Analysis of photoacoustic waveforms using the nonlinear least squares method

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Spectroscopy

Background:

• Pulsed-laser photoacoustics measures nanoscale enthalpic and volumetric changes.
• Analyzing photoacoustic data typically involves deconvolution for exponential decay sums.
• Existing methods, adapted from fluorescence, require significant modifications for photoacoustics due to wide decay time ranges.

Purpose of the Study:

• To develop an improved numerical method for analyzing photoacoustic data with complex exponential decays.
• To overcome limitations of approximation methods like Simpson's rule in convolution integrals.
• To compare the resolution of different transducers using the new method.

Main Methods:

• Developed a novel quadratic-fit convolution program for direct evaluation of convolution integrals.
• Constructed a continuous instrumental response function by quadratic fitting of discrete data.
• Applied the program to simulated and experimental data, including a benzophenone photochemical system.

Main Results:

• The quadratic-fit convolution method successfully addresses wide ranges of transient decay times.
• Demonstrated the program's success and limitations using simulated data.
• Experimental data analysis showed advantages of a broadband, heavily damped transducer for improved resolution.

Conclusions:

• The developed quadratic-fit convolution program offers a more robust approach to photoacoustic data analysis.
• This method enhances the ability to resolve fast transient processes in photoacoustic spectroscopy.
• The study highlights the importance of transducer characteristics in achieving high-resolution photoacoustic measurements.