Μm In Air Research Articles

High-speed ultrahigh-resolution spectral domain optical coherence tomography using high-power supercontinuum at 0.8 µm wavelength

We demonstrated high-speed ultrahigh-resolution (UHR) optical coherence tomography (OCT) in the 800 nm wavelength region. A high-power coherent supercontinuum (SC) and a high-speed line scan camera were used to construct a spectral domain OCT. The axial resolution was 3.1 µm in air and 2.3 µm in tissue. The dependence of sensitivity on the SC power and A-scan rate was examined. For the A-scan rate of 70 kHz, the sensitivity of 104 dB was achieved for the SC power higher than 60 mW. High-speed in vivo UHR-OCT imaging was demonstrated for zebrafish embryo and swimming medaka.

In-bore prostate transperineal interventions with an MRI-guided parallel manipulator: system development and preliminary evaluation.

Robot-assisted minimally-invasive surgery is well recognized as a feasible solution for diagnosis and treatment of prostate cancer in humans. This paper discusses the kinematics of a parallel 4 Degrees-of-Freedom (DOF) surgical manipulator designed for minimally invasive in-bore prostate percutaneous interventions through the patient's perineum. The proposed manipulator takes advantage of four sliders actuated by MRI-compatible piezoelectric motors and incremental rotary encoders. Errors, mostly originating from the design and manufacturing process, need to be identified and reduced before the robot is deployed in clinical trials. The manipulator has undergone several experiments to evaluate the repeatability and accuracy (about 1 mm in air (in x or y direction) at the needle's reference point) of needle placement, which is an essential concern in percutaneous prostate interventions. The acquired results endorse the sustainability, precision and reliability of the manipulator. Copyright © 2015 John Wiley & Sons, Ltd.

109 MHz optical tomography using temporal magnification.

Ultrafast optical tomographic imaging with a 109MHz A-scan rate is achieved by using temporal magnification. Based on two four-wave mixing (FWM) time lenses with carefully designed group delay dispersion, we construct a temporal imaging system with a magnification factor of 48.3×. The two time-lens scheme not only relaxes the requirement for the pump source but also facilitates the application for tomographic imaging. As a proof-of-concept demonstration, our system achieves an axial resolution of 140μm in air (∼105 μm in biosample) over a 28mm depth range with sensitivity up to 55dB. We then evaluate the imaging performance using a fish-eye lens at a 109MHz A-scan rate. Utilizing better dispersion-engineered nonlinear media, resolution of less than 5μm in the biosample with higher sensitivity may be achieved. We believe this scheme will provide a promising solution for video-rate 3D tomographic imaging.

Dual band dual focus optical coherence tomography for imaging the whole eye segment.

We developed an improved dual band dual focus spectral domain optical coherence tomography (SD-OCT) for in vivo 2D/3D imaging of the whole eye segment, including the whole anterior segment and retina. The system featured two OCT channels with two different bands centered at 840 nm and 1050 nm, which were designed to image the retina and the anterior segments of the eye, respectively. By combing the two probe light beams for co-axial scanning and separating them for focusing at different segments of the eye with a combination of three dichroic mirrors, we not only minimized the loss of the backscattered light from the sample but also improved the imaging depth, scan range and resolution. The full resolved complex (FRC) method was applied to double the imaging depth for the whole anterior segment imaging, with which an imaging depth of 36.71 mm in air was achieved. We demonstrated that this system was capable of measuring the dynamic changes of ocular dimensions, including the asphericity of the cornea and lens, during accommodation.

(Invited) Thin-Film Transistors Based on Donor-Acceptor Polymers

In this presentation we will describe device designs, modeling, and experimental results with several new diketopyrrolopyrrole DPP-based polymers and specifically discuss techniques to keep the operating voltage low (< 10 V) in small channel length (< 5 mm) devices. We have been able to obtain mobility values of ~4 cm2/V-s with some of the materials in such devices at low operating voltages for channel lengths of 4 mm in air. These devices possess very high temperature field-induced conductivity of any polymer FET and which exceeds that of most organic single crystal FETs reported so far. Our best devices designs possess a bilayer gate insulator which includes a thin interfacial low- dielectric constant insulator. We will demonstrate that the mobility improvement arises due to the suppression of the formation of Fröhlich polarons, which tend to reduce mobility when polar media such as high-k dielectrics are used with polymer semiconductors. We will also discuss charge transport in such polymers transistors both above and below the threshold voltage.

