Comparative Study of Some Fiber-Optic Remote Raman Probe Designs. Part I: Model for Liquids and Transparent Solids

We have developed models describing the sensitivity and sampling volume of various remote fiber-optic Raman probes—single-fiber, lensed, dual-fiber beveled-tip, dual-fiber flat-tipped, and multi-fiber flat-tipped. The models assume clear samples and incorporate radii, separation, bevel angle, and numerical aperture of the fibers; overlap geometry of illumination and excitation light cones; and refractive index of immersion medium. For the Raman spectra of solid samples in air, single-fiber and lensed probes are predicted to yield the highest Raman signal. Beveled probes should provide greater Raman signal strength than do flat-tipped probes because beveled probes can collect light from a restricted volume closer to the probe end. Although multiple collection fibers improve Raman signal strength, progressively distant concentric fiber rings contribute less and sample material further from the probe.

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Comparative Study of Some Fiber-Optic Remote Raman Probe Designs. Part II: Tests of Single-Fiber, Lensed, and Flat- and Bevel-Tip Multi-Fiber Probes

Applied Spectroscopy ◽

10.1366/0003702963905574 ◽

1996 ◽

Vol 50 (7) ◽

pp. 849-860 ◽

Cited By ~ 41

Author(s):

Thomas F. Cooney ◽

H. Trey Skinner ◽

S. M. Angel

Keyword(s):

Fiber Optic ◽

Focal Point ◽

Focal Length ◽

Numerical Aperture ◽

Optical Filters ◽

Organic Liquids ◽

Raman Signal ◽

Immersion Medium ◽

Lens Focal Length ◽

Overlap Model

We compare relative performances of flat-tipped, beveled (two-fiber and six-around-one), and single-lensed focused fiber-optic Raman probes and, where feasible, evaluate the utility of optical filters for reducing fiber background. The sensitivity profile of each probe is determined by measuring the relative intensity of light backscattered off a flat surface as a function of distance from the probe tip. The experimental results are compared with a simple light-cone-overlap model incorporating fiber numerical aperture, fiber and immersion medium refractive indices, separation between excitation and collection fibers, number of fibers, and fiber bevel angle and/or lens focal length. The model and sensitivity profiles are used to interpret the sampling regions for Raman spectra obtained by using each of the probes with a clear, transparent sample (single-crystal sparry calcite), a white, partially transparent sample (acetaminophen tablet), and a set of organic liquids of varying refractive index. The sensitivity of the tested commercial lensed probe drops off symmetrically about the focal point. For both solid samples, the intensity of fiber background follows a profile determined primarily by laser backscattering off the surface, whereas the sample Raman signal follows a profile dependent upon sampling depth.

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Novel In situ Probe for Monitoring Polymer Curing

Applied Spectroscopy ◽

10.1366/0003702963906212 ◽

1996 ◽

Vol 50 (3) ◽

pp. 382-387 ◽

Cited By ~ 29

Author(s):

Jeffrey F. Aust ◽

Karl S. Booksh ◽

Michael L. Myrick

Keyword(s):

Fiber Optic ◽

Single Fiber ◽

Probe Design ◽

Raman Signal ◽

Multivariate Techniques ◽

Polymer Thin Film ◽

Epoxy Curing ◽

Polymer Curing ◽

Rate Characteristic

A novel probe design for in situ fiber-optic Raman spectroscopy has been tested and employed for real-time monitoring of an epoxy curing. The epoxy system consists of diglycidylether of bisphenol-A and polyoxypropylenetriamine. The probe consists of a single fiber optic and a small section of Teflon® tubing. The tube acts as a waveguide and sample holder. Raman signal enhancements of 15 x were observed with the employment of the tube compared to those of spectra acquired with the single fiber alone. This analysis studied the C-H stretching region of the epoxide, where previously studies have centered around the fingerprint region. The small volume of the probe and large surface area allow it to be used effectively as a method of polymer thin-film measurement. It is also effective in bulk polymer measurements because of a negligible amount of heat trapped in the sample during curing. This gives the probe a temperature and reaction rate characteristic of the polymer surrounding it. Multivariate analysis was employed to interpret and analyze the numerous spectra taken during analyses. Multivariate techniques show that both curing and sample internal temperature information can be derived from the Raman spectra.

