By utilizing diffractive, refractive and graded-index optics technology, a miniature (1 mm x 1 mm x 2 mm) Computer-Tomography Imaging Spectrometer (CTIS) sensor has been designed with 16 independent optical channels working in a snap-shot mode for hyper-spectral imaging. The designed prototype covers a 400~700 nm wavelength range. One optical channel has been fabricated and characterized. By azimuthally rotating this optical channel along the optical axis and collecting different dispersed images to simulate the full sensor read-out, the full hyperspectral detection scheme has been demonstrated.
We introduce a thin-film spectrometer that is based on the superprism effect in photonic crystals. While the reliable fabrication of two and three dimensional photonic crystals is still a challenge, the realization of one-dimensional photonic crystals as thin-film stacks is a relatively easy and inexpensive approach. Additionally, dispersive thin-film stacks offer the possibility to custom-design the dispersion profile according to the application. The thin-film stack is designed such that light incident at an angle experiences a wavelength-dependent spatial beam shift at the output surface. We propose the monolithic integration of organic photo detectors to register the spatial beam position and thus determine the beam wavelength. This thin-film spectrometer has a size of approximately 5 mm2. We demonstrate that the output position of a laser beam is determined with a resolution of at least 20 μm by the fabricated organic photo detectors. Depending on the design of the thin-film filter the wavelength resolution of the proposed spectrometer is at least 1 nm. Possible applications for the proposed thin-film spectrometer are in the field of absorption spectroscopy, e.g., for gas analysis or biomedical applications.
In recent years, the use of long-period gratings (LPGs) as fiber optic chemical sensors has been proposed by
several authors. Such implementations take advantage of the changes in the LPG transmittance characteristics
with ambient refractive index and may make use of a polymer coating to enhance chemical selectivity and
sensitivity. While technically feasible, these designs are subject to fairly rigid constraints related to the optical
characteristics of the fiber and grating, as well as the thickness and refractive index of the chemically selective
polymer. Compromises in design may lead to sub-optimal sensor performance in terms dynamic range, sensitivity,
linearity, stability and response time. In this work, LPG sensor designs based on one-, two- and three-layer
geometries are explored, where the outer layer is the chemically selective polymer and the properties of the other
layers (thickness, refractive index) can be adjusted. It is demonstrated through calculations based on a hybrid
mode model that the use of more than one layer greatly enhances the flexibility of sensor design and allows the
response characteristics to be tuned for optimal performance. A case study is used to illustrate how the same
sensor can be optimized for several factors, including linearity, range, sensitivity, and stability.
Tunable Diode Laser Absorption Spectroscopy (TDLAS) has evolved over the past decade from a laboratory specialty to an accepted, robust, and reliable technology for trace gas sensing. Some applications include improving efficiency of gas leak detection surveying, monitoring and controlling trace gases in chemical and pharmaceutical processing, and monitoring emissions in energy production plants. The recent advent of lightweight battery-powered standoff TDLAS sensors is enabling novel applications for remote gas sensing and non-contact process monitoring. This paper provides an overview of these next-generation TDLAS tools.
Confocal fluorescence imaging of biological systems is an important method by which researchers can investigate
molecular processes occurring in live cells. We have developed a new 3D hyperspectral confocal fluorescence
microscope that can further enhance the usefulness of fluorescence microscopy in studying biological systems. The new
microscope can increase the information content obtained from the image since, at each voxel, the microscope records
512 wavelengths from the emission spectrum (490 to 800 nm) while providing optical sectioning of samples with
diffraction-limited spatial resolution. When coupled with multivariate curve resolution (MCR) analyses, the microscope
can resolve multiple spatially and spectrally overlapped emission components, thereby greatly increasing the number of
fluorescent labels, relative to most commercial microscopes, that can be monitored simultaneously. The MCR algorithm
allows the "discovery" of all emitting sources and estimation of their relative concentrations without cross talk, including
those emission sources that might not have been expected in the imaged cells. In this work, we have used the new
microscope to obtain time-resolved hyperspectral images of cellular processes. We have quantitatively monitored the
translocation of the GFP-labeled RelA protein (without interference from autofluorescence) into and out of the nucleus
of live HeLa cells in response to continuous stimulation by the cytokine, TNFα. These studies have been extended to
imaging live mouse macrophage cells with YFP-labeled RelA and GFP-labeled IRF3 protein. Hyperspectral imaging
coupled with MCR analysis makes possible, for the first time, quantitative analysis of GFP, YFP, and autofluorescence
without concern for cross-talk between emission sources. The significant power and quantitative capabilities of the new
hyperspectral imaging system are further demonstrated with the imaging of a simple fluorescence dye (SYTO 13)
traditionally used to stain the nucleus of live cells. We will demonstrate the microscope system's ability to actually
discover and quantify the presence of two separate SYTO 13 fluorescent species shifted in wavelength by only a few
nm. These two emission components exhibit very different spatial distributions in macrophage cells (i.e., nucleus vs.
cytoplasm + nucleus). Two highly overlapped autofluorescence components in addition to the two SYTO 13
components were also observed, and the spatial distributions of the two autofluorescence components were
quantitatively mapped throughout the cells in three dimensions.
