Comparison of OPO and Mark-III FEL for mid-infrared soft tissue ablation

Abstract

The goal of this study was to investigate a Q-switched Er:YAG pumped ZGP crystal Optical Parametric Oscillator (OPO) as a potential alternative source to the Mark-III Free Electron Laser (FEL) for delivering 6.45 micron light for clinical applications. In addition, this research increased the understanding of the role of the unique pulse structure of the FEL with respect to the ablation of soft tissue at 6.45 microns, which has been shown to ablate with very minimal collateral damage (<40 microns).The OPO operates from 6-8 microns in wavelength with a 100 ns pulse. Up to 250 micro-joules per pulse can be obtained with this laser. This provides up to three times the threshold energy for ablation given a diffraction limited spot of ~60 microns in diameter. The ablation threshold was determined using PROBIT analysis of 100 pulses on water at 6.1 and 6.45 microns in wavelength. The ablated crater depth was also measured on 90% w/w gelatin at both wavelengths for craters made with between 5 and 500 pulses.The results obtained with the OPO were then compared with a Mark-III FEL with a similar spotsize (~90 microns) to determine if there were any differences due to the unique pulse structure of the FEL, which consists of a 2.85 GHz train of picosecond pulses within a five microsecond envelope. The results showed no difference with respect to the ablation threshold; while the ablated crater depth was reduced for the FEL pulse for equivalent parameters. In addition, bright-field imaging was performed at three times the ablation threshold for both lasers and will be presented.

High-efficiency mid-infrared ZnGeP_2 optical parametric oscillator directly pumped by a lamp-pumped, Q-switched CrTmHo:YAG laser

“…Optical parametric oscillators (OPOs) that provide access to the 3 -12 m spectral range, the so-called molecular fingerprint region, are of high interest, e.g., identifying gas mixtures and chemical compounds. In addition, coherent sources operating in this spectral region have applications in the biomedical industry such as for the removal of soft tissue with wavelengths of ϳ6.5 m, provided by ZnGeP 2 -OPOs [1,2].…”