1.31 and 1.32 μm dual-wavelength Nd:LuLiF₄ laser

Highlights

• The 1.31 and 1.32 μm CW dual-wavelength Nd:LuLiF₄ laser has been reported.

• Higher output power is obtained by higher transmission of output coupler.

• Employing graphene as SA, QS dual-wavelength Nd:LuLiF₄ lasers were obtained.

• Shorter pulse duration was achieved by the lower transmission of output coupler.

Abstract

We demonstrate the operation of Nd:LuLiF₄ laser with efficient 1.31 and 1.32 μm dual-wavelength. Maximum continuous-wave output power of 1.63 W is obtained at an incident pump power of 9.97 W and 8% transmission of output coupler (OC), giving a slope efficiency of 17.9%. When monolayer graphene is employed as saturable absorber, stable passively Q-switched 1.31 and 1.32 μm dual-wavelength laser operation still remains. The maximum average output power of 1.33 W, the largest pulse energy of 17.3 μJ and the highest peak power of 111.6 W are achieved with the 8% OC. Meanwhile, the shortest pulse duration of 133 ns and the highest repetition rate of 91 kHz are rendered by the 3.8% OC cavity.

Introduction

Recently, simultaneous multiple wavelengths lasing attract great attentions due to the applications in the fields of medical instrumentation, optical frequency up-conversion, spectral analysis, and THz frequency generation, etc. As an important transition band besides 0.94 μm and 1.06 μm of Nd³⁺, laser emission at 1.3 μm could be utilized to produce red radiation by frequency doubling. The 1.31 and 1.32 μm dual-wavelength lasers have been attracted increasing attentions for their applications in the silver atom optical clock [1].

Dual-wavelength of the Nd-doping crystals has been investigated by several research groups. In 2009, Wang et al. reported the passively Q-switched (PQS) dual-wavelength ceramic Nd:YAG laser at 1052 and 1064 nm [2]. Using the identical host medium, 1319 and 1338 nm dual-wavelength operation was obtained by Guo et al. [3]. In 2013, Zhao et al. reported the dual-wavelength synchronously Q-switched solid-state Nd:LYSO laser at 1076 and 1079.7 nm with multi-layered graphene as saturable absorber for the first time [4]. Dual-wavelength Nd:YLF lasers at 1312 and 1322.6 nm have been demonstrated by Louyer et al. [1]. In 2013, Li et al. reported continuous-wave (CW) dual-wavelength Nd:LuLiF₄ (Nd:LLF) laser operation at 1314 and 1321 nm [5]. However, the PQS dual-wavelength Nd:LLF laser at 1.3 μm with V:YAG was only obtained with the 3% output coupling beyond a certain absorbed pump power. In this report, to realize superior performance, graphene monolayer is used as saturable absorber, the PQS dual-wavelength Nd:LLF lasers at 1.31 and 1.32 μm with different output couplers (OCs) are systematically investigated.

As known, passive Q-switching is another effective technology besides passive mode-locking to obtain short pulse duration and high peak power. Passive Q-switching possesses the merits of compact structure and simplicity of operation. Saturable absorber is an important component in the PQS laser, and the saturation intensity of saturable absorber is a crucial parameter determining the performance of Q-switching laser. The traditional saturable absorbers, such as GaAs, Cr:YAG, and semiconductor saturable absorber mirrors (SESAMs), are restricted by the wavelength sensitivity. Contrarily, graphene is a zero-bandgap material and wavelength insensitive. Meanwhile, graphene possesses honeycomb crystal lattices and a two-dimensional structure, which determines unique characteristics such as topological, electronic, and optical properties, etc. [6], [7], [8], [9], [10]. Recently, graphene has been demonstrated to present a saturation intensity of 0.7 MW/cm² which one order lower than SESAM [10]. The low saturation intensity is conducive to passive Q-switcher according to the analysis of Keller [11], [12]. Therefore, graphene is a promising saturable absorber for Q-switched laser operation.

In this paper, we demonstrate, for the first time to our knowledge, the efficient 1.31 and 1.32 μm dual-wavelength PQS Nd:LLF laser with monolayer graphene as saturable absorber. The threshold pump powers for stable PQS dual-wavelength lasers are 2.32 W and 2.65 W with 3.8% and 8% OCs, respectively. At 9.97 W pump power, the shortest pulse duration of 133 ns and the highest repetition rate of 91 kHz are obtained with 3.8% OC. The maximum average output power of 1.33 W, largest pulse energy of 17.3 μJ and highest peak power of 111.6 W are achieved by the 8% output coupling.