FTIR and Raman as a noninvasive probe for predicting the femtosecond laser ablation profile on heterogeneous human teeth.

For high precision laser surgery, noninvasive tool for prediction of laser ablation profile beforehand is imperative. The present study proposed a method to utilize nondestructive FTIR and Raman probes for predicting laser ablation profile overcoming the challenge of heterogeneity on individual target tissue. By ascribing the chemical heterogeneity of teeth drive their differential machining capability, the study establishes a correlation between the chemical composition and their ablation parameters (ω,D and F). The chemical composition of teeth was obtained by noninvasive tools (FTIR and Raman) in terms of absorption peak intensity. To further correlate with key laser ablation parameters, the laser irradiation study was carried out using 800 nm, 100 fs, Ti:Sapphire laser. The surface morphology of irradiated sample was measured by optical profiler. A strong correlation was observed between laser ablation parameters and peak intensity of phosphate group for both FTIR and Raman spectroscopy. The concentration of phosphate group shows a positive relationship to ablation threshold fluence, while the effective Gaussian beam radius and effective energy penetration depth show negative correlation. Both nondestructive probes show good linearity which enable us to extrapolate the key laser ablation parameters for predicting laser ablation profile on random dentin and enamel samples. The ablation profiles predicted based on both FTIR and Raman are well-matched in dentin, whereas it shows a slight deviation in enamel. The predicted profiles are consistent with experimental results at lower power whereas it shows a slight deviation at higher power due to screening effect. Thus, FTIR and Raman probes can be used to predict laser ablation profile nondestructively in real-time and obviate the need for trial runs. Furthermore, the present study has predicted the laser ablation rate and ablation efficiency for performing laser surgery in optimum laser processing conditions irrespective of teeth heterogeneity.