LETTER ARTICLE www.lpr-journal.org Fused Silica with Embedded 2D-Like Ag Nanoparticle Monolayer: Tunable Saturable Absorbers by Interparticle Spacing Manipulation Rang Li, Chi Pang, Ziqi Li, Ming Yang, Hiroshi Amekura, Ningning Dong, Jun Wang, Feng Ren, Qiang Wu, and Feng Chen* Saturable absorbers are key elements for generation of ultrafast laser pulses. The commercially available semiconductor saturable absorber mirrors are wavelength sensitive and with complex fabrication process and high cost. Fused silica is one of the basic materials for various optical applications. Plasmonic nanoparticles can be used to efficiently modulate the optical properties of dielectric materials owing to the enhanced field effects based on localized surface plasmonic resonance. Ion implantation is a direct technique to synthesize plasmonic nanoparticles inside dielectric materials, which can simultaneously tailor the optical nonlinearity of substrates significantly. In this work, Ag ion implantation into fused silica with tunable interparticle spacing is used to generate broadband optical nonlinearities and to endow silica with ultrafast saturable absorption property. This ion implantation forms a 2D-like Ag nanoparticle monolayer buried inside fused silica wafer. The fused silica with embedded 2D-like Ag nanoparticle monolayer is further applied as a new saturable absorber to generate ultrafast laser pulses with pulse duration of 27 ps and repetition rate of 6.5 GHz through the passive mode-locking process. This work opens up a new route to develop low-cost, highly stable saturable absorbers, and offers the possibility to build novel silica-based photonic systems through nanoparticle spacing manipulation. R. Li, C. Pang, Z. Li, Prof. F. Chen School of Physics State Key Laboratory of Crystal Materials Shandong University Jinan 250100, China E-mail: drfchen@sdu.edu.cn Prof. M. Yang National Key Laboratory of Science and Technology on Power Sources Tianjin Institute of Power Sources Tianjin 300384, China Dr. H. Amekura National Institute for Materials Science (NIMS) Tsukuba 305-0003, Japan The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/lpor.201900302 DOI: 10.1002/lpor.201900302 Ultrafast lasers play significant roles in a wide range of areas, such as high-speed optical communication, digital switch- ing, and nonlinear microscopy, etc. [1–4] In particular, rapid developments in multi- gigahertz (GHz) mode-locked lasers are stimulated by advances in the novel sat- urable absorber (SA) materials with supe- rior nonlinear optical (NLO) response. [5,6] Based on large optical nonlinearities and ultrafast dynamic responses, semi- conductor saturable absorber mirrors (SESAMs) and 2D materials (such as graphene, black phosphorus, and tran- sition metal dichalcogenides [TMDCs]) have become excellent SAs for ultrafast laser generation. [7–18] Nonetheless, tradi- tional commercially available SESAMs usually have the drawbacks of high-cost, complex fabrication process, and limited NLO response band. [11] In addition, re- markable progress of ultrafast SAs by low-dimensional materials (e.g., 2D ma- terials, carbon nanotubes, and various nanoparticles [NPs]) have been made in recent years; design and optimization of novel materials are required to meet the demand of more com- pact, stable, and low-cost properties in the development of ultra- fast pulsed light source. [19,20] Dr. N. Dong, Prof. J. Wang Laboratory of Micro-Nano Optoelectronic Materials and Devices Key Laboratory of Materials for High-Power Laser Shanghai Institute of Optics and Fine Mechanics Chinese Academy of Sciences Shanghai 201800, China Prof. F. Ren Department of Physics Center for Ion Beam Application and Center for Electron Microscopy Wuhan University Wuhan 430072, China Prof. Q. Wu Key Laboratory of Weak-Light Nonlinear Photonics Ministry of Education TEDA Institute of Applied Physics and School of Physics Nankai University Tianjin 300457, China Laser Photonics Rev. 2019, 1900302 © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1900302 (1 of 7)