Successful high-intensity focused ultrasound (HIFU) thermal tissue ablation relies on accurate information of the tissue temperature and tissue status. Often temperature measurements are used to predict and monitor the ablation process. In this study, we conducted HIFU ablation experiments with ex vivo porcine myocardium tissue specimens to identify changes in temperature associated with tissue coagulation and bubble/cavity formation. Using infrared (IR) thermography and synchronized bright-field imaging with HIFU applied near the tissue surface, parameters derived from the spatiotemporal evolution of temperature were correlated with HIFU-induced lesion formation and overheating, of which the latter typically results in cavity generation and/or tissue dehydration. Emissivity of porcine myocardium was first measured to be 0.857 ± 0.006 (n = 3). HIFU outcomes were classified into non-ablative, normal lesion, and overheated lesion. A marked increase in the rate of temperature change during HIFU application was observed with lesion formation. A criterion using the maximum normalized second time derivative of temperature change provided 99.1% accuracy for lesion identification with a 0.05 s(-1) threshold. Asymmetric temperature distribution on the tissue surface was observed to correlate with overheating and/or bubble generation. A criterion using the maximum displacement of the spatial location of the peak temperature provided 90.9% accuracy to identify overheated lesion with a 0.16 mm threshold. Spatiotemporal evolution of temperature obtained using IR imaging allowed determination of the cumulative equivalent minutes at 43 °C (CEM 43) for lesion formation to be 170 min. Similar temperature characteristics indicative of lesion formation and overheating were identified for subsurface HIFU ablation. These results suggest that parameters derived from temperature changes during HIFU application are associated with irreversible changes in tissue and may provide useful information for monitoring HIFU treatment.
New technologies are arriving on the scene that promise enhancement or new capabilities. Some of these technologies have potential for NASA and DOD space-based applications. In these cases, the technology must be demonstrated and validated to a degree that risk may be balanced for the space mission roles. Quantum Well Infrared Photodetector (QWIP) is one of these technologies. QWIP has a variety of space-based applications in the 8 to 16 μm wavelength range. Radiation tolerance and higher operating temperature are potentially significant benefits for long duration missions. In this paper, we describe the selection of and preparation for a mission that provides the opportunity to demonstrate and validate QWIP FPA in the natural, space radiation environment. We discuss the objectives of this demonstration opportunity, and the development and test steps required to deliver the QWIP Experiment to space
This paper reviews terahertz diode technology with regard to mixers, multipliers and sideband generation. Emphasis is placed on recent results and the improvements that are needed to ensure that this technology can not only meet the expanding needs of scientific researchers, but also be extended to future military and commercial applications
Certain point target detection algorithms applied to digital images can be evaluated through a formalism involving the generation of a threshold picture, i.e., replacing each actual pixel value with a threshold calculated from the background. Methods to evaluate the strengths and weaknesses of each algorithm are presented using this threshold picture. Moreover, the calculation of an electro-optical system sensitivity parameter (minimum detectable signal) is presented, based on the threshold image.
The conduction mechanism expected for a diluted magnetic semiconductor, Ga1−xMnxAs (x = 0.034 and x = 0.050), is presented. Infrared (IR) and far-infrared (FIR) spectroscopy reveal that the free carrier absorption spectrum cannot be observed, and that the broad absorption peak observed at 2000 cm−1 is ascribable to the optical transition from the ground states of the isolated acceptor, acceptor pair, triplet and cluster to their excited states and to the valence bands. The absorption peak exhibits Stokes shift from 2100 to 1900 cm−1 with decreasing temperature below the ferromagnetic ordering temperature TC = 43 K. These phenomena indicate that holes are redistributed in the spin splitting states leading to magnetization. Since Mn acceptors are in a random system, holes are weakly localized at Mn-sites and hop in the acceptor complexes. The absorption coefficient integrated from 50 to 150 cm−1 increases with decreasing temperature from TC and with increasing external magnetic field. These phenomena have been explained in terms of correlated many-hole hopping (CMHH). That is, the absorption is proportional to the number of holes which simultaneously hop in the Mn acceptor states. CMHH conduction depends mainly on the exchange energy between the hole spins and localized Mn spins. In addition, the many-body effects of CMHH conduction have been confirmed by IR and FIR reflection spectroscopy and analysis of the spectra. The effective mass ratio enhancement has been found to be as large as 1.7 at 10 K below TC. Thus, the authors have concluded that CMHH conduction mediates the ferromagnetic ordering in Ga1−xMnxAs (x = 0.034 and x = 0.050).
