Raman Radiation Research Articles

Synchronously-pumped all-solid-state SrMoO4 Raman laser generating at combined vibrational Raman modes with 26-fold pulse shortening down to 1.4 ps at 1220 nm

We report characteristics of a synchronously pumped picosecond all-solid-state Raman laser based on a SrMoO4 crystal at both 887 cm−1 stretching and 327 cm−1 bending anionic group symmetric vibrations. Lasing is obtained at not only the first Stokes wavelength of 1173 nm having a usual Raman shift of 887 cm−1 from the 1063-nm pumping, but also at the additional Stokes wavelength of 1220 nm with the combined 887 cm−1 + 327 cm−1 Raman shift. The strongest 26-fold shortening of the 1220-nm Raman radiation pulse down to 1.4 ps is achieved. This is close to very short dephasing time (1 ps) of the 327 cm−1 vibrational Raman line of the SrMoO4 crystal due to self-mode-locking of the 1220-nm cascaded Stokes field under intracavity pumping by the 1173-nm fundamental Stokes field.

Molecular recognition and detection of Pb(II) ions in water by aminobenzo-18-crown-6 immobilised onto a nanostructured SERS substrate

In this work, we propose a new sensitive, selective and portable surface enhanced Raman spectroscopy (SERS) methodology for the rapid on site detection of Pb(II) pollution in water. The new method utilises aminobenzo-18-crown-6 (AB18C6) as a selective recognition molecule to form a spontaneous complex with Pb(II) ions. The formed AB18C6-Pb(II) complex was rapidly immobilised onto a nanostructured gold substrate via Au-N bond formation and reproducibly screened by SERS using a handheld Raman device. For the SERS measurements, a substrate was fabricated by electrochemical deposition of gold nanostructures onto a flat gold disc, creating multiple hotspots for ultrasensitive SERS measurements. The limit of quantification (LOQ) for Pb(II) ions by the SERS method was 2.20pM. The limit of detection (LOD) was 0.69pM which is five orders of magnitude lower than the maximum Pb(II) level of 72nM allowed by the US Environmental Protection Agency. The high sensitivity of the SERS substrate is attributed to the coupling between the Surface Plasmon Polariton (SPP) of its gold surface, the localised Surface Plasmon Resonance (SPR) of the gold nanostructures and the Raman radiation from the immobilised AB18C6-Pb(II) complex. The new SERS detection method was successfully applied for the selective and rapid screening of Pb(II) ion contamination in water proving its practical application for environmental analysis.

Effects of thermal annealing and chemical abrasion on ca. 3.5 Ga metamict zircon and evidence for natural reverse discordance: Insights for U[sbnd]Pb LA-ICP-MS dating

We present a microstructural and UPb systematics study comparing pristine, thermally annealed (TA) and chemically abraded (CA) ~3500Ma zircon from a quartz-dioritic gneiss, with the aim to improve pre-analytical workflows for more accurate and precise LA-ICP-MS UPb dating of ancient zircon. Four zircon domains are identified: i) low- to medium-U concentric-oscillatory zoned cores, ii-iii) two porous high-U outer alteration domains, and iv) low-U narrow inward growing recrystallization rims. Raman spectroscopy on the pristine zircon reveals a positive correlation between increasing structural damage and U content. The porous high-U outer domains show a drastic increase in non-formula Ca above estimated amorphous fractions of ~0.8, which we ascribe to hydrothermal alteration of high-damage zircon characterized by percolating networks of amorphous areas. Upon treatment (TA, CA), hyper-spectral CL and Raman spectroscopy suggest structural recovery of point defects, but not full repair of high-damage amorphous areas. Calculated Raman radiation damage ages suggest that natural annealing affected all domains at ~500Ma, consistent with negligible laser ablation matrix effects comparing pristine and treated cores.We show that reverse discordance in pristine and TA cores is not an analytical artifact. High-U alteration domains are normal discordant and were partially reset at ca. 3410Ma. Upon CA, UPb discordance and scatter are reduced in the cores, yielding intercepts of 3503±14Ma and 560±550Ma (MSWD=1.0). The lower intercept matches the timing of Pb-loss recorded in the alteration domains and the Raman radiation damage age. We argue that short distance Pb redistribution within the cores, which led to reverse discordance, was controlled by UPb systematics recording both the crystallization age and the timing of Pb redistribution. Some excess Pb was redistributed from the partially re-set alteration domains into the cores, leading to mixed UPb systematics and further reverse discordance. Removal of the latter excess Pb upon CA suggests that radiogenic Pb from the alteration domains accumulated within distinct damage sites accessible for CA leaching.We conclude that standardization of pre-analytical treatment is not recommended; we propose to investigate the structural state of unknown specimen by means of Raman spectroscopy, in combination with commonly applied CL imaging. During LA-ICP-MS analyses, co-measurement of non-formula and selected trace elements is deemed highly valuable in detecting ablations for use in reliable UPb age determination.

