Hollow-waveguide-based transmission of Q-switched Nd:YAG laser beam for biological tissue ablation

The cyclic-olefin-polymer (COP)-coated silver hollow waveguide has been applied to transmit the 1064-nn, Q-switched Nd:YAG laser beam. The Nd:YAG laser pulses with 14 - 18 ns pulse widths (FWHM) were coupled to the 1-mm inner diameter, 1-m long waveguides. A single-shot laser energy of 142 mJ/pulse (9.8 MW) was transmitted with a transmission efficiency of 95.5% under the straight waveguide condition. The corresponding laser fluence and peak intensity at the waveguide output end reached as high as 18.1 J/cm(2) and 1.25 GW/cm(2) respectively. It was found that the waveguide bending and the increase in the pulse repetition rate caused decrease in the available maximum transmitted energy. But stable transmission of 50 mJ/pulse (6.5 J/cm(2)) was obtained at a pulse repetition rate of 10 Hz even under the 90 degrees-bent waveguide condition (R = 50 cm). We conclude that the hollow waveguide has the capability of transmitting high-peak-power (> 1MW) laser pulses for use in some medical applications including tissue-ablation-based treatments.