D.Y. Lin

Rapid and sensitive SERS method for determination of Rhodamine B in chili powder with paper-based substrates

Surface-enhanced Raman spectroscopy (SERS) was used for detecting Rhodamine B (RB) which is often added illegally to chili powder. Based on density functional theory, the Raman spectrum of RB was calculated and characteristic peaks of RB were assigned to the corresponding vibrational modes. RB was detected utilizing paper-based SERS substrates which were fabricated via a liquid–liquid interface-mediated self-assembly technique. Meanwhile, with simple sample pretreatment, the detection limit could reach 10−6 g g−1 for RB in chili powder (5 × 10−7 g mL−1 in extraction agent). Within the concentration range from 10−2 g g−1 to 10−6 g g−1, Raman intensity follows a certain function in relation to the concentration of RB. The recovery of this method ranges from 96.4% to 108.9%, which gives rapid and reliable quantitative detection of RB in chili powder. Therefore, the proposed SERS method is suitable for on-site detection and analysis of RB in chili powder.

The Current Trends in SBS and phase conjugation

The current trends in stimulated Brillouin scattering and optical phase conjugation are overviewed. This report is formed by the selected papers presented in the “Fifth International Workshop on stimulated Brillouin scattering and phase conjugation 2010” in Japan. The nonlinear properties of phase conjugation based on stimulated Brillouin scattering and photo-refraction can compensate phase distortions in the high power laser systems, and they will also open up potentially novel laser technologies, e.g., phase stabilization, beam combination, pulse compression, ultrafast pulse shaping, and arbitrary waveform generation.

Rapid fabrication of self-assembled interfacial film decorated filter paper as an excellent surface-enhanced Raman scattering substrate

An excellent paper-based SERS substrate was easily fabricated by utilizing interfacial films formed in the mixture of Ag colloid and CH2Cl2. This interfacial film coating method significantly improves the fabrication efficiency of SERS substrates. The substrate has a high coverage of silver nanoparticles (Ag NPs) and can be tailored to arbitrary shapes. The SERS substrate exhibits high sensitivity (EF ∼ 4 × 107) and gives uniform SERS signals with a relative standard deviation (RSD) of 8.08% (spot-to-spot) and 8.65% (batch-to-batch) using 4-mercaptobenzoic acid (4-MBA) as a Raman probe. In addition, this SERS substrate with excellent stability can be stored for more than 30 days. The limit of detection was found to be 10−8 M for 4-MBA. In general, this SERS substrate is qualified for rapid and simple trace detection of various analytes.

Generation of flat-top waveform in the time domain based on stimulated Brillouin scattering using medium with short phonon lifetime

A method of generating flat-top waveform in the time-domain based on stimulated Brillouin scattering (SBS) using medium with short phonon lifetime is proposed. In theory, the transmitted pulse is simulated in the case of several media with different phonon lifetime. In experiment, FC-72 and HT-270, which differ significantly in the phonon lifetime, are exploited in the experiment. Both the theoretical and experimental results indicate that, when choosing medium with short phonon lifetime, the top is almost a platform, while there is a peak in the front and a platform thereafter when choosing medium with long phonon lifetime.

Investigation on effect of medium temperature upon SBS and SBS optical limiting

The effect of medium temperature upon characteristic of stimulated Brillouin scattering (SBS) and SBS optical limiting is investigated. The physical mechanism behind is analyzed theoretically and experimentally verified in Continuum’s Nd: YAG Q-switched laser system using FC-72 as the SBS medium. The temperature affects the electrostrictive coefficient, refractive index, density and acoustic velocity of the medium weakly. In contrast, the kinematic viscosity, which is inversely proportional to the temperature, is related to gain coefficient and phonon lifetime and thus greatly affects the SBS characteristics. Therefore, in the low temperature, the kinematic viscosity is usually high, which can lead to a small gain coefficient and a short phonon lifetime. Therefore, the SBS characteristic can be changed by controlling the temperature to a great extent.

