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Three periods of Al0.1Ga0.9N/Al0.15Ga0.85 N multiple quantum wells (MQWs) were used as the active region of a p-i-n diode fabricated on 6H-SiC substrate. Electroluminescence (EL) of these MQWs has been investigated in both injection and avalanche modes. Band-to-band luminescence of the Al0.1Ga0.9N wells was found to peak at 364 nm in the injection mode and in the range of 364-372 nm in the avalanche mode. The most striking phenomenon is that band-to-band EL of the Al0.15Ga0.85N barriers has also been observed in the injection mode, while it is not seen in the avalanche mode. This is explained by considering different sources of carriers and different carrier transportation mechanisms in the two modes. The luminescence intensity I EL has a power-law dependence on the current I by I EL prop I 2 in the injection mode and by I EL prop I 4 in the avalanche mode. [ABSTRACT FROM PUBLISHER]

Two heavily doped n-type Zn0.46Cd0.54Se/Zn0.24 Cd0.25Mg0.51Se multiple quantum well (MQW) structures have been grown on InP (0 0 1) substrates by molecular beam epitaxy. Photoluminescence (PL), time-resolved PL, and Fourier transform infrared (FTIR) spectroscopy were performed to characterize their interband and intersubband (ISB) properties. These two MQW samples have similar structures except for different well widths and a different number of periods. Excitation-intensity-dependent PL shows no electronic coupling between the multiquantum wells. The integrated PL intensities and the PL decay times of the MQWs were measured as functions of temperature in the range from 77 to 290 K. Theoretical fittings of temperature dependences of integrated PL intensities and PL decay times indicate that the nonradiative recombination processes observed in our samples can be well described by hole capture by acceptor-like defect centers through multiphonon emissions. ISB absorption spectra of the samples were measured by FTIR and show peak absorption at wavelengths of 3.99 and 5.35 mum for the MQWs with well widths of 28 and 42 A, respectively. Theoretical calculations based on the envelope function approximation confirm that these peaks are due to the transitions from the ground state E1 to the first excited state E2. [ABSTRACT FROM PUBLISHER]

Optical imaging using independent component analysis (OPTICA) has been used for detection, 3D localization, and cross-section imaging of a tumor inside a model human breast composed of ex vivo human breast tissues. OPTICA uses a multisource target illumination and multidetector signal acquisition scheme to obtain multiple spatial and angular views of the sample for target localization. Independent component analysis of the perturbations in the spatial light intensity distribution measured on the sample boundary sorts out the signal originating from individual targets. A back-projection technique estimates the cross-section of each target. The approach correctly provided the positions of a tumor located at the mid-plane and two glandular structures located at different positions within the 33-mm thick model breast. The reconstructed cross-section images are in good agreement with known dimensions of the structures, and pathological findings. [ABSTRACT FROM PUBLISHER]

Steady-state and time-resolved fluorescence spectroscopy were measured for five species of bacteria (Bacillus subtilis, Staphylococcusaureus, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa) subjected to three bactericidal agents, formaldehyde, sodium hypochlorite (bleach), and hydrogen peroxide. For all species, the fluorescence was dominated by tryptophan emission with a fluorescence lifetime that can be described by a bi-exponential decay profile. Application of bleach resulted in an almost total loss of scattering and fluorescence, which indicated that total destruction of proteins and amino acids may have occurred. Hydrogen peroxide decreased the fluorescence intensity and shifted λmax to shorter wavelengths, except in S. aureus, which is resistant to oxidizing agents. The formaldehyde shifted λmax to shorter wavelengths for B. subtilis, S. aureus, E. faecalis, and E. coli. The formaldehyde shortened the lifetime of the slow component and increased the amplitude of the fast component relative to the slow component. This study demonstrates that fluorescence spectroscopy offers a method to evaluate the potential for killing bacteria and decontaminating areas by disinfecting agents. [ABSTRACT FROM PUBLISHER]

The multiplexing and ultrafast multichannel spatially-resolved demultiplexing of supercontinuum (SC) coherence data packets using a coherent time-to-space conversion is proposed as a novel approach for free-space ultrafast laser communication. The femtosecond coherence time of spectrally extended SC pulses is used on the femtosecond time scale without the need for femtosecond pulses. The proposed scheme for data packets coherence multiplexing and demultiplexing is experimentally demonstrated. This SC approach has the capability of processing multigigabits per second information for free-space laser communication applications. [ABSTRACT FROM PUBLISHER]

White supercontinuum (SC) produced from Fresnel diffraction was demonstrated in BK7 glasses using femtosecond laser pulses. For input pulse energy below the threshold for the onset of self-focusing and SC generation, an aperture was placed into the beam before the BK7 glass to redistribute the intensity by diffraction along the propagation axis to produce a stable SC. The SC occurred at various distances from the aperture containing odd number of Fresnel zones, mainly the first. This result plays an important role in studying the properties of SC sources as well as the diffraction field distribution. A distinct and stable interference ring pattern inside the conical four-photon emission is observed and attributed to the spatial arrangement of small-scale filaments at different distances in the glass. [ABSTRACT FROM PUBLISHER]

