Abstract
The femtosecond laser writing technique has been widely exploited for transparent materials processing. One of the useful features following laser irradiation is refractive index modification. The sign of refractive index change depends on irradiation conditions. Negative refractive index change can be 10-2, but it is accompanied with strong optical scattering. The laser induced positive refractive index change is about 10−3. For diffractive optics this is relatively small change and thus requires to modify a large physical thickness for inducing a significant optical phase delay. This can be achieved with Bessel beams [1]. However, an extended Bessel zone leads to higher stress around the laser affected zone, which can induce structural cracks with a high energy deposition level [2].
© 2019 IEEE
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