Raman Configurations Research Articles

Plasmonic Ag Nanoparticles on SiC for Use as SERS Substrate and in Integrated Optical Sensors for Bio-Chemical Applications

Development of optical chemical sensors for the detection of specific toxic chemicals at ultratrace levels and analysis of complex mixtures is crucial for new green and safe technologies [1, 2]. Metallic structures confined at the nanoscale acquire interesting properties such as strongly localizing E fields on their surfaces through Plasmonic Resonance under stimuli of light at certain wavelengths. This nanostructures are called plasmonic structures [3–5]. This effect is exploited to amplify the optical signal obtained by the molecules of interest, located near plasmonic structures [3, 6]. Purpose of the work is the development of innovative, easy to manufacture and cheap optical active layer consisting of Plasmonic Ag Nanoparticles on a Wide Band Gap semiconductor material such as Silicon Carbide to be used as substrate for Surface Enhanced Raman Scattering or for the fabrication of integrated optical sensor for remote chemical and biological applications. In this contest, the phenomenon of Ag thin film thermal dewetting on SiC substrate was implemented to develop a simple nanoparticles synthetic approach. Scanning Electron Microscopy confirmed the formation of Ag nanoparticles by thermal annealing of thin silver film. 4-MBA was used as probe molecule for SERS phenomenon investigation. The formation of a covalent bond between the silver nanostructures, acting as plasmonic "hot spots", and the species of interest enable its detection at very low concentrations, in the range of 10-5 M or less, in both Raman and UV-Vis configurations.

Assessment of WDM Based RoF Passive Optical Network

In this research, alternative Raman amplifier configuration were used in a wavelength division multiplexing (WDM)-passive optcal network (PON) system to investigate their effects on channel capacity and signal quality. Because of its scalability, energy efficiency, high capacity, low cost, and flexibility of data transfer ability, various Raman configurations are applied in different position to measure the output power. We used various techniques to evaluate the system performance such as varying the length of an optical fiber from 10 to 100 kms, number of users by increasing 8 to 16 channels. Various channel spacings are utilized in an 8 and 16 channels WDM system to calculate the system's bit error rate (BER) and signal-to-noise ratio (SNR). Another key concern is the high data rate and to achieve the maximum transmission speed. We get the maximum data rate of 128 Gb/s by 8 channels and 192 Gb/s by 16 channels. The maximum BER was 10-9and noise level was -6.35 dBm associated with the distance which was 70 kilometers long fiber channel. Finally, maximum data rate and its related eye diagrams was evaluated.

Polarization-dependent YVO4 crystal Raman laser operation with 816 and 890 cm−1 shifts

Polarization-dependent YVO4 crystal Raman laser operations for both X(ZZ)X and X(YY)X Raman configurations were demonstrated. An optical anisotropy Nd:YAP crystal was used as the laser crystal for polarized fundamental laser oscillation. Both first Stokes waves at 1184 nm and 1194 nm converted from 1080 nm were realized based on 816 cm−1 shift in X(YY)X Raman configuration and 890 cm−1 shift in X(ZZ)X Raman configuration, respectively. The maximum average output power of 1.18 W and the conversion efficiency of 16.3% for main output spectrum of 1183.7 nm and average output power of 1.09 W and the conversion efficiency of 15.1% for single output spectrum of 1194.4 nm were achieved with both Raman configurations, respectively. The results show that make full use of the polarization characteristics of YVO4 crystal and its different Raman shifts, the polarized laser output with different Stokes wavelengths could be realized.

Passively Q-switched YVO4 Raman operation with 816 and 890 cm-1 shifts by respective Raman configurations

Passively Q-switched operation of Nd:YAP/Cr4+:YAG/YVO4 Raman lasers with 816 and 890 cm-1 shifts were demonstrated. A Cr4+:YAG/YAG composite crystal was utilized for the passively Q-switched operation. Using an output coupler with different transmittance at both first-Stokes wavelengths, the single first-Stokes waves at 1183.7 nm and 1194.6 nm were obtained in X(ZZ)X and X(YY)X Raman configurations, respectively. Under an absorbed pump power of 8.21 W, the maximum output power of 0.85 W and 0.76 W were achieved, corresponding to the conversion efficiency of 10.4% and 9.3%, respectively. Experimental results show that although the transmittance losses of both Stokes wavelengths were quite different, their thresholds were similar and very close to that of the passively Q-switched fundamental wave in the cavity. The pulse repetition frequency was mainly determined by the Raman conversion efficiency. These laser output characteristics have some reference value for the design of passively Q-switched Raman lasers.

Analyte Co-localization at Electromagnetic Gap Hot-Spots for Highly Sensitive (Bio)molecular Detection by Plasmon Enhanced Spectroscopies.

