Fairy Lights in Femtoseconds: Aerial and Volumetric Graphics Rendered byFocused Femtosecond Laser Combined with Computational Holographic Fields
Yoichi Ochiai∗

Takayuki Hoshi

Kota Kumagai

Jun Rekimoto

Satoshi Hasegawa

Yoshio Hayasaki

Figure 1: Application images of Fairy Lights, aerial and volumetric graphics in air rendered by femtosecond lasers. (a) A “fairy” flying infront of a finger. (b) A “sprout” coming out from a seed. (c) Interference between a point cloud and a finger. (d) The SIGGRAPH logo.
We envision a laser-induced plasma technology in general applications for public use. If laser-induced plasma aerial images weremade available, many useful applications such as spatial aerial AR,
aerial user interfaces, volumetric images could be produced. This
technology could be used not only for aerial images, but also volumetric displays in certain media, e.g., in a water-filled pool. This
would be a highly effective display for the expression of threedimensional information. Volumetric expression has considerable
merit because the content scale corresponds to the human body;therefore, this technology could be usefully applied to wearable
materials or spatial user interactions. Further, laser focusing technology can add an additional dimension to conventional projection
technology, which is designed for surface mapping, while laser focusing technology is capable of volumetric mapping. This technology can be effectively used in real-world-oriented user interfaces.
High-power lasers are used to generate voxels in the air. The basic
concept was discussed and the working principle was demonstratedusing a nanosecond laser in [Kimura et al. 2006] and a rendering
speed of 100 dot/sec was achieved. Later, adoption of a femtosecond (100 fs) laser and 500 dot/sec was achieved. The color of lightdots in these systems was nearly white. An in-water type of laserbased volumetric display was developed [Kimura et al. 2011] and50,000 dot/sec was achieved. While no detailed principle was discussed, we infer that this in-water type is not based on laser plasma
but laser-induced cavitation. The green light dots generated by agreen laser can be explained as diffusion of the incident laser bymicrobubbles.
In this study, we use femtosecond lasers with pulse durations of30 fs, 100 fs, and 269 fs. This leads to calmer and safer plasma∗ email: ochyai@me.com, The University of Tokyo

Figure 2: Example of a computer-generated hologram (CGH). (a)An original image, (b) a converted spot-array image, and (c) a
CGH to be displayed on the SLM.

generation that can be incorporated into our daily lives. The design space and possible scenarios of the plasma-based 3D display
are discussed. In addition, we use an optical device, called the spatial light modulator (SLM), to modify the phases of light rays andproduce various spatial distributions of light based on interference.
A liquid crystal SLM (LCSLM) is used in this study, which contains
a nematic liquid crystal layer. The molecule directions within thislayer are controlled by electrodes, i.e., pixels, and the phases oflight rays reflected by this layer are spatially modulated according
to the directions of the liquid crystal molecules. In other words, thisdevice acts as an optical phased array. An example of a computergenerated hologam (CGH) is shown in Figure 2.
Figure 1 shows example images renderd in air by a femtosecondlaser. While the instantaneous energy is sufficiently high to inducea plasma in air, the time-avarage energy of a femto-second laser isso weak that one can touch the plasma images with a finger.

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