In this paper, we perform a finite element (FE)-based numerical analysis to calculate the photoacoustic (PA) signal generated by spherical gold-silver (Au-Ag) alloy nanoparticles (NPs). These spherical particles are size-controlled and monodispersed, with tunable plasmonic resonance wavelength via change of the alloy composition. This enables their use in photoacoustic imaging as a contrast agent. This theoretical framework self consistently solves the electromagnetic, thermodynamic and transient acoustic pressure physics using a multiphysics coupling approach. We model our system as an optically heterogeneous medium irradiated by a nanosecond laser pulse in the tissue therapeutic optical window (NIR irradiation, with wavelength of 800 nm). We calculate the photoacoustic signal generated by the photo-thermal expansion of both the particle and its surrounding medium. The results show the impact of the gold molar fraction (GMF) of Au-Ag alloy NPs on the PA signal for different NP sizes. We show that significantly stronger PA signals are achieved using Au-Ag alloy NPs (GMF = 0.55) in comparison with pure AuNPs (GMF = 1) and pure AgNPs (GMF = 0) of the same size and shape.
Fourier-transform absorption spectroscopy has been used in the laboratory to obtain absolute absorption coefficients a(v) in infrared bands of C1ONO2 in the 700-1800 cm -• spectral region. These data have been obtained over a temperature range (213-296 K) corresponding to stratospheric temperatures. The results are therefore applicable to retrievals of stratospheric C1ONO2 from remote-sensing observations. Room temperature absorption coefficients are some 25% larger than previously reported values, and large temperature dependences in the absorption coefficients have been observed. The/21 and/22 bands behave as simple fundamentals of a system which has low-energy vibrational or torsional modes, with little contribution from hot bands over the temperature range used. The intensity in the /22 Q branch increased by 53% over the temperature range 296-213 K. A similar increase was observed for the/24 Q branch, and significant hot-band features were seen in the /23, /24 spectral region. The /24 Q branch and the/22 Q branch were observed to obey the Beer-Lambert law over the range of pressure, temperature, absorber amount, and resolution employed. The absorption coefficients in the/24 Q branch and in the /22 band were modeled by equispaced absorption lines, each characterized by a central frequency, strength, lower-state energy, and pressure-broadened width.
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