Hollow waveguide for mid and thermal infrared radiation.

Objective: A novel type of flexible hollow waveguide that facilitates delivery of infrared radiation from source to treatment site, and made of polyimide tubes, was developed.

Summary Background Data: Polyimide tubes with flat internal wall and optimal conditions of deposition of guiding metal and dielectric layers were used to obtain low losses of radiation and high quality of beam shape.

Methods: Etching of the internal wall of polyimide tubes, high reflective metal (silver) layers and suitable dielectric layers (index of refraction and thickness) were deposited as guiding elements to obtain a waveguide suitable for infrared transmission.

Results: Polyimide waveguides of very low attenuation (transmission of approximately 95% through 1 meter length) beam profile of variable shape as a function of bending radius and type of tbe, large delivered radiation power (more than 25 Watts), constant delivered power as a function of time (during more than 250 seconds), and very low divergence of the delivered beam (angle of divergence less than 1 degree), were obtained. The polyimide waveguides also are very flexible and may be bent to a radius of bending less than 5 cm. The polyimide plastic hollow waveguide is suitable for medical applications (chemical and physical stable and nontoxic).

Conclusions: The optical and mechanical parameters correspond with those requested for applications in medicine for infrared laser treatments or radiometric measurements (non-contact thermometry). Waveguides for applications in surgery are under preparation.