Relationship between electrical conductivity and spatial arrangements of carbon nanotubes in polystyrene nanocomposites: The effect of thermal annealing and plasticization on electrical conductivity

The effect of both thermal annealing and plasticization of the polymeric matrix by low molecular weight compounds on the electrical conductivity of the polystyrene based carbon nanotubes (CNTs) composites were investigated. It was found that the electrical conductivity of the samples filled with 3 wt% of CNTs increased by nearly 2 orders of magnitude after thermal annealing for 10 h at 150 °C, and it further increased with increasing plasticizer content. The effect of the hierarchical CNT morphology on the electrical conductivity of composites was elucidated by in-situ Raman and Synchrotron Radiation Small Angle X-ray Scattering investigations. The synergistic effect between thermal treatment and matrix plasticization contributes to efficiently eliminate the residual stress at the interface between polymeric matrix and carbon nanotubes. This leads to the formation of a more effective CNTs network featured by more dense bundles, exhibiting a larger number of contacts between the CNTs which contributes to significantly enhance the electrical conductivity of composites.

Coherent backscattering of Raman light

Constructive interference is observed in the inelastically backscattered Raman radiation from nanostructured media. The effect is studied at a macroscopic scale and is explained in the context of Rayleigh–Raman random walks inside strongly scattering materials.

Observation of the effective linear polarization induced by the asymmetrical Raman gain of YVO4 crystal

We originally present a linearly polarized Raman radiation emitted from an actively Q-switched Nd:YAG/YVO4 laser. An 1175.25 nm Raman output was achieved using a uniaxial a-cut YVO4 crystal in a Z-shape laser cavity. The stable Raman power of 1.8 W was obtained, corresponding conversion efficiency of 8.8% from 1064 nm to 1175 nm. The Raman radiation with a polarization extinction ratio of 10.4-dB was observed for the first time. Our experimental results demonstrate that the asymmetrical Raman crystal gain can result in a uniform linear polarization and permit emitting orthogonal polarization radiation in a cascaded Raman laser.

Controlling cross pumping between C-N and C-H vibration in nitromethane by selective fluorescence-enhanced stimulated Raman scattering.

To investigate the vibrational features of nitromethane (NM), which is a kind of energy material and a well known low-sensitivity and high explosive, experiments are performed to obtain the stimulated Raman scattering (SRS) of NM by employing a 532 nm pulsed pump laser. The Raman signal involves two stimulated emissions at 918 and 2,963 cm-1, attributed to the C-N and C-H stretching vibrations, respectively. To overcome the complexity of cross pump in the pure NM, one stimulated Raman radiation is chosen as a pump source to excite the other Raman mode. Two fluorescence dyes were added to selectively enhance each Raman cross section. By internally seeding the Raman gain medium with fluorescent photons, a significant modification in the stimulated Raman scattering spectrum has been observed. The enhanced Stokes emission at 918 cm-1 was able to induce the 2,963 cm-1 vibration mode when the all-trans-β-carotene was internal seeding in the NM, while the Raman radiation at 2,963 cm-1 was enhanced to excite the C-N mode with the addition of m-Cresol purple. The output energy of both 918 and 2,963 cm-1 under different input energy was also measured to illustrate this result.

Combining field effect scanning electron microscopy, deep UV fluorescence, Raman, classical and synchrotron radiation Fourier transform Infra-Red Spectroscopy in the study of crystal-containing kidney biopsies

Crystal formation in kidney tissue is increasingly recognized as a major cause of severe or acute renal failure. Kidney biopsies are currently performed and analyzed using different staining procedures. Unfortunately, none of these techniques are able to distinguish the different Ca phosphates (e.g., amorphous or nanostructured Ca phosphate apatite, octacalcium phosphate, brushite…) or Ca oxalates (whewellite and weddellite). Moreover, the crystal’s morphology, a structural parameter proven as a major information to the clinician regarding kidney stones, is not taken into account. Such major limitations call for a different research approach, based on physicochemical techniques. Here we propose classical observations through field-emission scanning electron microscopy experiments combined with energy dispersive spectroscopy as well as measurements through Raman and μFourier transform Infra-Red Spectroscopy. If necessary, in the case of microcrystals, observations using cutting edge technology such as Synchrotron Radiation (SR) – FTIR or SR-UV visible spectroscopy can be subsequently performed on the same sample. Taken together this set of diagnostic tools will help clinicians gather information regarding the nature and the spatial distribution at the subcellular scale of different chemical phases present in kidney biopsies as well as on the crystal morphology and therefore obtain more precise diagnosis.