We investigate the use of a flexible grid architecture for hyperspectral image processing. Recording data in tens or hundreds of narrow contiguous spectral intervals, hyperspectral data outperform multispectral imagery by allowing the detection of relatively small differences in material composition and of targets occupying a surface smaller than the one covered by a pixel (called subpixel targets). However, with increased spatial and spectral resolution, processing such data often leads to computational costs prohibitive to regular computer systems. While distributed or parallel computing are often found as solutions, many current configurations are still unable to reach the computational complexity level that is required for exhaustive search solutions. In this environment, grid computing becomes a viable alternative. Grid computing, an emerging computing model, is based on the concept of distributing processes across a parallel infrastructure. Throughput is further increased by networking many heterogeneous resources across administrative boundaries to model a virtual computer architecture. Compared to distributed clusters or parallel machines, grid systems are often inexpensive or even free since they can consist of non-dedicated computer systems that are underutilized and have extra CPU cycles that can be spared.
We present general considerations on grid architectures and discuss the current grid environment we have deployed. Next, we investigate exhaustive band search, a data processing problems that suffers from large computational requirements and present our grid based solutions for it. Our experimental results indicate a significant speedup in obtaining results and even solving of problems otherwise not tractable in regular computing environments.
Several technologies have attempted to deliver the analytical capabilities of Raman and fluorescence spectroscopies to developing nanotechnologies. They have, however, two limitations when applied to nanoscale structures: (i) diffraction limit and (ii) weak signal due to a small sampling volume. To overcome the first obstacle, researchers traditionally use aperture-limited near-field optics based on optical fibers with extremely small apertures (down to ~50 nm). Low transmission through the apertures exacerbates the second limitation by strongly decreasing the measured optical signal. An alternative method based on plasmon optics, strong and very local enhancement of the electric field of light in the vicinity of plasmon nanoparticles (usually Ag or Au), helps to overcome both problems. We overview developments in apertureless near-field optics that are based on a combination of optical spectroscopy and scanning probe microscopy (SPM), with SPM tips modified to have plasmon resonance at the apex. Apertureless near-field microscopy enables traditional confocal optical imaging, scanning probe microscopy (SPM), and a combination of optical and SPM imaging with spatial resolution ~10-20nm, unprecedented for optical techniques. We demonstrate simultaneous Raman and SPM imaging of semiconductor structures and also discuss the challenges facing widespread applicability of this emerging technology, for areas as far ranging as biomedical, semiconductor, and composite materials research.
Raman maps, when acquired and processed successfully, produce Raman chemical images, which provide detailed
information on the spatial distribution and morphology of individual chemical species in samples. The advantages of
Raman chemical images are most significant when the sample is chemically and structurally complicated. In
pharmaceutical applications, these Raman chemical images can be used to understand and develop drug formulations,
drug delivery mechanisms, and drug-cellular interactions. Studies using Raman hyperspectral imaging - the term that
encompasses the entire procedure from data measurement to processing and interpretation - is increasing and gaining a
wider acceptance due to recent improvements in Raman instrumentation and software.
Since Raman maps are a collection of numerous Raman spectra of different chemical species, within a single data set,
spectral characteristics such as the scattering strength, fluorescence level, and baselines vary a great deal. To acquire and
process a Raman map successfully, this heterogeneity must be taken into the consideration. This paper will show the
impact of signal-to-noise ratio (S/N) on data processing strategies and their results. It will be demonstrated that the S/N
of original data is critical for good classification and scientifically meaningful results regardless of the processing
Portable hyperspectral imagers are becoming commonly available as a commercial product. A liquid crystal tunable
filter based CCD imager was evaluated and characterized for spectral stray light using a tunable laser facility. The
hyperspectral imager is currently being used to investigate the use of hyperspectral imaging in medical applications.
This paper discusses the imager design and performance, the characterization of this system, and medical imaging as a
related application. Imagers of this type may be fundamental to transferring radiometric scales using a hyperspectral
image projector. The use of the hyperspectral imager for use with a hyperspectral image projector is also discussed.
