Laser display has been attractive because extremely wide color expression can be realized by choosing the wavelength of laser sources. The highly efficiency and small etendue of laser sources contribute to downsizing, and long lifetime is also another merit for users. High power and compact red, green, and blue (RGB) lasers have been expected to realize the practical laser display. In this paper, highly efficient RGB lasers based on laser diodes and second harmonic generation devices are introduced. Also laser projection systems by using these lasers and illumination optics for speckle noise reduction are demonstrated with wide color gamut and low electric power consumption.
Red high power semiconductor lasers are expected to be used for the light source of laser projection display systems. We have achieved 6.6 W CW operation of red semiconductor array lasers at a wavelength of 640nm. The energy conversion efficiency is as high as 29.7% at 25°C and the degradation rate after 1000-hours is less than 10%. The uniform near field pattern has been obtained by applying index-guided structure for broadstripe laser. We have developed projection display systems including hybrid light sources of UHP lamp andred semiconductor lasers, which can emphasize red color gamut. Speckle noise is dramatically reduced by moving screen that consist of gently rotating diffusion sheet and fixed diffusion plate.
This paper reports an optical MEMS (Micro Electro Mechanical System) scanner developed for projectiontype image display. A 3-micron-thick PZT film was deposited onto an SOI (Silicon-On-Insulator) wafer tocompose piezoelectric unimorph actuators. Two-dimensional scanning mirror mechanisms were designedwith a fast resonant axis of 11.2kHz for the horizontal line scan of image and a slow off-resonant axis for the vertical frame refresh at 60Hz. Technical requirement for the optical scanner is discussed in terms of the scan angle and speed for the VGA (Video Graphics Array) resolution. Optical scan angles of horizontal 39 degrees and vertical 29 degrees were experimentally obtained at drive voltages upwards of 40V. A simple demonstration of bitmap image projection with a laser light source is presented.
High-power pure blue laser diodes (LDs) are expected to be adapted to the light sources for full color laser display systems. We have succeeded in fabricating high-power blue LDs by optimizing the structure of ridgewaveguide LDs. The typical operating current, voltage and wall-plug efficiency of these LDs with an optical output power of 500mW were 480mA, 4.8V, and 21.7%, respectively. After 5,000 hours operation, the lifetime was estimated to be over 30,000 hours.
Wavelength converters are reviewed for a compact high-power green laser. Quasi-Phase-Matched (QPM) second-harmonic-generation realized high efficiency even in a single-pass conversion with a continuous wave laser. Materials and device configurations are introduced for different power levels from sub watt to multi watt. Future directions for an efficient wavelength-conversion laser will be discussed.
Utilizing high-power GaN laser diodes emitting light at 444nm, which have been developed for a blue light source in laser rear projection displays, high-power coherent red light at 639nm, which is also useful for laser rear projection displays, becomes available from Pr3+ doped LiYF4 lasers. In this paper, development of Pr3+: LiYF4 lasers are reviewed. In our experiment, the highest laser power of 112mW was achieved with the optical-optical conversion efficiency of 33.5%. Characteristics of this laser at elevated temperatures were also investigated for practical applications such as a laser projector.
A low fluence UV laser ablation technique combined with Laser-Induced Fluorescence (LIF) spectroscopy is developed for an extreme trace element analysis of solid surface with a nanometer-scale depth resolution. Since the behavior of scattering atoms by the laser ablation was significant for improving the sensitivity of the analysis, the spatial distributions of the scattering atoms were investigated by a two dimensional imaging LIF spectroscopy method. Influences of a buffer gas and an assist mask on the atomic distributions were also investigated for enhancing the sensitivity of the analysis.
Since most biomolecules have a specific molecular vibration mode in the mid-infrared (MIR) wavelength range, they absorb the MIR light energy of a specific wavelength. An MIR laser can be used to analyze several optical characteristics of biomolecules. The free electron laser (FEL) at Osaka University can be continuously varied in a wavelength range of 5.0-20.0μm. The pulse width is-5ps, and its peak power with 5 MW is higher than common laser systems. In this study, we measured the reflectance spectra of dentin and gelatin using FEL to estimate applications as a spectroscopic light source. Reflectance spectra resembled the transmission spectra by the Fourier Transform Infrared Spectrometer (FT-IR) method.