General nanomoulding with bulk metallic glasses

Bulk metallic glasses (BMGs) are ideal for nanomoulding as they possess desirable strength for molds as well as for moldable materials and furthermore lack intrinsic size limitations. Despite their attractiveness, only recently Pt-based BMGs have been successfully molded into pores ranging 10–100 nm (Kumar et al 2009 Nature 457 868–72). Here, we introduce a quantitative theory, which reveals previous challenges in filling nanosized pores. This theory considers, in addition to a viscous and a capillary term, also oxidation, which becomes increasingly more important on smaller length scales. Based on this theory we construct a nanomoulding processing map for BMG, which reveals the limiting factors for BMG nanomoulding. Based on the quantitative prediction of the processing map, we introduce a strategy to reduce the capillary effect through a wetting layer, which allows us to mold non-noble BMGs below 1 μm in air. An additional benefit of this strategy is that it drastically facilitates demoulding, one of the main challenges of nanomoulding in general.

Imaging of spectral-domain optical coherence tomography using a superluminescent diode based on InAs quantum dots emitting broadband spectrum with Gaussian-like shape

We developed a low-coherence light source based on self-assembled InAs quantum dots (QDs) with controlled emission wavelengths and applied it to optical coherence tomography (OCT) imaging. A current-driven superluminescent diode (SLD) light source including four layers of QDs exhibits a broadband (80-nm-bandwidth) emission centered at approximately 1.2 µm with a Gaussian-like spectral shape at room temperature. Spectral-domain OCT (SD-OCT) using the QD-SLD as a light source was developed and imaging with the SD-OCT was demonstrated. The axial resolution was estimated to be approximately 8 µm in air and no apparent side lobes appeared beside the point spread function, indicating the effectiveness of the QD-SLD for high-resolution, noise-reduced OCT imaging.

Measuring flow dynamics in a microfluidic chip using optical coherence tomography with 1 µm axial resolution

An experimental verification of simulated flow dynamics in a novel design of microfluidic device can be difficult, especially, in devices such as mixers or deterministic lateral displacement (DLD) arrays. Doppler optical coherence tomography (DOCT) is one of the visualization modalities used to measure flow velocity profiles in microfluidic channels, capillaries and microvascular networks. Previously conducted flow measurements with high speed spectral-domain optical coherence tomography (SD-OCT) devices have had typical axial resolution in the range few microns which can be insufficient for accurate mapping of flow dynamics in microchannels. This paper introduces a high-speed SD-OCT system with an axial resolution of 1.2µm in air (below 1µm in water) to evaluate flow in a microfluidic chip. The A-line acquisition rate of the device is 123kHz. Flow velocities from 1% Intralipid suspension are obtained across the microfluidic channel with the specified height of 20µm and the width of 50µm. The results show that the utilized SD-OCT device can visualize flows as close as 1µm from the channel wall. The flow rate of 0.63µl/min, determined from the cross-sectional velocity map, agreed well with the value of 0.67µl/min set to the syringe pump.

Common Path Side Viewing Monolithic Ball Lens Probe for Optical Coherence Tomography

1 ; Common path probes are highly desirable for optical coherence tomography as they reduce system complexity and cost by eliminating the need of dispersion compensation and polarization controlling optics. In this work, we demonstrate a monolithic ball lens based, common path, side viewing probe that is suitable for Fourier domain optical coherence tomography. The probe design parameters were simulated in Zemax modeling software and the simulated performance parameters were compared with experimental results. We characterized the performance of the probe by measuring its collection efficiency, resolution, and sensitivity. Our results demonstrated that with a source input power of 25 mW, we could achieve sensitivity of 100.5 dB, which is within 7 dB of the maximum possible sensitivity that could be achieved using a separate reference arm. The axial resolution of the system was found to be 15.6 µm in air and the lateral resolution (full width half maximum) was approximately 49 µm. The probe optics were assembled in a 1 mm diameter hypotube with a 500 µm inner diameter. Images of finger skin acquired using this probe demonstrated clear visualization of the stratum corneum, epidermis, and papillary dermis, along with sweat ducts.

High resolution imaging of acne lesion development and scarring in human facial skin using OCT-based microangiography.

