We report an optimization of the fabrication method on arrays of vertically grown nanometer scaled silver rod using nanosphere (polystyrene) lift-off on SiO2 wafer as a surface-enhance Raman scattering substrate by thermal evaporation technology as well as real-time vapor phase detection of CHCl3 by the radiation of fiber optic coupled 785 nm diode laser. Raman peak at 668.2 cm-1 for CHCl3 (C-H stretching band) was compared to the peak at 1088.4 cm-1 of 1- propanethiol (CH3 rock band) and the detection limit of CHCl3 vapor phase contamination level was estimated as a function of the peak intensity ratio of 668.2 vs. 1088.4. The detectable range using Ag nanorod wells on SiO2 substrate was 20-800 ppm. We were able to make significant steps toward developing cost effective nano-pattern as a Raman sensor.
Because mammography, the gold standard of breast cancer screening and monitoring treatment efficacy, has limitations, there is a necessity to have a new method for breast cancer patients. Raman spectroscopy is considered as one of the best alternative approaches due to its ability of visualizing (bio)chemical information of a matter. In this study, we hypothesized that the change of biochemical composition occurs earlier than morphological change in breast cancer during chemotherapy, and attempted to prove it by employing fiber-optic Raman spectroscopy for longitudinal Raman measurement in small animal breast cancer model. To confirm the hypothesis, we measured Raman spectra of a tumor breast and the contralateral breast during chemotherapy for 4 fisher 344 female rats longitudinally. Principal component analysis and Raman spectral differences between breast tumor and contralateral normal breast did not show a clear difference between them which may have been caused by interference from skin. Thus, spatially-offset Raman spectroscopy will be employed in order to acquire the Raman signal directly from tumor while suppressing Raman signal from skin for the future study.
We have detected the surface-enhanced Raman scattering (SERS) signals of toluene and 1,2-dichlorobenzene (ODCB) vapors at parts per million concentrations using 1-propanethiol-linked Ag nanoparticles and a fiber optics–coupled Raman spectrograph. Calibration curves were constructed for each detector by plotting Raman band intensity ratios of toluene and ODCB with respect to that of 1-propanethiol as a function of vapor concentration. The detectors showed effective vapor sensing ranges of 0.6 to 600 and 10 to 600 ppm for toluene and ODCB, respectively, following vapor adsorption to the SERS hot spots. We provide evidence for the facility of the SERS detection system for instantaneously discriminating and quantifying respective vapors from a composite vapor.
Recent progress in modified Surface Enhanced Raman Scattering (SERS) using Ag nanoparticles makes them promising optical technique for direct gas sensing of interest. However, SERS has been shown to provide sub ppb level detection of the compounds in the vapor phase. The major problem with the sensitivity scaling-up was in the development of fabrication technology for stability and reproducibility of SERS substrates. We report an optimization of 1-propanethiol coated multiple Ag nanoparticle layers on SiO2 substrate as well as new records of real-time, simultaneous vapor phase detection of toluene and 1-2 dichlorobenzene by the radiation of fiber optic coupled 785 nm diode laser and spectrograph. Multiple depositions of Ag NPs were loaded on SiO2 and soaked in 1-propanethiol solution for 24 hours to modify the surface into hydrophobic due to the characteristics of vapor phase of our interests. Raman bands at 1003 cm-1 and 1130 cm-1 for toluene and 12DCB, respectively were compared to 1089 cm-1 and each gas concentration in 1000 mL flask were calculated as a function of each vapor phase ratio. The saturation of toluene and 12DCB were limited only by 800 ppm and the detectable range was 0.6-800 ppm.
