

BGS (BaGa4S7) Mid-IR Nonlinear Crystal for OPO and OPA, 0.35–13.7 µm
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BGS (barium gallium sulfide, BaGa4S7) is a mid-infrared nonlinear crystal with a wide band gap of 3.54 eV and stable chemical properties. It transmits from 0.35 µm to 13.7 µm and shows no two-photon absorption at 1 µm, so it can be pumped directly by 1064 nm Nd:YAG lasers or by commercially common 1030 nm femtosecond lasers. WaveQuanta supplies BGS as oriented blanks and as coated elements for OPO, OPA, DFG, SFG and OPG.
Key Features
- Transmission range 0.35–13.7 µm (UV cut-off 350 nm, IR cut-off 13.7 µm)
- Band gap 3.54 eV
- Nonlinear coefficient d33 = 12.7 pm/V
- No two-photon absorption at 1 µm, allowing pumping at 1064 nm or 1030 nm
- Chemically stable
- Flatness λ/8 @ 632.8 nm and parallelism 30″
Typical Applications
- Mid-IR OPO pumped by 1064 nm Nd:YAG lasers
- OPA and OPG pumped by 1030 nm femtosecond lasers
- Difference-frequency generation (DFG) in the mid-IR
- Sum-frequency generation (SFG)
Standard Sizes
| Size | Cut / orientation | Surface / coating | Mount |
|---|---|---|---|
| 5 × 5 × 3 mm | θ = 14°, φ = 0°, XZ-cut | AR/AR @ 1.0–1.3 µm + 6–11 µm | Unmounted |
| 5 × 5 × 9.8 mm | θ = 12.5°, φ = 0° | S1: AR @ 1–1.3 µm; S2: P-coating @ 8 µm | Unmounted |
| 5 × 5 × 10 mm | θ = 13°, φ = 0°, XZ-cut | Blank | Unmounted |
| 8 × 8 × 2.5 mm | θ = 47.6°, φ = 90°, YZ-cut | Blank | Unmounted |
| 8 × 8 × 3.5 mm | θ = 47.6°, φ = 90°, YZ-cut | Blank | Unmounted |
Availability of individual sizes changes; custom sizes, cut angles and coatings are available on request.
Related Products
- BGSe Crystal — selenide version
- LGS Crystal — 1 µm-pumped mid-IR
- AGGS Crystal — wide transparency
Browse all: Mid-IR Nonlinear Crystals · Nonlinear Crystals
Model: WQ-NLC-BGS · Custom sizes, orientations and coatings on request — contact WaveQuanta for a quote and lead time.
| Chemical Formula | BaGa4S7 |
| Transmission Range | 0.35–13.7 µm |
| UV Cut-off Edge | 350 nm |
| IR Cut-off Edge | 13.7 µm |
| Band Gap | 3.54 eV |
| Nonlinear Coefficient | d33 = 12.7 pm/V |
| Density | 3.95 g/cm³ |
| Two-Photon Absorption at 1 µm | None |
| Aperture Tolerance | +0/−0.1 mm |
| Length Tolerance | ±0.1 mm |
| Surface Quality | 40-20 scratch-dig |
| Flatness | λ/8 @ 632.8 nm (length ≥ 1 mm) |
| Perpendicularity | 10′ |
| Parallelism | 30″ |