InAs nanostructures on InAlAs/InP(0 0 1) have been fabricated using Stranski–Krastanov growth mode. Depending on growth conditions, a full coverage of the InAlAs surface by either InAs quantum wires or quantum dots can be achieved. Giant intraband absorptions are observed at mid-infrared wavelengths. The intraband resonances are strongly polarized in the layer plane as a consequence of the quantum confinement along the [1 1 0] direction. The absorption at normal incidence reaches 26% for 10 layers of n-doped InAs elongated dots. We also report on femtosecond pump–probe experiments aimed at measuring the electron capture time. Typical times range from 3 ps for broad wires to 6 ps for narrow wires.
Lead selenide epitaxial films were grown on silicon substrates using a thin (⩽100 nm) YbS buffer layer. The films were (001)-oriented and had structural, electrical and photoelectrical properties comparable with those of PbSe bulk crystals. The X-ray rocking curve halfwidths were of 100–200 arcsec which are within similar values for PbSe/BaF2(CaF2)/Si films, thoroughly investigated for infrared detector array applications. The films investigated exhibit relatively large photosensitivity in the temperature range T = 80–300 K. Minority carrier lifetime values τ ≈ 10−6s at 80K and their temperature dependencies are preferably determined by the Schockley-Read-Hall recombination mechanism through the deep levels in the band gap.
Effects of well number on temperature characteristics in 1.3-μm InGaAsP–InP multi-quantum-well lasers have been investigated. A smaller well number is suitable for lower threshold current and higher differential quantum efficiency at 25 °C, while larger well number produces better performances at 85 °C. Furthermore, lasers with a larger well number can achieve a less output power penalty at high temperature. For the first time, a theoretical model has been established to precisely explain the relationship between the characteristic temperature of threshold current and that of external differential efficiency.
The laser properties of 1.3 μm spectral region in Nd:YAG crystal and their simultaneous dual wavelength threshold condition are investigated. Three types of high power 1.3-μm Nd:YAG quasi continuous wave (QCW) lasers, which operate at 1.319 μm or 1.338 μm single wavelength, 1.319 μm and 1.338 μm simultaneous dual wavelength, are achieved with a maximum average output power of 138 W, 132 W and 120 W, respectively.
We have developed a 1.65 μm DFB diode laser absorption spectrometer to allow high sensitive detection of ammonia at this wavelength. The study was done over 1.66454 μm (6007.6 cm−1) component of ν2 + ν3 + ν4 ro-vibrational combination band of NH3. An apparatus sensitivity limit of 2 ppm-m of pure NH3 was measured by using a phase-sensitive low-wavelength-modulation (LWM) detection technique. Minimum detectable concentrations of 55 ppm-m of NH3 in N2, and 59 ppm-m of NH3 in O2 at a total pressure of 76 Torr and a temperature of 295 K were measured. Also, we have measured the unknown selfbroadening and foreign gas broadening coefficients for N2 and O2 for this line and their gas temperature dependence.
The 1.9 THz local-oscillator (LO) of the GREAT heterodyne receiver is presented. The LO is based on a frequency tripled backward-wave oscillator source. The frequency stabilization system is described and an astigmatic imaging system, developed for improved beam coupling, is presented. Allan variances and temperature dependent power drifts are analyzed. The LO is designed as a stand-alone system and fits into GREAT’s local-oscillator compartments. It produces more than 1.5 μW of stable output power to pump the hot electron bolometer mixers of the GREAT instrument.
Difference frequencies up to 176 GHz between CO2-laser transitions at 28 THz (10.7 μm) are generated by thin-film nanometer-scale NiNiONi diodes (MOM, MIM) with integrated bow-tie antennas and rhodium waveguides. A signal-to-noise (S/N) ratio of 47 dB was measured for a 58.7 GHz difference frequency and a 100 kHz bandwidth, while a S/N ratio of 14 dB was observed for a 176.2 GHz difference frequency and a 300 kHz bandwidth. The frequencies reported are considerably higher than those reported previously for thin-film diodes. The comparison of the mixing signals for the antenna parallel and perpendicular to the E-polarization of the infrared radiation yields a ratio of over 34 dB. These results imply the extension of millimeter-wave techniques to the infrared.
