A new method for estimating the extinction efficiency of polystyrene microsphere by micro-FTIR spectroscopy

Area of Science:

• Spectroscopy
• Optical Physics
• Materials Science

Background:

• Micro-Fourier Transform Infrared (Micro-FTIR) spectroscopy is crucial for analyzing small particles.
• Mie scattering theory describes light interaction with particles comparable to the wavelength of light.
• Polystyrene microspheres are common in various scientific applications.

Purpose of the Study:

• To measure the infrared (IR) spectra of isolated polystyrene spheres.
• To develop and validate a method for estimating extinction efficiency (Qext) of microspheres using Micro-FTIR.
• To assess the applicability of the method for mid-infrared (Mid-IR) sized particles with weak IR absorption.

Main Methods:

• Measurement of IR spectra of a single, isolated polystyrene sphere (4.46μm diameter) using a Micro-FTIR spectrometer.
• Application of Mie scattering theory to develop a method for calculating extinction efficiency (Qext).
• Comparison of Qext values obtained from Micro-FTIR spectroscopy with those from MiePlot software.

Main Results:

• Obvious scattering signals were observed in the IR spectra of the polystyrene microsphere.
• The proposed method successfully estimated the extinction efficiency (Qext) of the microsphere.
• Qext values derived from Micro-FTIR spectroscopy showed good agreement with MiePlot software results.
• The method is effective for microspheres in the Mid-IR range (2.5μm-25μm) exhibiting weak IR absorption.

Conclusions:

• A feasible method based on Micro-FTIR spectroscopy and Mie scattering theory can accurately estimate the extinction efficiency (Qext) of polystyrene microspheres.
• This technique is particularly useful for characterizing mid-infrared (Mid-IR) sized particles with weak IR absorption.
• The findings validate the use of Micro-FTIR for quantitative optical property measurements of microspheres.