High-Performance Birefringence of Periodic Nanostructures in FTO Thin Film Fabricated by IR-UV Femtosecond Laser

Abstract

By using infrared to ultraviolet (IR-UV) femtosecond laser directing, periodic nanostructures were efficiently fabricated on an F-doped tin oxide (FTO) film with a thickness of 650 nm. The morphology of the nanostructures and duty cycle were studied in detail by changing the laser fluence and scanning speed, where three lasers with central wavelengths of 343, 515, and 1,030 nm were used in the experiments. Under the 515 nm laser irradiation with scanning speed of 0.01 mm/s and laser fluence of 23 mJ/cm2, the periods Λ is 172 nm, the ablated nanogroove with width w2 is 52 nm, the birefringence Δn reached a maximum of 0.21, and the phase retardance was up to 135 nm. The morphology of the nanostructures and the birefringence effects of the FTO film prepared by a femtosecond laser at wavelengths of 1,030 and 343 nm were also studied, where the phase retardance of the nanostructured FTO film was much lesser than for the 515 nm laser because the thickness of the nanoripples layer, and, thus, the duty cycle of periodic nanoripples was smaller. Finally, a large-area FTO film with periodic nanostructures was fabricated efficiently by direct laser writing using a 515 nm fs laser beam focused via a cylindrical lens, and demonstrated the characteristics of a quarter-wave plate for 532 nm light.

Periodic transparent nanowires in ITO film fabricated via femtosecond laser direct writing

“…Efficient fabrication of regular and large-area LSFLs Laser processing parameters, including laser wavelength, fluence, and scanning speed, play crucial roles in the efficient and high-quality fabrication 30 . The transmittance of ITO film in the visible region is higher than 85%.…”

Regular Periodic Surface Structures on Indium Tin Oxide Film Efficiently Fabricated by Femtosecond Laser Direct Writing with a Cylindrical Lens

“…While for ITO films with a thickness of 600 nm, the laser fluence required for processing LSFLs was higher than 1.0 J/cm 2 at a scanning velocity of 3 mm/s. The heat accumulation during laser processing was very serious, which resulted in irregular LSFLs [ 5 , 52 , 53 , 68 ]. ITO film with a thickness of 175 nm was suitable for processing LSFLs with extreme regularity.…”

Effects of sub-picosecond direct laser interference patterning on the optoelectronic properties of fluorine-doped tin oxide thin films

“…In that study, LIPSS features with a spatial period of 300 nm were obtained at a wavelength of 1030 nm, while irregular HSFL with a spatial period of 126 nm could be obtained when using a 343 nm laser wavelength. 39 In addition, studies carried out by Scorticati et al 54,55 showed the formation of LIPSS when SnO 2 thin films were structured with a 343 nm ps-laser (6.7 ps). In these works, the authors reported that as the LIPSS had a spatial period in the range of 50-80 nm, i.e.…”

“…[36][37][38] To the best of our knowledge, only a few studies were published in which DLIP was employed to modify the optoelectronic characteristics of TCOs using stable and costeffective IR laser sources. 20,39 For instance, Zhang et al structured FTO thin films with a 1030 nm femtosecond laser, obtaining birefringence properties. The fabrication of nanogrooves with a spatial period of B300 nm was achieved and the birefringence (Dn) reached a value of 0.20.…”