The Cosine Similarity Technique: A new method for smart EXCIMER laser control

To introduce additional steps towards smart laser control in eye surgery, with the use of the cosine similarity technique to analyze the spectra of organic polymers obtained using non-contact photoacoustic spectroscopy (NCPAS). The experiments were performed with two organic polymers: polyethylene and polyamide. A 193 nm excimer laser was used for photoablation at a repetition rate of 200Hz. The resulting acoustic signal of the ablation process was recorded by a capacitor microphone and then preamplified and digitized. For each specimen, four measurements with 1000 single pulses were taken. The cosine similarity technique was then used to compare the spectra of the polymers. The performance of the discrimination technique was evaluated by receiver operating characteristic analysis. It was possible to correctly recognize a material with a probability of approximately 98% using the cosine similarity technique at a laser repetition rate and recording rate of 200 Hz, which represents the acoustic signal of one laser pulse. The determination of materials with the cosine similarity method (CSM) is a fast, precise and promising approach towards smart laser control. Additional steps could include the design of a database containing generic spectra, using higher repetition rates, and the combination of NCPAS results with the position of the laser beam.