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

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

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

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

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

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

Femtosecond Stimulated Raman Microscopy in C▬H Region of Raman Spectra of Biomolecules and Its Extension to Silent and Fingerprint Regions

Stimulated Raman scattering (SRS) microscopy, based on vibrational spectroscopy, is able to perform label-free imaging with high sensitivity, high spatial and spectral resolution, 3D sectioning, and fast time of image acquisition, i.e., a few seconds. In this chapter, the implementation of a femtosecond SRS microscope, working in C▬H or O▬H region (>2800 cm−1) of Raman spectra of biomolecules, is reported. Our microscope is realized by integration of a femtosecond (fs) SRS experimental setup with an inverted optical microscope equipped with fast mirror scanning unit. The microscope is provided with two femtosecond laser sources: a titanium-sapphire (Ti:Sa) laser oscillator and an optical parametric oscillator (OPO). In addition, the reliability of our system in C▬H region is tested by localizations of lipid droplets inside adipocyte cells. Finally, the extension of microscope to silent region of <1800 cm−1 and fingerprint region of 1800–2800 cm−1 is also achieved by adding a second-harmonic generator to cascade the OPO and double its energy radiation. Definitely, our microscope is able to take on some recent challenges of SRS microscopy, including improvements of sensitivity and detection specificity

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

Underwater light manipulation by the benthic diatom Ctenophora pulchella: from PAR efficient collection to UVR screening.

Several species of diatoms, unicellular microalgae which constitute the main component of phytoplankton, are characterized by an impressive photosynthetic efficiency while presenting a noticeable tolerance versus exposure to detrimental UV radiation (UVR). In particular, the growth rate of the araphid diatom Ctenophora pulchella is not significantly affected by harsh treatments with UVR, even in absence of detectable, specific UV-absorbing pigments and even if it is not able to avoid high UV exposure by motility. In this work we applied a multi-disciplinary approach involving numerical computation, photonics, and biological parameters in order to investigate the possible role of the frustule, micro- and nano-patterned silica shell which encloses the cell, in the ability of C. pulchella to efficiently collect photosynthetic active radiation (PAR) and to simultaneously screen the protoplasm from UVR. The characterization of the photonic properties of the frustule has been accompanied by in vivo experiments conducted in water in order to investigate its function as optical coupler between light and plastids