Acne is a common skin disease that often leads to scarring. Collagen and other tissue damage from the inflammation of acne give rise to permanent skin texture and microvascular changes. In this study, we demonstrate the capabilities of optical coherence tomography-based microangiography in detecting high-resolution, three-dimensional structural, and microvascular features of in vivo human facial skin during acne lesion initiation and scar development. A real time swept source optical coherence tomography system is used in this study to acquire volumetric images of human skin. The system operates on a central wavelength of 1,310 nm with an A-line rate of 100 kHz, and with an extended imaging range (∼12 mm in air). The system uses a handheld imaging probe to image acne lesion on a facial skin of a volunteer. We utilize optical microangiography (OMAG) technique to evaluate the changes in microvasculature and tissue structure. Thanks to the high sensitivity of OMAG, we are able to image microvasculature up to capillary level and visualize the remodeled vessels around the acne lesion. Moreover, vascular density change derived from OMAG measurement is provided as an alternative biomarker for the assessment of human skin diseases. In contrast to other techniques like histology or microscopy, our technique made it possible to image 3D tissue structure and microvasculature up to 1.5 mm depth in vivo without the need of exogenous contrast agents. The presented results are promising to facilitate clinical trials aiming to treat acne lesion scarring, as well as other prevalent skin diseases, by detecting cutaneous blood flow and structural changes within human skin in vivo.

ANIR: Atacama near-infrared camera for the 1.0 m miniTAO telescope

Abstract We have developed a near-infrared camera called ANIR (Atacama Near-InfraRed camera) for the University of Tokyo Atacama Observatory 1.0 m telescope (miniTAO) installed at the summit of Cerro Chajnantor (5640 m above sea level) in the north of Chile. The camera provides a field of view of 5${^{\prime}_{.}}$1 × 5${^{\prime}_{.}}$1 with a spatial resolution of 0${^{\prime\prime}_{.}}$298 pixel−1 in the wavelength range of 0.95 to 2.4 μm, using Offner relay optics and a PACE HAWAII-2 focal plane array. Taking advantage of the dry site, the camera is capable of narrow-band imaging observations at the hydrogen Paschen-α (Paα, λ = 1.8751 μm in air) wavelength ground-based observations of which have been quite difficult due to deep atmospheric absorption, mainly from water vapor. We have been successfully obtaining Paα images of Galactic objects and nearby galaxies since the first-light observation in 2009 with ANIR. The throughputs at the narrow-band filters (N1875, N191) including the atmospheric absorption show larger dispersion (∼ 10%) than those at broad-band filters (a few percent), indicating that they are affected by temporal fluctuations in precipitable water vapor (PWV) above the site. We evaluate the PWV content via the atmospheric transmittance at the narrow-band filters, and deduce that the median and the dispersion of the distribution of the PWV are 0.40 ± 0.30 and 0.37 ± 0.21 mm, for the N1875 and N191 data respectively, which are remarkably smaller (49% ± 38% for N1875 and 59% ± 26% for N191) than radiometry measurements at the base of Cerro Chajnantor (an altitude of 5100 m). The decrease in PWV can be explained by the altitude of the site when we assume that the vertical distribution of the water vapor is approximated at an exponential profile with scale heights within 0.3–1.9 km (previously observed values at night). We thus conclude that miniTAO/ANIR at the summit of Cerro Chajnantor indeed provides us an excellent capability for a ground-based Paα observation.

Synchronous scanning of reference mirror and objective lens for high-resolution full-field interferometry

We realized a long-scanning-range and high-resolution interferometry in a time-domain full-field microscopic scheme by adopting a simple configuration. A reference mirror was synchronously scanned with an objective lens, which was installed in a common path, to prevent lateral resolution degradation due to defocus at the mirror. High axial resolution was obtained using a broadband supercontinuum (SC) generated by a 1.55 µm pump. The SC was generated by propagating a femtosecond pulse at 1.55 µm through a highly nonlinear dispersion shifted fiber with a small dispersion slope. We designed and constructed an interferometer carefully to utilize the entire bandwidth. The broad bandwidth of the interferometer achieved an axial resolution of 2.50 µm in air. The synchronous scanning maintained a lateral resolution longer than 1 mm. The system successfully yielded a cross-sectional image of two layers of scotch tape along the 400-µm-depth and 90-nm-step surface profiles.

High resolution Fourier domain optical coherence tomography in the 2 μm wavelength range using a broadband supercontinuum source.

A 220 nm bandwidth supercontinuum source in the two-micron wavelength range has been developed for use in a Fourier domain optical coherence tomography (FDOCT) system. This long wavelength source serves to enhance probing depth in highly scattering material with low water content. We present results confirming improved penetration depth in high opacity paint samples while achieving the high axial resolution needed to resolve individual paint layers. This is the first FDOCT developed in the 2 μm wavelength regime that allows fast, efficient capturing of 3D image cubes at a high axial resolution of 13 μm in air (or 9 μm in paint).