This paper addresses approaches to achieve highly reflective thin film coatings at 1064 nm in the near infrared (NIR) spectral region. Different strategies, i.e. metal mirrors, homogeneous dielectric multilayer and hybrid multilayer (metal layer with multilayer enhancement) are suggested. These coatings are deposited with different techniques, and their optical and mechanical performances are analyzed and concluded. Compared to all-dielectric multilayer, metal-enhanced coatings show lower thickness and lower stress load, and therefore are very promising in substrate-sensitive applications.
We investigated the possibility of benzene monitoring in the ν14-band in the 10 μm region and ν4-band in the 14 μm region with regard to industrial applications. We were able to detect 80 ppm of benzene in ambient air.
We give a measurement of the refractive indices of the nematic liquid crystal E7 at a wavelength of 1550 nm as a function of temperature. This particular wavelength has been chosen because it is very important in telecommunications. The measurements have been performed by means of a refractometric method, using a wedge shaped liquid crystal cell.
Future astronomical instruments call for large format and high sensitivity far infrared focal-plane arrays to meet their science objectives. Arrays as large as 128 × 128 with sensitivities equal to or better than 10−18 W/√Hz are set as targets for the far IR instruments to be developed within the next 10 years. These seemingly modest goals present a not-so-modest quantum leap for far IR detector technology whose progress is hampered by a number of complexities; chief among them the development of low noise readouts operating at deep cryogenic temperatures and a viable hybridization scheme suitable for far IR detectors. In an effort to incrementally develop large-format photoconductor arrays, we have fabricated a 2 × 16 Ge:Sb array using the SBRC190 readout – a cryogenic 1 × 32 CTIA readout multiplexer initially developed for SOFIA’s AIRES instrument. In this paper we report the results of the extensive parametric tests performed on this array showing an impressive noise performance of 2.2 × 10−18 W/√Hz and a DQE of 0.41 despite some design limitations. With such an encouraging performance, this prototype array will serve as a platform for our future developmental effort.
A reliable procedure for remote high-accuracy laser detection of N2O as one of the principal destroyers of the protective ozone layer of the Earth has been developed. The procedure is based on using a CO2-laser system emitting efficiently in the ∼4.5 μm range. In this case lasing from isotopic modification 12C18O2 of carbon dioxide with its subsequent frequency doubling by a nonlinear crystal is used. With the object of reducing the price the composition of the active medium (both for TEA laser and low-pressure longitudinal-discharge-excitation laser) has been optimized. New high-efficiency intracavity frequency doubling schemes based on nonlinear AgGaSe2 crystals have been developed for CO2-lasers of both types. Low concentrations of N2O and concentrations of the principal background gases CO and H2O have been measured under real atmosphere conditions with the aid of the lidar complex built around these lasers.
Free standing metal screens have long been used as band pass filters in the infrared (IR) wavelength region. One adjusts the screens’ periodicity constant, its opening-to-periodicity aspect ratio and its thickness to achieve desired infrared transmission properties. Here we concentrate on thick screens in the near IR wavelength region (1–2 μm). In addition to experiments and simulations we have considered the role of screen imperfection on its transmission characteristics. Uneven surfaces, inclined and sometimes rough walls of the screen and waveguide channels may be the result of thick-film lithography which is used in the process for screen manufacturing. Understanding these effects is crucial to applications of these filters in the entire IR region.
A near-infrared diode laser spectrometer was used in the laboratory to study CO2 line parameters near 2.05 μm. The spectral region was studied with a new generation of laser: antimonide-based quantum-well diode laser from University of Montpellier––France. One line of the (2 00 1)III ← (0 0 0) band of CO2 that is suitable for the in situ sensing of the middle atmosphere has been thoroughly studied at 2.05 μm. The results are compared to previous determinations and available databases. We further demonstrate with this new-generation laser the possibility to detect CO2 at ground levels using the JETDLAG laboratory spectrometer.
