Viscoplastic Modeling of Surface Relief Grating Growth on Isotropic and Preoriented Azopolymer Films.

Area of Science:

• Polymer Science
• Optics
• Materials Science

Background:

• Surface relief gratings (SRGs) in azopolymer films are crucial for optical applications.
• Contradictory reports exist on the efficiency of surface relief grating inscription using specific interference patterns.

Purpose of the Study:

• To investigate and resolve two critical issues concerning SRG inscription in azopolymer thin films.
• To elucidate the influence of initial polymer backbone orientation and photosoftening effects on grating formation.

Main Methods:

• Utilized an orientation approach combined with viscoplastic modeling.
• Performed in situ experimental measurements of surface topography changes during irradiation with modulated light.
• Employed special pretreatments to control initial polymer orientation states.

Main Results:

• Demonstrated that the initial orientation state of azopolymer backbones significantly affects the phase and height of gratings formed by the SS interference pattern.
• Confirmed that a weak photosoftening effect promotes faster grating growth when using the RL interference pattern.
• Experimental and modeled results align, showing the relative growth efficiency order: RL > PP > SS.

Conclusions:

• The initial orientation state is a critical factor in the contradictory experimental findings for SS interference patterns.
• The photosoftening effect plays a key role in the enhanced inscription speed observed with RL interference patterns.
• This study provides a unified understanding of SRG inscription mechanisms in azopolymers under various light interference patterns.