Kota Kumagai

Fairy lights in femtoseconds: aerial and volumetric graphics rendered by focused femtosecond laser combined with computational holographic fields

We envision a laser-induced plasma technology in general applications for public use. If laser-induced plasma aerial images were made available, many useful applications such as spatial aerial AR, aerial user interfaces, volumetric images could be produced. This would be a highly effective display for the expression of three-dimensional 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 and 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.

Cross-Field Aerial Haptics: Rendering Haptic Feedback in Air with Light and Acoustic Fields

We present a new method of rendering aerial haptic images that uses femtosecond-laser light fields and ultrasonic acoustic fields. In conventional research, a single physical quantity has been used to render aerial haptic images. In contrast, our method combines multiple fields (light and acoustic fields) at the same time. 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 with laser haptics and ultrasonic haptics separately and tested their superposition. The results showed that the acoustic field affects the tactile perception of the laser haptics. We explored augmented reality/virtual reality (AR/VR) applications such as providing haptic feedback of the combination of these two methods. We believe that the results of this study contribute to the exploration of laser haptic displays and expand the expression of aerial haptic displays based on other principles.

Volumetric display with holographic parallel optical access and multilayer fluorescent screen.

We propose a volumetric display based on holographic parallel optical access and two-photon excitation using a computer-generated hologram displayed on a liquid crystal spatial light modulator and a multilayer fluorescent screen. The holographic parallel optical access increased the number of voxels of the volumetric image per unit time. This approach increased the total input energy to the volumetric display, that is, the total fluorescence power, because the maximum energy incident at a point in the multilayer fluorescent screen is limited by the damage threshold. The multilayer fluorescent screen was newly developed to display colored voxels. The thin layer construction of the multilayer fluorescent screen minimized the axial length of the voxels. A volumetric display with only blue-green voxels and a volumetric display with both blue-green and red voxels were demonstrated.

Volumetric bubble display

To develop a volumetric display of the kind we see in science fiction movies is a dream of many display researchers, including us. Here, we show a new volumetric display with microbubble voxels. The microbubbles are three-dimensionally generated in liquid by focused femtosecond laser pulses. The use of a high-viscosity liquid, which is a key part of the development of this idea, slows down the movement of the microbubbles, and, as a result, volumetric graphics can be displayed. This volumetric bubble display has a wide-angle view, simple refreshing, and no addressing wires, since the transparent liquid is accessed optically rather than electronically. It achieves full-color graphics composed of light-scattering voxels controlled by illumination light sources. Furthermore, a holographic laser drawing method based on a computer-generated hologram displayed on a liquid-crystal spatial light modulator controls the light intensity of the microbubble voxels with an increase in the number of voxels per unit time and the spatial shaping of the voxels.

Three-dimensionally structured voxels for volumetric display

A three-dimensional (3D) volumetric display has been the goal of the display research field for many years. However, volumetric displays capable of rendering multicolor and updatable graphics that users can view with the naked eye are still a challenge. Here, we show a new volumetric display using three-dimensionally structured fluorescent voxels. The fluorescent voxels were generated by two-photon excitation with a femtosecond laser. To realize colorization, volumetric graphics were spatially rendered on a fluorescent screen in which structured voxels having different luminescent colors were arranged in each layer. The color of the fluorescent voxels was changed by a holographic color switching method using computer-generated holograms displayed on a liquid-crystal spatial light modulator. Because this display employed RGB fluorescent voxels that are accessed optically, it has a number of advantages, such as being observable with the naked eye, and being capable of multicolor rendering and refreshable graphics. This technology will open up a wide range of applications in 3D displays, augmented reality, and computer graphics.