Mid-IR lasers based on Cr2+ and Fe2+ ions in II-VI tetrahedral crystal hosts have been proven useful as tunable solid-state
lasers operating over the 1.9-6 μm spectral range. However, the development of new effective gain media promising for
lasing over 3-4 μm and with wavelengths longer than 6 μm is still under progress. In this paper we report spectroscopic
characterization of Titanium doped AgGaS2 and Iron doped MgAl2O4 crystals with coordination number four. Polarized
absorption and luminescence spectra of titanium doped AgGaS2 crystals were measured at room and low temperatures. It
was shown that Ti ions in the AgGaS2 crystal were in both 1+ and 3+ valence states substituting silver and gallium sites,
correspondingly. Ti3+ ions in AgGaS2 and Fe2+ in MgAl2O4 crystals feature broad absorption bands with a maximums
near 2μm. These ions have no second excited state absorption bands and could potentially be used as effective saturable
absorbers for passive Q-switching of 2.1 μm holmium laser cavities. Broad emission covering the 3-6 μm spectral range
was observed under 1.9 μm excitation into Ti3+ absorption band. A luminescence signal between 3 and 6 μm was also
observed in the Fe:MgAl2O4 crystal.
Room temperature iron doped II-VI lasers have demonstrated broad band tunability between 3.5 and 6 μm with
efficiency ~40%. However, these lasers require pump sources with a wavelength ~3 μm which could be selected only
from a few available. Cobalt ions in the II-VI materials have strong absorption bands at 4A2→4T1(4P) and 4A2→4T1(4F)
transitions located at ~0.75 and 1.5 μm, respectively. A number of different laser sources (including diode lasers) could
be potentially used for cobalt excitation followed by energy transfer to iron ions. Here we report materials fabrication
and study of energy transfer in Co:Fe:ZnS(ZnSe) crystals. Iron-cobalt co-doped samples were prepared using a two-stage
post-growth thermal diffusion procedure with Fe concentrations of 8.5-19x1018 cm-3. Kinetics and photoluminescence
spectra reveal energy transfer under cobalt excitation at 4A2-4T1(4F) transition by 1.56 μm radiation and 4A2-4T1(4P)
transition by 0.7 μm radiation. Analysis shows effective energy transfer from 4T1(4F), 4T2 and 4T1(4F) Co2+ energy levels
to 5T2 excited level of Fe2+ ions the first realization of Fe2+ ions lasing at 3.6 μm and 3.8μm via Co-Fe energy transfer.
Demonstrated effective Co2+→Fe2+ energy transfer process could result in utilization of a more convenient laser pump
sources for the Fe2+:II-VI lasers.
We report an optimization of Fe:ZnSe crystals fabrication, as well as a fourfold increase of the output energy of the
gain-switched middle-infrared Fe:ZnSe laser pumped by the radiation of Q-switched Cr:Er:YSGG (2.8μm) laser. Lasing
was studied over 236-300K temperature range. In Fabry-Perot cavity with 18% OC reflectivity the maximum output
energy reached 4.7 mJ @ 4.3μm and 3.6 mJ @ 4.37μm at 236K and 300K, respectively and was limited only by
available pump energy. Threshold was about 8 mJ and was practically unchanged over studied temperature range. The
laser slope efficiencies decreased from 19% to 16 % with an increase of temperature from 236 to 300K.
This work is focused on study and optimization of diffusion of Fe in ZnSe from the metal phase, comparative
spectroscopic characterization of kinetic properties of Fe:ZnSe crystals with a wide range of concentrations, and energy
scaling of the Fe:ZnSe gain-switched laser. Iron doping of ZnSe polycrystals was performed by thermal diffusion from
the iron film made by thermal evaporation process. Special cleaning of the ZnSe surfaces and optimization of the ZnSe
substrate temperature and the rate of Fe evaporation resulted in significant enhancement of the diffusion process and
enabled fabrication of high optical density crystals with Fe concentration up to 2x1020 cm-3. The diffusion coefficient and
diffusion length of iron in ZnSe at 1000°C were estimated as 2.1x10-9 cm2/s and 1.3 mm, respectively. We report a
detailed absorption, emission, and kinetics of fluorescence of Fe:ZnSe spectroscopy performed over a broad range of Fe
concentrations (5x1018 - 2x1020 cm-3) and temperatures (14-300K) under direct 2.78μm excitation.
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