Ultrahigh-resolution optical coherence tomography and its application in inspection of industrial materials

Since many industrial materials have micro or submicro structures on the surface or subsurface, utrahigh-resolution is required in the inspection of these materials. Ultrahigh-resolution optical coherence tomography uses broadband light sources to achieve axial image resolutions on the scale of a few microns. We have been investigating an ultrahigh-resolution spectral-domain optical coherence tomography (SD-OCT) system using supercontinuum sources (SC) in free space. The effective SC spectrum has a full width at half maximum of 230 nm centered around 665 nm, and the imaging setup has an ultrahigh axial resolution of 0.9 μm in air, and a lateral resolution of 3.9 μm, with the system measurement range being 0.6 mm in axial direction. At a 50 μm axial position, the sensitivity can be 63 dB with 28600 axial scans per second at 2048 pixels per axial scan. Images of polystyrene microspheres solution with an average diameter of 5 μm and different sizes of industrial abrasive papers are presented to illustrate the performance of the system.

Ultrawide-field parallel spectral domain optical coherence tomography for nondestructive inspection of glass

Aiming at the requirements of real-time inspection in material industry, an ultrawide-field parallel SD-OCT system capable of visualizing cross-sectional image of internal structures by a single shot of a 2-D CMOS camera is developed. To achieve ultrawide-field parallel detection, one meniscus lens with negative dioptric is introduced as an additional relay lens and imaging optics including sample arm, relay lenses and spectrometer are optimized as a whole for desirable imaging quality. The developed system has an ultrawide-field of 35mm and an axial range of 8mm in air. The maximum on-axis sensitivity and the axial resolution are experimentally determined to be 65dB and 17.7μm, respectively. The on-axis lateral resolution is measured to be 44μm in parallel direction and 22μm in scanning direction. The system is applied to obtain 3-D volume images of a set of glass-samples covering an area of about 28mm by 15mm with thicknesses ranging between 2.1mm and 4mm, from which defects such as solid inclusion, micro-deformation and bubble are identified either on the surfaces or inside the samples.

MEMS-Based Handheld Fourier Domain Doppler Optical Coherence Tomography for Intraoperative Microvascular Anastomosis Imaging

PurposeTo demonstrate the feasibility of a miniature handheld optical coherence tomography (OCT) imager for real time intraoperative vascular patency evaluation in the setting of super-microsurgical vessel anastomosis.MethodsA novel handheld imager Fourier domain Doppler optical coherence tomography based on a 1.3-µm central wavelength swept source for extravascular imaging was developed. The imager was minimized through the adoption of a 2.4-mm diameter microelectromechanical systems (MEMS) scanning mirror, additionally a 12.7-mm diameter lens system was designed and combined with the MEMS mirror to achieve a small form factor that optimize functionality as a handheld extravascular OCT imager. To evaluate in-vivo applicability, super-microsurgical vessel anastomosis was performed in a mouse femoral vessel cut and repair model employing conventional interrupted suture technique as well as a novel non-suture cuff technique. Vascular anastomosis patency after clinically successful repair was evaluated using the novel handheld OCT imager.ResultsWith an adjustable lateral image field of view up to 1.5 mm by 1.5 mm, high-resolution simultaneous structural and flow imaging of the blood vessels were successfully acquired for BALB/C mouse after orthotopic hind limb transplantation using a non-suture cuff technique and BALB/C mouse after femoral artery anastomosis using a suture technique. We experimentally quantify the axial and lateral resolution of the OCT to be 12.6 µm in air and 17.5 µm respectively. The OCT has a sensitivity of 84 dB and sensitivity roll-off of 5.7 dB/mm over an imaging range of 5 mm. Imaging with a frame rate of 36 Hz for an image size of 1000(lateral)×512(axial) pixels using a 50,000 A-lines per second swept source was achieved. Quantitative vessel lumen patency, lumen narrowing and thrombosis analysis were performed based on acquired structure and Doppler images.ConclusionsA miniature handheld OCT imager that can be used for intraoperative evaluation of microvascular anastomosis was successfully demonstrated.

Dual spectrometer system with spectral compounding for 1-μm optical coherence tomography in vivo.

1 μm axial resolution spectral domain optical coherence tomography (OCT) is demonstrated for in vivo cellular resolution imaging. Output of two superluminescent diode sources is combined to provide near infrared illumination from 755 to 1105 nm. The spectral interference is detected using two spectrometers based on a Si camera and an InGaAs camera, respectively. Spectra from the two spectrometers are combined to achieve an axial resolution of 1.27 μm in air. Imaging was conducted on zebra fish larvae to visualize cellular details.

