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Research Article Vol. 30, No. 20 / 26 Sep 2022 / Optics Express 35807

F irst-principle s tu d y o f neu tron irradia ti on

i nd uc ed per fo rm an ce degra da ti on of amor ph ou s

p orous silica

QINGYI FENG,

1

HONGXIANG DENG,

1,*

BIYI WANG,

2

BO LI,

1

XIA

XIANG,

1

LI LI,

1

XIAODONG YUAN,

3

WANGUO ZHENG,

3

HONGDONG

YANG,

4

SEAN LI,

5

AND XIAOTAO ZU

1,6

1

School of Physics, University of Electronic Science and Technology of China, No. 2006, XiYuan Ave,

Chengdu 611731, China

2

Science and Technology on Electro-Optical Information Security Control Laboratory, Tianjin 300308,

China

3

Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China

4

Shanghai Institute of Space Power-Sources, No. 2965, Dongchuan Road, Shanghai 200245, China

5

School of Materials Science and Engineering, The University of New South Wales, Sydney 2052, Australia

6

[email protected]

*

[email protected]

Abstract:

Neutron irradiation induced degradation of porous silica ﬁlm is studied by Molecular

Dynamics and Density-Functional theory-based methods. The degradation of microscopic struc-

ture, thermal property, and optical property of porous silica ﬁlm are systematically investigated.

Low-energy recoil is used to simulate the neutron irradiation eﬀect. The pair and bond angle

distributions, and coordination number distributions reveal that, under neutron irradiation, the

microscopic structure of porous silica ﬁlm is obviously modiﬁed, and the coordination defects

are induced. We ﬁnd that the higher recoil energy, the more coordination defects are formed

in the ﬁlm. The increased defects lead to a decrease in thermal conductivity. In addition,

neutron irradiation induces additional optical absorption peaks in UV region and increasement

in refractive index, resulting in a noticeable reduction in light transmittance. The detailed

calculation of density of states reveals that these optical absorption peaks originate from the

irradiation induced defect states in band gap. Our work shows that low-energy neutron irradiation

can induce obvious defect density and degrade thermal and optical properties of porous silica

ﬁlm, which are responsible for subsequent laser-induced damage.

© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

1. Introduction

Antireﬂective ﬁlms are widely applied in laser systems to reduce the optical reﬂective losses

and accommodate the highest possible power densities [1,2]. Sol-gel-derived porous silica ﬁlm

is a conventional antireﬂection ﬁlm, which shows many good properties such as continuously

adjustable refractive index, easy preparation for large size, and high damage resistance in the

ultraviolet regime [3–6]. Due to these advantages, Sol-gel-derived porous silica ﬁlm has been

employed in high-power laser systems for pursuing inertial conﬁnement fusion (ICF), such as

National Ignition Facility (NIF) in the United States [7,8], Shenguang (SG) - III laser facility in

China [9], Laser Mégajoule (LMJ) in France [10] and high-power laser energy research facility

(HIPER) in Europe [11].

However, when porous silica ﬁlms suﬀer from the multi-pulse laser and ray irradiations in

the ICF facilities, the damage and decrease of the laser-induced damage threshold (LIDT) are

observed, limiting the optical lifetime of the ﬁlms and the stable operating ﬂux of ICF systems

[12,13]. This phenomenon is similar to “fatigue” in many materials such as glass [14], thin ﬁlm

#462862 https://doi.org/10.1364/OE.462862

Journal © 2022 Received 5 May 2022; revised 16 Aug 2022; accepted 5 Sep 2022; published 15 Sep 2022

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