Although heart disease remains the leading cause of death in the industrialized world, there is still no method, even
under cardiac catheterization, to reliably identify those atherosclerotic lesions most likely to lead to heart attack and
death. These lesions, which are often non-stenotic, are frequently comprised of a necrotic, lipid-rich core overlaid with a
thin fibrous cap infiltrated with inflammatory cells. InfraReDx has developed a scanning, near-infrared, optical-fiber-based,
spectroscopic cardiac catheter system capable of acquiring NIR reflectance spectra from coronary arteries through
flowing blood under automated pullback and rotation in order to identify lipid-rich plaques (LRP). The scanning laser
source and associated detection electronics produce a spectrum in 5 ms at a collection rate of 40 Hz, yielding thousands
of spectra in a single pullback. The system console analyzes the spectral data with a chemometric model, producing a
hyperspectral image (a Chemogram, see figure below) that identifies LRP encountered in the region interrogated by the
system. We describe the system architecture and components, explain the experimental procedure by which the
chemometric model was constructed from spectral data and histology-based reference information collected from
autopsy hearts, and provide representative data from ongoing ex vivo and clinical studies.
"NIR Hyperspectral Imaging" is a universal tool to measure and control chemical properties of objects. The combination of digital imaging and molecular spectroscopy exhibits a great benefit, especially for in- and on-line analysis. However, a wide use is impeded at present due to the expensive and complex system approach. One reason is the high cost of two dimensional InGaAs detector arrays, another one is the special glass that is used in the near infrared NIR.
In this paper a new approach for a NIR Imaging spectrometer is presented. The base of the new Pushbroom Hyperspectral Imager is a micromechanical scanning device with an integrated diffraction grating. This MOEMS device is made in a standard SOI fabrication process developed at Fraunhofer IPMS. For the Hyperspectral Imager, a new all-reflective optical system based on a Schiefspiegler setup has been developed. The simulated optical configuration and the achieved performance of the system will be presented.
This paper will discuss recent results obtained when applying a photoconductive linear MCT array in a demonstration spectrometer designed for the NIR wavelength range from 1300 to 2500 nm. A new 128x1 element MCT sensor was developed specifically for spectroscopy, i.e. with "tall", rectangular pixels in order to optimize both wavelength resolution and optical throughput. Also new read-out electronics was developed using multilayer LTCC (Low Temperature Co-Fired Ceramics) techniques, which is integrated into the package and realizes synchronous ("lock in") detection for each of the 128 channels. Advantages of this current-detection scheme include compatibility with chopped light sources (insensitivity to ambient stray light) and elimination of read-out noise (affecting charge-detection amplifiers). The first test results reported here confirm spectrometer operation and present encouraging performance, even though the system is not yet optimized. The spectrometer is very fast, with minimum integration time of 1.2 ms, while photometric noise will reduce with longer integration times. There is no fundamental limit in the maximal length of the integration time. Testing with integration times of 1.2, 12, 120 and 1200 ms resulted in absorbance noise levels of approximately 2500, 330, 94 and 49 μA units. Demonstration spectra were measured from lactose and copying paper samples. Thanks to high speed and parallel spectral recording of 128 wavelengths, MCT array technology appears highly potential for developing powerful on-line spectrometers for process analytical applications not only in the near infrared (NIR) but also for the lower mid-IR wavelengths, up to approximately 6 μm.
There is an increasing need for infrared spectroscopic instrumentation that is low-cost and extremely robust for
applications in agriculture, environmental monitoring, food science and medicine. This paper describes a MEMS-based
tunable Fabry-Perot filter that can be directly integrated on a detector. The fabrication process is detector independent,
and has been demonstrated on Si as well as one of the most unforgiving detector material systems, HgCdTe. Results are
presented that show that the technology is applicable for coverage of a wide spectral range, with examples of tuning from
~1600nm to ~2300nm and ~3800nm to ~4800nm using voltages <20V with line widths < 100nm and tuning speeds of
50kHz. Modeling shows that the device should be stable to shocks up to 250G. Line widths and tuning speeds can be
significantly improved using different actuator designs and removal of squeezed-film damping effects. The process uses
a maximum process temperature of 125°C, and is therefore compatible with a wide range of detector materials including
Si, Ge, InGaAs, InSb, as well as more specialized detector materials such as InAs quantum dots and InAs/GaSb
superlattices. Work is currently underway to demonstrate application of microspectrometers fabricated using this
technology in real-time testing of soils for agricultural applications.
We have developed thin film Fabry-Perot filters directly coated on fiber end-faces. The layer design of the filters and the deposition process were optimized for maximum transmission, and the width of the transmission peak. The optical performance of Fabry-Perot filters deposited on fiber end-faces of single-mode as well as multimode optical fibers have been investigated. We have performed laser-induced damage threshold (LIDT) measurements on the multi-layer systems to optimize the fiber preparation before deposition. The multi-layer systems were analyzed by means of atomic force microscopy and scanning electron microscopy.