Wireless Energy Transfer Through Magnetic Reluctance Coupling

Energy harvesting from human motion for body worn or implanted devices faces the problem of the wearer being still, e.g. while asleep. Especially for medical devices this can become an issue if a patient is bed-bound for prolonged periods of time and the internal battery of a harvesting system is not recharged. This article introduces a mechanism for wireless energy transfer based on a previously presented energy harvesting device. The internal rotor of the energy harvester is made of mild steel and can be actuated through a magnetic reluctance coupling to an external motor. The internal piezoelectric transducer is consequently actuated and generates electricity. This paper successfully demonstrates energy transfer over a distance of 16 mm in air and an achieved power output of 85 μW at 25 Hz. The device functional volume is 1.85 cm3. Furthermore, it was demonstrated that increasing the driving frequency beyond 25 Hz did not yield a further increase in power output. Future research will focus on improving the reluctance coupling, e.g. by investigating the use of multiple or stronger magnets, in order to increase transmission distance.

In vitro 3D anterior segment imaging in lamb eye with extended depth range swept source optical coherence tomography

A complex conjugate resolved, extended depth range, high speed 1 μm swept-source optical coherence tomography (SSOCT) provides a dense three-dimensional (3-D) imaging of the entire anterior segment of eye. SSOCT system utilizes “coherence revival” characteristics of the light source (external cavity tunable laser, ECTL), which is automatically phase modulated. We describe implementation of this with a common swept laser with built-in k-clock to allow imaging in high depth range, 10.5 mm in air, without any external MZI clock. The system is capable of generating long depth range without any modulators or frequency shifter. Most of the commercially available OCT systems are limited with this type of application due to low acquisition speed, resolution, and axial imaging range. The sensitivity fall-off profiles for extended imaging depth range were also presented with matched and mismatched interferometer optical path delays. The imaging feasibility of this system is demonstrated by in vitro 3D imaging of the full anterior segment of lamb eye.

Design and experimental testing of air slab caps which convert commercial electron diodes into dual purpose, correction-free diodes for small field dosimetry.

Two diodes which do not require correction factors for small field relative output measurements are designed and validated using experimental methodology. This was achieved by adding an air layer above the active volume of the diode detectors, which canceled out the increase in response of the diodes in small fields relative to standard field sizes. Due to the increased density of silicon and other components within a diode, additional electrons are created. In very small fields, a very small air gap acts as an effective filter of electrons with a high angle of incidence. The aim was to design a diode that balanced these perturbations to give a response similar to a water-only geometry. Three thicknesses of air were placed at the proximal end of a PTW 60017 electron diode (PTWe) using an adjustable "air cap". A set of output ratios (ORDet (fclin) ) for square field sizes of side length down to 5 mm was measured using each air thickness and compared to ORDet (fclin) measured using an IBA stereotactic field diode (SFD). kQclin,Qmsr (fclin,fmsr) was transferred from the SFD to the PTWe diode and plotted as a function of air gap thickness for each field size. This enabled the optimal air gap thickness to be obtained by observing which thickness of air was required such that kQclin,Qmsr (fclin,fmsr) was equal to 1.00 at all field sizes. A similar procedure was used to find the optimal air thickness required to make a modified Sun Nuclear EDGE detector (EDGEe) which is "correction-free" in small field relative dosimetry. In addition, the feasibility of experimentally transferring kQclin,Qmsr (fclin,fmsr) values from the SFD to unknown diodes was tested by comparing the experimentally transferred kQclin,Qmsr (fclin,fmsr) values for unmodified PTWe and EDGEe diodes to Monte Carlo simulated values. 1.0 mm of air was required to make the PTWe diode correction-free. This modified diode (PTWeair) produced output factors equivalent to those in water at all field sizes (5-50 mm). The optimal air thickness required for the EDGEe diode was found to be 0.6 mm. The modified diode (EDGEeair) produced output factors equivalent to those in water, except at field sizes of 8 and 10 mm where it measured approximately 2% greater than the relative dose to water. The experimentally calculated kQclin,Qmsr (fclin,fmsr) for both the PTWe and the EDGEe diodes (without air) matched Monte Carlo simulated results, thus proving that it is feasible to transfer kQclin,Qmsr (fclin,fmsr) from one commercially available detector to another using experimental methods and the recommended experimental setup. It is possible to create a diode which does not require corrections for small field output factor measurements. This has been performed and verified experimentally. The ability of a detector to be "correction-free" depends strongly on its design and composition. A nonwater-equivalent detector can only be "correction-free" if competing perturbations of the beam cancel out at all field sizes. This should not be confused with true water equivalency of a detector.