Volumetric graphics in liquid using holographic femtosecond laser pulse excitations

Much attention has been paid to the development of three-dimensional volumetric displays in the fields of optics and computer graphics, and it is a dream of we display researchers. However, full-color volumetric displays are challenging because many voxels with different colors have to be formed to render volumetric graphics in real three-dimensional space. Here, we show a new volumetric display in which microbubble voxels are three-dimensionally generated in a liquid by focused femtosecond laser pulses. Use of a high-viscosity liquid, which is the key idea of this system, slows down the movement of the microbubbles, and as a result, volumetric graphics can be displayed. This “volumetric bubble display” has a wide viewing angle and simple refresh and requires no addressing wires because it involves optical access to transparent liquid and achieves full-color graphics composed on light-scattering voxels controlled by illumination light sources. In addition, a bursting of bubble graphics system using an ultrasonic vibrator also has been demonstrated. This technology will open up a wide range of applications in three-dimensional displays, augmented reality and computer graphics.

Holographic-laser-drawing volumetric display

We propose a holographic-laser-drawing volumetric display using a computer-generated hologram displayed on a liquid crystal spatial light modulator and multilayer fluorescent screen. The holographic-laser-drawing technique has enabled three things; (i) increasing the number of voxels of the volumetric graphics per unit time; (ii) increasing the total input energy to the volumetric display because the maximum energy incident at a point in the multilayer fluorescent screen is limited by the damage threshold; (iii) controlling the size, shape and spatial position of voxels. In this paper, we demonstrated (i) and (ii). The multilayer fluorescent screen was newly developed to display colored voxels. The thin layer construction of the multilayer fluorescent screen minimized the axial length of the voxels. A two-color volumetric display with blue-green voxels and red voxels were demonstrated.

Volumetric display created by holographic laser drawing

Volumetric displays have received much attention for use as 3D displays in optics and computer graphics. These displays can produce 3D images that can be observed from any point of view without physical discomfort or the use of any special devices.1 Volumetric displays based on laser irradiation have been constructed using plasma,2, 3 quantum dots,4, 5 and rare earth elements.6, 7 These displays have a wide angle of view because they require no physical connection between the light source and the display volume. With previous approaches, however, the number of voxels in a volumetric display is not large enough to generate practical volumetric images because of limitations imposed by the repetition frequency of the laser and the speed of the 3D scanning system. We have generated a volumetric display using a holographic laser drawing technique and a multilayer fluorescent screen.8 We carry out holographic laser drawing by means of a computergenerated hologram (CGH), which is displayed on a liquidcrystal spatial light modulator (LCSLM) to increase the number of voxels in the volumetric display per unit time. We use the fluorescent screen to produce a multicolored display. Figure 1 shows the experimental setup of our volumetric display system. The light source was an amplified femtosecond laser (Micra and Legend Elite Duo, Coherent) with a center wavelength of 800nm, a repetition frequency of 1kHz, a pulse duration of <130fs, and an output power of 7W. A voxel was formed by two-photon absorption excited by a focused femtosecond laser pulse. We changed the position of the focus using a 3D beam scanner and a Fourier CGH. The 3D beam scanner comprised a Canon GM-1010 2D galvanometer scanner and an Optotune EL-10-30-C varifocal lens. The galvanometer scanner controlled the position of the focus in the horizontal direction. The maximum deflection angle was ̇20 degrees, the step response time was 280 s Figure 1. A holographic volumetric display is generated using a femtosecond laser and a multilayer fluorescent screen. SLM: Spatial light modulator.

Volumetric display with holographic multi-photon excitations

We developed a volumetric display with holographic two- and multi-photon excitations using a computer-generated hologram displayed on a liquid crystal spatial light modulator. The holographic technique has advantages of increasing the number of voxels of the volumetric graphics per unit time, increasing the total input energy to the volumetric display because the maximum energy incident at a point in the display material is limited by the damage threshold, and controlling the size, shape and spatial position of voxels. We demonstrated a volumetric display with stacked multi-color fluorescence plates.

Updatable bubble display

We propose an updatable volumetric display rendered by microbubbles induced by holographic femtosecond laser drawing using computer-generated holograms displayed on liquid crystal spatial light modulator and ultrasonic vibrator to refresh the graphics. We have made the system that consists of a femtosecond laser, a 3D beam scanner, a spatial light modulator and a glycerin. We have conducted experiments of observation shapes of microbubbles, rendering and erase the bubble graphics.