title: Mid infrared optical parametric oscillator (OPO) as a viable alternative to tissue ablation with the free electron laser (FEL).
abstract: OBJECTIVE
  Investigations with a Mark-III free electron laser, tuned to 6.45 microm 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.
  
  
  METHODS
  A five by seven grid of craters was made about the center of each cornea. Craters were made with a 60-microm spotsize with a 500-microm 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 microm was found to be 4.1 microm for the optical parametric oscillator (OPO) and 5.4 microm for the FEL. At 6.45 microm, the damaged zone was 7.2 microm for the OPO and 7.2 microm for the FEL. At 6.73 microm, the damaged zone was 6.3 microm for the OPO and 7.6 microm+/-0.3 microm 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.
authors.affiliation: Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee 37235, USA. mackanos@stanford.edu
authors.forename: Mark A
authors.initials: MA
authors.lastname: Mackanos
authors.forename: Dmitrii
authors.initials: D
authors.lastname: Simanovskii
authors.forename: Karen M
authors.initials: KM
authors.lastname: Joos
authors.forename: H Alan
authors.initials: HA
authors.lastname: Schwettman
authors.forename: E Duco
authors.initials: ED
authors.lastname: Jansen
mesh_terms: D000818:Animals; D003315:Cornea / Q000473:pathology / Q000601:surgery*; D053685:Laser Therapy / Q000295:instrumentation*; D023421:Models, Animal; D013552:Swine