White laser, a new research hotspot, is known to all that the laser is amplified by stimulated radiation, which has the characteristics of high brightness, good direction, strong coherence and excellent monochrome. It is because of these advantages which are different from ordinary light sources that laser is widely used in various fields nowadays. On the other hand, as a monochrome light source, the spectral bandwidth of the laser is very narrow, so that the color produced by a single laser can only cover one point of the NEAR-BOUNDARY region of the chromaticity map (Fig. 1), while the color of most areas of the chromaticity map center needs to be achieved by the combination of multiple colors or multiple lasers, which includes white light. Fig. 1 1931 Chroma Map (Image Source: CIE 1931) White light is widely used in illumination, display, imaging, communication and many other fields as a complex color light. Because monochrome laser can not produce white light directly, the white light in current application field is mainly:
1) By means of non-laser technology such as LED, incandescent lamp, etc.
2) It is produced by mixing several laser beams of different colors.
3) Ultrashort pulse and non-linear medium are used. Whether we can create a single device or chip to produce white laser directly, which has both the excellent characteristics of laser and the broad application prospects of white light, and covers a wider range of color areas, has become a research hotspot nowadays. It also poses a severe challenge for the growth of semiconductor materials. Correspondingly, white laser technology has also become an important research topic, in order to broaden the field of laser application and benefit more aspects of human life. Comparing the schemes of white-light laser realization, the schemes of white-light laser realization can be roughly divided into two categories: 1. The basic principle of white-light laser non-linear effect generation by supercontinuum spectrum generated by optical non-linearity effect is to use the combination of various non-linearity effects produced by ultrashort pulse laser in non-linear medium to produce a supercontinuum spectrum in visible light range. Laser. Because the scheme works well
Ultrafast laser is often used as the fundamental input light, which is very expensive and can not adapt to the miniaturization and integration of application scenarios. Compared with semiconductors, the conversion efficiency of lasers of non-linear materials is relatively low, which hinders their applications in many high-demand areas such as lighting, display and so on to a certain extent. In addition, the relative intensity of the supercontinuum spectrum or the high-order harmonic group produced by the non-linear scheme has been basically determined at the beginning of the design. It is difficult to realize the real-time control of the relative intensity of each spectral component. Therefore, it is difficult to dynamically control the color of the output laser, which limits its further development and promotion.
2. White-light laser based on red-green-blue laser synthesis is a common method in the field of research at present, which combines red, green and blue (RGB) three-color or multi-color laser synthesis to achieve white-light laser. Because of the use of three primary color mixing, each primary color is relatively independent and controllable. It is easy to realize the dynamic control of white laser color and color temperature. It can be more flexible in many fields, including laser projection television and laser multi-color display in the current market. The main difficulty and disadvantage of RGB-based three-color synthetic white-light laser scheme is that these different color lasers are usually manufactured and assembled separately. It is difficult to achieve miniaturization and batch integration, so the cost of production is expensive. It has been a long-term goal for scientists and engineers to produce multi-color or white laser sources because of the difficulty of single or single device white laser. The key difficulty lies in the creation of materials that emit multi-color or red-green-blue primary colors efficiently at the same time, as well as the spatial differentiation and amplification of these different colors of light into lasers through laser cavity resonance, respectively.
This is the case. Colloidal quantum dots (QDs) are a well-known technology, but it is difficult to distinguish the different colored QDs efficiently and accurately in space to achieve high-efficiency electric injection. Other non-semiconductor materials, such as rare earth-mixed silica, dye-mixed organic polymers, dye droplets and so on, face the problems of low luminescence efficiency, difficult to achieve high-efficiency electron injection and difficult integration. Semiconductor materials have been the preferred luminescent materials because of their high efficiency, easy electro-injection and easy integration. However, to realize white laser with semiconductor materials, a traditional technical problem needs to be solved: the lattice size of semiconductors emitted with different colors is often too different. This lattice mismatch makes these semiconductors with different colors grown at one time by thin film epitaxy contain a lot of defects, resulting in the decrease of photoelectric quality of crystals, which can not meet the optical gain of materials. Seek. Secondly, long-wavelength semiconductor materials will absorb the light emitted by short-wavelength semiconductor materials. If the light emitted by other materials can not be inhibited between different semiconductors, especially the short-wavelength (such as blue, green, etc.) is absorbed by narrow-band semiconductors (such as red-emitting semiconductors), the laser will not reach the threshold, and it will be difficult to form lasers. Therefore, how to solve these two technical problems has become the key to the realization of semiconductor white laser technology. In 2015, the author's research team from Arizona State University and Tsinghua University made unremitting efforts to overcome the multiple difficulties in device design and material growth. A breakthrough in semiconductor white laser technology was reported in Natural-Nanotechnology. With the help of nano-semiconductor technology, researchers from PhD students Fanfan, Sunay Turkdogan and Liu Zhicheng will be able to change the growth parameters of materials.