We have comparatively studied waveguide fabrication characteristics in various transparent materials by use of temporally shaped femtosecond laser pulses. The materials which we studied here are fused quartz, K-PG375 glass whose melting point is as low as 648 K, and polymethylmethacrylate (PMMA). We have measured amount of refractive index change, writing speed, and laser fluence threshold for waveguide writing in the above mentioned materials. To optimize the optical quality of internal modification of transparent materials by femtosecond laser pulses, we controlled the free electron density induced in the materials by tailoring energy injection as a function of time.
With a loosely focused femtosecond laser, refractive index change is induced in silica glass without any scanning process. By decrease numerical aperture of the incident laser, the induction of irregular structure can be avoided such as clacks and spatial splitting of the induced refractive index change region. We demonstrate controlling of the refractive index change by optimizing the numerical aperture and input energy and input pulsewidth and laser shot number. A new method of fabrication of photonic devices in silica glass is proposed.