Raman Radiation Patterns of Graphene.

We report the angular distribution of the G and 2D Raman scattering from graphene on glass by detecting back focal plane patterns. The G Raman emission can be described by a superposition of two incoherent orthogonal point dipoles oriented in the graphene plane. Due to double resonant Raman scattering, the 2D emission can be represented by the sum of either three incoherent dipoles oriented 120° with respect to each other, or two orthogonal incoherent ones with a 3:1 weight ratio. Parameter-free calculations of the G and 2D intensities are in excellent agreement with the experimental radiation patterns. We show that the 2D polarization ratio and the 2D/G intensity ratio depend on the numerical aperture of the microscope objective. This is due to the depolarization of the emission and excitation light when graphene is on a dielectric substrate, as well as to tight focusing. The polarization contrast decreases substantially for increasing collection angle, due to polarization mixing caused by the air-dielectric interface. This also influences the intensity ratio I(2D)/I(G), a crucial quantity for estimating the doping in graphene. Our results are thus important for the quantitative analysis of the Raman intensities in confocal microscopy. In addition, they are relevant for understanding the influence of signal enhancing plasmonic antenna structures, which typically modify the sample’s radiation pattern.

Optical Origin of Subnanometer Resolution in Tip-Enhanced Raman Mapping

Raman spectroscopy and imaging at the single-molecular level in both signal sensitivity and spatial resolution have been a long dream. A recent experimental study of single-molecule Raman mapping with a subnanometer resolution by using a tip-enhanced Raman scattering (TERS) technique is a great step closer to this great dream. However, how the subnanometer spatial resolution is possible with a Raman excitation light spot (“hot spot”) of diameter over 10 nm formed between the tip–substrate nanogap to excite and probe the molecule still remains mysterious. Here we present an optical theory of Raman scattering that accounts for the strong near-field self-interaction of molecule with the plasmonic nanogap due to multiple elastic scattering of light by the molecule. The result shows that the self-interaction effect strongly modulates the Raman excitation and radiation in both the signal intensity and spatial sensitivity, leading to a “super-hot spot” and subnanometer lateral resolution of Raman mapping. The optical theory can help to uncover the full picture of light-matter interaction of atoms and molecules with plasmonic nanostructures and explore unknown frontiers of physics and chemistry at nanoscale.

Optics and photonics at nanoscale: Principles and perspectives

Nanophotonics is a multidisciplinary frontier of science that merges nanoscience and nanotechnology with conventional optics and photonics. We focus on two principal issues of nanophotonics: manipulation of optical field and light-matter interaction via various optical nanostructures. These two issues are behind all the efforts to explore, design, and build nanophotonic devices to accomplish the fundamental cause of large-scale optical integration for information processing, interconnection, and computing. We discuss various mechanisms of light-matter interaction enhancement to realize bright fluorescence, Raman, and nonlinear optical radiation, and explore methodologies and various devices for highly sensitive optical sensing and detecting, ultrahigh spatial resolution imaging, and high-efficiency energy conversion between light and electricity, heat, and other forms. All these concepts, insights, methodologies, and technologies in nanophotonics will set a solid platform to explore and achieve better future information and energy technologies that use light as powerful information and energy carriers and as prominent media to probe and manipulate the intrinsic properties of matters via light-matter interaction.

Rotational Raman scattering as a source of polarized radiation for the calibration of polarization-based Thomson scattering

We discuss the use of rotational Raman scattering as a possible technique for the calibration of polarization based plasma diagnostics such as the polarimetric Thomson scattering (TS) systems proposed for the measurement of electron density ne and temperature Te in very hot fusion plasmas. First by using the Stokes vector formalism, we calculate the Mueller matrix of rotational Raman scattering from a diatomic gas (such as H2, D2 and N2) for a generic scattering angle and then we use it to describe in detail the polarization characteristics of the Raman radiation available in the typical conditions of a TS system in a fusion plasma. Then we consider the various experimental set-ups proposed for polarimetric TS and show that rotational Raman scattering can generate radiation with known intensity and polarization states that, although not equal to those of the TS radiation, are suitable for the calibration of polarimetric TS diagnostics. Finally we point out that in fusion experiments Raman polarimetry may be of interest also for the calibration of other polarization-based measurement systems, such as the motional Stark effect (MSE) diagnostics.

