The InGaN-based blue light-emitting diodes (LEDs) with double AlGaN/InGaN superlattice (SL) electron-blocking layers are investigated theoretically. The simulation results indicate that the output power, the radiative recombination rates, and the spontaneous emission rates of the blue LED with double AlGaN/InGaN superlattice layers are evidently improved, meanwhile, the efficiency droop phenomenon is remarkably alleviated, compared with the original structure. The reasons are that the new structure with double AlGaN/InGaN SLs can not only suppress the electron leakage but also enhance the hole injection. Specifically, it can improve the radiative recombination rates, which leads to higher output power than original structure.
In this article, the relationship between the states of Ag core-Au shell (core-shell) nanoparticles (NP) and the intensity of
Raman scattering of analytes dissolved in the water and adsorbed on the NP was studied. The core-shell NP were
synthesised by coating Au layers over Ag seeds by the method of "seed-growth". To highlight the advantage of the
core-shell NP, Ag colloid and Au colloid were chosen for contrasting. The analyte that were chosen for this testing were
methylene blue (MB) for the reason that MB has very strong signal in surface-enhanced Raman scattering (SERS). The
SERS activity of optimalizing states of Ag and Au colloids were compared with that of core-shell NP when MB was
used as analyte. In this study, sodium chloride, sodium sulfate and sodium nitrate were used as aggregating agents for
Ag, Au colloids and core-shell NP, because anions have a strong influence on the SERS efficiency and the stability of
colloids. The results indicate that core-shell NP can obviously enhance the SERS of MB. The aim of this study is to
prove that compared with the metal colloid, the core-shell NP is a high efficiency SERS active substrate.
Surface enhanced Raman scattering (SERS) is potentially tool in the characterization of biomolecules such as amino
acids, complicated peptides and proteins, and even tissues or living cells. Amino acids and short peptides contain
different functional groups. Therefore, they are suitable for the investigations of the competitive-interactions of these
functional groups with colloidal silver surfaces. In this paper, Normal Raman and SERS of amino acids Leucine and
Isoleucine and short peptide Leu-Leu were measured on the silver colloidal substrate. Raman shifts that stem from
different vibrational mode in the molecular inner structure, and the variations of SERS of the samples were analyzed in
this study. The results show that different connection of one methyl to the main chains of the isomer amino acids resulted
in different vibration modes in the Normal Raman spectra of Leucine and Isoleucine. In the SERS spectra of the isomer
amino acids, all frequency shifts are expressed more differently than those in Normal Raman spectra of solid state.
Orientation of this isomer amino acids, as well as specific-competitive interactions of their functional groups with the
colloidal silver surface, were speculated by detailed spectral analysis of the obtained SERS spectra. In addition, the
dipeptide Leu-Leu, as the corresponding homodipeptide of Leucine, was also measured adsorbed on the colloidal silver
surface. The SERS spectrum of Leu-Leu is different from its corresponding amino acid Leucine but both of them are
adsorbed on the silver surface through the carboxylate moiety.
The high contrast and high resolution photoacoustic tomography was used to image the gold nanoshell clearance in rat
brain in vivo. With our current imaging system, the acquisition of photoacoustic signals is realized through a circular
scan of a single-element transducer. Therefore, the data acquisition is slow. In this case, an improved simultaneous
iterative reconstruction algorithm was developed to reduce the acquisition time by using limited data in the experiments.
This algorithm is based on the least square principle; it can be used to reconstruct high quality images from the limited
data containing much noise. Furthermore, it is always convergent. So it can improve the imaging quality comparison
with conventional filter back-projection algorithm (FBP) and algebraic reconstruction algorithm (ART). Here we
accurately mapped rat brain structures with gold nanoshell contrast agents. We also imaged the clearance of gold
nanoshell in the rat brain. It provides an accurate non-invasive monitoring method for fluid pathways in biological
tissues, which makes photoacoustic tomography as a powerful method for imaging pathologic tumor vessels, delineating
neovascularization, and studying global and regional hemodynamic activities in the brain.
