Solid-State Lasers part 2
2 KTP Laser
KTP lasers are frequency-doubled Nd:YAG lasers using KTP crystals inside the cavity or externally with an emission wavelength of 532 nm in the green part of the visible spectrum.
3 Er:YAG Laser
The Er:YAG laser with a 2.94-mm wavelength is well suited for ablation of soft and hard biological tissue because the wavelength is highly absorbed in water (ma = 104 cm−1). Erbium ions are doped in high concentration (~50%) in YAG or other crystals (Er:YSGG: 2.78 mm; Cr:Er:YSGG: 2.80 mm; Cr:Tm:Er:YAG: 2.64 mm). This laser exists only as pulsed laser system because the rather complex energy-level scheme of erbium with important energy-transfer upconversion (ETU; see below Fig.) and cross-relaxation (CR) processes. The lower laser level has a longer lifetime of 9 ms compared to the upper laser level. Only by hard pumping and the efficient upconversion processes is lasing possible
Pulsed Er:YAG laser systems (pulse lengths from 100 to 500 ms) have a mean power of up to 30 W and repletion rates of up to 50 Hz, with efficiencies of 1-2%. They are used in dermatological applications for superficial tissue ablation, in dentistry, and in minimal invasive surgery. The laser light is transmitted either by an articulated arm or by fibres. Germanium oxide fibres proved to be stable in clinical routine work.