Laser for Minimally Invasive Surgery

Photo: Graphik

Tissue ablation with the novel all-
solid-state light source at 6.45
microns based on frequency
conversion in comparison with
two clinical lasers; © MBI

The idea goes back to an experiment performed in 1999: Scientists from the Vanderbilt University (Nashville, TN) removed a brain tumour from a patient with a free-electron laser at a wavelength of 6.45 microns. This wavelength in the mid-infrared spectral region had previously been identified in a number of preliminary experiments with different soft tissues as the most suitable one for such surgical operations.
That the method, however, has not found its way into the operating rooms has a simple reason: the free-electron lasers are huge and expensive accelerator-based facilities not suitable for routine use in clinical conditions. Unfortunately, the desired wavelength could be generated so far only with such lasers which are tunable in a broad spectral range, or in other words, one can select almost any arbitrary wavelength. On the contrary, solid-state or gas lasers, emit normally a well defined wavelength which depends on the active medium employed. In laser surgery, wavelengths of about 2, 2.8 and 10.6 microns are currently in use.

"There were so far no compact and reliable solid-state lasers emitting at the desired mid-infrared wavelength," said Doctor Valentin Petrov. The new laser emits short pulses exactly at 6.45 microns with a repetition rate of 100-200 Hz which ensures the targeted average power of over 1 Watt. The greatly reduced collateral damage at this wavelength is due to the combined absorption of water and resonant laser heating of non-aqueous components (proteins). The penetration depth at this wavelength is on the order of several microns, which is comparable to the cell size, and is therefore close to the optimum value, not achievable by any other state-of-the-art lasers.

2008, the project MIRSURG was launched with the objective to close up the gap for diode-pumped solid-state lasers in the mid-infrared spectral range around 6.45 microns. The project team presented now a rather compact all-solid-state prototype that fits on a table-top. The desired optical wavelength of 6.45 microns is generated by frequency conversion. A laser beam with a wavelength near 2 microns is converted to the mid-infrared by the use of nonlinear optical crystals.; Source: Forschungsverbund Berlin