Flexible waveguides for the delivery of high-power Er-YAG laser radiation

In a previous research project a flexible plastic hollow waveguide has been developed in our laboratory. The waveguide was prepared by depositing silver (Ag) layer and silver iodine (AgI) overlayer on the inner surface of a plastic tube. The said waveguide proved to be a very suitable means for delivering high power CO₂ laser energy (λ = 10.6 μm) in any desired tortuous path, having small attenuation. Through the same waveguide it is possible to transmit non-coherent infrared energy from a thermal energy source to a detector. In this paper we present a new type of waveguide which is suitable for the transmission of Er- YAG laser radiation (λ = 2.94 μm). Such energy can be employed for drilling and operating in hard tissues (bone, tooth). The essential factor which made this device possible for use as Er-YAG laser energy delivery system is based on the known data from the CO₂ waveguide research was the control over the thickness and the index of refraction of the dielectric layer (AgI). Another important factor was to avoid the roughness of the plastic substrate and of the Ag/AgI layers. Reducing the roughness enabled us to reduce the scattering of the transmitted radiation to a low value, which is essential for the good functioning of the waveguide. The performed experiments have shown that an energy of up to 900 mJ could be coupled into the flexible waveguide and delivered to a target in straight or bent trajectory. The transmission was 55% in straight and 40% in bent trajectory (waveguide length 1 m, internal diameter 1.9 mm minimum radius of bending 20 cm).