Electromagnetic hot-spots at ultranarrow plasmonic nanogaps carry immense potential to drive detection limits down to few molecules in sensors based on surface-enhanced Raman or fluorescence spectroscopies. However, leveraging the EM hot-spots requires access to the gaps, which in turn depends on the size of the analyte in relation to gap distances. Herein, we leverage a well-calibrated process based on self-assembly of block copolymer colloids on a full-wafer level to produce high-density plasmonic nanopillar arrays exhibiting a large number (>1010 cm-2) of uniform interpillar EM hot-spots. The approach allows convenient handles to systematically vary the interpillar gap distances down to a sub-10 nm regime. The results show compelling trends of the impact of analyte dimensions in relation to the gap distances toward their leverage over interpillar hot-spots and the resulting sensitivity in SERS-based molecular assays. Comparing the detection of labeled proteins in surface-enhanced Raman and metal-enhanced fluorescence configurations further reveal the relative advantage of fluorescence over Raman detection while encountering the spatial limitations imposed by the gaps. Quantitative assays with limits of detection down to picomolar concentrations are realized for both small organic molecules and proteins. The well-defined geometries delivered by a nanofabrication approach are critical to arriving at realistic geometric models to establish meaningful correlation between the structure, optical properties, and sensitivity of nanopillar arrays in plasmonic assays. The findings emphasize the need for the rational design of EM hot-spots that takes into account the analyte dimensions to drive ultrahigh sensitivity in plasmon-enhanced spectroscopies.

Sensitivity comparison of free-space and waveguide Raman for bulk sensing

The sensitivity advantage of waveguide-enhanced Raman spectroscopy (WERS) over free-space Raman, measured by the signal-to-noise ratio, is well established for thin molecular layer sensing, which traditionally relies on confocal Raman setups. However, for bulk liquid or gas samples, WERS must be benchmarked against nonconfocal Raman configurations. We use ray tracing to calculate the power collection efficiency of several model free-space systems, such as microscopes and probes, encompassing both single-objective and dual-lens systems. It is shown that considering only the focal volume of the source beam or the confocal volume of the microscope significantly underestimates the collected power from free-space Raman systems. We show that waveguide-based systems can still outperform high signal collection free-space systems in terms of both the signal collection efficiency and signal-to-noise ratio.

Crystalline Orientation Identification of Phosphorene Using Polarized Raman Spectroscopy without Analyzer

The unique photoelectric properties of phosphorene typically include anisotropy, hence the nondestructive and rapid identification of its crystal orientation is a key point to the investigation and application of phosphorene. Currently, the orientation identification by analyzing the Ag1 mode based on parallel-polarized Raman has severe requirements for the applicable Raman system. Therefore, it is necessary to develop a more general, convenient, and accurate method for determining the crystal orientation of phosphorene. In this paper, a method of orientation identification was proposed by using a Raman system without an analyzer and quantifying the correlation between the intensities of Ag1 and Ag2 modes with the change of the incident polarization direction. By using mechanically peeled phosphorene as specimens, Raman measurements were carried out under the Raman configurations of both parallel polarization and with no analyzer. The results show that the crystal orientation of phosphorene can be accurately identified by quantifying the Raman intensities of both Ag1 and Ag2 modes using the Raman system without an analyzer.

DWDM Networks When Using Raman Configurations with DCF Fibers

In this paper, the basic theoretical foundations regarding a DWDM [Dense Wavelength Division Multiplexing] network when using Raman configurations with DCF [Dispersion Compensation Fiber] are studied, through the revision of: linear effects, such as noise, loss, chromatic dispersion and PMD [Polarization Mode Dispersion]; and nonlinear effects, such as Self-Phase Modulation [SPM], Cross-Phase Modulation [XPM] and Four-Wave Mixing [FWM], compared to Optical Monitoring Parameters [OPM].

Comparison of 1.15 µm Nd:YAG\KTA Raman lasers with 234 and 671 cm-1 shifts.

Nd:YAG/KTA intra-cavity Raman lasers with two different Raman shifts are experimentally compared for eradiating around 1.15 µm. The different Raman processes are attributed to polarization dependent Raman gain of KTA crystal and nearly linear polarization of Nd:YAG fundamental light with Q-switch operation. Under an incident pump power of 10.2 W and a pulse repetition frequency of 15 kHz, 1.24 W output for the third-Stokes at 1150 nm in X(ZZ)X Raman configuration with the Raman shifts of 234 cm-1 and 1.21 W output for the first-Stokes at 1146 nm in X(YY)X Raman configuration with the Raman shifts of 671 cm-1were achieved by rotating the KTA crystal. The conversion efficiency in both Raman configurations were about 12% respect to the same incident pump power. The slight differences of spectra and pulses are investigated.

