No abstract

The nature of cubic and cascaded quadratic nonlinear responses in the KTiOPO4 crystal under picosecond pump is studied. The main attention is paid to determination of the origin and properties of the blue radiation accompanying the red light amplification process (the central wavelength ~685 nm, bandwidth ~20 nm) in a noncollinear optical parametric amplifier (NOPA) pumped by the second‐harmonic radiation of the picosecond Nd:YAG laser (532 nm). In NOPA, the amplified seed radiation (ωs) becomes so intense that it can participate in any nonlinear three‐wave interaction and also can play the role of the Stokes wave in the in the coherent anti‐Stokes Raman scattering‐process in which powerful pump radiation (ωp) of the main parametric process serves both as the pump wave and the probe wave. Possible causes of the blue light emanating from the KTP crystal and the mechanisms for their realization are analyzed. We interpret the ring of blue light around the axis located between the directions of propagation of the green pump beam and the red beam of the amplified seed radiation, as the emission of amplified parametric fluorescence (signal wave) under low‐frequency pump. This phenomenon can be used for effective amplification in picosecond NOPA of weak anti‐Stokes radiation in the experiments with time‐resolved broadband picosecond coherent Anti‐Stokes Raman Scattering.

We demonstrate generation of broadband high‐intensity picosecond pulses using a non‐collinear optical parametric amplifier, seeded with a broadband cavity‐less dye laser and pumped using the second harmonic of a picosecond Nd:YAG laser. With appropriate choice of the pump‐seed non‐collinearity angle, we observed energy conversion from the pump to the signal wave of around 15%, with the bandwidth of the amplified radiation around 445 cm−1 (20.7 nm) centered around 680 nm. An energy of 1.2 mJ per pulse of duration around 26 ps has been achieved. A light source with such parameters could be suitable for use in time‐resolved broadband picosecond Coherent anti‐Stokes Raman scattering. Copyright © 2014 John Wiley & Sons, Ltd.

Angiotensin I‐converting enzyme (ACE) is a glycoprotein, consisting of two homologous domains within a single polypeptide chain. ACE concentration in biological fluids is an important parameter of clinical observation; its increase or decrease may accompany various pathologies. Currently, the exact crystal structure of the two‐domain ACE form is still unknown because of microheterogeneity and intensity of the enzyme glycosylation. Raman spectroscopy provides the qualitative and quantitative analysis of many compounds, including proteins. For the first time, surface‐enhanced Raman scattering (SERS) spectra of native and thermo‐denatured human ACE have been demonstrated with full assignment. Denaturation leads to SERS intensity increase and bands shifting. Detailed band assignment and discussion are included to elucidate the potential site of ACE interaction with the silver surface. Based on SERS spectra, we characterized the region on the ACE molecule in contact with the substrate and demonstrated the model of the two‐domain ACE adsorbed on a silver matrix.

No abstract

Over the past few years, Raman spectroscopy has become a powerful diagnostic tool in the life sciences. The present work is devoted to the application of Raman microspectroscopy for distinction of neutrophils transformed during NETosis and the quantitative determination of the level of their transformation based on the analysis of the neutrophil Raman spectra acquired from the samples of human blood at different levels of transformation. NETosis is a process of the programmed neutrophil cell death involved in the development of many diseases, including those associated with high mortality. Our goal was to search for possible spectral markers in neutrophil Raman spectra, caused precisely by NETotic transformation of neutrophils. The results of the work were (a) obtaining of neutrophil Raman spectra at different levels of cell transformation; (b) creation of spectral archetypes of neutrophils (as a "representative" Raman spectrum for spectra group) with a given level of cell transformation; (c) detection of statistically significant differences in the spectral archetypes of the neutrophil Raman spectra at different levels of transformation. K E Y W O R D S human blood neutrophils, NETosis, microRaman spectroscopy, spectra preprocessing, spectral marker 1 | INTRODUCTION Raman microspectroscopy is widely used in the studies of cell biology, microbiology, and medicine for optical analysis of biological objects at the cellular level. [1-6] Raman microspectroscopy allows exploring intracellular transformations and their features [7-12] and helps to understand the processes occurring in the cell when studying the properties of the selective interaction of reagents in the cell. [13-15] Recently, achievements in Raman microspectroscopy have opened up new prospects for the rapid and sensitive detection of bacteria of various types. [16-21] Neutrophils are the most common human blood leukocytes, which are the most important part of the innate immunity and carry out a fast response to microbial invasion. In 2004, a new type of programmed cell death of neutrophils, called NETosis, [22] was described. Currently,

A cascade mechanism of the emerging of a radiation in blue and red spectral ranges in the KTP crystal—combined non‐collinear parametric down‐ and up‐conversion—was discovered and experimentally investigated. To become observable this mechanism needs to be accompanied by a process of parametric amplification of the seeding wave. The non‐collinear optical parametric amplifier based on the KTP crystal, pumped by 532 nm picosecond pulses, was exploited to study combined noncollinear down‐conversion and up‐conversion processes. Narrowband seeding was provided by radiation of a picosecond optical parametric generator pumped by 355‐nm picosecond pulses synchronized with 532‐nm pulses. The corresponding phase matching conditions for both down‐ and up‐conversion stages were found out on the basis of the tuning curves calculated for the type II phase matching in the XOZ plane of the KTP crystal. When the wavelength and noncollinearity angle of the seeding matched any signal wave of the down‐conversion stage, the seeding was amplified. Along with this, a radiation appeared in the visible part of the spectrum, which was not observed without seeding amplification. The wavelengths and spatial patterns of the radiation arisen, corresponded to some phasematched processes of sum frequency generation between the signal and idler waves existing in the crystal at the down‐conversion stage. Being very weak, these processes are usually unobserved. Thus, injection seeding allows from plenty possible processes to reveal and highlight only those, which correspond to the noncollinearity angle and the wavelength of the seeding. This phenomenon potentially can be exploited to control light at the outlet of a nonlinear crystal.

No abstract