Droplet detection: simplification and optimization of detecting conditions towards high sensitivity quantitative determination of melamine in milk without any pretreatment

A new droplet configuration was developed to simplify and optimize the SERS detecting condition using silver colloid as SERS substrate. Samples were measured in solution to improve the evenness of SERS response. The influences of the reflectivity of substrates and height of sample solution on Raman intensity have been studied systematically. Aluminum tape was employed as the supporting platform for SERS detection. Based on the high reflectivity and hydrophobicity of aluminum tape, this configuration is both highly efficient and convenient. The detection limit of melamine is 10−2 ppb in water and the distribution of SERS intensity is regular over the droplet profile with good reproducibility. Under this configuration, melamine in milk can be quantitatively detected without any sample pretreatment in a special order of agent addition. A good linear relationship was obtained at concentrations ranging from 0.05 to 10 ppm (R2 = 0.9963). Our scheme has advantages such as simplicity, improved reproducibility, less time and good accuracy over other methods, which offers tremendous potential for the on-site examination of trace melamine in three types of milk (pasteurized milk, skimmed milk, sweet milk).

Numerical investigation of the effects of smoothing by spectral dispersion on stimulated rotational Raman scattering

The effect of smoothing by spectral dispersion (SSD) on stimulated rotational Raman scattering (SRRS) in air has been investigated both numerically and theoretically. The suppression effect of SSD on SRRS process is verified and it is demonstrated and proposed that the suppression effect is attributed to two aspects: the decreasing of the laser fluence modulation degree and the reducing of Stokes gain coefficient caused by the temporal and spatial variation of the phase of the incident laser pulse. The simulation results show that the SRRS threshold distance can be lengthened by choosing appropriate SSD parameters.

Research on the SBS mediums used in high peak power laser system and their selection principle

In this paper, we designed an experiment to research the properties for the stimulated Brillouin scattering (SBS) medium of perfluorocarbon-compounds (PFCs) and perfluoropolyether (PFPE), then we proposed that the selection principle of the high load capacity SBS medium can be used in the high peak power SBS system. The results showed that, for PFCs, perfluorinated hydrocarbons (FC-72) has the highest optical breakdown threshold (OBT); for PFPE, the medium with average molecular weight (AMW) less than 1000 has small medium absorption coefficient (AC) and high OBT, for AMW, greater than 1000, the medium AC becomes high and the OBT becomes low. Further research shows that, for PFPE series SBS medium, the AC increases and the OBT decreases gradually with increasing of AMW. We find some SBS mediums can work stably under high peak power pump, which lays a good foundation for the application of SBS technology in a high-power laser system.

Investigation on efficiency of non-collinear serial laser beam combination based on Brillouin amplification

A non-collinear laser beam combination based on Brillouin amplification is proposed. The influence of non-collinear Brillouin amplification on the combination efficiency is analyzed and discussed theoretically. It is shown that an efficiency of 80% can be achieved with the angle between the Stokes and the pump limited to a range of 10°. The theoretical prediction is tested in experiment of non-collinear amplification of one Stokes and one pump. A two-beam combination scheme is designed and a high combination efficiency of 80% is also obtained in this experiment. According to these results, a 20-beam combination scheme is designed to achieve 13.2-J output energy. A very simple construction for a multiple beams combination is designed.

Direct and quantitative detection of dicyandiamide (DCD) in milk using surface-enhanced Raman spectroscopy

Dicyandiamide (DCD) is a contaminant found in New Zealands milk supply, which needs to be examined for security. In this study, the feasibility of using a SERS technique to detect DCD in milk was evaluated. Assignments of the DCD vibrational spectra have been conducted by DFT calculations. The influences of different aggregating agents and pH have been investigated in terms of their efficiency for detecting DCD. Two detection modes were established for detecting DCD in an aqueous solution. Among the three ions, SO42− provides the best performance in both acidic and alkaline conditions, and the limit of detection in alkaline conditions (with an enhancement factor of 2.88 × 105) is lower than that under acidic conditions. For real milk samples, based on a particular order of agent addition, DCD can be quantitatively detected without any sample pretreatment through an internal standard method. The linear coefficient is 0.99747 at a concentration range from 1 × 10−4 to 1 × 10−3 g mL−1. By exploiting the multi-component detection ability and high sensitivity of SERS, our scheme has advantages such as simplicity, reduced time and good accuracy over other methods, which shows a great promise for the on-site screening of DCD in milk products.