First remote measurements of stratospheric OH with an airborne vertical sounding far-infrared (FIR) heterodyne spectrometer are reported: Thermal emission from rotational transitions at 2,514 GHz were observed. The measurements were carried out from aboard the DLR jet aircraft FALCON at about 11 km altitude flying over Germany. Temperature contrast was optimized by observing at elevation angles around 20°. A previous feasibility study showed that improvements in stability and sensitivity will allow the determination of concentration profiles with an altitude resolution of about 10 km over an altitude range from 20 to 50 km.
The low cycle fatigue behaviour of the 2024-T3 aluminium alloy is examined in this paper in terms of both thermal measurements provided by an infrared camera and an energetic analysis performed with a suitable data processing. Oscillating variations of temperature are mainly due to the thermoelastic coupling. During the transient loading leading to the maximum stress value (higher than the yield stress of the material), sudden increases in temperature are observed. The heat sources produced by the material are assessed using the heat diffusion equation after an in-house filtering method. The mechanical dissipation attributed mainly to plastic strain is then estimated and the cumulative plastic damage is calculated by the temporal integral of it. Plastic damage fields are analysed for two geometries of specimens in order to underline structural effects and to study the initial damage state of the specimen before the steady-state cyclic loading.
An experimental study on beam dynamics in MIRRORCLE-20, a tabletop storage ring of 15 cm orbit radius, was performed. Measurement of the infrared (IR) synchrotron light is the tool of this study. The IR emission is enhanced by a circular optics, named photon storage ring (PhSR), placed around the electron orbit, and is collected by a magic mirror associated with two plane mirrors in the storage ring. The measured average IR power in mid-IR region (λ < 50 μm) is ∼59 mW. The observed stored beam current is about 1.2 A at maximum, which represents a record for a storage ring. The observed beam size is about 74 × 3 mm2. We conclude that this very long beam size is due to the large betatron oscillation of 2/3 resonance injection.
A fiber bundle is fabricated for use in three-dimensional spectroscopy. The bundle has 100 fibers with chalcogenide glass cores (As2S3) whose shape of the cutting surface is square. The fibers are arrayed 10 × 10, and 1 × 100 on the input and output side, respectively, whereby two-dimensional images are reformatted into a linear array. The output beams from fibers are dispersed by a grating and their spectra are detected simultaneously on a two-dimensional photo-detector. Preliminary results obtained by our fiber bundle are presented here.
We report two approaches using Quantum Well Infrared Photodetectors for detection in the [3–4.2 μm] atmospheric window. Taking advantage of the large band gap discontinuity we demonstrated a strained AlInAs/InGaAs heterostructure on InP. The optical coupling in this structure has been experimentally and numerically investigated. The results show that the coupling is mainly due to guided modes. The second approach is based on double barrier strained AlGaAs/AlAs/GaAs/InGaAs active layers on GaAs. The segregation of the elements III in these structures has been investigated using a transmission electron microscope. The results show a strong modification of the conduction band profile. We demonstrate peak wavelengths at 3.9 μm for the InP based detector and 4.0 μm for the GaAs based detector. We report a background limited peak detectivity (2π field of view, 300 K background) at 4.0 μm of about 2 × 1011 cm Hz1/2 W−1 at 77 K, and 1.5 × 1011 cm Hz1/2 W−1 at 100 K.
In this paper we present a compact tuneable continuous-wave infrared laser, based on difference-frequency generation (DFG) using quasi phase matching in periodically poled LiNbO3 (PPLN), for accurate line intensity measurements. Several 0.1 μW of infrared radiation (tuneable in the 3–5 μm range) are obtained using a diode-pumped Nd:YAG laser (output power about 800 mW at 1064 nm, linewidth 1 kHz) together with a tuneable external-cavity diode laser (output power about 500 μW–50 mW in the 805–885 nm region, linewidth 1 MHz). Using this infrared DFG laser for absorption experiments of gas-phase molecules, both very high-resolution (1 MHz) and a high signal-to-noise ratio (up to several 1000) can be achieved in measurement time of only a few minutes, as demonstrated using absorption spectra of N2O in different wavelength regions. The present paper focuses in particular on the accuracy of the wavelength calibration and on the determination of absorption coefficients with experimental uncertainties of less than 1%.