Co:Spinel (Co²⁺:MgAl₂O₄, Cobalt-Doped Magnesium Aluminate Spinel) Single Crystal

Advantages

• Broad absorption band for eye-safe wavelengths: Co:Spinel exhibits a wide saturable absorption band spanning 1200-1600 nm, with peak absorption near 1520 nm, making it the leading passive Q-switch material for erbium glass (Er:glass) lasers operating at the eye-safe 1.5 μm wavelength.
• High absorption cross-section enabling compact designs: The ground-state absorption cross-section is 3.5 × 10⁻¹⁹ cm² at 1540 nm (2.8 × 10⁻¹⁹ cm² at 1340 nm), sufficiently high to permit Q-switching of Er:glass lasers without intracavity focusing under both flash-lamp and diode-laser pumping.
• Negligible excited-state absorption for high Q-switch contrast: The ratio of initial (small-signal) to saturated absorption exceeds 10, ensuring efficient pulse generation with high contrast.
• Excellent thermal and mechanical properties: Thermal conductivity of ~17 W/(m·K), Mohs hardness of 8-8.2, and high damage threshold of >500 MW/cm² enable reliable operation in compact and high-power laser systems.
• Mechanical and chemical stability: The cubic spinel host is chemically stable, UV-resistant, and suitable for long-term device integration without degradation.

Typical Specifications

• Chemical formula: Co²⁺:MgAl₂O₄
• Crystal structure: Cubic, space group Fd3m
• Lattice constant: 8.07 Å
• Co²⁺ doping concentration: 0.05-0.35 wt%
• Working wavelength range: 1200-1600 nm
• Absorption peak: ~1520 nm
• Ground-state absorption cross-section: 3.5 × 10⁻¹⁹ cm² @ 1540 nm; 2.8 × 10⁻¹⁹ cm² @ 1340 nm
• Excited-state absorption cross-section: 1.0 × 10⁻²⁰ cm² @ 1540 nm; 2.0 × 10⁻²⁰ cm² @ 1340 nm
• Absorption coefficient: 0–7 cm⁻¹
• Initial transmission: 30–99% (customizable)
• Optical density: 0.1–0.9
• Figure of Merit (FOM): 100–300
• Damage threshold: >500 MW/cm²
• Density: 3.58–3.62 g/cm³
• Melting point: 2105 °C
• Refractive index: n = 1.6948 @ 1.54 μm
• Thermal conductivity: ~17 W/(m·K)
• Thermal expansion coefficient: 6.14 × 10⁻⁶/K
• Specific heat: 5.9 J/(g·K)
• Mohs hardness: 8.2
• Orientation: <100> or <111> ± 0.5°
• Extinction ratio: 25 dB

Standard Fabrication Specifications

• Clear aperture: >90%
• Dimension tolerance: ±0.1 mm
• Parallelism: <20 arcsec
• Perpendicularity: <5 arcmin
• Surface quality: 10-5 Scratch/Dig (per MIL-O-13830A)
• Surface flatness: <λ/10 @ 632.8 nm
• Protective chamfer: 0.1 mm at 45°
• AR coating: R < 0.2% @ 1540 nm

Main Applications

• The primary application of Co:Spinel. It enables compact, low-cost generation of short nanosecond pulses with high peak power around the eye-safe 1.5 μm wavelength, suitable for both flash-lamp and diode-pumped Er:glass laser systems.
• Laser rangefinders and LIDAR: The 1.5 μm eye-safe output is ideal for laser rangefinders, target designation, and LIDAR systems, benefiting from high atmospheric transparency and compatibility with InGaAs photodetectors.
• Optical telecommunications: 1.5 μm lasers are within the low-loss window of silica fibers, enabling applications in fiber-optic communication systems.
• Medical and cosmetic lasers: The eye-safe 1.5 μm wavelength is used in dermatological and surgical laser systems requiring precise tissue interaction.
• Ultrafast lasers and mode-locking: Co:Spinel is investigated for mode-locking of 1.3-1.6 μm lasers, enabling picosecond and femtosecond pulse generation.
• Q-switching of 1.3 μm Nd lasers: Co:Spinel also functions effectively at 1.34 μm for Q-switching of Nd:YAlO₃ (Nd:YAP) and other Nd-doped lasers.