The potential of surface‐enhanced Raman spectroscopy (SERS) as a highly sensitive and selective gas sensor was investigated experimentally. Especially, the relation between the temperature of a SERS film and gas adsorption or signal intensity was observed systemically and quantitatively, from which the enhancement of gas adsorption and signal intensity by up to 40 times was observed with the SERS film temperature of approx. −80 °C, which corresponds to theoretical anticipation and leads to detection sensitivity defined by limit of detection in 3σ ~1 ppb in case of benzene gas within 2‐min acquisition time. For SERS, Ag nanorod array films functionalized by propanethiol and a spectrometer with a fiber Raman probe and 785‐nm pump laser were employed. The target volatile organic compound gas was benzene. The detection sensitivity of the SERS sensor was ~1 ppm at room temperature within 2‐min acquisition time.

Abstract. We developed multimodal multiphoton microspectroscopy using a small-diameter probe with gradient-index lenses and applied it to unstained Alzheimer's disease (AD) brain samples. Our system maintained the image quality and spatial resolution of images obtained using an objective lens of similar numerical aperture. Multicolor images of AD brain samples were obtained simultaneously by integrating two-photon excited fluorescence and second-harmonic generation on a coherent anti-Stokes Raman scattering (CARS) microendoscope platform. Measurements of two hippocampal regions, the cornus ammonis-1 and dentate gyrus, revealed more lipids, amyloid fibers, and collagen in the AD samples than in the normal samples. Normal and AD brains were clearly distinguished by a large spectral difference and quantitative analysis of the CH mode using CARS microendoscope spectroscopy. We expect this system to be an important diagnosis tool in AD research. © The Authors.Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Aligned silver nanorod (AgNR) array films were fabricated by oblique thermal evaporation. The substrate temperature during evaporation was varied from 10 to 100 °C using a home-built water cooling system. Deposition angle and substrate temperature were found to be the most important parameters for the morphology of fabricated films. Especially, it was found that there exists a critical temperature at ~90 °C for the formation of the AgNR array. The highest enhancement factor of the surface-enhanced Raman scattering (SERS), observed in the Ag films coated with benzenethiol monolayer, was ~6 × 107. Hot spots, excited in narrow gaps between nanorods, were attributed to the huge enhancement factor by our finite-difference time-domain (FDTD) simulation reflecting the real morphology.

We report a new simple method for the signal enhancement of laser-induced breakdown spectroscopy using a pulsed buffer gas jet. The signal is enhanced up to more than 10 fold by using argon gas jets, which are injected through a pulsed nozzle onto the sample area to be analyzed. By synchronizing the buffer gas pulse with the laser pulse and optimizing the spatial arrangements between the gas jet and the sample surface, we have successfully exploited the useful properties of the buffer gas in open atmosphere. The signal-enhancement mechanism in our buffer gas jet has been discussed. Also, applications to various samples (metal, glass, and paper) have been demonstrated.

A remarkably sensitive and visible-blind ultraviolet photodetector based on ZnO nanorods is demonstrated through ZnO surface conversion into ZIF-8.

Abstract. A multimodal multiphoton nonlinear optical (NLO) microspectroscopy imaging system was developed using a femtosecond laser and a photonic crystal fiber. Coherent anti-Stokes Raman scattering (CARS) microspectroscopy was combined with two-photon excitation fluorescence and second-harmonic generation microscopy in one platform and the system was applied to diagnose liver fibrosis. Normal and liver fibrosis tissues were clearly distinguished with the great difference from CARS spectra as well as multimodal multiphoton NLO images. We expect the system to be a rapid diagnosis tool for liver fibrosis at tissue level with label-free imaging of significant biochemical components. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

We propose a highly birefringent and dispersion compensating photonic crystal fiber based on a double line defect core. Using a finite element method (FEM) with a perfectly matched layer (PML), it is demonstrated that it is possible to obtain broadband large negative dispersion of about -400 to -427 ps/(nm.km) covering all optical communication bands (from O to U band) and to achieve the dispersion coefficient of -425 ps/(nm.km) at 1.55µm. In addition, the highest birefringence of the proposed PCF at 1.55 μm is 1.92 × 10 -2 and the value of birefringence from the wavelength of 1.26 to 1.8 μm (covering O to U bands) is about 1.8 × 10 -2 to 1.92 × 10. It is confirmed that from the simulation results, the confinement loss of the proposed PCF is always less than 10 -3 dB/km at 1.55 μm with seven fiber rings of air holes in the cladding.

Silver nanorod (AgNR) array substrates were fabricated using an oblique angle thermal evaporation technique; their long-term stability, surface uniformity and reproducibility, which are primary requirements for their widespread realistic application and commercialization, were assessed using surface-enhanced Raman scattering (SERS) spectroscopy. The nanorod surfaces were functionalized using a series of organic thiols, which range from hydrophilic to hydrophobic, to mimic various conditions that often arise during detection of hydrophilic/phobic analytes in a realistic application field. A group of these functionalized substrates was stored in ambient laboratory atmosphere; another in light minimized, moisture-free vacuum; while another was stowed carefully and neatly in water to mimic realistic conditions. The effects of these storing conditions were studied. A surfactant was added to the water to maintain consistent surface wetting in the third group. SERS spectra of nanorod substrates prior to functionalization were also recorded to investigate the effect of adventitious carbonaceous contaminants. A meticulous systematic study on the reproducibility of SERS signals was carried out: spot-to-spot, substrate-to-substrate, batch-to-batch, day-to-day. The relative standard deviation (RSD) shown by the SERS signals acquired from various spots of a single substrate was less than 3%, which is very similar to the only account reported so far, in which RSD is reported as 2%. The wetting behavior of these thiol functionalized AgNR substrates are investigated using static contact angle measurements. The functionalized substrates have exhibited excellent long-standing stability over a period of six months when stored appropriately; hence, they are highly suitable for mass production towards realistic application.