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Cascaded Fiber-Optic Interferometers for Multi-Perimeter-Zone Intrusion Detection with a Single Fiber Used for Each Defended Zone

IEEE Sensors Journal ◽

10.1109/jsen.2021.3059645 ◽

2021 ◽

pp. 1-1

Author(s):

Yuan-Hung Lin ◽

Bo-Hong Zheng ◽

Likarn Wang

Keyword(s):

Intrusion Detection ◽

Fiber Optic ◽

Single Fiber

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Fabrication-friendly polarization-sensitive plasmonic grating for optimal surface-enhanced Raman spectroscopy

Journal of the European Optical Society Rapid Publications ◽

10.1186/s41476-020-00144-5 ◽

2020 ◽

Vol 16 (1) ◽

Author(s):

Arpan Dutta ◽

Tarmo Nuutinen ◽

Khairul Alam ◽

Antti Matikainen ◽

Peng Li ◽

...

Keyword(s):

Raman Spectroscopy ◽

Fill Factor ◽

Surface Enhanced Raman Spectroscopy ◽

Transverse Magnetic ◽

Raman Signal ◽

Optical Resonance ◽

Excitation Light ◽

Surface Enhanced ◽

Surface Enhanced Raman ◽

Plasmonic Gratings

Abstract Plasmonic nanostructures are widely utilized in surface-enhanced Raman spectroscopy (SERS) from ultraviolet to near-infrared applications. Periodic nanoplasmonic systems such as plasmonic gratings are of great interest as SERS-active substrates due to their strong polarization dependence and ease of fabrication. In this work, we modelled a silver grating that manifests a subradiant plasmonic resonance as a dip in its reflectivity with significant near-field enhancement only for transverse-magnetic (TM) polarization of light. We investigated the role of its fill factor, commonly defined as a ratio between the width of the grating groove and the grating period, on the SERS enhancement. We designed multiple gratings having different fill factors using finite-difference time-domain (FDTD) simulations to incorporate different degrees of spectral detunings in their reflection dips from our Raman excitation (488 nm). Our numerical studies suggested that by tuning the spectral position of the optical resonance of the grating, via modifying their fill factor, we could optimize the achievable SERS enhancement. Moreover, by changing the polarization of the excitation light from transverse-magnetic to transverse-electric, we can disable the optical resonance of the gratings resulting in negligible SERS performance. To verify this, we fabricated and optically characterized the modelled gratings and ensured the presence of the desired detunings in their optical responses. Our Raman analysis on riboflavin confirmed that the higher overlap between the grating resonance and the intended Raman excitation yields stronger Raman enhancement only for TM polarized light. Our findings provide insight on the development of fabrication-friendly plasmonic gratings for optimal intensification of the Raman signal with an extra degree of control through the polarization of the excitation light. This feature enables studying Raman signal of exactly the same molecules with and without electromagnetic SERS enhancements, just by changing the polarization of the excitation, and thereby permits detailed studies on the selection rules and the chemical enhancements possibly involved in SERS.

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Single fiber-optic fluorescence enzyme-based sensor

Analytical Chemistry ◽

10.1021/ac00156a012 ◽

1988 ◽

Vol 60 (5) ◽

pp. 433-435 ◽

Cited By ~ 58

Author(s):

Ming Ren S. Fuh ◽

Lloyd W. Burgess ◽

Gary D. Christian

Keyword(s):

Fiber Optic ◽

Single Fiber

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Rugged Fiber-Optic Raman Probe for Process Monitoring Applications

Applied Spectroscopy ◽

10.1366/0003702011953694 ◽

2001 ◽

Vol 55 (10) ◽

pp. 1337-1340 ◽

Cited By ~ 17

Author(s):

Pentti Niemelä ◽

Janne Suhonen

Keyword(s):

Fiber Optic ◽

Signal To Noise Ratio ◽

Notch Filter ◽

Laser Line ◽

Fiber Optic Probe ◽

Monitoring Applications ◽

Optic Probe ◽

Holographic Notch Filter ◽

Filter Thickness ◽

Raman Probe

We report on the development of a simple, rugged fiber-optic probe for process Raman measurements, in which laser line rejection is based on an absorptive longpass filter made from a direct bandgap CdTe semiconductor. The probe can be used with a fixed wavelength laser at 830 nm, and Raman spectra can be recorded down to 200 cm−1 from the laser line. The filter thickness can be adjusted for final turning of the filter edge, as the edge slope is almost independent of thickness in the range 0.1 to 1 mm. Other properties of the probe, such as its signal-to-noise ratio and signal-to-background ratio, are shown to compare well with those of a state-of-the-art probe based on holographic notch filter techniques.

