Meta-Deflectors Made of Dielectric Nanohole Arrays with Anti-Damage Potential

Abstract

In intense-light systems, the traditional discrete optical components lead to high complexity and high cost. Metasurfaces, which have received increasing attention due to the ability to locally manipulate the amplitude, phase, and polarization of light, are promising for addressing this issue. In the study, a metasurface-based reflective deflector is investigated which is composed of silicon nanohole arrays that confine the strongest electric field in the air zone. Subsequently, the in-air electric field does not interact with the silicon material directly, attenuating the optothermal effect that causes laser damage. The highest reflectance of nanoholes can be above 99% while the strongest electric fields are tuned into the air zone. One presentative deflector is designed based on these nanoholes with in-air-hole field confinement and anti-damage potential. The 1st order of the meta-deflector has the highest reflectance of 55.74%, and the reflectance sum of all the orders of the meta-deflector is 92.38%. The optothermal simulations show that the meta-deflector can theoretically handle a maximum laser density of 0.24 W/µm2. The study provides an approach to improving the anti-damage property of the reflective phase-control metasurfaces for intense-light systems, which can be exploited in many applications, such as laser scalpels, laser cutting devices, etc.

Reflective Meta-Films with Anti-Damage Property via Field Distribution Manipulation

“…The melting point of silicon is 1683 K. It is shown that the meta-film can handle the maximum laser power (0.0992 W per 0.36 µm 2 ), i.e., the laser density of 0.27 W/µm 2 . This power value is higher than that (0.24 W/µm 2 ) in our previous work of meta-deflectors [33].…”

“…Each unit-cell possesses an ellipse nanohole with diameters Dx and Dy. Compared to the rectangular shape in our previous work [33], the ellipse has a smoother edge and lower surface energy, leading to weaker localized fields and better thermal stability. Compared to symmetrical structures such as nanocylinders, ellipses have one more parameter (i.e., D vs. Dx, Dy) to tune the field distribution inside.…”

“…Anti-reflective coatings based on nanostructures are investigated [18,31], and the anti-damage feature has been obtained experimentally via manipulating a strong electric field into air zones [32]. In our previous work, the phase control of light reflected by the nanoholes with in-air confinement has been investigated for beam steering, and a meta-deflector with anti-damage properties was obtained [33]. Therefore, metasurfaces, which can manipulate electromagnetic fields in a subwavelength scale, can provide a new approach to address these issues of reflective films.…”

Theoretical Comparison of Optothermal Absorption in Transmissive Metalenses Composed of Nanobricks and Nanoholes

“…This method has been experimentally verified in anti-reflection nanotextures on fused silica, in which the strong electric field is tuned from nanostructures into the air and anti-damage properties are obtained successfully [27,28]. According to the method, our previous works also demonstrated that reflective metasurfaces made of dielectric nanoholes could be realized with high damage thresholds via field manipulation, and the electromagnetic mechanism has been explained via the electromagnetic distribution of excitation states [29,30]. To further demonstrate the principles of anti-damage metasurfaces, the optothermal mechanism in transmissive phase-control metalenses still requires investigation.…”