Continuous-wave photothermal deflection spectroscopy with fundamental and harmonic responses

Area of Science:

• Physics
• Spectroscopy
• Optics

Background:

• Photothermal deflection (PD) spectroscopy is a sensitive technique for material characterization.
• Existing geometric-optics theories cannot fully explain harmonic responses in PD spectroscopy.
• Understanding these harmonics is crucial for accurate analysis of complex samples.

Purpose of the Study:

• To develop a rigorous diffraction theory for continuous-wave photothermal deflection (PD) spectroscopy.
• To provide analytical solutions for fundamental and second-order harmonic responses.
• To extend the applicability of PD spectroscopy to diverse material structures.

Main Methods:

• Formulated a diffraction theory for continuous-wave PD spectroscopy.
• Derived analytical solutions for fundamental and second-order harmonic responses.
• Utilized probe beam centroid displacement as a rigorous PD measurement.

Main Results:

• The presented theory accurately describes both fundamental and harmonic PD responses.
• Harmonic responses are attributed to probe beam diffraction in the mirage region.
• The theory successfully explains phenomena beyond the scope of geometric-optics.

Conclusions:

• The developed diffraction theory offers a comprehensive framework for PD spectroscopy.
• This theory enables accurate analysis of bulk materials, thin films, and layered structures.
• Experimental validation confirms the theory's accuracy and broad applicability.