Enhanced backward-directed multiphoton-excited fluorescence from dielectric microcavities

Area of Science:

• Optics and Photonics
• Physical Chemistry

Background:

• Fluorescence is a key phenomenon in molecular spectroscopy.
• Microcavities can enhance light-matter interactions.
• Photon excitation offers unique spectroscopic pathways.

Purpose of the Study:

• To investigate the angular distribution of fluorescence from dye molecules in spherical microcavities.
• To quantify the fluorescence enhancement under one-, two-, and three-photon excitation.
• To explore the underlying physical principles governing this phenomenon.

Main Methods:

• Theoretical modeling of light propagation and fluorescence emission in microcavities.
• Experimental measurements of fluorescence intensity at different angles.
• Varying the number of photons involved in excitation (one, two, and three).

Main Results:

• Observed asymmetrical angular distribution of fluorescence.
• Demonstrated significant backward fluorescence enhancement.
• Quantified enhancement ratios: 1.8 (one-photon), 5 (two-photon), and 9 (three-photon) at 180° vs. 90°.
• Predicted greater enhancement for higher refractive index microspheres.

Conclusions:

• Backward fluorescence enhancement in microcavities is dependent on the number of photons involved in excitation.
• The reciprocity principle and wave concentration contribute to this directional effect.
• The phenomenon is expected to occur in nonspherical particles as well.