Photothermal lensing spectroscopy in a flowing medium: theory

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Physical Chemistry

Background:

• Photothermal lensing spectroscopy (PTLS) is a sensitive technique for detecting thermal properties of materials.
• Existing theoretical models often have limitations regarding excitation conditions and media flow.

Purpose of the Study:

• To develop a complete and general theoretical description of dual-beam photothermal lensing spectroscopy.
• To extend the applicability of PTLS theory to a wider range of experimental conditions.

Main Methods:

• Theoretical modeling of the photothermal effect.
• Analysis of heat diffusion and optical propagation in various media.
• Consideration of both continuous-wave (cw) and pulsed laser excitation.
• Inclusion of transverse and collinear optical geometries.

Main Results:

• A unified theoretical framework for dual-beam PTLS is established.
• The theory is valid for both flowing and stationary media.
• Results are applicable to arbitrary pulse lengths for pulsed excitation.
• The theory encompasses modulated and unmodulated cw excitation.
• Both transverse and collinear beam geometries are theoretically addressed.

Conclusions:

• The generalized theory significantly expands the utility of dual-beam photothermal lensing spectroscopy.
• This work provides a robust foundation for applying PTLS across diverse experimental setups and sample types.
• The comprehensive model facilitates more accurate data interpretation in PTLS analyses.