Fist-sized aerial volumetric display with femtosecond laser drawing

Images drawn in the air will be effective for the projection of a person or an avatar in telecommunication and man–machine communication. Direct drawing with femtosecond laser pulses can generate images anywhere without any special materials; therefore, there are fewer restrictions on image display location. The biggest challenge in research and development is to increase the display size. To increase the display size, it is necessary to make the objective lens have a longer focal length (lower numerical aperture), but increasing the focal length is accompanied by a decrease in excitation efficiency due to an increase in the focused size. Therefore, by measuring the luminous intensity and luminous size using lenses with several focal lengths, the possibility of realizing a display with a centimeter-sized (fist-sized) volume using a lens with a focal length of 100 mm was found. By reconstructing the optical system of the aerial volumetric display using a lens with a focal length of 100 mm, a drawing range of 68 mm on average in the lateral direction and 42 mm in the axial direction was achieved.