White light lasers have characteristics that traditional lasers do not have, making up for the shortcomings of traditional lasers; the research and development of white light laser pointer light sources can bring more fields of change and development, and generate new scientific fields and new applications; therefore, it is inevitable Become the object of many scientists chasing research. After the United States announced the birth of the first white laser, why has it been silent for many years without practical application? Why hasn’t the photonic crystal fiber white laser been widely popularized and applied?
Before answering these questions, let us re-understand what a laser is and the two important crystals of a laser: laser crystals and nonlinear crystals. The laser is generated by the expansion of stimulated emission light, has good monochromaticity, spatial coherence and temporal coherence, good directivity, and extremely high brightness.
These four characteristics of the laser show that the green laser pointer has a high coherent light intensity in a large coherent volume. Coherence is an important feature of laser. “Compared with white lasers, we exclude monochromaticity (because white light has no monochromaticity). All lasers must have good coherence, directivity, and high brightness before they can be called lasers.”
The solid-state laser contains 2 key crystals-laser crystal and nonlinear crystal. In practical applications, people need lasers with different wavelength ranges. The lasers provide people with the laser wavelengths required for practical applications, which depend on the nonlinear crystal; Kind of laser “. Based on this, we conclude that white light laser as an independent laser light source, if it is generated by a non-linear crystal, then it must possess all the characteristics of laser.
We can understand from this that the white laser produced by the American white light laser is based on three parallel segments of semiconductor materials, which respectively produce tunable three-primary-color lasers, which are finally combined to become a white laser. The article also explains how difficult it is to make three parallel gain media that produce white laser light. Seeing this, we have an important concept to remind everyone: different nonlinear crystals cannot produce lasers with the same coherence. Therefore, the white laser light generated by three different semiconductor materials shows incoherence in terms of coherence.
So there is the following conclusion: American white laser, because of the incoherence, therefore, does not have perfect laser characteristics. Moreover, the manufacturing process of the gain medium for generating white lasers is complicated, which hinders the promotion of white lasers. In the article “Quasi-white laser based on optical superlattice and all-solid-state laser technology”, the author gave a scientific title of “quasi-white laser” to the white laser that was born through the three primary colors and lacked the excellent characteristics of many lasers . The quasi-white laser lacks many excellent characteristics of the laser. It is not a perfect white laser, not a white laser in the true sense.
Although the white laser produced by the photonic crystal fiber laser has the characteristics of high power, broadband, and supercontinuum, “the pulse is affected by noise during the transmission of the white laser in the fiber transmission. Affected. If the supercontinuum is used as a broadband light source in the fields of medicine, metrology and optical pulse compression, it must have good coherence, so the coherence is also an important aspect of measuring supercontinuum. Research on Coherence of Supercontinuum in Optical Fibers. ” This shows that although the photonic crystal fiber laser can produce white laser light, because its coherence is destroyed, it can not be regarded as a high-quality laser light source. This may be an important reason why its application range is blocked. We believe that white laser light produced by photonic crystal fiber lasers lacking coherence also belongs to “quasi-white laser light”.