Ultra-Conservative Minimally Invasive Surgery (UCMIS) with Pulsed Non-Gaussian CO₂ Laser Beams Focused Through the Shortest Possible Focal Length

Abstract

The minimal focal length value f(min)=0.013? for a TEM(22) laser beam profile can be used for reference in UCMIS procedures using commercially available pulsed CO2 lasers at the wavelength of 10.6??m. No laser thermoablation of compact PMMA samples is possible below f(min) while delivering I(min)=7.6?mW on its spot. Gaussian beams showing TEM00 profile need longer focal lengths for the same minimally ablated volume. Suggestions about the calibration requirements for such a lens are presented. More investigations are needed to validate the whole procedure before any preliminary surgical utilization can be considered.

"Analysis of the Evaporation to Sublimation Phase Transition during Minimal Invasive Surgery Procedures via Pulsed CO2 lasers"

“…Where T1b is the temperature after the on-set of evaporation,  is the absorption coefficient of PMMA at the wavelength of the CO 2 laser and v 1b is the minimal volume following LCA (Appendix). This formula regulates the conditions for the on-set of the minimal evaporation under UCMIS regime for any arbitrary focal length which is now, per definition, larger of the minimal one presented in (5). The ablation and the evaporation times are closely linked: after a very short initial ablative-only phase (happening from 0 J/cm 2 up to max.…”

“…Then, these new values would be numerically positioned outside the tolerance limits of the presented calculations and outside also the thermodynamic uncertainties of the PMMA data reported in the Literature. This assumption would also imply the existence of a higher or a lower absolute minimal volume beyond the same tolerance limits of the model used to calculate the results of Equation 9 this is impossible per definition [5].…”

“…The other threshold (even for W min , [5] is between 16-19 J/cm 2 with a rapid Increase in the material removal rate due to evaporation followed by combustion. It is interesting to observe that the range 16-19 J/cm 2 is respected even by the notacceptable focal: The reasons which makes them unacceptable must be found in parameters, such the evaporated volume and the total exposure time, which go beyond any mathematical and physical acceptance, such as evaporated volumes of several cubic centimeters and exposure time pulse width longer than 10s.…”

“…The direct scission events, as in photochemicalprocesses, lead to modification of material and consequent reduction of molecular weight and cohesiveenergy of the polymer chain. However, the photochemical processes alone would require very highfluencies to increase the energy density and number of broken bonds [5].…”