Cr4+:YAG has become the solid-state passive Q-switch material of choice for 1 micron laser systems, offering several significant advantages over active acousto-optic and electro-optic devices, including:
A small fraction of the chromium ions in YAG can be induced to change valence from the normal Cr3+ to Cr4+ with the addition of charge compensating impurities such as Mg2+ or Ca2+. The best measure of the Cr4+ concentration is the low power absorption coefficient alpha at 1064 nm. The typical values of alpha vary from 1-7 cm-1 for passive Q-switch applications.
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| Orientation | <100> standard, <110> optional |
| Surface Flatness | < λ/10 |
| Surface Finish | 10-5 Scratch-Dig (Per MIL-O-13830A) |
| Absorption Coefficient ( λ specific) | 1.0 cm-1 — 7 cm-1 |
| Coating | AR @ 1064 nm (<0.2%) |
| Diameter / Cross section | <10 mm |
| Thickness | 1-5 mm (+/- 1.0)mm |
| Specify Either:
Optical Density or Absorption Coeficient or % Transmission |
0.1 to 0.8
1.0 cm-1 — 7 cm-1 10% to 90% |
| Charge compensating ion | Ca2+ |
| Crystal Structure | Cubic |
| Molecular Weight | 593.7 g mol-1 |
| Melting Point | 1965°C |
| Density | 4.56 g cm-3 |
| Thermal Expansion Coefficient | 6.14 x 10-6 K-1 |
| Thermal Conductivity | 11.2 W m-1 K-1 |
| Specific Heat (Cp) | 0.59 J g-1 K-1 |
| MOHS Hardness | 8.2 |
| Young’s Modulus | 335 GPa |
| Tensile Strength | 2 GPa |
| Thermal Shock Resistant | 800 W m-1 |
| Host Refractive Index @ 632.8 nm | 1.83 |
1) Some fundamental theory is given by, A.E. Siegman, "Lasers", University Science Books, Mill Valley, CA (1986), Chapter 26
2) Practical devices are described by, W. Koechner, "Solid State Laser Engineering", Springer-Verlag, New York (1988). Chapter 8
3) A review article "Cr4+-doped crystals: their use as lasers and passive Q-switches" is given by, Y. Kalisky, Progress in Quantum Electronics 28 (2004) 249-303
4) A comprehensive reference for the optical properties of Cr4+ in YAG is given in A.G. Okhrimchuk and A.V. Shestakov, Optical Materials 3, 1-13 (1994)
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Laser Materials