Mott-transition-induced period doubling in transient-grating experiments in CdS

Area of Science:

• Solid-state physics
• Optics
• Materials science

Background:

• Free-carrier gratings are crucial for optical applications.
• Understanding their dynamics is key to controlling light-matter interactions.
• Picosecond laser pulses induce complex grating structures.

Purpose of the Study:

• To investigate the presence of higher-order Fourier components in a sinusoidal free-carrier index grating.
• To analyze the decay dynamics of these components.
• To identify the underlying physical mechanism responsible for the observed phenomena.

Main Methods:

• Fabrication of a sinusoidal free-carrier index grating in Cadmium Sulfide (CdS) using interference of two picosecond light pulses.
• Simultaneous monitoring of the first- and second-order diffraction intensity of a transparent probe pulse.
• Analysis of diffraction decay curves to determine grating properties.

Main Results:

• Demonstration of higher-order Fourier components in the free-carrier grating.
• Observation of a pronounced contribution with a doubled period.
• Decay dynamics of first- and second-order diffraction intensities were measured.

Conclusions:

• The formation of an exciton phase grating, resulting from the binding of electrons and holes within the free-carrier grating, causes the doubled period.
• This exciton phase grating contributes significantly to the observed higher-order components.
• The findings provide insights into the complex dynamics of photoinduced gratings in semiconductors.