Photothermal Deflection Spectroscopy Heating Cooling Discrimination

The patent extracts and eliminates the requirement for multiple pump laser wavelengths from the PDS system. By using a single pump laser wavelength and instead varying the probe laser wavelength across the absorption spectrum, the system achieves reliable heating-cooling differentiation without the complexity of multiple pump lasers. This extraction of the multi-wavelength requirement from the pump laser and relocation to the probe laser resolves the technical contradiction.

The patent substitutes the mechanical/optical complexity of switching between multiple pump laser wavelengths with a spectral scanning approach using a single pump laser and a tunable probe laser. The probe laser is tuned across the absorption spectrum to identify the peak wavelength, and measurements are taken at wavelengths on either side of the peak. This substitution maintains measurement precision while dramatically improving ease of operation by eliminating the need for multiple pump lasers and their associated alignment and switching mechanisms.

The patent implements a feedback-based methodology where the probe laser wavelength is tuned to identify the absorption peak, and then measurements are taken at specific wavelength offsets from the peak. The system uses the sign of the PDS signal at these offset wavelengths to determine whether heating or cooling is occurring. This feedback approach, combined with the specific wavelength selection strategy, provides unambiguous identification of heating-cooling transitions without relying on phase reversal alone, thereby improving reliability while maintaining reasonable detection complexity.