Waveguide-coupled directional Raman radiation for surface analysis.

Kretschmann-type waveguide structures, including Plasmon Waveguide (PW) and Resonant Mirror (RM), have been applied in interfacial Raman spectroscopy due to the following unique features: (1) unlike the classic surface enhanced Raman scattering (SERS) substrates made of either gold or silver, both PW and RM can be prepared using a large variety of inexpensive materials; (2) the field enhancement factors using these structures can be theoretically predicted and experimentally controlled, which enables us to manipulate the surface Raman sensitivity with high repeatability; (3) the use of transverse electric (TE) and transverse magnetic (TM) modes for Raman excitation allows us to evaluate the orientation of target molecules immobilized on the waveguide surface; (4) the unwanted impact of noble metals on the Raman fingerprints of target molecules, which is often observed for conventional SERS substrates, can be avoided upon the use of dielectric waveguides. In this paper, guided-mode-coupled directional Raman emission, which is an additional important feature of the waveguide Raman technique, was theoretically investigated based on the optical reciprocity theorem combined with the Fresnel equations. The simulation results indicate that the directional Raman emission from a dipole located within the field confinement and penetration depth of a guided mode depends on both the orientation of the dipole and its distance from the waveguide surface. Raman light from the TE-oriented dipoles is launched into the prism coupler at the TE-mode resonance angle and that from the non-TE-oriented dipoles propagates at the TM-mode resonance angle. The intensity of the guided-mode-excited Raman signal propagating at the mode resonance angle is proportional to the fourth power of the mode field (E(4)) at the depth of the dipole from the waveguide surface. This means that the guided-mode-excited and guided-mode-coupled directional Raman spectroscopy has a detection depth that is as small as a quarter of the evanescent-field penetration depth, indicating the excellent surface selectivity of this technique. The directional Raman emission also facilitates high-efficiency signal collection compared with conventional SERS. It is worth noting that Raman light from the dipoles confined in the core layer of a single-mode waveguide can be simultaneously coupled into both the guided mode and the substrate mode, especially the surface plasmon resonance (SPR) mode for PW.

Resonant Mirror Enhanced Raman Spectroscopy

A resonant mirror as a high-Q dielectric resonator can accumulate a strong evanescent field at its surface, and this field has been proposed for surface/interface Raman enhancement applications for a while. However, the theoretically predicted large Raman enhancement effect of a resonant mirror had never been experimentally demonstrated until our work reported here, primarily due to the difficulties confronting the experimentalists in determining the resonant conditions for this optical device and optimizing the collection efficiency of Raman radiation from molecules at its surface. In this study, taking advantage of the rationally designed and well-fabricated high-quality planar dielectric optical waveguides, and overcoming the two difficulties aforementioned through the use of m-line spectroscopy and waveguide-coupled directional Raman emission techniques, we present the first experimental demonstration of resonant mirror enhanced Raman spectroscopy (RMERS). Considerable signal enhancement that enabled ...

Generation of 1.3 μm and 1.5 μm high-energy Raman radiations in α-BaTeMo2O9 crystals

The generations of high energy 2nd- and 3rd-order stimulated Raman scattering lasers based on the α-BaTeMo2O9 crystal were demonstrated for the first time. The Raman gain coefficient has been compared with that of the YVO4 crystal. A maximum total Stokes radiation energy of 27.3mJ was obtained, containing 20.1mJ 2nd-order Stokes energy at 1318nm, together with 7.2mJ 3rd-order Stokes energy at 1497nm, giving an overall conversion efficiency of 35.9% and a slope efficiency of 54.5%. With an optical coating design, a total 3rd- and 4th-order Stokes energy of 16.5mJ was generated. The maximum energy for 4th-order Stokes radiation at 1731nm was 2mJ. The pulse durations for the 2nd-, 3rd-, and 4th-order Stokes shift were 10ns, 8.6ns, and 5.2ns, respectively. Our experimental results show that the α-BTM crystal is a promising Raman crystal for the generations of eye-safe radiations.

