New strategy for designing promising mid-infrared nonlinear optical materials: narrowing the band gap for large nonlinear optical efficiencies and reducing the thermal effect for a high laser-induced damage threshold

Abstract

A new strategy towards the search for practical IR NLO materials not restricted by the NLO–LIDT incompatibility is verified.

Sn7Br10S2: The First Ternary Halogen‐Rich Chalcohalide Exhibiting a Chiral Structure and Pronounced Nonlinear Optical Properties

“…[38] Apart from the band gap, several other factors like thermal expansion anisotropy (TEA) also has important influences on the LIDT, [39] which can be evaluated by temperature-dependent lattice parameters. Some NLO compounds possessing smaller TEA could suffer greater thermal shock, [12,28,40] and thus possess higher LIDT values under laser irradiation. As illustrated in Table S8 and Figure S6, the measured TEA of Sn 7 Br 10 S 2 (1.44) is smaller than that of AGS (2.95), [12] and the result suggests that Sn 7 Br 10 S 2 can bear a larger high-power laser irradiation and has an important influence on obtaining a higher LIDT than AGS, which is consistent with the experimental result.…”

“…[24a,b] Compared with the Pb 2 + ion, the lighter analogue Sn 2 + ion-based IR NLO materials are a lot less well known (Table S2). In general, the valence electron configuration of Sn is 5s 2 5p 2 and Sn is usually in the tetravalent oxidation state in chalcogenide compounds, such as Li 4 CdSn 2 S 7 , [25] Li 2 CdSnSe 4 , [26] BaZnSnSe 4 , [27] Na 2 Ga 2 SnSe 6 , [28] and CsM 3 Se 6 (M = Ga/Sn, In/Sn). [29] Nevertheless, the NCS Sn 2 + -based compounds are still worthy of exploration, since the lone-pair Sn 2 + cation could generate strong polarizability and the compounds may exhibit strong SHG responses.…”

HgCuPS4: An Exceptional Infrared Nonlinear Optical Material with Defect Diamond-like Structure

“…Nevertheless, these IR-NLO materials still suffer from some disadvantages (e.g., strong two-photon absorption, non-phase-matching (NPM) feature, and low laser-induced damage thresholds (LIDT)), thereby hindering their further development. In principle, for a practical and available IR-NLO material, several key conditions such as noncentrosymmetric (NCS) space group (SG), suitable birefringence (Δ n ) for phase matching (PM), large second harmonic generation response ( d ij ), high LIDT, wide transparent window, and good physicochemical properties should be achieved. − For the above-mentioned prerequisites, a large number of IR-NLO candidates have been discovered and prepared through various strategies in the past few decades. − Among them, metal chalcogenides with diamond-like (DL) structure are supposed to be the most promising IR-NLO candidates, owing to the following advantages: (i) rich asymmetric building motifs (ABMs) constructed by covalent M–Q (Q = chalcogen) bonds, including [M I Q 4 ] (M I = Li, Cu, and Ag), [M II Q 4 ] (M II = Mg, Mn, Zn, Cd, and Hg), [M III Q 4 ] (M III = B, Al, Ga, and In), [M IV Q 4 ] (M IV = Si, Ge, and Sn), and [M V Q 4 ] (M V = P, As, and Sb); (ii) intrinsic NCS crystal structures derived from the alignment of the aforementioned ABMs; (iii) wide optical transparency windows in the IR range activated by the covalent M–Q bonds; and (iv) strong polarizabilities to realize the coexistence of a large d ij and suitable Δ n . On the basis of the valence electron concentration (VEC) rule, these materials can generally be divided into two types: normal and defect DL metal chalcogenides.…”

A2SnS5: A Structural Incommensurate Modulation Exhibiting Strong Second‐Harmonic Generation and a High Laser‐Induced Damage Threshold (A=Ba, Sr)

“…The thermal expansion anisotropy (TEA) is a key factor determining the thermal damage level caused by the incident laser as a material with a smaller TEA is less likely to be damaged by the temperature increase upon laser irradiation, leading to a higher LIDT. [23,24] Figure 3 shows the variations in the lattice parameters of Ba 2 SnS 5 and Sr 2 SnS 5 as a function of temperature according to in situ powder X-ray diffraction measurements from 298 to 623 K. Based on these data, the TEA values defined by TEA = a Lmax /a Lmin (where a L is the thermal expansion coefficient) were calculated to be 1.51 and 2.08, respectively, giving rise to an increasing trend of Ba 2 SnS 5 < Sr 2 SnS 5 < AGS (2.97) [24] (Table 1). This increasing trend and the opposite trend of the experimental LIDTs demonstrate that the higher LIDTs of Ba 2 SnS 5 and Sr 2 SnS 5 originate from the reduced anisotropic thermal expansion, greatly reducing the thermal damage.…”