Laser-Induced Galfenol Embedded Multi-Layer Graphene-Oxide in Solution

The proposed work demonstrates the direct synthesis of nanomaterial-embedded laser-induced few-layer graphene-oxide by directly ablating galfenol in a water-based solution for the first time. Laser-induced multilayer graphene-oxide (GO) embedded with galfenol (gallium–iron alloy) nanoparticles (NPs) is created through a method of direct laser inscription of bulk galfenol in deionized (DI) water with femtosecond laser ablation. The NP-embedded GO is achieved by irradiating a near-infrared (near-IR) femtosecond laser at 1040 nm on a bulk galfenol material submerged in a solution comprising DI water and a small concentration (5%/wt.) of polyvinylpyrrolidone followed by a second ablation in pure DI water. Results show nanoparticles with a mean diameter of ∼30 nm embedded in GO sheets with visible folds spaced at ∼0.63 nm. The composition of iron and gallium shifts by less than 2% during the laser ablation process, and the few-layer GO sheets exhibit similar Raman peaks to bulk graphite

Towards the Design of a Wideband Reflective Long Period Grating Distributed Sensor

In this paper, we computationally investigate the effects of metal coating length and coating coverage on the reflected spectrum of a long period grating (LPG) over a broad bandwidth. Simulation results indicate that coating the tail end of the fiber between the LPG and the end facet of the fiber provides a reflected spectrum that mimics the LPG transmission spectrum shape over a 400 nmbandwidth. Based on single LPG simulation results, we present the design of a distributed LPG structure containing a multiple number (n) of LPGs in reflection mode for the first time. Simulation results for n = 1, 2, and 3 are presented here to demonstrate the concept of a distributed reflective LPG design. It is expected that such a sensor will open a new window for distributed sensing using reflective LPGs

Experimental Validation of a Reflective Long Period Grating Design Methodology

In this work, we present an experimental demonstration of our previously published modeling work on reflective long period grating (LPG). To provide the practical realization of the modeling work, we coat a long segment of fiber both in the tail length and the end facet beyond the gratings with silver to invert the transmission mode LPG to reflection mode LPG. We then measure the LPG characteristics in both the transmission and reflection mode and validate our findings from modeling work. We further build temperature and refractive index (RI) sensors and demonstrate temperature sensing from 21 °C to 191 °C with similar temperature sensitivity coefficients of 54.4 ± 2.9 pm/°C and 53.2 ± 2.6 pm/°C for transmission and reflection mode LPG, respectively whereas same RI sensitivity coefficient of 370 ± 2.2 nm/RIU

Real-Time Measurement of Parametric Influences on the Refractive Index and Length Changes in Silica Optical Fibers

In this paper, we present a simple cascaded Fabry-Perot interferometer (FPI) that can be used to measure in real-time the refractive index (RI) and length variation in silica optical fibers caused due to external physical parameters, such as temperature, strain, and radiation. As a proof-of-concept, we experimentally demonstrate real-time monitoring of temperature effects on the RI and length and measure the thermo-optic coefficient (TOC) and thermal expansion coefficient (TEC) by using the cascaded FPI within a temperature range of 21–486°C. The experimental results provide a TEC of 5.53 × 10−7 /°C and TOC of 4.28 × 10−6 /°C within the specified temperature range. Such a simple cascaded FPI structure will enable the design of optical sensors to correct for measurement errors by understanding the change in RI and length of optical fiber caused by environment parameters

A Novel High Temperature Sensor Architecture for Harsh Environments

High temperature sensors capable of operating in harsh environments and providing real-time information on hot spots and temperature profile play a critical role in preventing disasters and improving safety within nuclear reactors. A method widely employed in existing nuclear reactors is the melt wires technique, which suffers from being an after-effect sensor and lower resolution. Our work is focused on the design and fabrication of low power consuming, small size, reversible sensors by combining phase change properties of chalcogenide glasses and compactness of radiation hard optical waveguides to create a highly accurate and real-time temperature sensing system

Interaction of clusters with ultra short X-ray free electron laser pulses

textBiomolecular imaging has become one of the most exciting potential applications of the Linear Coherent Light Source (LCLS), which is a source of intense femtosecond X-rays. It has been predicted that a highly intense pulse with pulse lengths on the order of a few femtoseconds should be sufficient to capture the image of a biomolecule before it is destroyed. However, the rate at which a large biomolecule explodes during exposure is a large unknown, and will likely be one of the major factors in determining if such imaging will succeed. Clusters were chosen as a size dependant model system, ideal to study the evolution of complex systems in X-ray fields. From earlier intense near-infrared (IR) experiments, it is known that depending on size and Z constitution, clusters explode by Coulomb or hydrodynamic forces. These two limits have very different cluster explosion times and signatures. Coulomb explosion is too fast to allow imaging, whereas a hydrodynamically expanding cluster is a much slower process. The ionization process leading to cluster explosion is strongly wavelength dependent as one passes from IR through XUV to the X-ray regime because the kinetic energy of the released electrons determines the charge imbalance within the cluster, and therefore, determines the explosion dynamics. Unlike in previous experiments performed with near IR or XUV pulses, irradiation by photons at the LCLS will lead to the ejection of energetic photo- and Auger- electrons which could easily escape from the cluster, leaving behind positive ions. The buildup of this charge during exposure can lead to a Coulomb explosion of the sample. On the other hand, if the charge accumulates, the photoelectrons will be held inside the cluster, where they could contribute to the cluster temperature and form a nanoplasma and expand hydrodynamically. The main goal of the thesis was to study the explosion dynamics of clusters generated due to their interaction with intense X-rays and look at its dependencies on the X-ray energy, photon fluence, absorption cross sections, sample constituency and sample size. This thesis also compares the results from X-rays with the corresponding results obtained using ultrashort XUV and Infrared lasers.Electrical and Computer Engineerin

Fiber Optic Sensors for Real Time Temperature Monitoring in Harsh Environments

Multiparameter sensing capability of long period grating (LPG) fiber optic sensor makes it attractive for applications in measuring temperature, strain and external refractive index. Positioning of appropriate metal coating inverts the conventional transmissive mode LPG sensor into the reflection mode one, which has added a new dimension to the fiber optic sensors. The influence of coating length and coating coverage on the spectrum of LPG is presented her

A Highly Sensitive, Polarization Maintaining Photonic Crystal Fiber Sensor Operating in the THz Regime

In this paper, a high sensitivity, polarization preserving photonic crystal fiber (PCF), based on circular air holes for sensing in the terahertz (THz) band, is presented. The finite element method, a practical and precise computational technique for describing the interactions between light and matter, is used to compute the modal properties of the designed fiber. For the designed PCF, comprising of circular air holes in both the cladding and in the porous core, a relative sensitivity of 73.5% and a high birefringence of 0.013 are achieved at 1.6 THz. The all circular air-hole structure, owing to its simplicity and compatibility with the current fiber draw technique for PCF fabrication, can be realized practically. It is anticipated that the designed fiber can be employed in applications such as detection of biological samples and toxic chemicals, imaging, and spectroscopy

Role of Metal Coating Parameters on the Reflective Long Period Grating Spectrum

The role of metal coating length and coating coverage on the spectrum of a reflective long period grating is presented