Stimulated Raman Scattering in Micro- and Nanophotonics

Micro- and nanophotonics explore behavior of light on the micro-/nanoscale and the interaction of micro-/nanoobjects with light. The driving force for their development is the aim to go beyond the limit of photonics. Because of the diffraction limit, photonics components are not able to confine light to the microscale or nanoscale dimension; therefore, one of the key challenges for micro- and nanophotonics is a reduction in the size of integrated optical devices, while maintaining a high level of performance. As far as light amplifiers and laser sources based on stimulated Raman scattering (SRS) are concerned, important accomplishments have been achieved in the fields of fiber optics amplification and integrated photonics devices. In this chapter, the most interesting investigations in the field of stimulated Raman scattering in micro- and nanophotonics are reviewed. These findings provide promising perspectives for integrated micro-/nano-Raman lasers

Analysis of Pulses Bandwidth and Spectral Resolution in Femtosecond Stimulated Raman Scattering Microscopy

In the last decade, stimulated Raman scattering (SRS) imaging has been demonstrated to be a powerful method for label-free, non-invasive mapping of individual species distributions in a multicomponent system. This is due to the chemical selectivity of SRS techniques and the linear dependence of SRS signals on the individual species concentrations. However, even if significant efforts have been made to improve spectroscopic coherent Raman imaging technology, what is the best way to resolve overlapped Raman bands in biological samples is still an open question. In this framework, spectral resolution, i.e., the ability to distinguish closely lying resonances, is the crucial point. Therefore, in this paper, the interplay among pump and Stokes bandwidths, the degree of chirp-matching and the spectral resolution of femtosecond stimulated Raman scattering microscopy are experimentally investigated and the separation of protein and lipid bands in the C-H region, which are of great interest in biochemical studies, is, in principle, demonstrated

Repeated successful use of eltrombopag in chronic primary immune thrombocytopenia: description of an intriguing case.

Thrombopoietin receptor agonists (TPO-RAs) are used as effective alternative treatments in ITP patients unresponsive to first-/second-line therapies. TPO- RAs can also be used to normalize platelet count to safely perform invasive pro- cedures and chemotherapy, in case of malignancies. In few responsive patients, TPO-RAs can be suspended maintaining a sustained respons

Therapeutic opportunities to modulate immune tolerance through the metabolism-chromatin axis

: The ability of the immune system to discriminate external stimuli from self-components - namely immune tolerance - occurs through a coordinated cascade of events involving a dense network of immune cells. Among them, CD4+CD25+ T regulatory cells are crucial to balance immune homeostasis and function. Growing evidence supports the notion that energy metabolites can dictate T cell fate and function via epigenetic modifications, which affect gene expression without altering the DNA sequence. Moreover, changes in cellular metabolism couple with activation of immune pathways and epigenetic remodeling to finely tune the balance between T cell activation and tolerance. This Review summarizes these aspects and critically evaluates novel possibilities for developing therapeutic strategies to modulate immune tolerance through metabolism via epigenetic drugs

Investigation of Strain and Wetting in Porous Silicon and Feasibility of an Optical Sensor for Chemical Monitoring

Abtract In this paper an experimental study of wetting phenomena in porous silicon by Raman scattering is reported and the feasibility of an optical sensor for chemical monitoring is addressed. First, a systematic study of strain effects in 'as formed porous silicon layers' of different porosity and thickness is described. Samples of greater thickness (20 µm) and higher porosity (70%) have been individuated as the best candidates for the observation of wetting phenomena. Then, an experimental investigation of wetting phenomena in PS layers by Raman scattering is reported. The experimental results prove a reversible blue-shift of PS Raman speak of wetted porous silicon layers by isopropanol or ethanol with respect to unperturbed layers. We ascribe the shift to a compressive stress due to the increased lattice mismatch between the porous silicon layer and the bulk silicon substrate in wetting conditions. Finally, the feasibility of an optical sensor for chemical monitoring, using an approach based on porous silicon wetting and Raman scattering measurements is discussed. We conclude that being the measured shift of Raman peak very small, this mechanism could be not useful 'as a transducer' for sensing application i.e. to monitor vapors and liquids in an environment

Noises investigations and image denoising in femtosecond stimulated Raman scattering microscopy

In the literature of SRS microscopy, the hardware characterization usually remains separate from the image processing. In this article, we consider both these aspects and statistical properties analysis of image noise, which plays the vital role of joining links between them. Firstly, we perform hardware characterization by systematic measurements of noise sources, demonstrating that our in-house built microscope is shot noise limited. Secondly, we analyze the statistical properties of the overall image noise, and we prove that the noise distribution can be dependent on image direction, whose origin is the use of a lock-in time constant longer than pixel dwell time. Finally, we compare the performances of two widespread general algorithms, that is, singular value decomposition and discrete wavelet transform, with a method, that is, singular spectrum analysis (SSA), which has been adapted for stimulated Raman scattering images. In order to validate our algorithms, in our investigations lipids droplets have been used and we demonstrate that the adapted SSA method provides an improvement in image denoising

Unlabeled Semen Analysis by Means of the Holographic Imaging

The morphology, the motility, and the biochemical structure of the spermatozoon have often been correlated with the outcome of in vitro fertilization and have been shown to be the sole parameters of the semen analysis in predicting the success of intracytoplasmic sperm injection and intracytoplasmic morphologically selected sperm injection. In this context, digital holography has demonstrated to be an attractive technique to perform a label-free, noninvasive, and high-resolution technique for characterization of live spermatozoa. The aim of this chapter is to summarize the recent achievements of digital holography in order to show its high potentiality as an efficient method for healthy and fertile sperm cell selection, without injuring the specimen and to explore new possible applications of digital holography in this field

Advanced Label-Free Optical Methods for Spermatozoa Quality Assessment and Selection

Current in vitro fertilization (IVF) techniques require a severe selection of sperm, generally based on concentration, morphology, motility, and DNA integrity. Since routinely separation methods may damage the viability of the sperm cell, there is a growing interest in providing a method for noninvasively analyzing spermatozoa taking into account all those parameters. This chapter first reviews the state-of-the-art of label-free sperm cell imaging for IVF, highlighting the limitations of the used techniques. Then, our innovative approach combining Raman spectroscopy and digital holography will be described and its advantages detailed. These include the ability to perform a simultaneous and correlative morphological and biochemical analysis of sperm cells, without labeling, in a fast and reliable way. Finally, the difficulty in reaching clinical use will be discussed, as well as the possible solutions offered by new technological improvements

Volume Holographic Optical Elements as Solar Concentrators

In this chapter, we investigate the possibility to realize a holographic solar concentrator by using a new photopolymeric material as recording medium. Therefore, two different configurations of holographic lenses (lenses with spherical and cylindrical symmetry) are described in terms of both recording process and optical response characterization. Finally, we propose the possibility to use this new photopolymer to realize holographic solar concentrator for space applications