Pulsed laser interference patterning of polyimide grating for dye-doped polymer laser

Abstract

Direct laser interference patterning of polyimide (PI) films was performed by using a pulsed 355-nm laser. At laser fluence of 0.4 J/cm 2 , gratings with spatial periods of 3.8 μ m to 344 nm were created. The highest aspect ratio of the grating structure (0.8) was obtained for the 344-nm grating. An all-polymer dye laser was then fabricated by spin-coating a layer of disodium fluorescein (DF)-doped polyvinyl alcohol (PVA) film on bare and patterned PI substrate. Green laser emission was obtained when transversely pumped by a 355-nm laser. The lasing threshold reduced by ∼10 times for the sample with 344-nm grating while the laser intensity was ∼18 times higher. The enhancements are ascribed to the 344-nm grating structures, which act as an efficient distributed feedback resonator and distributed Bragg reflector grating for DF-doped PVA emitting at ∼563 nm , on top of being a passive light-trapping structures.