Mid infrared optical parametric oscillator (OPO) as a viable alternative to tissue ablation with the free electron laser (FEL)

Background and Objectives: Investigations with a Mark-III free electron laser, tuned to 6.45 mu m in wavelength have demonstrated minimal collateral damage and high ablation yield in ocular and neural tissues. While the use of mid-IR light produced by the free electron laser (FEL) has shown much promise for surgical applications, further advances are limited due the high costs of its use. Further investigation and widespread clinical use of six-micron radiation requires the development of an alternative laser source. In this research, we compared a Mark-III FEL and an Er:YAG pumped ZGP-OPO with respect to the effect of pulse duration on ablation efficiency and thermal damage on porcine cornea. Study Design/Materials and Methods: A five by seven grid of craters was made about the center of each cornea. Craters were made with a 60-mu m spotsize with a 500-mu m spacing. Ablation craters were made using 50 pulses per crater at approximately three times the ablation threshold (for water). Histological analysis was used to determine crater depth and thermal damage. Results: The average zone of thermal damage at 6.1 mu m was found to be 4.1 mu m for the optical parametric oscillator (OPO) and 5.4 mu m for the FEL. At 6.45 mu m, the damaged zone was 7.2 mu m for the OPO and 7.2 mu m for the FEL. At 6.73 mu m, the damaged zone was 6.3 mu m for the OPO and 7.6 mu m 0.3 mu m for the FEL. Conclusions: The OPO caused similar or significantly less thermal damage in porcine cornea when compared with the FEL while generating significantly deeper craters. We determined that the ZGP-OPO has much promise as a bench-top replacement for the FEL for soft tissue ablation.