Improving of solid state Er:YAG pulse laser performance for use in medicine

The large quadratic electrooptic effect of PLZT ceramics allows to design small size modulators for the solid state infrared Er:YAG laser (lasing at λ = 2.94 μm - at the most pronounced absorption band of water) which has found application in medicine for efficient ablation of hard and soft tissues. In the free running mode the Er:YAG laser emits spikes that form the pulse envelope with duration of 150-800 μs. An extracavity PLZT8.5/65/35 ceramics modulator (aperture of 4×6 mm² and length of 18 mm) was used to obtain Π-shape segments with the rise and decay times less than 5 μs. That allows to reduce considerably the fraction of the pulse energy below the ablation threshold so avoiding undesirable heating of tissues. The halfwave voltage of such modulator was 1350 V with an additional DC bias of 300 V. The contrast ration K>15:1. The Q-switching technique was applied to obtain high intensity small duration monopulses using modulators of the same PLZT8.5/65/35 ceramics. PLZT ceramics Q-switches (tested in two schemes - as a λ/4 switch placed perpendicular to the beam with a length of 6 mm without antireflection coatings; and as a λ/2 switch with a length of 3 mm placed at the Brewster angle) allowed to obtain monopulses with the energy of 5-8 mJ and with a pulse width of 150 ns.