Human rectum-membrane-prostate tissue samples were studied using a near-infrared spectral polarization imaging technique to detect small objects and structural changes inside prostate tissues through the rectum. Four modeling samples were made with a small piece of absorber or prostate tissue dyed with a contrast agent (indocyanine green) embedded inside a large piece of prostate tissue in rectum-membrane-prostate structures. The depth of the foreign objects underneath the surface of the rectum-membrane-prostate structures was varied from a millimeter to a centimeter to obtain the critical imaging distance. Different spectral polarization imaging methods with and without contrast agents were performed and compared. The results show that small objects hidden inside the host prostate tissues in the rectum-membrane-prostate structures at depths of 2.5, 4.0, and 7.5 mm can be imaged and identified using the scattering light imaging, tissue emission wing imaging, and contrast agent fluorescence imaging methods, respectively. Our results indicate the potential of imaging and detecting structural changes and cancers inside prostate tissue though rectum-membrane-prostate tissues using this noninvasive spectral polarization imaging technique. [ABSTRACT FROM PUBLISHER]

Light extinction and angular scattering measurements were performed on three species of bacteria with different sizes and shapes ( Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis). The Gaussian ray approximation of anomalous diffraction theory was used to determine the average bacteria size from transmission measurements. A rescaled spectra combining multiple angular data was analyzed in the framework of the Rayleigh-Gans theory of light scattering. Particle shape and size distribution is then obtained from the rescale spectra. Particle characteristics (size and/or shape) retrieved from both methods are in good agreement with size and shape measured under scanning electron microscopy. These results demonstrate that light scattering may be able to detect and identify microbial contamination in the environment. [ABSTRACT FROM PUBLISHER]

The photon distribution, as a function of position, angle, and time, is computed using the analytical cumulant solution of the Boltzmann radiative transfer equation (RTE). A linear forward model for light propagation in turbid media for three-dimensional (3-D) optical tomography is formed based on this solution. The model can be used with time resolved, continuous wave (CW), and frequency-domain measurements in parallel geometries. This cumulant forward model (CFM) is more accurate than that based on the diffusion approximation of RTE. An inverse algorithm that incorporates this CFM is developed, based on a fast 3-D hybrid-dual-Fourier tomographic approach using multiple detectors and multiple sources in parallel geometries. The inverse algorithm can produce a 3-D image of a turbid medium with more than 20 000 voxels in 1-2 min using a personal computer. A 3-D image reconstructed from simulated data is presented. [ABSTRACT FROM PUBLISHER]

The Stokes-shifted emission spectra were measured for various photoactive biomolecules in aqueous solution and tissue such as tryptophan, collagen, nicotinamide adenine dinucleotide, and flavin. Information is obtained on the molecular activity in the tissue. This new approach allows for the extraction of some new information not obtained from excitation and/or fluorescence spectroscopy for a single spectral scan. [ABSTRACT FROM PUBLISHER]

Near-infrared (NIR) time-resolved and spectroscopic transillumination imaging techniques are used to investigate normal tissues and Warthin's tumor of human parotid glands. The time-sliced imaging arrangement uses 120-fs, 1-kHz repetition-rate, 800-nm pulses from a Ti: sapphire laser and amplifier system for sample illumination and an ultrafast gated intensified camera system (UGICS) for recording two-dimensional (2-D) images using transmitted light. Images recorded with earlier temporal slices (approximately first 100 ps) of transmitted light highlight the tumor, while those recorded with later temporal slices (later than 200 ps) accentuate normal tissues. The spectroscopic imaging arrangement uses 1210-1300 nm tunable output of a Cr: forsterite laser for sample illumination, a Fourier space gate to discriminate against multiple-scattered light, and a NIR area camera to record 2-D images. The tumor region in the specimen appears brighter than the normal region in spectroscopic images recorded with light of different wavelengths. A wavelength-dependent variation in the ratio of light transmission through the tumor to that through the normal parotid gland is observed. Differences in scattering and wavelength-dependent absorption characteristics of normal parotid gland and Warthin's tumor provide a consistent explanation of these observed features. Histopathological analysis of the specimen sheds light on the probable origin of the differences in scattering and absorption characteristics [ABSTRACT FROM PUBLISHER]

Two new near-infrared (NIR) tunable lasers were used to investigate weld repair strength. The tensile strengths of the shell membrane of hen eggs and the Wistar rat skin welding model were measured for the varying laser wavelengths: 1220, 1240, 1270, 1300 nm (from the forsterite laser) and 1360, 1430 nm (from the cunyite laser). The tensile strength was measured with a digital force gauge. The highest tensile strength was achieved at 1430 nm in the shell membrane of 0.81±0.11 N and in the skin welding model of 0.64±0.16 N. The weld strength follows the absorption spectrum of water [ABSTRACT FROM PUBLISHER]

Two-dimensional in vivo optical images of metacarpal bones of a human palm and in vitro images of turkey and chicken bones embedded in tissues were obtained in the near-infrared region using femtosecond pulse transillumination and picosecond electronic time-sliced detection technique. A small hole drilled in chicken bone and embedded in chicken breast tissue was imaged using early arriving light. Time-gated fluorescence images of an interior marrow region of a bone injected with a fluorescent dye were recorded. The techniques have potential for monitoring bone fracture, bone diseases such as, osteoporosis and arthritis, and diseases that originate in or affect bone marrow [ABSTRACT FROM PUBLISHER]