Coherent backscattering from high-gain scattering media.

Area of Science:

• Optics
• Condensed Matter Physics
• Materials Science

Background:

• Coherent backscattering (CBS) is a wave phenomenon resulting from constructive interference of time-reversed light paths.
• In scattering media, CBS exhibits a characteristic cone shape with an intensity enhancement factor of approximately 2.
• High-gain scattering media exhibit light amplification, which can significantly alter wave propagation and interference phenomena.

Purpose of the Study:

• To experimentally investigate the effect of significant light amplification on coherent backscattering signals.
• To explore the interplay between gain and scattering in determining the CBS cone characteristics.
• To understand how amplification influences the enhancement factor and cone width in scattering media.

Main Methods:

• Fabrication of polymer sheets doped with optically pumped dyes as the gain medium.
• Incorporation of titanium dioxide (TiO2) nanoparticles to provide light scattering.
• Measurement of coherent backscattering profiles under varying optical pump intensities to control amplification.

Main Results:

• Observation of coherent backscattering signals in a high-gain scattering regime where amplification occurs over one transport length.
• Experimental evidence that the width of the coherent backscattering cone narrows as amplification increases.
• Demonstration that the CBS enhancement factor remains largely unchanged despite increasing gain.

Conclusions:

• Significant light amplification in scattering media modifies the coherent backscattering cone width.
• The enhancement factor of coherent backscattering is robust against changes in amplification in this regime.
• These findings provide insights into wave transport and interference in active scattering systems.