Underwater giant enhancement of broadband diffraction efficiency of surface diffraction gratings fabricated by femtosecond laser

Abstract

In this study, a simple approach is proposed to improve the diffraction efficiency of surface diffraction gratings on fused silica fabricated by femtosecond laser. Effects of grating period, pulse energy, scanning speed and wavelength on the total diffraction efficiency are also investigated. In addition, the mechanism of the diffraction efficiency's giant enhancement is discussed by finite difference time domain (FDTD) and optical phase shift structure calculation. It is revealed that: (1) Compared with the diffraction efficiency obtained in air, the underwater image via diffraction grating is clearer than that in air and diffraction pattern in water is much brighter; (2) The diffraction efficiency increases with an increase in wavelength and scanning speed, whereas it decreases while the laser pulse energy is high; and (3) This giant enhancement is attributed to the degree of Mie scattering and refraction, which is effectively reduced for the existence of water.

Red shift of absorption edge and band gap shrinkage in perovskite Pb(Zr0.35Ti0.65)O3thin film from heat generation for solar cells application

“…Correspondingly, the temperature difference of n and k signing of dn/dT and dk/dT, as shown in Fig.4(b), exhibit a sudden change at around 560 K, which is close to previous reports 27). The change point indicates a complex ferroelectric phase transition in perovskite PZT thin films, expressing the appearance of local polarization via the quadratic electro-optic effect in crystal structure 28). Consequently, the inspection of dn/dT and dk/dT could be effectively employed to explore intrinsic ferroelectric phase transition in thin films.The film thickness of PZT apparently decreases from 193.1 nm to 187.7 nm with enlarging temperature from 293 K to 643 K, as shown in Fig.4(c).…”

“…27) The change point indicates a complex ferroelectric phase transition in perovskite PZT thin films, expressing the appearance of local polarization via the quadratic electro-optic effect in crystal structure. 28) Consequently, the inspection of dn/dT and dk/dT could be effectively employed to explore intrinsic ferroelectric phase transition in thin films.…”

Quasi-periodic concave microlens array for liquid refractive index sensing fabricated by femtosecond laser assisted with chemical etching

“…5(c) and (d) depict the change of different order diffraction efficiency of MLA on fused silica as a function of laser pulse energy at a fixed period of 15 μm assisted with 30 minutes chemical etching. As the laser pulse energy raised from 5 μJ to 60 μJ, the diffraction efficiency of order 00 monotonously decreases due to the enhancement of surface scattering and absorption 37 . Otherwise, the diffraction efficiency of order 10 distinctly raises with the increase of laser pulse energy, which could be devoted to the enlargement of optical phase shift on account of augment of microlens sag height under high power femtosecond laser irradiation 38 .…”