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Measurement of Scattering and Absorption Cross Sections of Microspheres for Wavelengths between 240 nm and 800 nm.

Gaigalas AK, Wang L, Choquette S - J Res Natl Inst Stand Technol (2013)

Bottom Line: The value of ni at 266 nm was about 0.0060±0.0016 for microspheres with diameters of 1.5 μm, 2.0 μm, and 3.0 μm.The scattering cross section, absorption cross section, and the quantum yield at 266 nm of microsphere with a diameter of 2.0 μm was 5.65±0.01 μm(2), 1.54±0.03 μm(2), and 0.027±0.002 respectively.The styrene absorption reduces the scattering cross section by 20 % at 266 nm.

View Article: PubMed Central - PubMed

Affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899.

ABSTRACT
A commercial spectrometer with a 150 mm integrating sphere (IS) detector was used to estimate the scattering and absorption cross sections of monodisperse polystyrene microspheres suspended in water. Absorbance measurements were performed with the sample placed inside the IS detector. The styrene absorption was non zero for wavelengths less than 300 nm. Correction for fluorescence emission by styrene was carried out and the imaginary part of the index of refraction, ni, was obtained. Absorbance measurements with the sample placed outside the IS detector were sensitive to the loss of photons from the incident beam due to scattering. The absorbance data was fitted with Lorenz-Mie scattering cross section and a correction for the finite acceptance aperture of the spectrometer. The fit parameters were the diameter, the suspension concentration, and the real part of the index of refraction. The real part of the index was parameterized using an expansion in terms of powers of the inverse wavelength. The fits were excellent from 300 nm to 800 nm. By including the imaginary part obtained from the absorbance measurements below 300 nm, it was possible to obtain a good fit to the observed absorbance data over the region 240 nm to 800 nm. The value of ni at 266 nm was about 0.0060±0.0016 for microspheres with diameters of 1.5 μm, 2.0 μm, and 3.0 μm. The scattering cross section, absorption cross section, and the quantum yield at 266 nm of microsphere with a diameter of 2.0 μm was 5.65±0.01 μm(2), 1.54±0.03 μm(2), and 0.027±0.002 respectively. The styrene absorption reduces the scattering cross section by 20 % at 266 nm.

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(a) The dotted trace labeled A1–A3 shows the measured absorbance due to scattering. The trace was obtained by subtracting the measured absorbance, A3, for a sample inside the IS from the measured absorbance, A1, for a sample outside the IS. In both cases, the buffer contribution was subtracted. The dotted trace labeled A3 shows the absorption due to styrene polymer. (b) The solid circles reproduce the trace labeled A1–A3 from part (a), and the solid trace is a best fit to the apparent L-M cross section for PS microspheres with a diameter of 3.0 μm.
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f2-jres.118.001: (a) The dotted trace labeled A1–A3 shows the measured absorbance due to scattering. The trace was obtained by subtracting the measured absorbance, A3, for a sample inside the IS from the measured absorbance, A1, for a sample outside the IS. In both cases, the buffer contribution was subtracted. The dotted trace labeled A3 shows the absorption due to styrene polymer. (b) The solid circles reproduce the trace labeled A1–A3 from part (a), and the solid trace is a best fit to the apparent L-M cross section for PS microspheres with a diameter of 3.0 μm.

Mentions: Figure 2 shows measurements and analysis for a suspension of 3.0 μm microspheres in distilled water. The suspension was prepared by pipetting 10 μL of stock suspension obtained from Polysciences, Inc, (catalog number 17134, lot 621930) into 10 mL of distilled water1. The Lambda 850 spectrometer was scanned from 800 nm to 220 nm in increments of 1 nm with an integration time of 0.8 s, and a slit width of 2 nm. Four measurements were taken with a water sample and a suspension sample placed sequentially in holders outside and inside the IS. The solid circles in Fig. 2a show the measured absorbance due to scattering (trace A1–A3) and the absorbance due to molecular absorption (trace A3).The absorbance due to scattering was obtained by subtracting the measured absorbance of a sample placed inside the IS (A3) from the measured absorbance of the sample placed outside the IS (A1). In both cases, the measured absorbance of the cuvette filled with water was subtracted. The solid trace in Fig. 2b shows the best fit to the trace A1–A3 of a model based on the calculation of the L-M scattering cross section in the wavelength range from 300 nm to 800 nm. The Lorenz-Mie calculations were performed using MatLab with Maetzler [2] code for Mie scattering. The fit resulted in a diameter of 3.011 μm which was consistent with the value, (3.004±0.065) μm, provided by the manufacturer. The best fit shown in Fig. 2b was obtained from the minimization of residuals defined in Eq. (4).(4)Residuals=∑λ(A1−A3c−Mie(d,n)+∫0Δdσdθ(d,n,θ)dθ)c=N⋅0.01/2.303d=diametern=indexofrefractionΔ=acceptanceangle


Measurement of Scattering and Absorption Cross Sections of Microspheres for Wavelengths between 240 nm and 800 nm.

