In this report we demonstrate the application of direct laser writing technology for recording a fully functional Fresnel axicon (Fraxicon) [1] under a glass surface. This technology is based on recording of refractive index change modifications (type I) in volume of transparent materials [2]. The phase shift of the embedded modifications is described by their value of refractive index change and axial length, which appears due to induced spherical aberrations by refractive index mismatch between air and glass interface [3].

The axial length was measured by recording a single modification and observing it with optical microscope. The index change was estimated by recording rectangular prisms made out of type I modifications with different overlay values. The Michelson interferometer was used to validate the refractive index change [4].

Commonly used 1 ° axicon was recorded for characterization with HeNe laser. This Fraxicon diffraction efficiency reached 70 %. After observation and minor adjustments bigger aperture Fraxicon was recorded and tested in the laser system used in experiments. The results were compared with the same apex angle Thorlabs axicon.

[1] I. Golub, Fresne axicon, Optics Letters, 31, 1890–1892 (2006).

[2] K. Miura, J. Qiu, H. Inouye, T. Mitsuyu and K. Hirao, Photowritten optical waveguides in various glasses with ultrashort pulse laser, Applied Physics Letters, 71, 3329–3331 (1997).

[3] Q. Sun, H. Jiang, Y. Liu, Y. Zhou, H. Yang and Q. Gong, Effect of spherical aberration on the propagation of a tightly focused femtosecond laser pulse inside fused silica, Pure and Applied Optics, 7, 655–659 (2005).

[4] A. Žukauskas, I. Maltulaitienė, D. Paipulas, M. Malinauskas and R. Gadonas, Tuning the refractive index in 3D direct laser writing lithography: towards GRIN microoptics, Laser Photonics, 9, 706-712 (2015).