A New Nonlinear Optical Selenide Crystal AgLiGa₂Se₄ with Good Comprehensive Performance in Mid‐Infrared Region

Abstract

Mid‐infrared (mid‐IR) nonlinear optical (NLO) crystals are indispensable for the mid‐IR lasers generation with tunable wavelengths from 3 to 20 µm. AgGaSe2 is a commercial mid‐IR NLO crystal with the highest figures of merit, but suffers low laser damage threshold (LDT). To achieve the balance of optical transmission, NLO effect, and LDT, it is proposed to molecularly modify the AgGaSe2 structure by introducing the [LiSe4] tetrahedra, and successfully grow large crystals of a new selenide AgLiGa2Se4. The replacement of half of the heavy Ag+ cations with light Li+ increases the band gap to 2.2 eV (vs. 1.7 eV in AgGaSe2). The LDT value in AgLiGa2Se4 increases five times compared to that in AgGaSe2, while keeping a relatively large NLO susceptibility of 26 pm V−1. Moreover, the thermal expansion coefficients in AgLiGa2Se4 are approximately two times lower in absolute value compared with AgGaSe2, which is beneficial to the large crystal growth. All these advantages would make AgLiGa2Se4 a new promising NLO crystal for mid‐IR laser applications.

Toward the Rational Design of Mid‐Infrared Nonlinear Optical Materials with Targeted Properties via a Multi‐Level Data‐Driven Approach

“…Owing to the extremely rich structure types and amazing performances, chalcogenide has become one preferred system to explore mid‐IR NLO materials. [ 19–21 ] Accordingly, a batch of chalcogenides such as LiMQ 2 (M = Ga, In, Q = S, Se), [ 22–24 ] BaM 4 Q 7 (M = Al, Ga, Q = S, Se), [ 25–28 ] Li 2 In 2 MQ 6 (M = Si, Ge; Q = S, Se), [ 29 ] BaGa 2 MQ 6 (M = Si, Ge; Q = S, Se), [ 30 ] AXHg 3 P 2 S 8 (A = Rb, Cs; X = Cl, Br), [ 31 ] AgLiGa 2 Se 4 , [ 32 ] Na 2 ZnGe 2 S 6 , [ 33 ] CuZnPS 4 , [ 34 ] and CuCd 3 PS 6 [ 35 ] have been reported and exhibited good NLO properties in some specific aspects such as bandgap and/or SHG response. This stimulates us to continue to search for promising sulfides/selenides for mid‐IR NLO applications.…”

The Combination of Structure Prediction and Experiment for the Exploration of Alkali‐Earth Metal‐Contained Chalcopyrite‐Like IR Nonlinear Optical Material

“…[ 6 ] Among them, selenides normally exhibit wider IR transparent regions, larger SHG responses, and lower melting points, but smaller band gaps than sulfides. [ 7 ] Over the past decades, a plenty of selenides with good NLO properties like LiGaSe 2 , [ 8 ] α ‐BaGa 4 Se 7 , [ 9 ] β ‐BaGa 4 Se 7 , [ 10 ] β ‐BaGa 2 Se 4 , [ 11 ] Li 2 ZnMSe 4 (M = Ge, Sn), [ 12 ] Li 2 CdMSe 4 (M = Ge, Sn), [ 13 ] Li 2 In 2 MSe 6 (M = Si, Ge), [ 14 ] Na 4 MgM 2 Se 6 (M = Si, Ge), [ 15 ] BaGa 2 MSe 6 (M = Si, Ge), [ 16 ] γ ‐NaAsSe 2 , [ 17 ] Na 6 MSe 4 (M = Zn, Cd), [ 18 ] CsM 3 Se 6 (M = Ga/Sn, In/Sn), [ 19 ] and AgLiGa 2 Se 4 [ 20 ] have been designed and synthesized successfully. However, to enhance the LIDT, the band gaps in selenides are still highly expected to be further improved.…”

Hg3P2S8: A New Promising Infrared Nonlinear Optical Material with a Large Second-Harmonic Generation and a High Laser-Induced Damage Threshold

“…For example, AGS and AGSe show low laser-induced damage thresholds (LIDTs), induced by small band gaps, in which a high-power laser output in mid-IR and far-IR regions is difficult to realize, and ZGP cannot be used for the high-efficiency mid-IR laser pumped by mature 1 μm laser sources due to the strong multi-photon absorption at ∼1 μm in the compound. To obtain a high-efficiency laser output, a large NLO coefficient (>1 × AGS) − is expected in the applied NLO material, and for a high-power laser, a large LIDT (>1 × AGS) , is essential, which is usually related to a wide band gap. What is more, for practical applications, stable physicochemical properties and good crystal growth habits to obtain large-scale single crystals are also expected. − Therefore, the exploration of new IR NLO materials with a strong SHG response, high LIDT, and excellent overall properties is an urgent need but challenging. − …”