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Degradation of multiphoton signal and resolution when focusing through a planar interface with index mismatch: Analytical approximation and numerical investigation

Journal of Innovative Optical Health Sciences ◽

10.1142/s1793545818500207 ◽

2018 ◽

Vol 11 (04) ◽

pp. 1850020

Author(s):

Ping Qiu ◽

Chen He

Keyword(s):

Spherical Aberration ◽

Numerical Aperture ◽

Analytical Approximation ◽

Planar Interface ◽

Excitation Wavelength ◽

Physical Parameters ◽

Approximate Analytical Expression ◽

Excitation Light ◽

Analytical Expression ◽

Imaging Depth

Multiphoton microscopy (MPM) is an invaluable tool for visualizing subcellular structures in biomedical and life sciences. High-numerical-aperture (NA) immersion objective lenses are used to deliver excitation light to focus inside the biological tissue. The refractive index of tissue is commonly different from that of the immersion medium, which introduces spherical aberration, leading to signal and resolution degradation as imaging depth increases. However, the explicit dependence of this index mismatch-induced aberration on the involved physical parameters is not clear, especially its dependence on index mismatch. Here, from the vectorial equations for focusing through a planar interface between materials of mismatched refractive indices, we derive an approximate analytical expression for the spherical aberration. The analytical expression explicitly reveals the dependence of spherical aberration on index mismatch, imaging depth and excitation wavelength, from which we can expect the following qualitative behaviors: (1) Multiphoton signal and resolution degradation is less for longer excitation wavelength, (2) a longer wavelength tolerates a higher index mismatch, (3) a longer wavelength tolerates a larger imaging depth and (4) both signal and resolution degradations show the same dependence on imaging depth, regardless of NA or immersion on the condition that the integration angle is the same. Detailed numerical simulation results agree quite well with the above expectations based on the analytical approximation. These theoretical results suggest the use of long excitation wavelength to better suppress index mismatch-induced signal and resolution degradation in deep-tissue MPM.

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Fiber-optic Raman probe based on single-crystal sapphire fiber

10.1117/12.920780 ◽

2012 ◽

Author(s):

Tongqing Liu ◽

Ming Han ◽

Cody Raml ◽

Dennis R. Alexander ◽

Xiangnan He ◽

...

Keyword(s):

Single Crystal ◽

Fiber Optic ◽

Single Crystal Sapphire ◽

Raman Probe ◽

Sapphire Fiber

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Performance Analysis of Scattering-Level Multiplexing (SLMux) in Distributed Fiber-Optic Backscatter Reflectometry Physical Sensors

Sensors ◽

10.3390/s20092595 ◽

2020 ◽

Vol 20 (9) ◽

pp. 2595 ◽

Cited By ~ 1

Author(s):

Daniele Tosi ◽

Carlo Molardi ◽

Wilfried Blanc ◽

Tiago Paixão ◽

Paulo Antunes ◽

...

Keyword(s):

Optical Fibers ◽

Rayleigh Scattering ◽

Fiber Optic ◽

Single Fiber ◽

Distributed Sensor ◽

The Core ◽

Physical Sensors ◽

Core Section ◽

Boundary Limits ◽

Multiple Fibers

Optical backscatter reflectometry (OBR) is a method for the interrogation of Rayleigh scattering occurring in each section of an optical fiber, resulting in a single-fiber-distributed sensor with sub-millimeter spatial resolution. The use of high-scattering fibers, doped with MgO-based nanoparticles in the core section, provides a scattering increase which can overcome 40 dB. Using a configuration-labeled Scattering-Level Multiplexing (SLMux), we can arrange a network of high-scattering fibers to perform a simultaneous scan of multiple fiber sections, therefore extending the OBR method from a single fiber to multiple fibers. In this work, we analyze the performance and boundary limits of SLMux, drawing the limits of detection of N-channel SLMux, and evaluating the performance of scattering-enhancement methods in optical fibers.

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