Gaigalas AK, Wang L, Choquette S - J Res Natl Inst Stand Technol (2013)

(a) The dotted trace labeled A1–A3 shows the measured absorbance due to scattering. The trace was obtained by subtracting the measured absorbance, A3, for a sample inside the IS from the measured absorbance, A1, for a sample outside the IS. In both cases, the buffer contribution was subtracted. The dotted trace labeled A3 shows the absorption due to styrene polymer. (b) The solid circles reproduce the trace labeled A1–A3 from part (a), and the solid trace is a best fit to the apparent L-M cross section for PS microspheres with a diameter of 3.0 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4487312&req=5

f2-jres.118.001: (a) The dotted trace labeled A1–A3 shows the measured absorbance due to scattering. The trace was obtained by subtracting the measured absorbance, A3, for a sample inside the IS from the measured absorbance, A1, for a sample outside the IS. In both cases, the buffer contribution was subtracted. The dotted trace labeled A3 shows the absorption due to styrene polymer. (b) The solid circles reproduce the trace labeled A1–A3 from part (a), and the solid trace is a best fit to the apparent L-M cross section for PS microspheres with a diameter of 3.0 μm.
Mentions: Figure 2 shows measurements and analysis for a suspension of 3.0 μm microspheres in distilled water. The suspension was prepared by pipetting 10 μL of stock suspension obtained from Polysciences, Inc, (catalog number 17134, lot 621930) into 10 mL of distilled water1. The Lambda 850 spectrometer was scanned from 800 nm to 220 nm in increments of 1 nm with an integration time of 0.8 s, and a slit width of 2 nm. Four measurements were taken with a water sample and a suspension sample placed sequentially in holders outside and inside the IS. The solid circles in Fig. 2a show the measured absorbance due to scattering (trace A1–A3) and the absorbance due to molecular absorption (trace A3).The absorbance due to scattering was obtained by subtracting the measured absorbance of a sample placed inside the IS (A3) from the measured absorbance of the sample placed outside the IS (A1). In both cases, the measured absorbance of the cuvette filled with water was subtracted. The solid trace in Fig. 2b shows the best fit to the trace A1–A3 of a model based on the calculation of the L-M scattering cross section in the wavelength range from 300 nm to 800 nm. The Lorenz-Mie calculations were performed using MatLab with Maetzler [2] code for Mie scattering. The fit resulted in a diameter of 3.011 μm which was consistent with the value, (3.004±0.065) μm, provided by the manufacturer. The best fit shown in Fig. 2b was obtained from the minimization of residuals defined in Eq. (4).(4)Residuals=∑λ(A1−A3c−Mie(d,n)+∫0Δdσdθ(d,n,θ)dθ)c=N⋅0.01/2.303d=diametern=indexofrefractionΔ=acceptanceangle

Bottom Line: The value of ni at 266 nm was about 0.0060±0.0016 for microspheres with diameters of 1.5 μm, 2.0 μm, and 3.0 μm.The scattering cross section, absorption cross section, and the quantum yield at 266 nm of microsphere with a diameter of 2.0 μm was 5.65±0.01 μm(2), 1.54±0.03 μm(2), and 0.027±0.002 respectively.The styrene absorption reduces the scattering cross section by 20 % at 266 nm.

View Article: PubMed Central - PubMed

Affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899.

ABSTRACT
A commercial spectrometer with a 150 mm integrating sphere (IS) detector was used to estimate the scattering and absorption cross sections of monodisperse polystyrene microspheres suspended in water. Absorbance measurements were performed with the sample placed inside the IS detector. The styrene absorption was non zero for wavelengths less than 300 nm. Correction for fluorescence emission by styrene was carried out and the imaginary part of the index of refraction, ni, was obtained. Absorbance measurements with the sample placed outside the IS detector were sensitive to the loss of photons from the incident beam due to scattering. The absorbance data was fitted with Lorenz-Mie scattering cross section and a correction for the finite acceptance aperture of the spectrometer. The fit parameters were the diameter, the suspension concentration, and the real part of the index of refraction. The real part of the index was parameterized using an expansion in terms of powers of the inverse wavelength. The fits were excellent from 300 nm to 800 nm. By including the imaginary part obtained from the absorbance measurements below 300 nm, it was possible to obtain a good fit to the observed absorbance data over the region 240 nm to 800 nm. The value of ni at 266 nm was about 0.0060±0.0016 for microspheres with diameters of 1.5 μm, 2.0 μm, and 3.0 μm. The scattering cross section, absorption cross section, and the quantum yield at 266 nm of microsphere with a diameter of 2.0 μm was 5.65±0.01 μm(2), 1.54±0.03 μm(2), and 0.027±0.002 respectively. The styrene absorption reduces the scattering cross section by 20 % at 266 nm.

No MeSH data available.


Related in: MedlinePlus