Electromagnetic radiation barriers and waveguides, including barriers and waveguides for light, are disclosed. The barriers and waveguides are fabricated by directing charged particles, for example, ions, into crystalline substrates, for example, single-crystal sapphire substrates, to modify the crystal structure and produce a region of varying refractive index. These substrates are then heated to temperatures greater than 200 degrees C. to stabilize the modified crystal structure and provide the barrier to electromagnetic radiation. Since the treatment stabilizes the crystal structure at elevated temperature, for example, above 500 degrees C. or above 1000 degrees C., the barriers and waveguides disclosed are uniquely adapted for use in detecting conditions in harsh environments, for example, at greater than 200 degrees C. Sensors, systems for using sensors, and methods for fabricating barriers and waveguides are also disclosed.