Excitation dynamics involving homogeneous multistate interactions: one and two color VMI and REMPI of HBr.

Velocity map imaging (VMI) data and mass resolved REMPI spectra are complementarily utilized to elucidate the involvement of homogeneous multistate interactions in excited state dynamics of HBr. The H1Σ+(v' = 0) and E1Σ+(v' = 1) Rydberg states and the V1Σ+(v'= m + 7) and V1Σ+(v'= m + 8) ion-pair states are explored as a function of rotational quantum number in the two-photon excitation region of 79 100-80 700 cm-1. H+ and Br+ images were recorded by one- as well as two-color excitation schemes. Kinetic energy release (KER) spectra and angular distributions were extracted from the data. Strong-to-medium interactions between the E(1) and V(m + 8)/V(m + 7) states on one hand and the H(0) and V(m + 7)/V(m + 8) states on the other hand were quantified from peak shifts and intensity analysis of REMPI spectra. The effects of those interactions on subsequent photoionization and photolytic pathways of HBr were evaluated in one-color VMI experiments of the H+ and two-color VMI experiments of the Br+ photoproducts.

Rydberg and valence state excitation dynamics: a velocity map imaging study involving the E-V state interaction in HBr.

Photoexcitation dynamics of the E((1)Σ(+)) (v' = 0) Rydberg state and the V((1)Σ(+)) (v') ion-pair vibrational states of HBr are investigated by velocity map imaging (VMI). H(+) photoions, produced through a number of vibrational and rotational levels of the two states were imaged and kinetic energy release (KER) and angular distributions were extracted from the data. In agreement with previous work, we found the photodissociation channels forming H*(n = 2) + Br((2)P3/2)/Br*((2)P1/2) to be dominant. Autoionization pathways leading to H(+) + Br((2)P3/2)/Br*((2)P1/2) via either HBr(+)((2)Π3/2) or HBr(+)*((2)Π1/2) formation were also present. The analysis of KER and angular distributions and comparison with rotationally and mass resolved resonance enhanced multiphoton ionization (REMPI) spectra revealed the excitation transition mechanisms and characteristics of states involved as well as the involvement of the E-V state interactions and their v' and J' dependence.

Slice imaging of methyl bromide photofragmentation at 193 nm.

The photodissociation of methyl bromide at 193 nm is studied using slice imaging. From the measured photofragment translational energy and angular distributions we were able to extract methyl-state-specific dissociation channel yields and crossing probabilities between (3)Q0 and (1)Q1 surfaces. The angular distributions for the Bromine photofragments show a strong dependence on the total translational energy release. Nonadiabatic transition probabilities from the (3)Q0 to (1)Q1 surface dominate the dynamics in this excitation energy region and for most of the methyl vibrational states probed.

Driving photochemistry by clustering: the ICl-Xe case.

We present slice imaging data demonstrating the influence of clustering on the photodissociation dynamics of a diatomic molecule: iodine monochloride (ICl) was dissociated at 235 nm in He and Xe seed gasses, probing both Cl and I photofragment energy and angular distributions. We observe that the kinetic energy releases of both Cl and I fragments change from He to Xe seeding. For Cl fragments, the seeding in Xe increases the kinetic energy release of some Cl fragments with a narrow kinetic energy distribution, and leads to some fragments with rather broad statistical distribution falling off exponentially from near-zero energies up to about 2.5 eV. Iodine fragment distribution changes even more dramatically from He to Xe seeding: sharp features essentially disappear and a broad distribution arises reaching to about 2.5 eV. Both these observations are rationalized by a simple qualitative cluster model assuming ICl dissociation inside larger xenon clusters and "on surface" of smaller Xe species.

Scatterer size-based analysis of optical coherence tomography images using spectral estimation techniques.

A novel spectral analysis technique of OCT images is demonstrated in this paper for classification and scatterer size estimation. It is based on SOCT autoregressive spectral estimation techniques and statistical analysis. Two different statistical analysis methods were applied to OCT images acquired from tissue phantoms, the first method required prior information on the sample for variance analysis of the spectral content. The second method used k-means clustering without prior information for the sample. The results are very encouraging and indicate that the spectral content of OCT signals can be used to estimate scatterer size and to classify dissimilar areas in phantoms and tissues with sensitivity and specificity of more than 90%.

Feasibility study of smartphone-based Near Infrared Spectroscopy (NIRS) for salted minced meat composition diagnostics at different temperatures.

This research work evaluates the feasibility of a smartphone-based spectrometer (740-1070 nm) for salted minced meat composition diagnostics at industrial scale. A commercially available smartphone-based spectrometer and a benchtop NIR spectrometer (940-1700 nm) were used for acquiring 1312 spectra from meat samples stored at four different temperatures ranging from -14 °C to 25 °C. Thereafter, for each spectrometer, PLS and Random Forest regression models specific for each temperature and global models were created to predict the fat, moisture and protein contents. Fat and moisture can be estimated with the global model in a wide range of temperatures by using the smartphone-based spectrometer, which has an acceptable accuracy for quality control purposes (RPD > 7) and comparable to the accuracy of a benchtop spectrometer.

AM-FM techniques in the analysis of optical coherence tomography signals.

The subtle tissue changes associated with the early stages of malignancies, such as cancer, are not clearly discernible even at the current, improved, resolution of optical coherence tomography (OCT) systems. However, these changes directly affect the spectral content of the OCT image that contains information regarding these unresolvable features. Spectral analysis of OCT signals has recently been shown to provide additional information, resulting in improved contrast, directly related to scatterer size changes. Amplitude modulation-frequency modulation (AM-FM) analysis, a fast and accurate technique for the estimation of the instantaneous frequency, phase, and amplitude of a signal, can also be applied to OCT images to extract scatterer-size information. The proposed technique could make available an extremely valuable tool for the investigation of disease characteristics that now remain below the resolution of OCT and could significantly improve the technology's diagnostic capabilities.