Many studies have focused on NLO materials that are used in highpower pulsed lasers in the ultraviolet, visible, and near-infrared (IR) spectral ranges. Constrained by the currently available mid-IR NLO materials, mid-IR pulsed lasers with a wavelength range from 2.5 to 20 µm are underdeveloped. [5,6] NLO materials with saturable absorption properties are often used as the SAs of passively Q-switched lasers and modelocked lasers. Saturable absorption is one kind of NLO effect induced by the imaginary part of the complex third-order susceptibility. The saturable absorber (SA), which is the key component of a pulsed laser, is used to generate a high-energy pulse according to the material's saturable absorption characteristics. Traditional SAs are mainly divided into two categories: ion-doped crystals, such as chromium (Cr)-doped yttrium aluminum garnet (Cr:YAG) crystals or ceramics, and semiconductor saturable absorber mirrors. However, traditional SAs have the disadvantages of a complex preparation process, wavelength sensitivity, and a narrow modulation bandwidth. [7][8][9][10] In recent years, many new SAs were reported and demonstrated, including polarizer [11] and various 2D materials. [12,13] Benefiting from an adjustable bandgap, broadband transmittance, large nonlinearity, high carrier density and mobility, 2D SAs such as graphene, [14,15] black phosphorus, [16,17] topological insulators, [18,19] and transition metal dichalcogenides [20] have attracted attention in materials and optics research. However, the low laser damaged threshold (LDT) and uneven quality of 2D SAs greatly limit their application in the field of high-power solidstate lasers. In addition, the lack of scalable, reliable synthesis methods for 2D materials is a significant impediment that needs to be addressed. Hence, it is necessary and urgent to study new ultra-wideband NLO materials with excellent performance, especially over the wide range of IR bands. Ideal IR NLO materials should possess a wide range of transmission bands, strong NLO effects, and a high LDT. [21,22] Cr-ion-doped crystals play important roles in laser modulation. The valence states of Cr ions mainly include Cr 2+ , Cr 3+ , Cr 4+ , and Cr 5+ . The most common Cr 4+ -ion-doped crystals are typical SA materials for producing pulsed lasers near 1 µm in passively Q-switched and mode-locked lasers. For example, a dual-wavelength pulsed laser was achieved at 1.06 and 1.33 µm with a Nd:GdVO 4 laser using a Cr 4+ :YAG SA in 2016. [23] Crystals doped with Cr ions of other valences (Cr 2+ and Cr 5+ ) Nonlinear optical (NLO) materials with saturable absorption have attracted increasing attention because of their broad applications in the fields of optical communication, materials processing, biological detection, and surgery. However, their development is limited in the mid-infrared (IR) range due to a lack of available materials with a wideband NLO response. Herein, the optical properties and applications of the transition metal oxychloride CrOCl, which has a broadband transpare...