The existing laser technology has always had a shortcoming, that is, it can only emit light of a single wavelength or a narrow band. How to expand the frequency of the laser to form an ultra-wideband, super-continuum, coherent white light laser covering the ultraviolet, visible and infrared bands is still a dream that has not been realized by mankind and is a scientific and technological problem worldwide. This is because the laser pointer is composed of an optical resonator, a gain medium, and a pump source.
The wavelength of the laser is determined by the energy level structure of the atoms, molecules or ions in the gain material. Due to the great limitations of the nature of the laser crystal material in the gain frequency range and gain bandwidth, the laser cannot produce lasers of any wavelength. Will this perfect white laser be created? What changes and developments can it bring to the application of lasers? As we all know, everything grows by the sun, and sunlight brings light and heat to the earth. The sunlight that people are familiar with is a kind of white light, and its spectrum covers ultraviolet-visible-near-infrared waves.
In the visible light band (400-700nm), the radiant energy is the strongest, covering seven colors of red orange yellow green blue blue purple, and continuous distribution and transition in the spectrum. Because sunlight is white light, rainbows are often seen in the sky after rain, or seven colors of light bands appear when sunlight passes through a glass prism (Figure 2). This is a common experience in people’s daily lives. One thing people are not so familiar with is that sunlight is a completely incoherent light. In terms of spatial coherence, sunlight cannot be collimated and highly divergent. In terms of temporal coherence, there is no phase correlation and locking between different colors of sunlight.
Therefore, sunlight can only be used to generate energy, which is used in heating, water heaters, solar cells, etc. However, the application of modern science and technology, such as the use of sunlight to transmit information, seems overwhelming. green laser pointer is another major invention of mankind since the 20th century, after atomic energy, computers, and semiconductors. The laser has the characteristics of good directivity, high brightness and good monochromaticity. Its comprehensive performance far exceeds traditional sunlight, incandescent lamps, fluorescent lamps, LED lamps and other light sources. It is a revolutionary way for humans to use the information and energy of light.