Broadband CrOCl Saturable Absorber with a Spectral Region Extension to 10.6 µm

Abstract

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...

Review of Anisotropic 2D Materials: Controlled Growth, Optical Anisotropy Modulation, and Photonic Applications

“…Q-switched bulk lasers can be developed by combining BP SA with Pr:GdLiF 4 , Nd:GdVO 4 , and Tm:Ho:YGG laser at 639 nm, 1.06 μm, and 2.1 μm. [252] The recent studies also have reported the adoption of various anisotropic 2D materials, including Ta 2 NiS 5 , [253] Ta 2 NiSe 5 , [254] ReS 2 , [255] CrOCl, [256] and PdSe 2 [257] as the SA of bulk lasers for ultrafast pulse generation. However, the polarized laser pulse generation has yet to be achieved in bulk laser with 2D SAs since the fabrication of single-crystalline 2D SAs large enough to cover the beam radius of the bulk laser remains a challenge.…”

Magnetic Phase Transitions and Magnetoelastic Coupling in a Two-Dimensional Stripy Antiferromagnet

“…CrOCl has recently been reported as a promising air-stable vdW antiferromagnetic (AFM) insulator. , The neutron scattering studies − describe the magnetic ground state of CrOCl as an unconventional SDW along the b -axis with an easy axis of the c -axis, that is, a stripy- y AFM order. As the temperature decreases, CrOCl first transforms from a paramagnetic state into an incommensurate SDW state at ∼27 K ( T mag ), then into a commensurate state with an SDW wavelength of 4 b ( b is the lattice constant) at the Néel temperature of ∼14 K. Both neutron scattering , and X-ray diffraction (XRD) results show that the magnetic phase transition at Néel temperature is accompanied by a structural phase transition from orthorhombic space group Pmmn to monoclinic space group P 2 1 / m , indicating sizable magnetoelastic coupling in CrOCl.…”

Pushing Optical Switch into Deep Mid-Infrared Region: Band Theory, Characterization, and Performance of Topological Semimetal Antimonene

“…Although exploring broadband saturable absorbers (SAs) has been a research hotspot in recent decade, few SAs have been proved to be effective in deep mid-infrared . So far, commercial semiconductor saturable mirrors (SESAMs) have been the most mature SAs, but their working wavelengths are limited below ∼3 μm wavelength .…”

“…Although exploring broadband saturable absorbers (SAs) has been a research hotspot in recent decade, few SAs have been proved to be effective in deep mid-infrared. 27 commercial semiconductor saturable mirrors (SESAMs) have been the most mature SAs, but their working wavelengths are limited below ∼3 μm wavelength. 28 The investigations of lowdimensional materials including carbon nanotubes, graphene, topological insulators, transition metal dichalcogenides (TMDs), and black phosphorus (BP) have aroused wide interests due to their broadband optical responses.…”