Research progress on mid-IR nonlinear optical crystals with high laser damage threshold in China

Abstract

Nonlinear optical (NLO) crystals have been playing an increasingly important role in laser science and technology. The NLO crystals used in the middle infrared (mid-IR) region, compared with the NLO crystals in the other wavelength regions, are still not good enough for the application of high-energy laser. The main defect is that their laser damage thresholds (LDT) are low. Chinese scientists have made a lot of important contributions to the UV and visible NLO crystals. In the last decade, they also did a lot of work on the mid-IR NLO materials. The main purpose of these researches is to increase the LDT and simultaneously balance the other properties. This paper presents a brief summary of their research progress in this topic on three types of materials: chalcogenides, oxides, and halides. The emphasis is put on the design strategy and quality control of the crystals.

Ba2Si3P6: 1D Nonlinear Optical Material with Thermal Barrier Chains

“…Results show that Ba 2 Si 3 P 6 exhibits a much higher LDT (48.5 MW/cm 2 ) than that of AgGaS 2 (29.6 MW/cm 2 ) (Table 1), which is also higher than that of recently discovered MgSiAs 2 (33.2 MW/ cm 2 ) as well as those of other typical IR-NLO materials such as AgGaSe 2 and ZnGeP 2 . 27,38,39,64,65 Recently reported MnSiP 2 NLO material crystallizing in the chalcopyrite structure type also exhibits high LDT, although measured on a single crystal (70 MW/cm 2 ), thus confirming that silicon-phosphides are a good platform for novel NLO materials. 60 The promising SHG coefficient in addition to the high LDT makes Ba 2 Si 3 P 6 a promising candidate for IR-NLO applications.…”

Prediction and Characterization of NaGaS2, A High Thermal Conductivity Mid-Infrared Nonlinear Optical Material for High-Power Laser Frequency Conversion

“…Indeed, most NLO materials designed thus far have excellent nonlinear coefficients, but their thermal properties and LIDT, which are key indices to characterize the performance of mid-infrared NLO materials, are inadequate . Previous studies have shown that electron absorption causes thermal and electronic effects, thereby leading to laser damage . A wide band gap (wider than 3.0 eV) usually corresponds to high LIDT and low TPA in an IR NLO crystal.…”

“…Several IR NLO crystals (e.g., chalcopyrite-type AgGaS 2 , AgGaSe 2 , and ZnGeP 2 ) have been commercially available since the 1970s . Nevertheless, their properties severely restrict their wider applications . AgGaS 2 and AgGaSe 2 have not only low LIDT, resulting from TPA due to a narrow band gap, but also poor thermal conductivity and anisotropic thermal expansion.…”

Design of Infrared Nonlinear Optical Compounds with Diamond-like Structures and Balanced Optical Performance

“…However, in the mid-IR to far-IR regions, only AgGaSe 2 , AgGaS 2 , and ZnGeP 2 could be the mature NLO materials due to their large NLO responses and wide IR transmission ranges. Unfortunately, the inevitable defects , such as the small band gaps which could result in the strong multiphoton absorption at ∼1 μm in ZnGeP 2 and the low lattice thermal conductivity which could lead to the limited life cycle and low conversion efficiency in AgGaSe 2 and AgGaS 2 have seriously hindered their further applications in modern laser technology . Therefore, it is an urgent need to explore promising IR NLO candidates with outstanding comprehensive performances.…”