Noninvasive monitoring of the microvascular network and detection the angiogenesis around tumors is one of the most
active areas in biomedical research. In this paper, we present a multi-element photoacoustic imaging system for fast
imaging the blood vessels. In this system, a Q-switched Nd: YAG pulse laser operated at 532nm with a 6 ns pulse width
is used to generate a photoacoustic signals; a 64-element linear transducer array with the central frequency of 7.5MHz is
used to measure the photoacoustic waves. The limited-field filtered back projection algorithm is used to reconstruct the
optical absorption distribution in tissue. The experiments of a phantom model and in vitro blood vessels were performed
with this system. A clear photoacoustic image of microvascular network was obtained with high resolution. The
experimental results demonstrate that our multi-element photoacoustic imaging system has the ability of imaging
microvascular network and may potentially be used to monitor the angiogenesis around tumors.
A unique photoacoustic system was developed for neovascular imaging during tumor photodynamic therapy (PDT). In
this system, a single pulse laser beam is used as the light source for both PDT treatment and for concurrently generating
ultrasound signals for photoacoustic imaging. To demonstrate its feasibility, this system was used to observe vascular
changes during PDT treatment of chicken chorioallantoic membrane (CAM) tumors. The photosensitizer used in this
study was protoporphyrin IX (PpIX) and the laser wavelength was 532 nm. Damage of the vascular structures by PDT
was imaged before, during and after treatment. Rapid, real-time determination of the size of targeted tumor blood vessels
was achieved, using time difference of positive and negative ultrasound peaks during PDT treatment. The experimental
results show that a pulse laser can be conveniently used to hybridize PDT treatment and photoacoustic imaging and that
this integrated system is capable of quantitatively monitoring the structural change of blood vessels during PDT. This
method could be potentially used to guide PDT and other phototherapies using vascular changes during treatment to
optimize treatment protocols, by choosing appropriate types and doses of photosensitizers, and doses of light.
The optoacoustic technique is a noninvasive imaging method with high spatial resolution. It potentially can be used to monitor anatomical and physiological changes. Photodynamic therapy (PDT)-induced vascular damage is one of the important mechanisms of tumor destruction, and real-time monitoring of vascular changes can have therapeutic signicance. A unique optoacoustic system is developed for neovascular imaging during tumor phototherapy. In this system, a single-pulse laser beam is used as the light source for both PDT and for concurrently generating ultrasound signals for optoacoustic imaging. To demonstrate its feasibility, this system is used to observe vascular changes during PDT treatment of chicken chorioallantoic membrane (CAM) tumors. The photosensitizer used in this study is protoporphyrin IX (PpIX) and the laser wavelength is 532 nm. Neovascularization in tumor angiogenesis is visualized by a series of optoacoustic images at different stages of tumor growth. Damage of the vascular structures by PDT is imaged before, during, and after treatment. Rapid, real-time determination of the size of targeted tumor blood vessels is achieved, using the time difference of positive and negative ultrasound peaks during the PDT treatment. The vascular effects of different PDT doses are also studied. The experimental results show that a pulsed laser can be conveniently used to hybridize PDT treatment and optoacoustic imaging and that this integrated system is capable of quantitatively monitoring the structural change of blood vessels during PDT. This method could be potentially used to guide PDT and other phototherapies using vascular changes during treatment to optimize treatment protocols, by choosing appropriate types and doses of photosensitizers and doses of light.
In this paper, we have constructed an integrative fast photoacoustic (PA) imaging system for fast photoacoustic
imaging, which includes a fiber, ultrasonic coupling medium, and a multi-element linear transducer array (MLTA).
The PA signals were received by the MLTA in a reflection mode arid collected by a computer, reconstructed by
limited-field filtered back projection algorithm. The PA images of different depth of phantom and animal blood
vessels of different diameters were obtained. The lateral resolution of the system was 0.2mm. It would provide a new
approach to tissue functional images in vivo and may have potentials in developing into an appliance for clinic
diagnosis of disease.
The purpose of present study is to determine and compare the optical properties of normal human pulmonary artery
tissue in vitro at 650, 680, 710, 740, 780 nm wavelengths of Ti:Sapphire laser. The optical parameters of tissue samples
were determined using a double integrating sphere set-up. The inverse Adding-doubling method was used to determine
the optical properties from the measurements. The results of measurement showed that the absorption coefficients for
pulmonary arteries increase with increase of laser wavelength, the maximum absorption coefficient is 0.277 mm-1 at
780 nm, and the minimum absorption coefficient is 0.160 mm-1 at 650nm, and the reduced scattering coefficients for
pulmonary arteries increase with decrease of laser wavelength, the maximum reduced scattering coefficient is 48.8
mm-1 at 650 urn, and the minimum reduced scattering coefficient is 13.3 mm-1 at 780 nm. The optical penetration depths
for pulmonary arteries increase with increase of laser wavelength, the maximum optical penetration depth is 0.298 mm
at 780 nm, and the minimum optical penetration depth is 0.206 mm at 650 nm. The backscattered reflectances for
normal human pulmonary arteries increase with decrease of laser wavelength, the maximum backscattered reflectance
is 0.794 at 650 nm, and the minimum backscattered reflectance is 0.561 at 780 nm.
