Spectral optimization of a pulsed HF chemical laser for efficient energy delivery through a low-loss fluoride glass optical fiber

Abstract

Pulsed HF chemical lasers oscillating in the midinfrared region of the spectrum where water can strongly absorb are suitable for the organic tissue ablation. For such a medical application, a flexible energy delivery system using an optical fiber is indispensable. The fluoride glass optical fiber may be used for low-loss optical energy delivery of the pulsed HF laser. Using an intracavity CO2 absorption cell, we have optimized pulsed multiline HF chemical laser spectrum for low-loss energy delivery through a fluoride glass optical fiber whose transmission loss is theoretically estimated to be minimum around 2.5 μm. The fractional output energy of P1-0(3) and P1-0(4) lines, which are sitting in the lowest loss spectral region of the practical fluoride glass fiber, exceeded half the multiline output energy using a line selective intracavity CO2 gas cell. The P1-0(4) line extracted from the resonator with a diffraction grating was successfully delivered through a 3-m-long commercial fluoride glass fiber (core/cladding diameter=450/500 μm). The delivered energy of 11.9 mJ was achieved with the corresponding energy fluence of 12 J/cm2 and peak intensity of 22 MW/cm2 at the exit core surface without optical damage.