Use of Raman spectroscopy and chemometrics to distinguish blue ballpoint pen inks

The objective of this work is assessing whether the combination of Raman spectroscopy and chemometric tools is appropriate to differentiate blue ballpoint pen inks. Fourteen commercial blue ballpoint pen inks from different brands and models were studied and Raman spectra were obtained on ink lines written on A4 sulfite paper. First, a study of the best Raman configurations, in terms of laser intensity used and acquisition mode, was carried out to ensure sufficient spectroscopic quality without damaging the sample. Chemometric methods were applied first to improve the definition of spectral bands and to suppress fluorescence contributions from the signal. Once the spectra were suitably preprocessed, principal component analysis (PCA) and hierarchical cluster analysis (HCA) were applied to explore whether the different inks could be distinguished from their Raman spectra. Almost all inks could be gradually differentiated, through successive PCA analyses or looking at the different levels of the dendrogram structure provided by HCA. From these exploratory results, a tree structure was constructed based on PCA and HCA results in order to reflect the degree of similarity among ink classes. This tree structure was used as the basis to develop hierarchical classification models based on partial least squares-discriminant analysis (PLS-DA). Correct classification of inks was achieved by these PLS-DA models built and the most important regions to identify the ink classes were detected using the variable importance in projection plots (VIPs). The combination of Raman spectroscopy and chemometrics has been proven to be a promising fast non-destructive tool to differentiate among very similar ink types in documents.

MATLAB Simulink modeling of Raman hybrid amplification for long-distance hut-skipped undersea optical fiber transmission systems

We present a modeling of the Raman amplification of various types of fibers employed for transmission and dispersion compensation in cascaded optical amplified transmission systems including (1) the physical properties and operational characteristics and (2) its implementation in the lightwave-modulated envelop propagation equation for transmission of 40 Gbits/s signals in mutliplexed wavelength optical systems. We demonstrate, by simulation using MATLAB Simulink, the integration of the Raman amplification gain and noise into the transmission system by (1) numerical techniques to solve these design parameters for a single channel bidirectionally pumped system operating in the C-band (1525 to 1565 nm) range at 1550 nm; (2) evaluations of the amplifier parameters such as the gain, the noise figure, and the dispersion factor of distributed and discrete Raman configurations. We design an optimum condition for hut-skipped undersea long-haul transmission using a hybrid combination of Raman and Er-doped fiber amplifers. The long-haul numerical solution is adapted from the average power to a Gaussian pulse operating at 40 Gbits/s and the propagation distributed along the fiber for integration into differential phase shift keying modulation format optical signals using models based on MATLAB Simulink.

L-lysine monohydrochloride dihydrate as novel elasto- and electrooptical materials

We have studied optical parametrical effects (electrooptical and elastooptical ones) at wavelength 1150 nm generated by continuous He–Ne laser. We have found that the maximal value of the effective electrooptics coefficient is equal to about 12.6 pm/V and of the elastooptical coefficient was 12 · 10 14 m 2/N and was achieved at temperature about 300 K. l-lysine monohydrochloride dihydrate (C 6H 14N 2O 2, HCl·2H 2O, LLMHCl), a semiorganic potential nonlinear optically active crystal belongs to noncentrosymmetry class P2 1. FTIR and FT Raman of this crystal have been studied at room temperature. The vibrational spectral characterization has been carried out for different Raman configurations and has been interpreted following existed crystal structural data and factor group analysis. Following the performed analysis it was discovered that the principal role in the observed electrooptics group plays the vibrational bands originating of the functional groups such as [NH 3] +, C=O, O–H, C–H, C–N, O–C=O, C–N–C–C ring, C–OH. For elastooptical effects the principal role belongs to the modes situated at 3500–1500 cm − 1 originating from stretching vibrations of [NH 3] +, CH 2, C=O, COO − and C–N groups.

Fluorescence suppression within Raman spectroscopy using annular beam excitation

This letter demonstrates how the use of an annular beam can significantly reduce the detected fluorescence from optical components within a Raman spectroscopic arrangement. The fluorescence from the excitation beam has a reduced generation and collection efficiency compared to the standard Gaussian beam. Crucially, the Raman signal from the annular beam is collected through the dark center of the excitation light field. This robust and simple technique may be immediately applied to all Raman configurations and may find broader applicability for any spectroscopic methodology which utilizes a high numerical aperture lens and requires the detected fluorescence to be suppressed.

Raman scattering structural evaluation of CuInS 2 thin films

This work reports the spectral characterisation of CuInS 2 (CIS) layers for solar cell devices by Raman scattering. The Raman spectrum from CIS is characterised by a dominant A 1 mode at approximately 290 cm −1, being the position and width of the mode sensitive to the CIS structural quality. Besides, layers with poor structural quality show the appearance in the spectra of an additional line, not allowed for chalcopyrite crystals, at approximately 305 cm −1. The relative intensity of this line has been proposed as a further marker for film quality. To deepen in the knowledge of the origin of this mode, Raman scattering measurements are performed in both polycrystalline and epitaxial layers under different conditions, including resonant Raman and different polarisation configurations. The origin of the mode is discussed in terms of (i) the presence of phases with different symmetry as Cu-Au ordering, and (ii) the possible existence of defect-related local vibrational modes.

MACROSCOPIC SQUEEZING FROM A REGULAR ARRAY OF THREE-LEVEL ATOMS

It is shown that the resonance fluorescence from N regularly arrayed three-level atoms in V-configuration could be a source of macroscopic squeezing. The V-configuration exhibits squeezing in both the transitions, whereas the cascade and the Raman configurations shown squeezing only in the lower and Rayleigh transitions respectively.