging the speckle pattern with a CCD
camera. Preliminary studies demonstrated that hyper-osmotic agents such as glycerol not only make tissue temporarily
translucent, but also reduce blood flow. The blood perfusion was measured every 3 minutes up to 36-60 minutes after
diffusion of anhydrous glycerol. Small capillaries blood flow reduced significantly within 3-9 minutes. Perfusion rate in
lager blood vessels i.e. all arteries and some veins decreased (speckle contrasts increased from 0.0115 to 0.384) over
time. However, the blood flow in some veins reduced significantly in 36 minutes. After 24 hours the blood perfusion
further reduced in capillaries. However, the blood flow increased in larger blood vessels in 24 hours compared to an hour
after application of glycerol. For further investigation the speckle contrast measurement were verified with color
Doppler optical coherence tomography.
This paper is a review of current astronomy projects at Raytheon/SBRC in the near-IR band. Another paper in this same session (3354-11) covers astronomy projects in longer wavelengths. For ground-based astronomy, InSb arrays with formats of 256 X 256, 512 X 512, and 1024 X 1024 have been developed and tested. For space-based astronomy, four projects are discussed with array formats ranging from 256 X 256 to 2K X 2K. The space projects support instruments on the SIRTF, IRIS, NGST, and Rosetta missions. Representative data are presented from 1024 X 1024 and 256 X 256 arrays obtained by test facilities at NOAO and the University of Rochester.
Raytheon/SBRC has demonstrated high quality Si:As IBC IR FPAs for both ground-based and space-based Mid-IR astronomy applications. These arrays offer in-band quantum efficiencies of approximately 50 percent over a wavelength range from 6 micrometers to 26 micrometers and usable responses from 2 micrometers to 28 micrometers . For high background, ground-based applications the readout input circuit is a direct injection (DI) FET, while for low background, space-based applications a source follower per detector (SFD) is used. The SFD offers extremely low noise and power dissipation, and is implemented in a very small unit cell. The DI input circuit offers much larger bucket capacity and better linearity compared with the SFD, and is implemented in a 50 micrometers unit cell. SBRC's Si:As IBC detector process results in very low dark current sand our Raytheon/MED readout process is optimized for very low redout noise at low temperature operation. SBRC is committed to achieving still better performance to serve the future needs of the IR astronomy community.