Cobalt-doped magnesium aluminate spinel, commonly referred to as Co:Spinel, is a sophisticated material utilized as a saturable absorber for passive Q-switching in solid-state lasers. This advanced material is engineered to operate efficiently at the eye-safe wavelength of 1.5 µm, making it ideal for applications such as telemetry. The Co:Spinel's unique absorption spectrum, characterized by a broad band in the 1200–1600 nm range, indicates that Co²⁺ ions replace the tetrahedrally coordinated Mg²⁺ ions within the MgAl₂O₄ lattice. This substitution is pivotal in facilitating passive Q-switching, a technique favored for its ability to produce compact and cost-effective laser sources capable of generating nano and sub-nanosecond pulses.

The 1.5 µm wavelength emitted by lasers using Co:Spinel is particularly appealing for various industrial applications. This is primarily due to its eye-safety, high atmospheric transparency, and compatibility with fused-silica waveguides. Additionally, the availability of sensitive room-temperature light detectors, such as Ge and InGaAs photodiodes, further enhances its utility. These attributes make 1.5 µm lasers highly suitable for use in range-finding, environmental sensing, telecommunications, and even medical procedures like surgery.

The absorption peak of Co:Spinel at approximately 1520 nm aligns closely with the most frequently utilized wavelengths in eye-safe laser technology. Co:Spinel is recognized for several intrinsic properties that enhance its performance as a saturable absorber. It boasts a high absorption cross-section, particularly at 1520 nm, and a long excited lifetime, ensuring consistent and reliable operation. The cobalt ions are evenly distributed throughout the material, contributing to a wide absorption band that supports ultra-compact pulsed diode-pumped laser systems. These features underscore Co:Spinel's role as a vital component in modern laser technology, offering significant advantages in both performance and safety.