We developed a fast microwave-induced thermoacoustic tomography system based on a 320-element phase-controlled
linear transducer array. A 1.2GHz microwave generator transmits microwave with pulse duration of 0.5 us and an
incident energy density of 0.45 mJ/cm2. Compared to single transducer collection, the system with multi-element linear
transducer array can eliminate the mechanical rotation of the transducer, so can effectively reduce the image blurring and
improve the image resolution. Using phase-controlled technique to collect thermoacoustic signals, the data need not be
averaged because of the high signal-to-noise ratio, resulting in the total data acquisition time of less than 5 s. The system
thus provide a rapid and reliable approach to thermoacoustic imaging. which can potentially be developed as a powerful
diagnostic tool for early-stage breast caners.
In this paper, Influences of the acoustic path difference on photoacoustic (PA) images caused by mismatch of ultrasonic
velocities were studied. We first proposed using the concentration-adjustable glycerite as an ultrasonic transmitting
medium. By switching a appropriate concentration of the glycerite, it can make the velocities of the PA signals keep
constant between transmitting medium and biological tissues, and avoid the acoustic path difference (APD) in image
reconstruction. The experiments demonstrate that the acoustic path difference influences the imaging qualities badly:
especially, the spatial resolution of PA image is extremely reduced. After matching ultrasonic velocity by glycerite the
contrast of the reconstructed image is improved greatly and the background artifacts are reduced obviously. The spatial
resolution of the reconstructed image is improved from 0.5mm to
0.15mm. It has great practical significance for applying
photoacoustic tomography to noninvasive clinic diagnosis of cancer.
This paper presents a novel model of photoacoustic tomography with an ultrasonic probe beam. A strict theory describes
the nonlinear interaction between photoacoustic wave and ultrasonic probe beam. When a pulse laser irradiates on
biological tissues, the laser energy will be absorbed by the identity molecule of the tissues, and be converted into heat.
Subsequently, the thermal expansion of the instantaneously heated tissues induces photoacoustic waves. So the density,
temperature and compressibility of the absorption area will be changed. A focus ultrasonic probe beam with a single
frequency passes through the irradiated area, the changes of the properties of the irradiated medium will be coupled with
the ultrasonic probe beam, which will propagate through the medium with minimal distortion and can be detected at the
surface of the medium. The PA signal in situ can be obtained by demodulating the detected ultrasonic beam. It will take
out much more information from the interaction area, which can reflect not only the intrinsic optical properties but also
the mechanical and acoustical properties of the tissue. In our experimentation, a Q-switched Nd: YAG pulse laser
operated at 1064nm was employed to generate photoacoustic signal, the frequency of ultrasonic probe beam is l0M. By
demodulating the detected ultrasonic beam, we obtained very high quality tomography images. So it will provide a new
promising method for tumour detection and noninvasion function imaging.
The purpose of the study is to analyze and compare differences in the optical properties between normal and adenomatous human colon tissues in vitro at 630-, 680-, 720-, 780-, 850-, and 890-nm wavelengths using a Ti:sapphire laser. The optical parameters of tissue samples are determined using a double integrating sphere setup at seven different laser wavelengths. The inverse Monte Carlo simulation is used to determine the optical properties from the measurements. The results of measurement show that the optical properties and their differences vary with a change of laser wavelength for normal and adenomatous colon mucosa/submucosa and normal and adenomatous colon muscle layer/chorion. The maximum absorption coefficients for normal and adenomatous human colon mucosa/submucosa are 680 nm, and the minimum absorption coefficients for both are 890 nm. The maximum difference of the absorption coefficients between both is 56.8% at 780 nm. The maximum scattering coefficients for normal and adenomatous colon mucosa/submucosa are 890 nm, and the minimum scattering coefficients for both are 780 nm. The maximum difference of the scattering coefficients between both is 10.6% at 780 nm. The maximum absorption coefficients for normal and adenomatous colon muscle layer/chorion are 680 nm, and the minimum absorption coefficients for both are 890 nm. The maximum difference of the absorption coefficients between both is 47.9% at 780 nm. The maximum scattering coefficients for normal and adenomatous colon muscle layer/chorion are 890 nm, and the minimum scattering coefficients for both are 680 nm. The maximum difference of the scattering coefficients between both is 9.61% at 850 nm. The differences in absorption coefficients between normal and adenomatous tissues are more significant than those in scattering coefficients.