Realization and Design Aspects of Mini Laser Raman Spectroscope Electronics for Planetary Surface Exploration

Mini Laser Raman Spectroscope (MLRS) is currently under development at LEOS-ISRO, which will be part of rover in the follow up missions to Moon and Mars. Amidst the variety of instruments that were flown or are to be flown in space missions, the instruments based on Raman Spectroscopy are one of the best-suited tools for analyzing minerals on planetary surfaces. This paper primarily focuses on the design requirements for realizing MLRS electronics. It discusses the wavelength stabilization aspects of the laser diode source (785 nm) and the CCD readout electronics designed to capture the relatively weak scattered Raman radiations. Also the paper sheds light on the realization aspects of the data acquisition system that will be used to characterize and verify the functionality of the instrument.

Raman Frequency Conversion of Picosecond Pulses in the YVO4 Crystal

We compare the stimulated Raman scattering (SRS) performance of a-cut and c-cut YVO4 in a single-pass Raman experiment. The undoped YVO4 crystal shows its good SRS capability in a quasi-transient field. The non-axial scattering angles of Raman radiation are also studied, and the result is in good agreement with the physical model based on the phase matching condition. High-order Raman Stokes and anti-Stokes lights with good beam quality are obtained by means of Raman amplification. Our experiments show that Raman amplification is a practical way to avoid unexpected nonlinear effects and to obtain new wavelength picosecond lasers.

O2(1Δ) Yield Measurement by Raman Spectroscopy With Elimination of Chlorine Fluorescence Interference

Deleterious chlorine fluorescence was found to occur at the same frequency as the Raman scattering of O2(1Δ) and O2(3Σ), seriously affecting the O2(1Δ) yield measurement in the reaction of chlorine with basic hydrogen peroxide by use of the Raman spectroscopy technique. To solve this problem we have taken advantage of the fact that Raman radiation is always strongly polarized while fluorescence is essentially non-polarized in a gaseous medium. When chlorine utilization of a singlet oxygen generator is 88%, O2(1Δ) yield reaches (42.4±7.4)% with the effect of chlorine fluorescence completely eliminated.

Trace gas detection of molecular hydrogen H2 by photoacoustic stimulated Raman spectroscopy (PARS)

Photoacoustic stimulated Raman spectroscopy (PARS) has been used for sensitive and selective trace gas detection of molecular hydrogen under ambient conditions. In one experiment, 532 nm output of a seeded pulsed Nd:YAG laser is employed as Raman pump source and a Raman shifter filled with gaseous H(2) to obtain Stokes shifted radiation at 683 nm, suitable to stimulate H(2) Raman detection in a photoacoustic cell. A noise equivalent detection limit of 40 ppm by volume H(2) in 1 atm N(2) is obtained (14 mJ at 532 nm, 18 mJ at 683 nm, 10 Hz repetition rate, 58 s measurement time). Another experiment employs a dye laser for stimulating Raman radiation between 681-684 nm, allowing tuneable PARS. A Gaussian spectral fitting procedure has been applied giving a noise equivalent detection limit of 4.6 ppm by volume H(2) in 1 atm N(2) (35 mJ pulse energy at 532 nm, 45 mJ at 681-684 nm, 10 Hz repetition rate, 256 s measurement time). Spectroscopic detection offers the advantage of high selectivity along with the ability to obtain temperature and dynamic information from the rotational population and a line shape analysis, and also allows the discrimination between ortho- and para-H(2).

Simultaneous acquisition of all four forms of circular polarization Raman optical activity: results for α‐pinene and lysozyme

AbstractA new circularly polarized (CP) Raman spectrometer is described that demonstrates simultaneous acquisition of all four forms of circular polarization Raman optical activity (ROA). The instrument is a design extension of a commercially available back scattering circular polarization (SCP) ROA spectrometer. Circular polarization of the incident beam is introduced with a quarter‐wave plate, and a half‐wave plate alternately positioned in and out of the beam controls the modulation between right circular polarization (RCP) or left circular polarization (LCP) states. Combining this modulation with the simultaneous detection of RCP and LCP scattered Raman radiation allows the measurement of incident circular polarization (ICP), SCP, in‐phase dual circular polarization(DCPI) and out‐of‐phase DCPII‐ROA. In addition, three different forms of backscattered Raman spectra, namely unpolarized, highly polarized, and depolarized Raman spectra, as well as a degree of circularity spectrum are obtained. The performance of the new all‐CP ROA spectrometer is evaluated with neat α‐pinene and aqueous hen lysozyme solution. Copyright © 2011 John Wiley & Sons, Ltd.