Holographic 3D microfabrication by femtosecond pulse laser

Abstract

In accordance with the development of various optical devices, an urgent need for innovative 3D microfabrication method arises. It requires not only rapid processing time or high energy efficiency but also high flexibility in designing 3D structure. Hence we established new 3D microfabrication method to satisfy all of these seemingly-contradictory factors. This method uses only single femtosecond laser pulse and phase CGH (computer generated hologram); the phase distribution of the pulse is controlled by the CGH and an arbitrary 3D microstructure is fabricated inside transparent material by multi photon absorption. It means that this method costs extremely short time and low power for the fabrication of an arbitrary complex 3D microstructure. In this report, the microfabrication of 3D spiral array which consists of 24 dot elements is demonstrated. It is very difficult to process multiple elements at different depths simultaneously, because the light intensity depends on the numerical aperture number of the objective lens and the distance from the CGH. Hence we improved the CGH calculation by considering these dependencies so that the light intensity of each element could be controlled separately. By this intensity adjustment, the shape of all elements becomes homogeneous. The other side of this intensity control is that it is able to process different shape elements intentionally by varying the intensity of each element. This intensity control is confirmed by the microfabrication with another CGH which forms 7 dot elements of different shapes. This result proves the high flexibility in designing 3D structure of this method.