Q-switched laser system, in particular for laser lithotripsy

#The invention relates to a Q-switched laser system of the type which includes a laser-active medium in a resonator construction, an arrangement for optical pumping, and a passive Q-switch.

#Solid-body laser systems for laser lithotripsy are known from the publications WO 90/12544, WO 90/04358, WO 91/05332 and AT-B-380634. In these systems, which operate with short, single pulses, the fiber which transmits the energy to the location of application is destroyed very quickly in practical use because of the short pulse lengths used in the systems. Moreover, the technical structures of these laser systems are very cost- and maintenance-intensive.

#In addition, experimental investigations have revealed that it is favorable to operate with a so-called double pulse in laser lithotripsy, which involves the transmission in rapid succession of two pulses to the location of application, with the one pulse being shifted toward the actual energy-carrying pulse toward the short-wave range ("blue") typically representing the harmonic of the carrier wave length. This combination permits premature ignition of the optical breakdown (plasma) at the rock surface to be broken up, and thus allows for a greater effectiveness in rock breaking. However, the disadvantage associated herewith is rapid fiber burnup in practical use.

#FIG. 1a is a schematic representation of a laser system according to an embodiment of the invention,

#FIG. 1b is a schematic representation of the primary optical components of a laser system according to an embodiment of the invention which is modified with respect to FIG. 1a,

#FIG. 2a is the schematic representation of the path of the beam in a multi-pass waveguide as a component of a further embodiment of the invention, and

#FIG. 1a schematically shows a preferred optical arrangement of a long-pulse, solid-body lithotripsy laser as an embodiment of the invention. In this instance, an assembly 1 comprises a focussing lens 1.3, a fiber-optic resonator extension 1.2 and an arched resonator end mirror 1.1, whose arch and spacing from the exit of the fiber of the resonator extension (1.2) are dimensioned such that, taking into consideration the numerical aperture of the fiber, the radius of curvature corresponds approximately to half the distance between the fiber end surface and the mirror surface.

#An assembly 2 includes a conventional laser cavity. Here 2.1 indicates a laser crystal, preferably Nd:YAG or Nd:YAlo3, 2.2 indicates a flash lamp for optical pumping, and 2.3 a unit for energy supply and system control.

#An assembly 3 includes a partially-transparent resonator end mirror 3.4, a non-linear crystal 3.3 for frequency doubling, typically a KTP crystal, and a passive Q-switch 3.2, typically Cr 4+:YAG or LiF(F2-), and a relay optics 3.1 for collimating the radiation.