Simultaneous all-optical determination of molecular concentration and extinction coefficient

Area of Science:

• Spectroscopy
• Chemical Analysis
• Physical Chemistry

Background:

• Accurate determination of molecular concentration and extinction coefficients is crucial for chemical analysis.
• Traditional methods often require standard samples for calibration, limiting their applicability.
• Nonlinear spectroscopic techniques offer potential for advanced quantitative measurements.

Purpose of the Study:

• To develop a novel optical method for simultaneous determination of absolute molecular number concentration and extinction coefficient.
• To establish a calibration-free approach for quantitative spectroscopic measurements.
• To extend the applicability of spectroscopic methods to transient chemical species.

Main Methods:

• Utilizing femtosecond pump-probe spectroscopy to measure absolute signals.
• Developing a closed-form expression for molecular concentration based on optical parameters.
• Accounting for laser pulse characteristics and pulse propagation effects.
• Determining extinction coefficients from absorbance spectra and calculated concentration.

Main Results:

• Achieved simultaneous determination of molecular concentration and extinction coefficient through optical measurements.
• Demonstrated a calibration-free "photonumeric" method.
• Validated the method with fluorescein in methanol, showing agreement within 10% with gravimetric determination.
• The method is applicable to a wide range of concentrations (0.032–0.540 mM).

Conclusions:

• The developed photonumeric method provides an accurate and efficient way to determine molecular properties optically.
• This approach eliminates the need for chemical standards, simplifying quantitative analysis.
• The technique shows promise for analyzing transient species where conventional methods fail.