Aerial Interaction with Femtosecond Laser Induced Plasma
Yoichi Ochiai∗
Digital Nature Group, University of Tsukuba

Figure 1: These figures show the example applications of proposed laser-based graphics technology. (a) Images superposed on a hand anda box. (b) Floating button with haptic feedback. (c and d) Volumetric images rendered in open and closed areas.

Abstract
In this article we report case studies on the aerial interaction withlaser induced plasma as computational voxels. Laser inducedplasma of air can be utilized to generate light source or tactile components for aerial interactions. In current studies we transformedordinary air into interactive visual media [Ochiai et al. 2016b] andhaptic media [Ochiai et al. 2016a]. To implement these interactive
media, we employed Computer Generated Hologram and renderedwith laser induced plasma generated by femtosecond laser sources
with Spatial Light Modulators and ultrasound generated by acoustic phased array. In article, we introduce the concept through thesestudies and results of our research group in aerial touch display
project called Fairy Lights in Femtoseconds [Ochiai et al. 2016b].
Keywords: Aerial Display, Haptic Display, Augmented Reality.
Concepts: •Hardware → Emerging optical and photonic technologies;

1

Plasma Light Source

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 three
dimensionalinformation. 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 tech∗ e-mail:wizard@slis.tsukuba.ac.jp
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c 2016 Copyright held by the owner/author(s).
the owner/author(s). ⃝SA ’16, December 05-08 2016, , Macao
ISBN: 978-1-4503-4548-4/16/12
DOI: http://dx.doi.org/10.1145/2992138.2992153

nology 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. In [Ochiai et al. 2016a; Ochiai
et al. 2016b], we achieved high resolution and interactive application with Spatial Light Modulators and Femtosecond laser source.
The design space and possible scenarios of the plasma-based 3D
display are shown in Figure 1. Adding to femtosecond laser sorce,
we use an optical device, called the spatial light modulator (SLM),
to modify the phases of light rays and produce 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 this layer are controlled
by electrodes, i.e. pixels, and the phases of light rays reflected bythis layer are spatially modulated according to the directions of theliquid crystal molecules. In other words, this device acts as an optical phased array. Figure 2 shows example images rendered in air
by a femtosecond laser. While the instantaneous energy is sufficiently high to induce a plasma in air, the time-average energy ofa femtosecond laser is relatively low energy that one can touch theplasma images with a finger.

Figure 2: Images rendered by femtosecond plasma.

Figure 3: System and Applications: Left(1-3) Fairy Lights in Femtoseconds [Ochiai et al. 2016b], Right (1-3) Cross-Field Haptics [Ochiaiet al. 2016a]

2Case Studies: Visio Haptic Media

Here we introduce the project named Fairy Lights in Femtoseconds[Ochiai et al. 2016b] and additinal haptic project called Cross-Field
Aerial Haptics [Ochiai et al. 2016a].
Systems are shown in Figure 3 (1)-left and (1)-right. We have utilized femtoseconds laser source and spatial light modulator to generate laser induced plasma by laser light fields in three dimensionally positions.
[Ochiai et al. 2016b] is a display method of rendering aerial andvolumetric graphics using femtosecond lasers. A high-intensity
laser excites physical matter to emit light at an arbitrary threedimensional position. There are two methods of rendering graphics
with a femtosecond laser in air: producing holograms using spatial
light modulation technology and scanning of a laser beam by a galvano mirror. The display workspace of the system proposed here
occupy a volume of up to 1 cm3 ; however, this size is scalable depending on the optical devices and their setup. We tested two laser
sources: an adjustable (30-100 fs) laser that projects up to 1,000
pulses/s at an energy of up to 7 mJ/pulse and a 269 fs laser thatprojects up to 200,000 pulses/s at an energy of up to 50 J/pulse. We
confirmed that the spatiotemporal resolution of volumetric displays
implemented using these laser sources is 4,000 and 200,000 dots/s,
respectively (Figure 2(left)). The spatial resolution of voxels is
100 m interval and participants in this study states that displayed
object cannot be distinguished from physical solid materials.
[Ochiai et al. 2016a] is haptic display project combined with acoustic holograms. In this project we presented a new method of rendering aerial haptic images that uses femtosecond-laser light fieldsand ultrasonic acoustic fields.

While these fields have no direct interference, combining them provides benefits such as multi-resolution haptic images and a synergistic effect on haptic perception. We conducted user studies withlaser haptics and ultrasonic haptics separately and tested their superposition. The results showed that the acoustic field affects thetactile perception of the laser haptics. We explored augmented reality/virtual reality (AR/VR) applications (Figure 2 (Right-2,3)) suchas providing haptic feedback of the combination of these two methods. Our results show that the acoustic field affects tactile perception of the laser haptics. The findings are as follows; laser tactile
sensation is repressed in an acoustic field; some users can differentiate spatial patterns rendered with laser plasma; users can detectthe 3D position of the laser stimulation better than the ultrasonicstimulation.

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