Photoacoustic tomography is a potential and noninvasive medical imaging technology. It combines the advantages of pure optic imaging and pure ultrasound imaging. Photoacoustic signals induced by a short pulse laser cover a wide spectral range. We have explored the frequency spectrum of absorbers with different sizes and the influence of photoacoustic signals with different spectral components on photoacoustic imaging. The simulations and experiments demonstrated that the major frequency ranges of photoacoustic pressures of absorbers with diameters of ~cm, ~mm and hundreds of mm are about 20kHz~300kHz, 70kHz~2.5MHz and 400kHz~20MHz, respectively. The low spectral components of photoacoustic signals contribute to the non-boundary region of absorbers, and the high spectral components contribute to small structures, especially, to boundaries. It suggests that the ultrasonic transducers used to detect photoacoustic pressures should be designed and selected according to the frequency ranges of absorbers.
We examine the optical properties of native and coagulated human liver tissues in vitro at four different wavelengths of argon ion laser, 476.5, 488, 496.5 and 514.5 nm, and the differences in the optical parameters of the tissues between 630nm and 790nm. The optical properties, μa, μs and g, of liver tissue were determined by measuring the diffuse reflectance, diffuse transmission and collimated transmission in a double integrating sphere set-up, and the inverse adding-doubling algorithm was used to calculate the optical properties from the measurements. The investigative results showed that there were significant differences respectively in the absorption coefficients, scattering coefficients and anisotropy factors between native and coagulated human liver tissues at the same laser wavelength (P<0.01), these large differences of the absolute values in optical properties indicate that there were large differences in compositions and structures between both, and large differences in compositions and structures induce large differences in absorption and scattering properties between both, and these differences vary with a change of laser wavelength. The scattering coefficients for per tissue type exceed the absorption coefficients by at least one order of magnitude. Hence the conclusions may be helpful to diagnostics and therapeutic applications in liver tissue.
We have studied Raman spectra of glucose aqueous solutions by using a long Teflon-AF2400 liquid core optical fiber (LCOFs), and have measured the glucose concentrations in solutions according to Raman spectra of solutions. We also have compared Raman Spectra of aqueous glucose solutions collected in LCOFs with those collected in a conventional 90° scattering geometry, and have obtained a detection sensitivity enhancement factor more than 100. A clear correlation between glucose Raman signals and glucose concentrations has been established by data analysis. It has shown that compared to conventional methods. LCOFs can provide higher Raman signal intensities, higher detection sensitivity and signal-to-noise rate in Raman spectroscopy measurements, in which the effective optical path length through the liquid sample is much longer than it would normally be. This study demonstrates the feasibility of measuring accurately glucose concentration by Raman spectroscopy using LCOFs, and can be used to evaluate the potential of Raman spectroscopy using LCOFs to perform microanalysis and measurements of liquid analytes in solutions with clinical accuracy. This technique is capable of measuring the concentration of other Raman-active liquid samples and complicated biology system.
Human gallstones were immersed with chloroform, ethanol and ether. The insoluble components were studied by normal Raman (SER) and FT-infrared (IR) spectroscopy. The results show that bilirubinate salts and proteins are the main components in the insoluble materials of gallstones. The secondary structure of the proteins in gallstones are dominated by (alpha) -helix structure. The results suggest that proteins play a key role in the formation of gallstones.
The characteristics of the magnetic confined discharges under high gas pressure (> 104 Pa) are investigated, e.g. electron motion equation under electromagnetic fields, electron transport coefficients, the influences of magnetic field and gas pressure on the discharge behavior. The electron mobility (mu) and conductivity (sigma) in the discharge space may change under the influences of magnetic field. Other side, as the increase of gas pressure, the impact frequency between electron and gas molecule will increase, this will increase the electron mobility (mu) and conductivity (sigma) . In the high gas pressure the stable discharge can be obtained only with the high magnetic flux density. This conclusions are proved from the experiments of TEA---CO2 laser and excimer laser.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.