Bonded crystals (also: diffusion-bonded crystals) consist of at least two crystals with the same host lattice but different dopants. During production, the crystals are combined with optical contact. At a high temperature near the melting point, the crystals are further bonded together under pressure. Diffusion processes take place in the process. These bonded crystals are then slowly cooled.
Different combinations result in different advantages:
If undoped crystals are used as crystal ends, thermal effects can be reduced. Due to lower temperature peaks during laser operation, the thermal lens effect as well as thermal breaks are reduced. In disk lasers, ASE (enhanced spontaneous emission) can be reduced by using an undoped crystal end. Likewise, such a disk laser is mechanically more stable and has fewer stress fractures.
A crystal consisting of segments of different dopants can be used for end-pumped solid-state lasers. This "smoothes" the absorption curve so that the absorption in the crystal is as uniform as possible. This in turn leads to a uniform temperature distribution in the crystal, so that higher output power, higher pump efficiency and better beam quality can be achieved.
In a bonded crystal with different dopants, the crystal with one type of doping serves as a gain medium, while the crystal with the other doping serves as a saturable absorber for passive Q-switching. This effectively reduces the size of a passively Q-switched laser at the expense of flexibility.
IMPEX produces the following bonded crystals, for example:
- Nd:YAG + Cr:YAG
- YAG + Nd:YAG + YAG
- Nd:YVO4 + YVO4
- Nd:GdVO4 + GdVO4
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