A Survey of the Action of Lasers on Stones

Summary

Continuous wave lasers vaporise calculi relatively ineffectively via fibres since temperatures of > 3000° C are required. A train of pulses at just above the fragmentation threshold is preferred to single giant pulses which tend to propel the stone violently. Pulse durations in the range of 10 nanoseconds are difficult to transmit through fibres regardless of wavelength. The bare fibre cannot be used close to a stone because it tends to disrupt. Microsecond pulses cause the most elimination of material per pulse and are easy to transmit via fibres. The bare fibre can be held in contact with the stone surface. The optimum parameters for stone fragmentation in clinical practice are using microsecond pulses via fine quartz fibres touching the stone surface. A plasma is formed just beyond the tip of the fibre only when there is sufficient absorption. By selecting the wavelength at close to 500 nm there is maximal differential absorption so that a plasma forms readily at the stone surface but not at the ureteric wall.