AGS Crystals
What Are AGS Crystals?
Fig 1. The unit cell of AgGaS2 crystal
and three kinds of tetrahedrons. [1]
Silver Gallium Sulfide (AgGaS2, AGS) is a well-established I–III–VI2 chalcopyrite crystal prized for mid-infrared nonlinear optics. Transparent from the near- to deep-IR, AGS combines a sizable second-order nonlinearity with measurable birefringence and a wide bandgap, giving it a high figure-of-merit and robust resistance to optical damage. These traits make AGS an excellent choice for efficient frequency conversion processes such as second-harmonic generation (SHG), sum-frequency generation (SFG) and optical parametric oscillation (OPO).
One distinctive capability of AGS is room-temperature, non-critical 90° phase matching. That property enables practical parametric upconversion schemes — for example, converting CO2-range radiation (≈10.2–11.6 μm) into visible green light near 0.566 μm across typical operating temperatures (0–100 °C). Because of its combination of performance, stability, and manufacturability, AGS is widely used in tunable mid-IR sources and sensors.
Alfa Chemistry supplies high-quality AGS crystals for both the scientific and industrial markets. Our advanced growth technology ensures excellent optical homogeneity with minimal scatter and wavefront distortion, guaranteeing superior beam quality and conversion efficiency.
Features
- Broad Transparency Range: Transmits from 0.0.47 μm to 13 μm, providing exceptional coverage across the entire mid-infrared region, which is critical for spectroscopy and sensing applications.
- Proven Nonlinear Performance: Effective second-order coefficients suitable for OPO/OPA, SHG and DFG in the near- and mid-IR, enabling robust performance in various setups.
- Good Laser Damage Threshold: Surface damage thresholds in the range of ~30 MW/cm2 for ~10 ns pulses at 1.06 μm are commonly reported (varies with pulse length, surface polish and coating).
- Workable Mechanical/Processing Properties: AGS can be cut, polished, AR-coated, and mounted into OPO/OPA assemblies with standard optical fabrication techniques; typical surface quality and angle tolerances are available on request.
Specifications Product Options Applications
| Product Name | KTA Crystals |
| Catalog No. | OPTIX-0013 |
| Chemical Formula | AgGaS2 |
| Crystal Structure | Tetragonal |
| Lattice Parameters | a=5.756Å, c=10.301 Å |
| Density | 4.48g/cm3 |
| Mohs Hardness | 3.0 - 3.5 |
| Melting Point | 993℃ |
| Negative Uniaxial Crystal | no>ne (λ<0.497µm, ne>no) |
| Bandgap | 2.7eV |
| Orientation Accuracy | < ±0.1° |
| Parallelism | 30″ |
| Perpendicularity | 10′ |
| Surface Quality (Scratch/Dig) | 20/10 per MIL-O-13830A |
| Flatness | λ/8 @ 632.8 nm for T ≥ 1 mm |
| Length Tolerance | ±0.1 mm |
| Clear Aperture Tolerance | +0 / -0.1 mm |
| Chamfer | <0.2mm×45° |
| Nonlinear Optical Properties |
| NLO Coefficient | d36 = 12.5 pm/V @ 10.6 μm |
| SHG Phase Matchable Range | 1.8-11.2 µm |
| Damage Threshold | 30 MW/cm2 (surface) @ 1.064 μm, 10 ns |
| Linear Optical Properties |
| Transparency Range | 470 ~ 1300 nm |
| Absorption Coefficients | <0.05 cm-1 @ 1.064 µm
<0.02 cm-1 @ 10.6 µm |
| Birefringence | 0.0231@0.53 µm, 0.0504@0.694 µm,
0.0542@1.06 µm, 0.0533@5.3 µm
0.0542@10.6 µm |
| Sellmeier Equations (λ in μm) | no2=3.3970+2.3982λ2/( λ2– 0.09311) +2.1640 λ2 /(λ2-950)
ne2=3.5873+1.9533λ2/(λ2 – 0.11066) + 2.3391λ2/(λ2-1030.7) |
| Thermal and Electrical Properties |
| Thermal Conductivity | 1.0 W/M/℃ |
| Thermal Expansivity | ‖C: -8.1 x 10-6 /°C
⊥C: +19.8 x 10-6 /°C |
| Thermo-Optic Coefficients | dno/dt=15.4 x 10-5/℃
dne/dt=15.5 x 10-5/℃ |
Note: The data provided is for reference purposes. We recommend consulting with our technical team to verify suitability for your application.
AGS Crystal Product Options
We offer AGS in a range of standard and custom configurations:
- Sizes: from small pieces (e.g., 3×3×0.5 mm) up to larger blanks (custom lengths and apertures); typical plates, rods, and discs available.
- Cut Types: X/Y/Z oriented, Brewster, phase-matching cuts, custom angles for Type I/II SHG and OPO phase matching.
- Polish & Flatness: standard optical polish (λ/8 or better), scratch/dig down to 10/5 on request.
- AR Coatings: broadband or narrowband AR optimized for NIR/MIR (we recommend coating specs matched to your operating wavelength and pulse regime).
- Quality Control: each piece can be supplied with interferometry, transmission/absorption measurement, and a certificate of conformance upon request.
- Optical Parametric Oscillators (OPOs): The premier choice for pumping with Nd:YAG (1.064 μm) or other lasers to generate tunable output in the 3-5 μm mid-IR range.
- Second-Harmonic Generation (SHG): Efficiently doubles the output of CO₂ lasers (10.6 μm) to 5.3 μm and other IR laser lines.
- Difference Frequency Generation (DFG): Creates precise, tunable IR sources for high-resolution spectroscopy, environmental gas monitoring, and chemical detection.
- Sum Frequency Generation (SFG): Used in various research applications to combine wavelengths.
- Terahertz (THz) Wave Generation: Employed in systems for generating and detecting THz radiation.
Handling & Storage Recommendations
Store in a dry, dust-free environment and handle with gloves. Some sulfide crystals show surface absorption/oxidation over long storage if exposed to humidity — we recommend dry-box storage and periodic inspection.
Avoid high-energy focused beams on uncoated or poor-quality surfaces; use appropriate AR coatings and clean, well collimated beams in high-power applications.
Why Choose Our AGS Crystals?
- Expertise in Crystal Growth: We have perfected the growth process of AGS to minimize defects and ensure superior optical uniformity and high laser-induced damage threshold (LIDT).
- Custom Engineering & Rapid Prototyping: in-house cutting, polishing, orientation metrology and AR coating services — fast turnarounds on custom cuts and prototypes.
- Design Support: our applications team helps select crystal orientation, cut angle and coating to maximize conversion efficiency and damage resistance for your pump wavelength and pulse regime.
- Batch Testing & Documentation: transmission/absorption curves, interferometry, and laser-damage tests available on request.
Reference
- Wu, Jun, et al. Crystal Growth & Design 20.5 (2020): 3140-3153.
