Alexandrite Laser with a Two-Wavelength Mixed Pulse (750/375 nm) for Lithotripsy

Abstract

The alexandrite laser combines the advantages of a solid state laser (compactness) and a dye laser (long pulses). A systematic comparison is described e.g. in [1]. It turned out that — once the fragmentation threshold is exceeded — the question of the right wavelength is less important than expected. In some cases, however, the fragmentation threshold may be so high that up to pulse energies of 60 mJ there is still no fragmentation. One necessary prerequisite for fragmentation is the plasma ignition either in the surrounding liquid or on the surface of the stone, concommitant with the so-called “ticking”. There are, in principal, three possibilities to lower the threshold for this process:

• enhancement of absorption of surrounding liquid (adding of appropriate solution)

• enhancement of absorption of stone material (staining of stone surface)

• admixing of a (low energy) pulse of strongly absorbed wavelength (optical staining)